The Life of the Caterpillar

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THE LIFE OF THE CATERPILLAR [[2]]

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BOOKS BY J. HENRI FABRE

• [THE LIFE OF THE SPIDER]
• THE LIFE OF THE FLY
• [THE MASON-BEES]
• [BRAMBLE-BEES AND OTHERS]
• THE HUNTING WASPS
• THE LIFE OF THE CATERPILLAR

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THE LIFE OF THE
CATERPILLAR

BY
J. HENRI FABRE
TRANSLATED BY
Alexander Teixeira de Mattos
FELLOW OF THE ZOOLOGICAL SOCIETY OF LONDON

NEW YORK
DODD, MEAD AND COMPANY
1916

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COPYRIGHT, 1916
BY DODD, MEAD AND COMPANY, INC. [[5]]

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CONTENTS

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TRANSLATOR’S NOTE

This, the sixth volume of the Collected Edition of Fabre’s Entomological Works in English, is the first that I am preparing for publication since the author’s death, on the 11th of October, 1915, at an exceedingly advanced age. It contains all the essays, fourteen in number, which he wrote on Butterflies and Moths, or their caterpillars.

Three of these, the chapters entitled The Great Peacock, The Banded Monk and The Sense of Smell, are included under the titles of The Great Peacock, The Oak Eggar and A Truffle-hunter: the Bolboceras Gallicus in a volume of miscellaneous extracts from the Souvenirs entomologiques translated by Mr. Bernard Miall and published by the Century Company. The volume in question is named Social Life in the Insect World; and I strongly recommend it to the reader, if only because of the excellent photographs from nature with which it is illustrated.

Chapter III. of the present volume, The Pine Processionary: the Procession, has appeared [[8]]in the Fortnightly Review; and Chapter XIV., The Cabbage Caterpillar, the last essay but one from the author’s pen, written, I believe, within two or three years of his death, was first printed in the Century Magazine, some time before its publication in the original. It does not form part of the Souvenirs entomologiques. The remaining essays are new in their English guise.

Once more I wish to record my gratitude to Miss Frances Rodwell for the faithful assistance which she has lent me in the preparation of this volume, as in that of all the earlier volumes of the series.

Alexander Teixeira de Mattos.

Chelsea, 1916. [[9]]

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CHAPTER I

THE PINE PROCESSIONARY: THE EGGS AND THE HATCHING

This caterpillar has already had his story told by Réaumur,[1] but it was a story marked by gaps. These were inevitable in the conditions under which the great man worked, for he had to receive all his materials by barge from the distant Bordeaux Landes. The transplanted insect could not be expected to furnish its biographer with other than fragmentary evidence, very weak in those biological details which form the principal charm of entomology. To study the habits of insects one must observe them long and closely on their native heath, so to speak, in the place where their instincts have full and natural play.

With caterpillars foreign to the Paris climate and brought from the other end of France, Réaumur therefore ran the risk of [[10]]missing many most interesting facts. This is what actually happened, just as it did on a later occasion in the case of another alien, the Cicada.[2] Nevertheless, the information which he was able to extract from a few nests sent to him from the Landes is of the highest value.

Better served than he by circumstances, I will take up afresh the story of the Processionary Caterpillar of the Pine. If the subject does not come up to my hopes, it will certainly not be for lack of materials. In my harmas[3] laboratory, now stocked with a few trees in addition to its bushes, stand some vigorous fir-trees, the Aleppo pine and the black Austrian pine, a substitute for that of the Landes. Every year the caterpillar takes possession of them and spins his great purses in their branches. In the interest of the leaves, which are horribly ravaged, as though there had been a fire, I am obliged each winter to make [[11]]a strict survey and to extirpate the nests with a long forked batten.

You voracious little creatures, if I let you have your way, I should soon be robbed of the murmur of my once so leafy pines! Today I will seek compensation for all the trouble I have taken. Let us make a compact. You have a story to tell. Tell it me; and for a year, for two years or longer, until I know more or less all about it, I shall leave you undisturbed, even at the cost of lamentable suffering to the pines.

Having concluded the treaty and left the caterpillars in peace, I soon have abundant material for my observations. In return for my indulgence I get some thirty nests within a few steps of my door. If the collection were not large enough, the pine-trees in the neighbourhood would supply me with any necessary additions. But I have a preference and a decided preference for the population of my own enclosure, whose nocturnal habits are much easier to observe by lantern-light. With such treasures daily before my eyes, at any time that I wish and under natural conditions, I cannot fail to see the Processionary’s story unfolded at full length. Let us try. [[12]]

And first of all the egg, which Réaumur did not see. In the first fortnight of August, let us inspect the lower branches of the pines, on a level with our eyes. If we pay the least attention, we soon discover, here and there, on the foliage, certain little whitish cylinders spotting the dark green. These are the Bombyx’ eggs: each cylinder is the cluster laid by one mother.

The pine-needles are grouped in twos. Each pair is wrapped at its base in a cylindrical muff which measures about an inch long by a fifth or sixth of an inch wide. This muff, which has a silky appearance and is white slightly tinted with russet, is covered with scales that overlap after the manner of the tiles on a roof; and yet their arrangement, though fairly regular, is by no means geometrical. The general aspect is more or less that of an immature walnut-catkin.

The scales are almost oval in form, semitransparent and white, with a touch of brown at the base and of russet at the tip. They are free at the lower end, which tapers slightly, but firmly fixed at the upper end, which is wider and blunter. You cannot detach them either by blowing on them or by [[13]]rubbing them repeatedly with a hair-pencil. They stand up, like a fleece stroked the wrong way, if the sheath is rubbed gently upwards, and retain this bristling position indefinitely; they resume their original arrangement when the friction is in the opposite direction. At the same time, they are as soft as velvet to the touch. Carefully laid one upon the other, they form a roof that protects the eggs. It is impossible for a drop of rain or dew to penetrate under this shelter of soft tiles.

The origin of this defensive covering is self-evident: the mother has stripped a part of her body to protect her eggs. Like the Eider-duck, she has made a warm overcoat for them out of her own down. Réaumur had already suspected as much from a very curious peculiarity of the Moth. Let me quote the passage:

“The females,” he says, “have a shiny patch on the upper part of their body, near the hind-quarters. The shape and gloss of this disk attracted my attention the first time that I saw it. I was holding a pin, with which I touched it, to examine its structure. The [[14]]contact of the pin produced a little spectacle that surprised me: I saw a cloud of tiny spangles at once detach themselves. These spangles scattered in every direction: some seemed to be shot into the air, others to the sides; but the greater part of the cloud fell softly to the ground.

“Each of those bodies which I am calling spangles is an extremely slender lamina, bearing some resemblance to the atoms of dust on the Moths’ wings, but of course much bigger.… The disk that is so noticeable on the hind-quarters of these Moths is therefore a heap—and an enormous heap—of these scales.… The females seem to use them to wrap their eggs in; but the Moths of the Pine Caterpillar refused to lay while in my charge and consequently did not enlighten me as to whether they use the scales to cover their eggs or as to what they are doing with all those scales gathered round their hinder part, which were not given them and placed in that position to serve no purpose.”

You were right, my learned master: that dense and regular crop of spangles did not grow on the Moth’s tail for nothing. Is [[15]]there anything that has no object? You did not think so; I do not think so either. Everything has its reason for existing. Yes, you were well-inspired when you foresaw that the cloud of scales which flew out under the point of your pin must serve to protect the eggs.

I remove the scaly fleece with my pincers and, as I expected, the eggs appear, looking like little white-enamel beads. Clustering closely together, they make nine longitudinal rows. In one of these rows I count thirty-five eggs. As the nine rows are very nearly alike, the contents of the cylinder amount in all to about three hundred eggs, a respectable family for one mother!

The eggs of one row or file alternate exactly with those in the two adjoining files, so as to leave no empty spaces. They suggest a piece of bead-work produced with exquisite dexterity by patient fingers. It would be more correct still to compare them with a cob of Indian corn, with its neat rows of seeds, but a greatly reduced cob, the tininess of whose dimensions makes its mathematical precision all the more remarkable. The grains of the Moth’s spike have a slight tendency to be hexagonal, because of their mutual [[16]]pressure; they are stuck close together, so much so that they cannot be separated. If force is used, the layer comes off the leaf in fragments, in small cakes always consisting of several eggs apiece. The beads laid are therefore fastened together by a glutinous varnish; and it is on this varnish that the broad base of the defensive scales is fixed.

It would be interesting, if a favourable opportunity occurred, to see how the mother achieves that beautifully regular arrangement of the eggs and also how, as soon as she has laid one, all sticky with varnish, she makes a roof for it with a few scales removed one by one from her hind-quarters. For the moment, the very structure of the finished work tells us the course of the procedure. It is evident that the eggs are not laid in longitudinal files, but in circular rows, in rings, which lie one above the other, alternating their grains. The laying begins at the bottom, near the lower end of the double pine-leaf; it finishes at the top. The first eggs in order of date are those of the bottom ring; the last are those of the top ring. The arrangement of the scales, all in a longitudinal direction and attached by the end facing the [[17]]top of the leaf, makes any other method of progression inadmissible.

Let us consider in the light of reflection the elegant edifice now before our eyes. Young or old, cultured or ignorant, we shall all, on seeing the Bombyx’ pretty little spike, exclaim:

“How handsome!”

And what will strike us most will be not the beautiful enamel pearls, but the way in which they are put together with such geometrical regularity. Whence we can draw a great moral, to wit, that an exquisite order governs the work of a creature without consciousness, one of the humblest of the humble. A paltry Moth follows the harmonious laws of order.

If Micromégas[4] took it into his head to leave Sirius once more and visit our planet, would he find anything to admire among us? Voltaire shows him to us using one of the diamonds of his necklace as a magnifying-glass in order to obtain some sort of view of the three-master which has run aground on his thumb-nail. He enters into conversation [[18]]with the crew. A nail-paring, curved like a horn, encompasses the ship and serves as a speaking-trumpet; a tooth-pick, which touches the vessel with its tapering end and the lips of the giant, some thousand fathoms above, with the other, serves as a telephone. The outcome of the famous dialogue is that, if we would form a sound judgment of things and see them under fresh aspects, there is nothing like changing one’s planet.

The probability then is that the Sirian would have had a rather poor notion of our artistic beauties. To him our masterpieces of statuary, even though sprung from the chisel of a Phidias, would be mere dolls of marble or bronze, hardly more worthy of interest than the children’s rubber dolls are to us; our landscape-paintings would be regarded as dishes of spinach smelling unpleasantly of oil; our opera-scores would be described as very expensive noises.

These things, belonging to the domain of the senses, possess a relative æsthetic value, subordinated to the organism that judges them. Certainly the Venus of Melos and the Apollo Belvedere are superb works; but even so it takes a special eye to appreciate them. [[19]]Micromégas, if he saw them, would be full of pity for the leanness of human forms. To him the beautiful calls for something other than our sorry, frog-like anatomy.

Show him, on the other hand, that sort of abortive windmill by means of which Pythagoras, echoing the wise men of Egypt, teaches us the fundamental properties of the right-angled triangle. Should the good giant, contrary to our expectation, happen not to know about it, explain to him what the windmill means. Once the light has entered his mind, he will find, just as we do, that there is beauty there, real beauty, not certainly in that horrible hieroglyphic, the figure, but in the unchangeable relation between the lengths of the three sides; he will admire as much as we do geometry the eternal balancer of space.

There is, therefore, a severe beauty, belonging to the domain of reason, the same in every world, the same under every sun, whether the suns be single or many, white or red, blue or yellow. This universal beauty is order. Everything is done by weight and measure, a great statement whose truth breaks upon us all the more vividly as we probe more deeply into the mystery of things. [[20]]

Is this order, upon which the equilibrium of the universe is based, the predestined result of a blind mechanism? Does it enter into the plans of an Eternal Geometer, as Plato had it? Is it the ideal of a supreme lover of beauty, which would explain everything?

Why all this regularity in the curve of the petals of a flower, why all this elegance in the chasings on a Beetle’s wing-cases? Is that infinite grace, even in the tiniest details, compatible with the brutality of uncontrolled forces? One might as well attribute the artist’s exquisite medallion to the steam-hammer which makes the slag sweat in the melting.

These are very lofty thoughts concerning a miserable cylinder which will bear a crop of caterpillars. It cannot be helped. The moment one tries to dig out the least detail of things, up starts a why which scientific investigation is unable to answer. The riddle of the world has certainly its explanation otherwhere than in the little truths of our laboratories. But let us leave Micromégas to philosophize and return to the commonplaces of observation.

The Pine Bombyx has rivals in the art of [[21]]gracefully grouping her egg-beads. Among their number is the Neustrian Bombyx, whose caterpillar is known by the name of “Livery,” because of his costume. Her eggs are assembled in bracelets around little branches varying greatly in nature, apple- and pear-branches chiefly. Any one seeing this elegant work for the first time would be ready to attribute it to the fingers of a skilled stringer of beads. My small son Paul opens eyes wide with surprise and utters an astonished “Oh!” each time that he comes upon the dear little bracelet. The beauty of order forces itself upon his dawning attention.

Though not so long and marked above all by the absence of any wrapper, the ring of the Neustrian Bombyx reminds one of the other’s cylinder, stripped of its scaly covering. It would be easy to multiply these instances of elegant grouping, contrived now in one way, now in another, but always with consummate art. It would take up too much time, however. Let us keep to the Pine Bombyx.

The hatching takes place in September, a little earlier in one case, a little later in another. So that I may easily watch the new-born caterpillars in their first labours, I have [[22]]placed a few egg-laden branches in the window of my study. They are standing in a glass of water which will keep them properly fresh for some time.

The little caterpillars leave the egg in the morning, at about eight o’clock. If I just lift the scales of the cylinder in process of hatching, I see black heads appear, which nibble and burst and push back the torn ceilings. The tiny creatures emerge slowly, some here and some there, all over the surface.

After the hatching, the scaly cylinder is as regular and as fresh in appearance as if it were still inhabited. We do not perceive that it is deserted until we raise the spangles. The eggs, still arranged in regular rows, are now so many yawning goblets of a slightly translucent white; they lack the cap-shaped lid, which has been rent and destroyed by the new-born grubs.

The puny creatures measure a millimetre[5] at most in length. Devoid as yet of the bright red that will soon be their adornment, they are pale-yellow, bristling with hairs, some shortish and black, others rather longer and white. The head, of a glossy black, is big [[23]]in proportion. Its diameter is twice that of the body. This exaggerated size of the head implies a corresponding strength of jaw, capable of attacking tough food from the start. A huge head, stoutly clad in horn, is the predominant feature of the budding caterpillar.

These macrocephalous ones are, as we see, well-armed against the hardness of the pine-needles, so well-armed in fact that the meal begins almost immediately. After roaming for a few moments at random among the scales of the common cradle, most of the young caterpillars make for the double leaf that served as an axis for the native cylinder and spread themselves over it at length. Others go to the adjacent leaves. Here as well as there they fall to; and the gnawed leaf is hollowed into faint and very narrow grooves, bounded by the veins, which are left intact.

From time to time, three or four who have eaten their fill fall into line and walk in step, but soon separate, each going his own way. This is practice for the coming processions. If I disturb them ever so little, they sway the front half of their bodies and wag their [[24]]heads with a jerky movement similar to the action of an intermittent spring.

But the sun reaches the corner of the window where the careful rearing is in progress. Then, sufficiently refreshed, the little family retreats to its native soil, the base of the double leaf, gathers into an irregular group and begins to spin. Its work is a gauze globule of extreme delicacy, supported on some of the neighbouring leaves. Under this tent, a very wide-meshed net, a siesta is taken during the hottest and brightest part of the day. In the afternoon, when the sun has gone from the window, the flock leaves its shelter, disperses around, sometimes forming a little procession within a radius of an inch, and starts browsing again.

Thus the very moment of hatching proclaims talents which age will develop without adding to their number. In less than an hour from the bursting of the egg, the caterpillar is both a processionary and a spinner. He also flees the light when taking refreshment. We shall soon find him visiting his grazing-grounds only at night.

The spinner is very feeble, but so active that in twenty-four hours the silken globe attains [[25]]the bulk of a hazel-nut and in a couple of weeks that of an apple. Nevertheless, it is not the nucleus of the great establishment in which the winter is to be spent. It is a provisional shelter, very light and inexpensive in materials. The mildness of the season makes anything else unnecessary. The young caterpillars freely gnaw the logs, the poles between which the threads are stretched, that is to say, the leaves contained within the silken tent. Their house supplies them at the same time with board and lodging. This excellent arrangement saves them from having to go out, a dangerous proceeding at their age. For these puny ones, the hammock is also the larder.

Nibbled down to their veins, the supporting leaves wither and easily come unfastened from the branches; and the silken globe becomes a hovel that crumbles with the first gust of wind. The family then moves on and goes elsewhere to erect a new tent, lasting no longer than the first. Even so does the Arab move on, as the pastures around his camel-hide dwelling become exhausted. These temporary establishments are renewed several times over, always at greater heights than the last, so much so that the tribe, which was hatched on [[26]]the lower branches trailing on the ground, gradually reaches the higher boughs and sometimes the very summit of the pine-tree.

In a few weeks’ time, a first moult replaces the humble fleece of the start, which is pale-coloured, shaggy and ugly, by another which lacks neither richness nor elegance. On the dorsal surface, the various segments, excepting the first three, are adorned with a mosaic of six little bare patches, of a bright red, which stand out a little above the dark background of the skin. Two, the largest, are in front, two behind and one, almost dot-shaped, on either side of the quadrilateral. The whole is surrounded by a palisade of scarlet bristles, divergent and lying almost flat. The other hairs, those of the belly and sides, are longer and whitish.

In the centre of this crimson marquetry stand two clusters of very short bristles, gathered into flattened tufts which gleam in the sun like specks of gold. The length of the caterpillar is now about two centimetres[6] and his width three or four millimetres.[7] Such is the costume of middle age, which, like the earlier one, was unknown to Réaumur. [[27]]

[1] René Antoine Ferchault de Réaumur (1683–1757), inventor of the Réaumur thermometer and author of Mémoires pour servir à l’histoire naturelle des insectes.—Translator’s Note. [↑]

[2] For the Cicada or Cigale, an insect remotely akin to the Grasshopper and found more particularly in the south of France, cf. Social Life in the Insect World, by J. H. Fabre, translated by Bernard Miall: chaps. i to iv.—Translator’s Note. [↑]

[3] The harmas was the enclosed piece of waste ground in which the author used to study his insects in their natural state.—Translator’s Note. [↑]

[4] The eponymous hero of Voltaire’s story of “the little great man,” published in 1752 in imitation of Gulliver’s Travels.—Translator’s Note. [↑]

[5] .039 inch.—Translator’s Note. [↑]

[6] About three-quarters of an inch.—Translator’s Note. [↑]

[7] .117 to .156 inch.—Translator’s Note. [↑]

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CHAPTER II

THE PINE PROCESSIONARY: THE NEST; THE COMMUNITY

November arrives, however, bringing cold weather; the time has come to build the stout winter tabernacle. High up in the pine the tip of a bough is chosen, with suitably close-packed and convergent leaves. The spinners surround it with a spreading network, which bends the adjacent leaves a little nearer and ends by incorporating them into the fabric. In this way they obtain an enclosure half silk, half leaves, capable of withstanding the inclemencies of the weather.

Early in December the work has increased to the size of a man’s two fists or more. In its ultimate perfection, it attains a volume of nearly half a gallon by the end of winter.

It is roughly egg-shaped, tapering to a certain length below and extended into a sheath which envelops the supporting branch. The origin of this silky extension is as follows: every evening between seven and nine o’clock, [[28]]weather permitting, the caterpillars leave the nest and go down the bare part of the bough which forms the pole of the tent. The road is broad, for this axis is sometimes as wide as the neck of a claret-bottle. The descent is accomplished without any attempt at order and always slowly, so much so that the first caterpillars to come out have not yet dispersed before they are caught up by the others. The branch is thus covered by a continuous bark of caterpillars, made up of the whole community, which gradually divides into squads and disperses to this side and that on the nearest branches to crop their leaves. Now not one of the caterpillars moves a step without working his spinneret. Therefore the broad downward path, which on the way back will be the ascending path, is covered, as the result of constant traffic, with a multitude of threads forming an unbroken sheath.

It is obvious that this sheath, in which each caterpillar, passing backwards and forwards on his nocturnal rambles, leaves a double thread, is not an indicator laid down with the sole object of simplifying the journey back to the nest: a mere ribbon would be enough for that. Its use might well be to strengthen the [[29]]edifice, to give it deeper foundations and to join it by a multitude of cables to the steady branch.

The whole thing thus consists, above, of the home distended into an ovoid and, below, of the stalk, the sheath surrounding the support and adding its resistance to that of the numerous other fastenings.

Each nest that has not yet had its shape altered by the prolonged residence of the caterpillars shows in the centre a bulky, milk-white shell, with around it a wrapper of diaphanous gauze. The central mass, formed of thickly-woven threads, has for a wall a thick quilt into which are absorbed, as supports, numbers of leaves, green and intact. The thickness of this wall may be anything up to three-quarters of an inch.

At the top of the dome are round openings, varying greatly in number and distribution, as wide across as an ordinary lead-pencil. These are the doors of the house, through which the caterpillars go in and out. All around the shell are projecting leaves, which the insects’ teeth have respected. From the tip of each leaf there radiate, in graceful, undulating curves, threads which, loosely interlaced, form [[30]]a light tent, a spacious verandah of careful workmanship, especially in the upper part. Here we find a broad terrace on which, in the daytime, the caterpillars come and doze in the sun, heaped one upon the other, with rounded backs. The network stretching overhead does duty as an awning: it moderates the heat of the sun’s rays; it also saves the sleepers from a fall when the bough rocks in the wind.

Let us take our scissors and rip open the nest from end to end longitudinally. A wide window opens and allows us to see the arrangement of the inside. The first thing to strike us is that the leaves contained in the enclosure are intact and quite sound. The young caterpillars in their temporary establishments gnaw the leaves within the silken wrapper to death; they thus have their larder stocked for a few days without having to quit their shelter in bad weather, a condition made necessary by their weakness. When they grow stronger and start working on their winter home, they are very careful not to touch the leaves. Why these new scruples?

The reason is evident. If bruised, those leaves, the framework of the house, would [[31]]very soon wither and then be blown off with the first breath of wind. The silken purse, torn from its base, would collapse. On the other hand, if the leaves are respected, they remain vigorous and furnish a stout support against the assaults of winter. A solid fastening is superfluous for the summer tent, which lasts but a day; it is indispensable to the permanent shelter which will have to bear the burden of heavy snows and the buffeting of icy winds. Fully alive to these perils, the spinner of the pine-tree considers himself bound, however importunate his hunger, not to saw through the rafters of his house.

Inside the nest, therefore, opened by my scissors I see a thick arcade of green leaves, more or less closely wrapped in a silky sheath whence dangle shreds of cast skin and strings of dried droppings. In short, this interior is an extremely unpleasant place, a rag-shop and a sewage-farm in one, and corresponds in no way with the imposing exterior. All around is a solid wall of quilting and of closely-woven leaves. There are no chambers, no compartments marked off by partition-walls. It is a single room, turned into a [[32]]labyrinth by the colonnade of green leaves placed in rows one above the other throughout the oval hall. Here the caterpillars stay when resting, gathered on the columns, heaped in confused masses.

When we remove the hopeless tangle at the top, we see the light filtering in at certain points of the roof. These luminous points correspond with the openings that communicate with the outer air. The network that forms a wrapper to the nest has no special exits. To pass through it in either direction, the caterpillars have only to push the sparse threads aside slightly. The inner wall, a compact rampart, has its doors; the flimsy outer veil has none.

It is in the morning, at about ten o’clock, that the caterpillars leave their night-apartment and come to take the sun on their terrace, under the awning which the points of the leaves hold up at a distance. They spend the whole day there dozing. Motionless, heaped together, they steep themselves deliciously in warmth and from time to time betray their bliss by nodding and wagging their heads. At six or seven o’clock, when it grows dark, the sleepers awake, bestir themselves, [[33]]separate and go their several ways over the surface of the nest.

We now behold an indeed delightful spectacle. Bright-red stripes meander in every direction over the white sheet of silk. One goes up, another comes down, a third moves aslant; others form a short procession. And, as they solemnly walk about in a splendid disorder, each glues to the ground which it covers the thread that constantly hangs from its lip.

Thus is the thickness of the shelter increased by a fine layer added immediately above the previous structure; thus is the dwelling strengthened by fresh supports. The adjoining green leaves are taken into the network and absorbed in the building. If the tiniest bit of them remains free, curves radiate from that point, increasing the size of the veil and fastening it at a greater distance. Every evening, therefore, for an hour or two, great animation reigns on the surface of the nest, if the weather permits; and the work of consolidating and thickening the structure is carried on with indefatigable zeal.

Do they foresee the future, these wary ones who take such precautions against the rigours of winter? Obviously not. Their few [[34]]months’ experience—if indeed experience can be mentioned in connection with a caterpillar—tells them of savoury bellyfuls of green stuff, of gentle slumbers in the sun on the terrace of the nest; but nothing hitherto has made them acquainted with cold, steady rain, with frost, snow and furious blasts of wind. And these creatures, knowing naught of winter’s woes, take the same precautions as if they were thoroughly aware of all that the inclement season holds in store for them. They work away at their house with an ardour that seems to say:

“Oh, how nice and warm we shall be in our beds here, nestling one against the other, when the pine-tree swings aloft its frosted candelabra! Let us work with a will! Laboremus!”

Yes, caterpillars, my friends, let us work with a will, great and small, men and grubs alike, so that we may fall asleep peacefully; you with the torpor that makes way for your transformation into Moths, we with that last sleep which breaks off life only to renew it. Laboremus!

Anxious to watch my caterpillars’ habits in detail, without having to sally forth by lantern-light, [[35]]often in bad weather, to see what happens in the pine-trees at the end of the enclosure, I have installed half-a-dozen nests in a greenhouse, a modest, glazed shelter which, though hardly any warmer than the air outside, at least affords protection from the wind and rain. Fixed in the sand, at a height of about eighteen inches, by the base of the bough that serves as both an axis and a framework, each nest receives for rations a bundle of little pine-branches, which are renewed as soon as they are consumed. I take my lantern every evening and pay my boarders a visit. This is the way in which most of my facts are obtained.

After the day’s work comes the evening meal. The caterpillars descend from the nest, adding a few more threads to the silvery sheath of the support, and reach the posy of fresh green stuff which is lying quite near. It is a magnificent sight to see the red-coated band lined up in twos and threes on each needle and in ranks so closely formed that the green sprigs of the bunch bend under the load.

The diners, all motionless, all poking their heads forward, nibble in silence, placidly. Their broad black foreheads gleam in the [[36]]rays of the lantern. A shower of granules drops on the sand below. These are the residues of easy-going stomachs, only too ready to digest their food. By to-morrow morning the soil will have disappeared under a greenish layer of this intestinal hail. Yes, indeed, it is a sight to see, one far more stimulating than that of the Silk-worms’ mess-room. Young and old, we are all so much interested in it that our evenings almost invariably end in a visit to the greenhouse caterpillars.

The meal is prolonged far into the night. Satisfied at last, some sooner, some later, they go back to the nest, where for a little longer, feeling their silk-glands filled, they continue spinning on the surface. These hard workers would scruple to cross the white carpet without contributing a few threads. It is getting on for one or even two o’clock in the morning when the last of the band goes indoors.

My duty as a foster-father is daily to renew the bunch of sprigs, which are shorn to the last leaf; on the other hand, my duty as an historian is to enquire to what extent the diet can be varied. The district supplies me with Processionaries on the Scotch pine, the maritime pine and the Aleppo pine indifferently, [[37]]but never on the other Coniferæ. Yet one would think that any resin-scented leaf ought to suit. So says chemical analysis.

We must mistrust the chemist’s retort when it pokes its nose into the kitchen. It may succeed in making butter out of tallow-candles and brandy out of potatoes; but, when it tells us that the products are identical, we shall do well to refuse these abominations. Science, astonishingly rich as it is in poison, will never provide us with anything fit to eat, because, though the raw substance falls to a large extent within its domain, that same substance escapes its methods the moment that it is wanted organized, divided and subdivided indefinitely by the process of life, as needed by the stomach, whose requirements are not to be met by measured doses of our reagents. The raw material of cell and fibre may perhaps be artificially obtained, some day; cell and fibre themselves, never. There’s the rub with your chemical feeding.

The caterpillars loudly proclaim the insurmountable difficulty of the problem. Relying on my chemical data, I offer them the different substitutes for the pine growing in my enclosure: the spruce, the yew, the thuja, the [[38]]juniper, the cypress. What! Am I asking them, Pine Caterpillars, to bite into that? They will take good care not to, despite the tempting resinous smell! They would die of hunger rather than touch it! One conifer and one only is excepted: the cedar. My charges browse upon its leaves with no appreciable repugnance. Why the cedar and not the others? I do not know. The caterpillar’s stomach, fastidious as our own, has its secrets.

Let us pass to other tests. I have just slit open longitudinally a nest whose internal structure I want to explore. Owing to the natural shrinkage of the split swan’s-down, the cleft reaches two fingers’ breadth in the centre and tapers at the top and bottom. What will the spinners do in the presence of such a disaster? The operation is performed by day, while the caterpillars are slumbering in heaps upon the dome. As the living-room is deserted at this time, I can cut boldly with the scissors without risk of damaging any part of the population.

My ravages do not wake the sleepers: all day long not one appears upon the breach. This indifference looks as though it were due [[39]]to the fact that the danger is not yet known. Things will be different to-night, when the busy work begins again. However dull they may be, the caterpillars will certainly notice that huge window which freely admits the deadly draughts of winter; and, possessing any amount of padding, they will crowd round the dangerous gap and stop it up in a trice. Thus do we argue, forgetting the animal’s intellectual darkness.

What really happens is that, when night falls, the indifference of the caterpillars remains as great as ever. The breach in the tent provokes not a sign of excitement. They move to and fro on the surface of the nest; they work, they spin as usual. There is no change, absolutely none, in their behaviour. When the road covered chances to bring some of them to the brink of the ravine, we see no alacrity on their part, no sign of anxiety, no attempt to close up the two edges of the slit. They simply strive to accomplish the difficult crossing and to continue their stroll as though they were walking on a perfect web. And they manage it somehow or other, by fixing the thread as far as the length of their body permits. [[40]]

Having once crossed the gulf, they pursue their way imperturbably, without stopping any more at the breach. Others come upon the scene and, using the threads already laid as foot-bridges, pass over the rent and walk on, leaving their own thread as they go. Thus the first night’s work results in the laying over the cleft of a filmy gauze, hardly perceptible, but just sufficient for the traffic of the colony. The same thing is repeated on the nights that follow; and the crevice ends by being closed with a scanty sort of Spider’s web. And that is all.

There is no improvement by the end of the winter. The window made by my scissors is still wide open, though thinly veiled; its black spindle shape shows from the top of the nest to the bottom. There is no darn in the split texture, no piece of swan’s-down let in between the two edges to restore the roof to its original state. If the accident had happened in the open air and not under glass, the foolish spinners would probably have died of cold in their cracked house.

Twice renewed with the same results, this test proves that the Pine Caterpillars are not alive to the danger of their split dwelling. [[41]]Expert spinners though they be, they seem as unconscious of the ruin of their work as the spools in a factory are of a broken thread. They could easily make good the damage by stopping up the breach with the silk that is lavished elsewhere without urgent need; they could weave upon it a material as thick and solid as the rest of the walls. But no, they placidly continue their habitual task; they spin as they spun yesterday and as they will spin to-morrow, strengthening the parts that are already strong, thickening what is already thick enough; and not one thinks of stopping the disastrous gap. To let a piece into that hole would mean weaving the tent all over again from the beginning; and no insect, however industrious, goes back to what it has already done.

I have often called attention to this feature in animal psychology; notably I have described the ineptitude of the caterpillar of the Great Peacock Moth.[1] When the experimenter lops the top off the complicated eel-trap which forms the pointed end of the cocoon, this caterpillar spends the silk remaining [[42]]to him in work of secondary importance, instead of making good the series of cones, each fitting into the other, which are so essential to the hermit’s protection. He continues his normal task imperturbably, as though nothing out of the way had taken place. Even so does the spinner in the pine-tree act with his burst tent.

Your foster-parent must perpetrate yet another piece of mischief, O my Processionary; but this time it shall be to your advantage! It does not take me long to perceive that the nests intended to last through the winter often contain a population much greater than that of the temporary shelters woven by the very young caterpillars. I also notice that, when they have attained their ultimate dimensions, these nests differ very considerably in size. The largest of them are equal to five or six of the smallest. What is the cause of these variations?

Certainly, if all the eggs turned out well, the scaly cylinder containing the laying of a single mother would be enough to fill a splendid purse: there are three hundred enamelled beads here for hatching. But in families which swarm unduly an enormous waste always [[43]]takes places and restores the balance of things; if the called are legion, the chosen are a well thinned-out troop, as is proved by the Cicada, the Praying Mantis[2] and the Cricket.

The Pine Processionary, another crucible of organic matter of which various devourers take advantage, is also reduced in numbers immediately after the hatching. The delicate mouthful has shrunk to a few dozens of survivors around the light globular network in which the family passes the sunny autumn days. Soon they will have to be thinking of the stoutly-built winter tent. At such a time, it would be a boon if they could be many, for from union springs strength.

I suspect an easy method of fusion among a few families. To serve them as a guide in their peregrinations about the tree, the caterpillars have their silk ribbon, which they follow on their return, after describing a bend. They may also miss it and strike another, one differing in no respect from their own. This new ribbon marks the way to some nest situated in the neighbourhood. The strayed [[44]]caterpillars, failing to distinguish it from their own ribbon, follow it conscientiously and in this manner end by reaching a strange dwelling. Suppose them to be peacefully received: what will happen?

Once fused, the several groups assembled by the accident of the path will form a powerful city, fitted to produce great works; the concerted weaklings will give rise to a strong, united body. This would explain the thickly-populated, bulky nests situated so near to others that have remained puny. The former would be the work of a syndicate incorporating the interests of spinners collected from different parts; the latter would belong to families left in isolation by the luck of the road.

It remains to be seen whether the chance-comers, guided by a strange ribbon, meet with a good reception in the new abode. The experiment is easily made upon the nests in the greenhouse. In the evening, at the hours devoted to grazing, I remove with a pruning-shears the different little branches covered with the population of one nest and lay them on the provisions of the neighbouring nest, which provisions are also overrun with caterpillars. [[45]]Or I can make shorter work of it by taking the whole bunch, well covered with the troop, of the first pouch and planting it right beside the bunch of the second, so that the leaves of the two mingle a little at the edges.

There is not the least quarrelling between the real proprietors and the new arrivals. Both go on peacefully browsing, as though nothing had happened. And all without hesitation, when bed-time comes, make for the nest, like brothers who have always lived together; all do some spinning before retiring to rest, thicken the blanket a little and are then swallowed up in the dormitory. By repeating the same operation next day and, if necessary, the day after, in order to collect the laggards, I succeed without the slightest difficulty in wholly depopulating the first nest and transferring all its caterpillars to the second.

I venture to do something better still. The same method of transportation allows me to quadruple the output of a spinning-mill by adding to it the workers of three similar establishments. And, if I limit myself to this increase, the reason is not that any confusion [[46]]manifests itself in this shifting of quarters, but that I see no bounds to my experiment, so cheerfully do the caterpillars accept any addition to their number. The more spinners, the more spinning: a very judicious rule of conduct.

Let us add that the caterpillars which have been transported cherish no regrets for their old house. They are quite at home with the others and make no attempt to regain the nest whence they were banished by my artifices. It is not the distance that discourages them, for the empty dwelling is only half a yard away at most. If, for the purpose of my studies, I wish to restock the deserted nest, I am obliged once more to resort to transportation, which invariably proves successful.

Later, in February, when an occasional fine day allows of long processions on the walls and the sand-covered shelf of the greenhouse, I am able to watch the fusing of two groups without personally intervening. All that I have to do is patiently to follow the evolutions of a file on the march. I see it sometimes, after leaving one nest, enter a different one, guided by some fortuitous [[47]]change of route. Thenceforward the strangers form part of the community on the same footing as the others. In a like fashion, when the caterpillars walk abroad upon the tree at night, the scanty groups of the outset must increase and gather the number of spinners which an extensive building requires.

Everything for everybody. So says the Pine Processionary, nibbling his leaves without quarrelling in the least over his neighbours’ mouthfuls, or else entering—and being always peacefully received—another’s home precisely as he would his own. Whether a member of the tribe or a stranger, he finds room in the refectory and room in the dormitory. The others’ nest is his nest. The others’ grazing-ground is his grazing-ground, in which he is entitled to his fair share, one neither greater nor smaller than the share of his habitual or casual companions.

Each for all and all for each. So says the Processionary, who every evening spends his little capital of silk on enlarging a shelter that is often new to him. What would he do with his puny skein, if alone? Hardly anything. But there are hundreds and hundreds of them in the spinning-mill; and the result [[48]]of their infinitesimal contributions, woven into a common stuff, is a thick blanket capable of resisting the winter. In working for himself, each works for the others; and these on their side work as zealously for each. O lucky animals that know nothing of property, the mother of strife! O enviable cenobites, who practise the strictest communism!

These habits of the caterpillars invite a few reflections. Generous minds, richer in illusions than in logic, set communism before us as the sovran cure for human ills. Is it practicable among mankind? At all times there have been, there still are and there always will be, fortunately, associations in which it is possible to forget in common some small part of the hardships of life; but is it possible to generalize?

The caterpillars of the pine can give us much valuable information in this respect. Let us have no false shame: our material needs are shared by the animals; they struggle as we do to take part in the general banquet of the living; and the manner in which they solve the problem of existence is not to be despised. Let us then ask ourselves what [[49]]are the reasons that cause cenobitism to flourish among the Processionaries.

One answer suggests itself inevitably, to begin with: the food problem, that terrible disturber of the world’s tranquillity, is here non-existent. Peace reigns as soon as the stomach is certain of being filled without a struggle. A pine-needle or even less suffices for the caterpillar’s meal; and that needle is always there, waiting to be eaten, is there in inexhaustible numbers, almost on the threshold of the home. When dinner-time arrives, we caterpillars go out, we take the air, we walk a little in procession; then, without laborious seeking, without jealous rivalries, we seat ourselves at the banquet. The table is plentifully spread and will never be bare, so large and generous is the pine; all that we need do is, from one evening to the next, to move our dining-room a little farther on. Consequently, there are no present and no future cares on the subject of provisions: the caterpillar finds food to eat almost as easily as he finds air to breathe.

The atmosphere feeds all creatures on air with a bounty which it is not necessary to crave. All unknown to itself, without the [[50]]agency of any effort or labour, the animal receives its share of the most vital of elements. The niggardly earth, on the contrary, surrenders its gifts only when laboriously forced. Not fruitful enough to satisfy every need, it leaves the division of the food to the fierce eagerness of competition.

The mouthful to be procured engenders war between consumers. Look at two Ground-beetles coming at the same time upon a bit of Earth-worm. Which of the two shall have the morsel? The matter shall be decided by battle, desperate, ferocious battle. With these famished ones, who eat at long intervals and do not always eat their fill, communal life is out of the question.

The Pine Caterpillar is free from these woes. He finds the earth as generous as the atmosphere; he finds eating as easy as breathing. Other instances of perfect communism might be named. All occur among species living on a vegetable diet, provided however that victuals are plentiful and obtainable without a hard search. An animal diet, on the contrary, a prey, always more or less difficult to secure, banishes cenobitism. Where the [[51]]portion is too small for one, what excuse would there be for guests?

The Pine Processionary knows nothing of privation. He knows as little of family ties, another source of unrelenting competition. To make ourselves a place in the sun is but a half of the struggle imposed upon us by life: we must also, as far as possible, prepare a place for our successors; and, as the preservation of the species is of greater importance than that of the individual, the struggle for the future is even fiercer than the struggle for the present. Every mother regards the welfare of her offspring as her primary law. Perish all else, provided that the brood flourish! Every one for himself is her maxim, imposed by the rigours of the general conflict; every one for himself is her rule, the safeguard of the future.

With maternity and its imperious duties, communism ceases to be practicable. At first sight, certain Hymenoptera[3] seem to declare the contrary. We find, for instance, the Mason-bees of the Sheds[4] nesting in myriads [[52]]on the same tiles and building a monumental edifice at which all the mothers work. Is this really a community? Not at all. It is a city in which the inhabitants have neighbours, not collaborators. Each mother kneads her pots of honey; each amasses a dowry for her offspring and nothing but a dowry for her offspring; each wears herself out for her family and only for her family. Oh, it would be a serious business if some one merely came and alighted on the brim of a cell that did not belong to her; the mistress of the house would give her to understand, by means of a sound drubbing, that manners such as those are not to be endured! She would have to skedaddle very quickly, unless she wanted a fight. The rights of property are sacred here.

Even the much more social Hive-bee is no exception to the rule of maternal egoism. To each hive one mother. If there be two, civil war breaks out and one of them perishes by the other’s dagger or else quits the country, followed by a part of the swarm. Although virtually fit to lay eggs, the other Bees, to the number of some twenty thousand, renounce maternity and vow themselves to celibacy in order to bring up the prodigious [[53]]family of the one and only mother. Here, communism reigns, under certain aspects; but, for the immense majority, motherhood is forthwith abolished.

Even so with the Wasps, the Ants, the Termites[5] and the various social insects. Life in common costs them dear. Thousands and thousands remain incomplete and become the humble auxiliaries of a few who are sexually endowed. But, whenever maternity is the general portion, individualism reappears, as among the Mason-bees, notwithstanding their show of communism.

The Pine Caterpillars are exempt from the duty of preserving the race. They have no sex, or rather are obscurely preparing one, as undecided and rudimentary as all that is not yet but must one day be. With the blossoming of maternity, that flower of adult age, individual property will not fail to appear, attended by its rivalries. The insect now so peaceable will, like the others, have its displays of selfish intolerance. The mothers will isolate themselves, jealous of the double pine-needle in which the cylinder of eggs is to be fixed; the males, fluttering their wings, [[54]]will challenge one another for the possession of the coveted bride. It is not a serious struggle among these easy-going ones, but still it presents a faint picture of those mortal affrays which the mating so often produces. Love rules the world by battle; it too is a hotbed of competition.

The caterpillar, being almost sexless, is indifferent to amorous instincts. This is the first condition for living pacifically in common. But it is not enough. The perfect concord of the community demands among all its members an equal division of strength and talent, of taste and capacity for work. This condition, which perhaps is the most important of all, is fulfilled preeminently. If there were hundreds, if there were thousands of them in the same nest, there would be no difference between any of them.

They are all the same size and equally strong; all wear the same dress; all possess the same gift for spinning; and all with equal zeal expend the contents of their silk-glands for the general welfare. No one idles, no one lounges along when there is work to be done. With no other stimulus than the satisfaction of doing their duty, every evening, [[55]]when the weather is favourable, they all spin with equal industry and drain to the last drop their reservoirs of silk, which have become distended during the day. In their tribe there is no question of skilled or unskilled, of strong or weak, of abstemious or gluttonous; there are neither hard-workers nor idlers, neither savers nor spendthrifts. What one does the others do, with a like zeal, no more and no less well. It is a splendid world of equality truly, but, alas, a world of caterpillars!

If it suited us to go to school to the Pine Processionary, we should soon see the inanity of our levelling and communistic theories. Equality is a magnificent political catchword, but little more. Where is it, this equality of ours? In our social groups, could we find as many as two persons exactly equal in strength, health, intelligence, capacity for work, foresight and all the other gifts which are the great factors of prosperity? Where should we find anything analogous to the exact parity prevailing among caterpillars? Nowhere. Inequality is our law. And a good thing, too.

A sound which is invariably the same, however often multiplied, does not constitute a [[56]]harmony. We need dissimilarities, sounds loud and soft, deep and shrill; we need even discords which, by their harshness, throw into relief the sweetness of the chords. In the same way, human societies are harmonious only with the aid of contraries. If the dreams of our levellers could be realized, we should sink to the monotony of the caterpillar societies; art, science, progress and the lofty flights of the imagination would slumber indefinitely in the dead calm of mediocrity.

Besides, if this general levelling were effected, we should still be very far from communism. To achieve that, we should have to do away with the family, as the caterpillars and Plato teach us; we should need abundance of food obtained without any effort. So long as a mouthful of bread is difficult to acquire, demanding an industry and labour of which we are not all equally capable, so long as the family remains the sacred reason for our foresight, so long will the generous theory of all for each and each for all be absolutely impracticable.

And then should we gain by abolishing the struggle for the daily bread of ourselves and those dependent on us? It is very doubtful. [[57]]We should be getting rid of this world’s two great joys, work and the family, the only joys that give any value to life; we should be stifling exactly that which makes our greatness. And the result of this bestial sacrilege would be a community of human caterpillars. Thus does the Pine Processionary teach us by his example. [[58]]

[1] In the course of an essay on aberration of instinct in a certain Mason-wasp which is not yet translated into English.—Translator’s Note. [↑]

[2] A predatory insect, akin to the Locusts and Crickets, which, when at rest, adopts an attitude resembling that of prayer. Cf. Social Life in the Insect World: chaps. v to vii.—Translator’s Note. [↑]

[3] The order of insects embracing the Bees, Wasps, Ants, Saw-flies, Ichneumon-flies, etc.—Translator’s Note. [↑]

[4] Cf. The Mason-bees, by J. Henri Fabre, translated by Alexander Teixeira de Mattos, passim.—Translator’s Note. [↑]

[5] White Ants.—Translator’s Note. [↑]

[[Contents]]

CHAPTER III

THE PINE PROCESSIONARY: THE PROCESSION

Drover Dingdong’s Sheep followed the Ram which Panurge had maliciously thrown overboard and leapt nimbly into the sea, one after the other, “for you know,” says Rabelais, “it is the nature of the sheep always to follow the first, wheresoever it goes; which makes Aristotle mark them for the most silly and foolish animals in the world.”[1]

The Pine Caterpillar is even more sheep-like, not from foolishness, but from necessity: where the first goes all the others go, in a regular string, with not an empty space between them.

They proceed in single file, in a continuous row, each touching with its head the rear of the one in front of it. The complex twists and turns described in his vagaries by the caterpillar leading the van are scrupulously described by all the others. No Greek theoria winding its way to the Eleusinian festivals was [[59]]ever more orderly. Hence the name of Processionary given to the gnawer of the pine.

His character is complete when we add that he is a rope-dancer all his life long: he walks only on the tight-rope, a silken rail placed in position as he advances. The caterpillar who chances to be at the head of the procession dribbles his thread without ceasing and fixes it on the path which his fickle preferences cause him to take. The thread is so tiny that the eye, though armed with a magnifying-glass, suspects it rather than sees it.

But a second caterpillar steps on the slender footboard and doubles it with his thread; a third trebles it; and all the others, however many there be, add the sticky spray from their spinnerets, so much so that, when the procession has marched by, there remains, as a record of its passing, a narrow white ribbon whose dazzling whiteness shimmers in the sun. Very much more sumptuous than ours, their system of road-making consists in upholstering with silk instead of macadamizing. We sprinkle our roads with broken stones and level them by the pressure of a heavy steam-roller; they lay over their paths a soft satin [[60]]rail, a work of general interest to which each contributes his thread.

What is the use of all this luxury? Could they not, like other caterpillars, walk about without these costly preparations? I see two reasons for their mode of progression. It is night when the Processionaries sally forth to browse upon the pine-leaves. They leave their nest, situated at the top of a bough, in profound darkness; they go down the denuded pole till they come to the nearest branch that has not yet been gnawed, a branch which becomes lower and lower by degrees as the consumers finish stripping the upper storeys; they climb up this untouched branch and spread over the green needles.

When they have had their suppers and begin to feel the keen night air, the next thing is to return to the shelter of the house. Measured in a straight line, the distance is not great, hardly an arm’s length; but it cannot be covered in this way on foot. The caterpillars have to climb down from one crossing to the next, from the needle to the twig, from the twig to the branch, from the branch to the bough and from the bough, by a no less angular path, to go back home. It [[61]]is useless to rely upon sight as a guide on this long and erratic journey. The Processionary, it is true, has five ocular specks on either side of his head, but they are so infinitesimal, so difficult to make out through the magnifying-glass, that we cannot attribute to them any great power of vision. Besides, what good would those short-sighted lenses be in the absence of light, in black darkness?

It is equally useless to think of the sense of smell. Has the Processional any olfactory powers or has he not? I do not know. Without giving a positive answer to the question, I can at least declare that his sense of smell is exceedingly dull and in no way suited to help him find his way. This is proved, in my experiments, by a number of hungry caterpillars that, after a long fast, pass close beside a pine-branch without betraying any eagerness or showing a sign of stopping. It is the sense of touch that tells them where they are. So long as their lips do not chance to light upon the pasture-land, not one of them settles there, though he be ravenous. They do not hasten to food which they have scented from afar; they stop at a branch which they encounter on their way. [[62]]

Apart from sight and smell, what remains to guide them in returning to the nest? The ribbon spun on the road. In the Cretan labyrinth, Theseus would have been lost but for the clue of thread with which Ariadne supplied him. The spreading maze of the pine-needles is, especially at night, as inextricable a labyrinth as that constructed for Minos. The Processionary finds his way through it, without the possibility of a mistake, by the aid of his bit of silk. At the time for going home, each easily recovers either his own thread or one or other of the neighbouring threads, spread fanwise by the diverging herd; one by one the scattered tribe line up on the common ribbon, which started from the nest; and the sated caravan finds its way back to the manor with absolute certainty.

Longer expeditions are made in the daytime, even in winter, if the weather be fine. Our caterpillars then come down from the tree, venture on the ground, march in procession for a distance of thirty yards or so. The object of these sallies is not to look for food, for the native pine-tree is far from being exhausted: the shorn branches hardly count amid the vast leafage. Moreover, the caterpillars [[63]]observe complete abstinence till nightfall. The trippers have no other object than a constitutional, a pilgrimage to the outskirts to see what these are like, possibly an inspection of the locality where, later on, they mean to bury themselves in the sand for their metamorphosis.

It goes without saying that, in these greater evolutions, the guiding cord is not neglected. It is now more necessary than ever. All contribute to it from the produce of their spinnerets, as is the invariable rule whenever there is a progression. Not one takes a step forward without fixing to the path the thread hanging from his lip.

If the series forming the procession be at all long, the ribbon is dilated sufficiently to make it easy to find; nevertheless, on the homeward journey, it is not picked up without some hesitation. For observe that the caterpillars when on the march never turn completely; to wheel round on their tight-rope is a method utterly unknown to them. In order therefore to regain the road already covered, they have to describe a zig-zag whose windings and extent are determined by the leader’s fancy. Hence come gropings and [[64]]roamings which are sometimes prolonged to the point of causing the herd to spend the night out of doors. It is not a serious matter. They collect into a motionless cluster. To-morrow the search will start afresh and will sooner or later be successful. Oftener still the winding curve meets the guide-thread at the first attempt. As soon as the first caterpillar has the rail between his legs, all hesitation ceases; and the band makes for the nest with hurried steps.

The use of this silk-tapestried roadway is evident from a second point of view. To protect himself against the severity of the winter which he has to face when working, the Pine Caterpillar weaves himself a shelter in which he spends his bad hours, his days of enforced idleness. Alone, with none but the meagre resources of his silk-glands, he would find difficulty in protecting himself on the top of a branch buffeted by the winds. A substantial dwelling, proof against snow, gales and icy fogs, requires the cooperation of a large number. Out of the individual’s piled-up atoms, the community obtains a spacious and durable establishment.

The enterprise takes a long time to complete. [[65]]Every evening, when the weather permits, the building has to be strengthened and enlarged. It is indispensable, therefore, that the corporation of workers should not be dissolved while the stormy season continues and the insects are still in the caterpillar stage. But, without special arrangements, each nocturnal expedition at grazing-time would be a cause of separation. At that moment of appetite for food there is a return to individualism. The caterpillars become more or less scattered, settling singly on the branches around; each browses his pine-needle separately. How are they to find one another afterwards and become a community again?

The several threads left on the road make this easy. With that guide, every caterpillar, however far he may be, comes back to his companions without ever missing the way. They come hurrying from a host of twigs, from here, from there, from above, from below; and soon the scattered legion reforms into a group. The silk thread is something more than a road-making expedient: it is the social bond, the system that keeps the members of the community indissolubly united.

At the head of every procession, long or [[66]]short, goes a first caterpillar whom I will call the leader of the march or file, though the word leader, which I use for want of a better, is a little out of place here. Nothing, in fact, distinguishes this caterpillar from the others: it just depends upon the order in which they happen to line up; and mere chance brings him to the front. Among the Processionaries, every captain is an officer of fortune. The actual leader leads; presently he will be a subaltern, if the file should break up in consequence of some accident and be formed anew in a different order.

His temporary functions give him an attitude of his own. While the others follow passively in a close file, he, the captain, tosses himself about and with an abrupt movement flings the front of his body hither and thither. As he marches ahead he seems to be seeking his way. Does he in point of fact explore the country? Does he choose the most practicable places? Or are his hesitations merely the result of the absence of a guiding thread on ground that has not yet been covered? His subordinates follow very placidly, reassured by the cord which they hold between their legs; he, deprived of that support, is uneasy. [[67]]

Why cannot I read what passes under his black, shiny skull, so like a drop of tar? To judge by actions, there is here a small dose of discernment which is able, after experimenting, to recognize excessive roughnesses, over-slippery surfaces, dusty places that offer no resistance and, above all, the threads left by other excursionists. This is all or nearly all that my long acquaintance with the Processionaries has taught me as to their mentality. Poor brains, indeed; poor creatures, whose commonwealth has its safety hanging upon a thread!

The processions vary greatly in length. The finest that I have seen manœuvring on the ground measured twelve or thirteen yards and numbered about three hundred caterpillars, drawn up with absolute precision in a wavy line. But, if there were only two in a row, the order would still be perfect: the second touches and follows the first.

By February I have processions of all lengths in the greenhouse. What tricks can I play upon them? I see only two: to do away with the leader; and to cut the thread.

The suppression of the leader of the file produces nothing striking. If the thing is [[68]]done without creating a disturbance, the procession does not alter its ways at all. The second caterpillar, promoted to captain, knows the duties of his rank off-hand: he selects and leads, or rather he hesitates and gropes.

The breaking of the silk ribbon is not very important either. I remove a caterpillar from the middle of the file. With my scissors, so as not to cause a commotion in the ranks, I cut the piece of ribbon on which he stood and clear away every thread of it. As a result of this breach, the procession acquires two marching leaders, each independent of the other. It may be that the one in the rear joins the file ahead of him, from which he is separated by but a slender interval; in that case, things return to their original condition. More frequently, the two parts do not become reunited. In that case, we have two distinct processions, each of which wanders where it pleases and diverges from the other. Nevertheless, both will be able to return to the nest by discovering sooner or later, in the course of their peregrinations, the ribbon on the other side of the break.

These two experiments are only moderately [[69]]interesting. I have thought out another, one more fertile in possibilities. I propose to make the caterpillars describe a close circuit, after the ribbons running from it and liable to bring about a change of direction have been destroyed. The locomotive engine pursues its invariable course so long as it is not shunted on to a branch-line. If the Processionaries find the silken rail always clear in front of them, with no switches anywhere, will they continue on the same track, will they persist in following a road that never comes to an end? What we have to do is to produce this circuit, which is unknown under ordinary conditions, by artificial means.

The first idea that suggests itself is to seize with the forceps the silk ribbon at the back of the train, to bend it without shaking it and to bring the end of it ahead of the file. If the caterpillar marching in the van steps upon it, the thing is done: the others will follow him faithfully. The operation is very simple in theory but very difficult in practice and produces no useful results. The ribbon, which is extremely slight, breaks under the weight of the grains of sand that stick to it and are lifted with it. If it does not break, the caterpillars [[70]]at the back, however delicately we may go to work, feel a disturbance which makes them curl up or even let go.

There is a yet greater difficulty: the leader refuses the ribbon laid before him; the cut end makes him distrustful. Failing to see the regular, uninterrupted road, he slants off to the right or left, he escapes at a tangent. If I try to interfere and to bring him back to the path of my choosing, he persists in his refusal, shrivels up, does not budge; and soon the whole procession is in confusion. We will not insist: the method is a poor one, very wasteful of effort for at best a problematical success.

We ought to interfere as little as possible and obtain a natural closed circuit. Can it be done? Yes. It lies in our power, without the least meddling, to see a procession march along a perfect circular track. I owe this result, which is eminently deserving of our attention, to pure chance.

On the shelf with the layer of sand in which the nests are planted stand some big palm-vases measuring nearly a yard and a half in circumference at the top. The caterpillars often scale the sides and climb up to the [[71]]moulding which forms a cornice around the opening. This place suits them for their processions, perhaps because of the absolute firmness of the surface, where there is no fear of landslides, as on the loose, sandy soil below; and also, perhaps, because of the horizontal position, which is favorable to repose after the fatigue of the ascent. It provides me with a circular track all ready-made. I have nothing to do but wait for an occasion propitious to my plans. This occasion is not long in coming.

On the 30th of January, 1896, a little before twelve o’clock in the day, I discover a numerous troop making their way up and gradually reaching the popular cornice. Slowly, in single file, the caterpillars climb the great vase, mount the ledge and advance in regular procession, while others are constantly arriving and continuing the series. I wait for the string to close up, that is to say, for the leader, who keeps following the circular moulding, to return to the point from which he started. My object is achieved in a quarter of an hour. The closed circuit is realized magnificently, in something very nearly approaching a circle. [[72]]

The next thing is to get rid of the rest of the ascending column, which would disturb the fine order of the procession by an excess of newcomers; it is also important that we should do away with all the silken paths, both new and old, that can put the cornice into communication with the ground. With a thick hair-pencil I sweep away the surplus climbers; with a big brush, one that leaves no smell behind it—for this might afterwards prove confusing—I carefully rub down the vase and get rid of every thread which the caterpillars have laid on the march. When these preparations are finished, a curious sight awaits us.

In the uninterrupted circular procession there is no longer a leader. Each caterpillar is preceded by another on whose heels he follows, guided by the silk track, the work of the whole party; he again has a companion close behind him, following him in the same orderly way. And this is repeated without variation throughout the length of the chain. None commands, or rather none modifies the trail according to his fancy; all obey, trusting in the guide who ought normally to lead the [[73]]march and who in reality has been abolished by my trickery.

From the first circuit of the edge of the tub the rail of silk has been laid in position and is soon turned into a narrow ribbon by the procession, which never ceases dribbling its thread as it goes. The rail is simply doubled and has no branches anywhere, for my brush has destroyed them all. What will the caterpillars do on this deceptive, closed path? Will they walk endlessly round and round until their strength gives out entirely?

The old schoolmen were fond of quoting Buridan’s[2] Ass, that famous Donkey who, when placed between two bundles of hay, starved to death because he was unable to decide in favour of either by breaking the equilibrium between two equal but opposite attractions. They slandered the worthy animal. The Ass, who is no more foolish than any one else, would reply to the logical snare by feasting off both bundles. Will my caterpillars [[74]]show a little of his mother wit? Will they, after many attempts, be able to break the equilibrium of their closed circuit, which keeps them on a road without a turning? Will they make up their minds to swerve to this side or that, which is the only method of reaching their bundle of hay, the green branch yonder, quite near, not two feet off?

I thought that they would and I was wrong. I said to myself:

“The procession will go on turning for some time, for an hour, two hours perhaps; then the caterpillars will perceive their mistake. They will abandon the deceptive road and make their descent somewhere or other.”

That they should remain up there, hard pressed by hunger and the lack of cover, when nothing prevented them from going away, seemed to me inconceivable imbecility. Facts, however, forced me to accept the incredible. Let us describe them in detail.

The circular procession begins, as I have said, on the 30th of January, about midday, in splendid weather. The caterpillars march at an even pace, each touching the stern of the one in front of him. The unbroken chain eliminates the leader with his changes of direction; [[75]]and all follow mechanically, as faithful to their circle as are the hands of a watch. The headless file has no liberty left, no will; it has become mere clock-work. And this continues for hours and hours. My success goes far beyond my wildest suspicions. I stand amazed at it, or rather I am stupefied.

Meanwhile, the multiplied circuits change the original rail into a superb ribbon a twelfth of an inch broad. I can easily see it glittering on the red ground of the pot. The day is drawing to a close and no alteration has yet taken place in the position of the trail. A striking proof confirms this.

The trajectory is not a plane curve, but one which, at a certain point, deviates and goes down a little way to the lower surface of the cornice, returning to the top some eight inches farther. I marked these two points of deviation in pencil on the vase at the outset. Well, all that afternoon and, more conclusive still, on the following days, right to the end of this mad dance, I see the string of caterpillars dip under the ledge at the first point and come to the top again at the second. Once the first thread is laid, the road to be pursued is permanently established. [[76]]

If the road does not vary, the speed does. I measure nine centimetres[3] a minute as the average distance covered. But there are more or less lengthy halts; the pace slackens at times, especially when the temperature falls. At ten o’clock in the evening the walk is little more than a lazy swaying of the body. I foresee an early halt, in consequence of the cold, of fatigue and doubtless also of hunger.

Grazing-time has arrived. The caterpillars have come crowding from all the nests in the greenhouse to browse upon the pine-branches planted by myself beside the silken purses. Those in the garden do the same, for the temperature is mild. The others, lined up along the earthenware cornice, would gladly take part in the feast; they are bound to have an appetite after a ten hours’ walk. The branch stands green and tempting not a hand’s breadth away. To reach it they need but go down; and the poor wretches, foolish slaves of their ribbon that they are, cannot make up their minds to do so. I leave the famished ones at half-past ten, persuaded that they will take counsel with their pillow and [[77]]that on the morrow things will have resumed their ordinary course.

I was wrong. I was expecting too much of them when I accorded them that faint gleam of intelligence which the tribulations of a distressful stomach ought, one would think, to have aroused. I visit them at dawn. They are lined up as on the day before, but motionless. When the air grows a little warmer, they shake off their torpor, revive and start walking again. The circular procession begins anew, like that which I have already seen. There is nothing more and nothing less to be noted in their machine-like obstinacy.

This time it is a bitter night. A cold snap has supervened, was indeed foretold in the evening by the garden caterpillars, who refused to come out despite appearances which to my duller senses seemed to promise a continuation of the fine weather. At daybreak the rosemary-walks are all asparkle with rime and for the second time this year there is a sharp frost. The large pond in the garden is frozen over. What can the caterpillars in the conservatory be doing? Let us go and see.

All are ensconced in their nests, except the [[78]]stubborn processionists on the edge of the vase, who, deprived of shelter as they are, seem to have spent a very bad night. I find them clustered in two heaps, without any attempt at order. They have suffered less from the cold, thus huddled together.

’Tis an ill wind that blows nobody any good. The severity of the night has caused the ring to break into two segments which will, perhaps, afford a chance of safety. Each group, as it revives and resumes its walk, will presently be headed by a leader who, not being obliged to follow a caterpillar in front of him, will possess some liberty of movement and perhaps be able to make the procession swerve to one side. Remember that, in the ordinary processions, the caterpillar walking ahead acts as a scout. While the others, if nothing occurs to create excitement, keep to their ranks, he attends to his duties as a leader and is continually turning his head to this side and that, investigating, seeking, groping, making his choice. And things happen as he decides: the band follows him faithfully. Remember also that, even on a road which has already been travelled and beribboned, the guiding caterpillar continues to explore. [[79]]

There is reason to believe that the Processionaries who have lost their way on the ledge will find a chance of safety here. Let us watch them. On recovering from their torpor, the two groups line up by degrees into two distinct files. There are therefore two leaders, free to go where they please, independent of each other. Will they succeed in leaving the enchanted circle? At the sight of their large black heads swaying anxiously from side to side, I am inclined to think so for a moment. But I am soon undeceived. As the ranks fill out, the two sections of the chain meet and the circle is reconstituted. The momentary leaders once more become simple subordinates; and again the caterpillars march round and round all day.

For the second time in succession, the night, which is very calm and magnificently starry, brings a hard frost. In the morning the Processionaries on the tub, the only ones who have camped out unsheltered, are gathered into a heap which largely overflows both sides of the fatal ribbon. I am present at the awakening of the numbed ones. The first to take the road is, as luck will have it, outside [[80]]the track. Hesitatingly he ventures into unknown ground. He reaches the top of the rim and descends upon the other side on the earth in the vase. He is followed by six others, no more. Perhaps the rest of the troop, who have not fully recovered from their nocturnal torpor, are to lazy to bestir themselves.

The result of this brief delay is a return to the old track. The caterpillars embark on the silken trail and the circular march is resumed, this time in the form of a ring with a gap in it. There is no attempt, however, to strike a new course on the part of the guide whom this gap has placed at the head. A chance of stepping outside the magic circle has presented itself at last; and he does not know how to avail himself of it.

As for the caterpillars who have made their way to the inside of the vase, their lot is hardly improved. They climb to the top of the palm, starving and seeking for food. Finding nothing to eat that suits them, they retrace their steps by following the thread which they have left on the way, climb the ledge of the pot, strike the procession again and, without further anxiety, slip back into the ranks. [[81]]Once more the ring is complete, once more the circle turns and turns.

Then when will the deliverance come? There is a legend that tells of poor souls dragged along in an endless round until the hellish charm is broken by a drop of holy water. What drop will good fortune sprinkle on my Processionaries to dissolve their circle and bring them back to the nest? I see only two means of conjuring the spell and obtaining a release from the circuit. These two means are two painful ordeals. A strange linking of cause and effect: from sorrow and wretchedness good is to come.

And, first, shrivelling as the result of cold. The caterpillars gather together without any order, heap themselves some on the path, some, more numerous these, outside it. Among the latter there may be, sooner or later, some revolutionary who, scorning the beaten track, will trace out a new road and lead the troop back home. We have just seen an instance of it. Seven penetrated to the interior of the vase and climbed the palm. True, it was an attempt with no result, but still an attempt. For complete success, all that need be done would have been to take the [[82]]opposite slope. An even chance is a great thing. Another time we shall be more successful.

In the second place, the exhaustion due to fatigue and hunger. A lame one stops, unable to go farther. In front of the defaulter the procession still continues to wend its way for a short time. The ranks close up and an empty space appears. On coming to himself and resuming the march, the caterpillar who has caused the breach becomes a leader, having nothing before him. The least desire for emancipation is all that he wants to make him launch the band into a new path which perhaps will be the saving path.

In short, when the Processionaries’ train is in difficulties, what it needs, unlike ours, is to run off the rails. The side-tracking is left to the caprice of a leader who alone is capable of turning to the right or left; and this leader is absolutely non-existent so long as the ring remains unbroken. Lastly, the breaking of the circle, the one stroke of luck, is the result of a chaotic halt, caused principally by excess of fatigue or cold.

The liberating accident, especially that of fatigue, occurs fairly often. In the course of [[83]]the same day, the moving circumference is cut up several times into two or three sections; but continuity soon returns and no change takes place. Things go on just the same. The bold innovator who is to save the situation has not yet had his inspiration.

There is nothing new on the fourth day, after an icy night like the previous one; nothing to tell except the following detail. Yesterday I did not remove the trace left by the few caterpillars who made their way to the inside of the vase. This trace, together with a junction connecting it with the circular road, is discovered in the course of the morning. Half the troop takes advantage of it to visit the earth in the pot and climb the palm; the other half remains on the ledge and continues to walk along the old rail. In the afternoon the band of emigrants rejoins the others, the circuit is completed and things return to their original condition.

We come to the fifth day. The night frost becomes more intense, without however as yet reaching the greenhouse. It is followed by bright sunshine in a calm and limpid sky. As soon as the sun’s rays have warmed the panes a little, the caterpillars, lying in [[84]]heaps, wake up and resume their evolutions on the ledge of the vase. This time the fine order of the beginning is disturbed and a certain disorder becomes manifest, apparently an omen of deliverance near at hand. The scouting-path inside the vase, which was upholstered in silk yesterday and the day before, is to-day followed to its origin on the rim by a part of the band and is then abandoned after a short loop. The other caterpillars follow the usual ribbon. The result of this bifurcation is two almost equal files, walking along the ledge in the same direction, at a short distance from each other, sometimes meeting, separating farther on, in every case with some lack of order.

Weariness increases the confusion. The crippled, who refuse to go on, are many. Breaches increase; files are split up into sections each of which has its leader, who pokes the front of his body this way and that to explore the ground. Everything seems to point to the disintegration which will bring safety. My hopes are once more disappointed. Before the night the single file is reconstituted and the invincible gyration resumed. [[85]]

Heat comes, just as suddenly as the cold did. To-day, the 4th of February, is a beautiful, mild day. The greenhouse is full of life. Numerous festoons of caterpillars, issuing from the nests, meander along the sand on the shelf. Above them, at every moment, the ring on the ledge of the vase breaks up and comes together again. For the first time I see daring leaders who, drunk with heat, standing only on their hinder prolegs at the extreme edge of the earthenware rim, fling themselves forward into space, twisting about, sounding the depths. The endeavour is frequently repeated, while the whole troop stops. The caterpillars’ heads give sudden jerks; their bodies wriggle.

One of the pioneers decides to take the plunge. He slips under the ledge. Four follow him. The others, still confiding in the perfidious silken path, dare not copy him and continue to go along the old road.

The short string detached from the general chain gropes about a great deal, hesitates long on the side of the vase; it goes half-way down, then climbs up again slantwise, rejoins and takes its place in the procession. This time the attempt has failed, though at the foot of [[86]]the vase, not nine inches away, there lay a bunch of pine-needles which I had placed there with the object of enticing the hungry ones. Smell and sight told them nothing. Near as they were to the goal, they went up again.

No matter, the endeavour has its uses. Threads were laid on the way and will serve as a lure to further enterprise. The road of deliverance has its first landmarks. And two days later, on the eighth day of the experiment, the caterpillars—now singly, anon in small groups, then again in strings of some length—come down from the ledge by following the staked-out path. At sunset the last of the laggards is back in the nest.

Now for a little arithmetic. For seven times twenty-four hours the caterpillars have remained on the ledge of the vase. To make an ample allowance for stops due to the weariness of this one or that and above all for the rest taken during the colder hours of the night, we will deduct one-half of the time. This leaves eighty-four hours’ walking. The average pace is nine centimetres[4] a minute. [[87]]The aggregate distance covered, therefore, is 453 metres, a good deal more than a quarter of a mile, which is a great walk for these little crawlers. The circumference of the vase, the perimeter of the track, is exactly 1 m. 35.[5] Therefore the circle covered, always in the same direction and always without result, was described three hundred and thirty-five times.

These figures surprise me, though I am already familiar with the abysmal stupidity of insects as a class whenever the least accident occurs. I feel inclined to ask myself whether the Processionaries were not kept up there so long by the difficulties and dangers of the descent rather than by the lack of any gleam of intelligence in their benighted minds. The facts, however, reply that the descent is as easy as the ascent.

The caterpillar has a very supple back, well adapted for twisting round projections or slipping underneath. He can walk with the same ease vertically or horizontally, with his back down or up. Besides, he never moves forward until he has fixed his thread to the ground. With this support to his feet, he [[88]]has no falls to fear, no matter what his position.

I had a proof of this before my eyes during a whole week. As I have already said, the track, instead of keeping on one level, bends twice, dips at a certain point under the ledge of the vase and reappears at the top a little farther on. At one part of the circuit, therefore, the procession walks on the lower surface of the rim; and this inverted position implies so little discomfort or danger that it is renewed at each turn for all the caterpillars from first to last.

It is out of the question then to suggest the dread of a false step on the edge of the rim which is so nimbly turned at each point of inflexion. The caterpillars in distress, starved, shelterless, chilled with cold at night, cling obstinately to the silk ribbon covered hundreds of times, because they lack the rudimentary glimmers of reason which would advice them to abandon it.

Experience and reflection are not in their province. The ordeal of a five hundred yards’ march and three to four hundred turns teach them nothing; and it takes casual circumstances to bring them back to the nest. They [[89]]would perish on their insidious ribbon if the disorder of the nocturnal encampments and the halts due to fatigue did not cast a few threads outside the circular path. Some three or four move along these trails, laid without an object, stray a little way and, thanks to their wanderings, prepare the descent, which is at last accomplished in short strings favoured by chance.

The school most highly honoured to-day is very anxious to find the origin of reason in the dregs of the animal kingdom. Let me call its attention to the Pine Processionary. [[90]]

[1] Book IV., chap. viii.—Translator’s Note. [↑]

[2] Jean Buridan (circa 1300–circa 1360), a famous scholastic doctor, who was several times rector of the university of Paris and subsequently founded the university of Vienna. He forms the subject of many legends, including that of the argument known by his name, of which no trace is to be found in any of his works.—Translator’s Note. [↑]

[3] 3½ inches.—Translator’s Note. [↑]

[4] 3½ inches.—Translator’s Note. [↑]

[5] 4 feet 5 inches.—Translator’s Note. [↑]

[[Contents]]

CHAPTER IV

THE PINE PROCESSIONARY: METEOROLOGY

In January a second moult occurs, leaving the caterpillar less fair to the eye, while at the same time endowing him with some very peculiar organs. When the moment has come to shed their skins, the Processionaries cluster higgledy-piggledy on the dome of the nest and there, if the weather be mild, remain motionless day and night. It would seem as though the fact of their contact, of their mutual discomfort, while thus heaped together, furnishes a resistance, a fulcrum, which favours the process of excoriation.

After this second moult, the hairs on the middle of the back are of a dull reddish colour, which is made paler still by the interposition of numerous long white hairs. But this faded costume is accompanied by the singular organs which attracted the attention of Réaumur, who was greatly perplexed as to their function. In the place originally occupied by the scarlet mosaic, eight segments of the caterpillar are now cleft by a broad [[91]]transversal gash, a sort of thick-lipped mouth, which opens and gapes wide at the caterpillar’s will, or closes without leaving a visible trace.

From each of these expanding mouths rises a tumour with a fine, colourless skin, as though the creature were exposing its tender inside and inflating it, for the appearance is almost that which would be presented by the viscera protruding through skin incised by the scalpel. Two large dark-brown dots occupy the front face of the protuberance. At the back are two short, flat tufts of russet bristles, which in the sunlight shine with a rich brilliancy. All around is a radiating border of long white hairs, spread almost flat.

This protuberance is extremely sensitive. At the slightest irritation it goes in again and disappears under the dark integument. In its place opens an oval crater, a sort of huge stoma, which swiftly brings its lips together, closes and entirely disappears. The long white hairs that form a moustache and imperial around this mouth follow the movements of the contracting lips. After first radiating from a centre and lying flat, these hairs rise like levelled wheat which the wind [[92]]has caught from beneath and meet to form a transversal crest, perpendicular to the creature’s back.

This hairy erection produces a sudden modification in the caterpillar’s aspect. The red shiny bristles have disappeared, buried under the dark skin; the white hairs, now standing on end, form a hirsute mane; an ashy tinge has crept into the general colour of the costume.

When calm is restored, as soon happens, the slits open and yawn afresh; the sensitive protuberances emerge, quick to disappear once more should any cause for alarm occur. These alternate expansions and contractions are rapidly repeated. I provoke them at will in various ways. A slight puff of tobacco-smoke immediately causes the stomata to yawn and the protuberances to emerge. One would think that the insect was putting itself on its guard and displaying some special apparatus of information. Before long the protuberances go in again. A second puff of smoke brings them out once more. But, if the smoke is too abundant, too acrid, the caterpillar wriggles and writhes without opening his apparatus. [[93]]

Or else I touch one or other of these uncovered protuberances, very delicately, with a bit of straw. The pimple affected immediately contracts, draws into itself, like the horns of the Snail, and is replaced by a gaping mouth, which in its turn closes. Usually, but not always, the segment excited by the contact of my straw is imitated by the others, both front and back, which close their apparatus one by one.

When undisturbed and in repose, the caterpillar generally has his dorsal slits expanded; in moving, he sometimes opens and sometimes closes them. In either case expansion and contraction are frequently repeated. Constantly coming together and retreating under the skin, the lips of the mouth-like opening therefore end by losing their brittle moustaches of russet hairs, which break off. In this way a sort of dust collects at the bottom of the crater, a dust formed of broken hairs, which, thanks to their barbs, soon collect into little tufts. When the slit expands rather suddenly, the central projection shoots out on the insect’s sides its load of hairy remnants, which the least breath blows into a cloud of golden atoms highly disagreeable to the observer. [[94]]I shall have something to say presently of the itch to which he is at such times exposed.

Are these peculiar stomata designed merely to collect the adjoining bristles and to grind them to powder? Are these fine-skinned papillæ, which inflate and ascend from the depths of their hiding-place, intended to get rid of the accumulation of broken hairs? Or is it the sole function of this peculiar apparatus to prepare, at the expense of the caterpillar’s fleece, an irritant dust which shall act as a means of defence? Nothing tells us so.

Certainly the caterpillar is not armed against the enquirer who from time to time takes it into his head to come and examine him through a magnifying-glass. It is even very doubtful whether he troubles at all about those passionate caterpillar-lovers, Calosoma sycophanta[1] among insects and the Cuckoo among birds. Those who consume such fare have a stomach expressly fashioned for the purpose, a stomach that laughs at blistering hairs and possibly finds an appetizing stimulant in their sting. No, I do not see the motives that prompted the Processionary to [[95]]cleave his back with so many slits, if he merely strips himself of his hair to throw an irritating dust in our eyes. There must certainly be something else in question.

Réaumur mentions these openings, of which he made a brief study. He calls them stigmata and is inclined to take them for exceptional breathing-holes. That they are not, O my master; no insect contrives air-holes on its back! Moreover, the magnifying-glass reveals no channel of communication with the interior. Respiration plays no part here; the solution of the enigma must lie elsewhere.

The protuberances that rise from those expanded cavities are formed of a soft, pale, hairless membrane, which gives the impression of a visceral hernia, as though the caterpillar were wounded and exposing its delicate entrails to the air. The sensitiveness just here is great. The lightest touch with the point of a hair-pencil causes the immediate indrawing of the protuberances and the closing of the containing lips.

The touch of a solid object even is not essential. I pick up a tiny drop of water on the point of a pin and, without shaking it off, present this drop to the sensitive projection. [[96]]At the moment when contact occurs the apparatus contracts and closes up. The recoil of the Snail’s horns, withdrawing the visual and olfactory organs into their sheaths, is no prompter.

Everything seems to prove that these optional tumours, appearing and disappearing at the caterpillar’s will, are instruments of sensorial perception. The caterpillar exposes them to obtain information; he shelters them under his skin to preserve their delicate functions. Now what is it that they perceive? This is a difficult question, in which the habits of the Processionary alone can afford us a little guidance.

During the whole winter, the Pine Caterpillars are active only at night. In the daytime, when the weather is fine, they readily repair to the dome of the nest and there remain motionless, gathered into heaps. It is the hour of the open-air siesta, under the pale December and January sun. As yet none leaves the home. It is quite late in the evening, towards nine o’clock, when they set out, marching in an irregular procession, to browse on the leaves of the branches hard by. Their grazing is a protracted affair. The flock returns [[97]]late, some time after midnight, when the temperature falls too low.

Secondly, it is in the heart of winter, during the roughest months, that the Processionary displays his full activity. Indefatigably at this time of year he spins, adding each night a new web to his silken tent; at this time, whenever the weather permits, he ventures abroad on the neighbouring boughs to feed, to grow and to renew his skein of silk.

By a very remarkable exception, the harsh season marked by inactivity and lethargic repose in other insects is for him the season of bustle and labour, on condition, of course, that the inclemencies of the weather do not exceed certain limits. If the north wind blow too violently, so that it is like to sweep the flock away; if the cold be too piercing, so that there is a risk of freezing to death; if it snow, or rain, or if the mist thicken into an icy drizzle, the caterpillars prudently stay at home, sheltering under their weatherproof tent.

It would be convenient to some extent to foresee these inclemencies. The caterpillar dreads them. A drop of rain sets him in a flutter; a snowflake exasperates him. To [[98]]start for the grazing-grounds at dark of night, in uncertain weather, would be dangerous, for the procession goes some distance and travels slowly. The flock would fare ill before regaining shelter did any sudden atmospheric trouble supervene, an event of some frequency in the bad season of the year. So that he may be informed in this particular during his nocturnal winter rambles, can the Pine Caterpillar be endowed with some sort of meteorological aptitudes? Let us describe how the suspicion occurred to me.

Divulged I know not how, my rearing of caterpillars under glass acquired a certain renown. It was talked about in the village. The forest-ranger, a sworn enemy to destructive insects, wanted to see the grazing of the famous caterpillars, of whom he had retained a too poignant memory ever since the day when he gathered and destroyed their nests in a pine-wood under his charge. It was arranged that he should call the same evening.

He arrives at the appointed hour, accompanied by a friend. For a moment we sit and chat in front of the fire; then, when the clock strikes nine, the lantern is lit and we [[99]]all three enter the greenhouse. The visitors are eager for the spectacle of which they have heard such wonderful things, while I am certain of satisfying their curiosity.

But, but … what is this? Not a caterpillar on the nests, not one on the fresh ration of branches! Last night and on the previous nights they came out in countless numbers; to-night not one reveals himself. Can it be that they are merely late in going to dinner? Can their habitual punctuality be at fault because appetite has not yet arrived? We must be patient.… Ten o’clock. Nothing. Eleven. Still nothing. Midnight was at hand when we abandoned our watch, convinced that it would be vain to prolong the sitting. You can imagine what an abject fool I looked at having thus to send my guests away.

Next day I thought that I dimly perceived the explanation of this disappointment. It rained in the night and again in the morning. Snow, not the earliest of the year, but so far the most abundant, whitened the brow of the Ventoux.[2] Had the caterpillars, more [[100]]sensitive than any of us to atmospheric changes, refused to venture forth because they anticipated what was about to happen? Had they foreseen the rain and the snow, which nothing seemed to announce, at all events to us? After all, why not? Let us continue to observe them and we shall see whether the coincidence is fortuitous or not.

On this memorable day, therefore, the 13th of December, 1895, I institute the caterpillars’ meteorological observatory. I have at my disposal absolutely none of the apparatus dear to science, not even a modest thermometer, for my unlucky star continues in the ascendant, proving as unkind to-day as when I learnt chemistry with pipe-bowls for crucibles and bottles that once contained sweets for retorts. I confine myself to visiting nightly the Processionaries in the greenhouse and those in the garden. It is a hard task, especially as I have to go to the far end of the enclosure, often in weather when one would not turn a Dog out of doors. I set down the acts of the caterpillars, whether they come out or stay at home; I note the state of the sky during the day and at the moment of my evening examination. [[101]]

To this list I add the meteorological chart of Europe which the Temps publishes daily. If I want more precise data, I request the Normal School at Avignon to send me, on occasions of violent disturbances, the barometrical records of its observatory. These are the only documents at my disposal.

Before we come to the results obtained, let me once more repeat that my caterpillars’ meteorological institute has two stations: one in the greenhouse and one in the open air, on the pines in the enclosure. The first, protected against the wind and rain, is that which I prefer: it provides more regular and more continuous information. In fact, the open-air caterpillars often enough refuse to come out, even though the general conditions be favourable. It is enough to keep them at home if there be too strong a wind shaking the boughs, or even a little moisture dripping on the web of the nests. Saved from these two perils, the greenhouse caterpillars have only to consider atmospheric incidents of a higher order. The small variations escape them; the great alone make an impression on them: a most useful point for the observer and going a long way towards solving the [[102]]problem for him. The colonies under glass, therefore, provide most of the material for my notes; the colonies in the open air add their testimony, which is not always quite clear.

Now what did they tell me, those greenhouse caterpillars who, on the 13th of December, refused to show themselves to my guest, the forest-ranger? The rain that was to fall that night could hardly have alarmed them: they were so well sheltered. The snow about to whiten Mont Ventoux was nothing to them: it was so far away. Moreover, it was neither snowing yet nor raining. Some extraordinary atmospheric event, profound and of vast extent, must have been occurring. The charts in the Temps and the bulletin of the Normal School told me as much.

A cyclonic disturbance, coming from the British Isles, was passing over our district; an atmospheric depression the like of which the season had not as yet known, had spread in our direction, reaching us on the 13th and persisting, in a more or less accentuated form, until the 22nd. At Avignon the barometer suddenly fell half an inch, to 29.1 in., on the 13th and lower still, to 29 in., on the 19th. [[103]]

During this period of ten days, the garden caterpillars made no sortie on the pine-trees. True, the weather was changeable. There were a few showers of fine rain and some violent gusts of the mistral; but more frequently there were days and nights when the sky was superb and the temperature moderate. The prudent anchorites would not allow themselves to be caught. The low pressure persisted, menacing them; and so they stopped at home.

In the greenhouse things happen rather differently. Sorties take place, but the staying-in days are still more numerous. It looks as though the caterpillars, alarmed at first by the unexpected things happening overhead, had reassured themselves and resumed work, feeling nothing, in their shelter, of what they would have suffered out of doors—rain, snow and furious mistral blasts—and had then suspended their work again when the threats of bad weather increased.

There is, indeed, a fairly accurate agreement between the oscillations of the barometer and the decisions of the herd. When the column of mercury rises a little, they come out; when it falls they remain at home. Thus [[104]]on the 19th, the night of the lowest pressure, 29 in., not a caterpillar ventures outside.

As the wind and rain can have no effect on my colonies under glass, one is led to suppose that atmospheric pressure, with its physiological results, so difficult to define, is here the principal factor. As for the temperature, within moderate limits there is no need to discuss it. The Processionaries have a robust constitution, as behoves spinners who work in the open air in midwinter. However piercing the cold, so long as it does not freeze, when the hour comes for working or feeding they spin on the surface of the nest or browse on the neighbouring branches.

Another example. According to the meteorological chart in the Temps, a depression whose centre is near the Iles Sanguinaires, at the entrance of the Gulf of Ajaccio, reaches my neighbourhood, with a minimum of 29.2 in., on the 9th of January. A tempestuous wind gets up. For the first time this year there is a respectable frost. The ice on the large pond in the garden is two or three inches thick. This wild weather lasts for five days. Of course, the garden caterpillars do not [[105]]sally forth on the pine-trees while these are battered by such a gale.

The remarkable part of the business is that the greenhouse caterpillars do not venture out of their nests either. And yet for them there are no boughs dangerously shaken, no cold piercing beyond endurance, for it is not freezing under the glass. What keeps them in can be only the passage of that wave of depression. On the 15th the storm ceases; and the barometer remains between 29.6 and 30 in. for the rest of the month and a good part of February. During this long period there are magnificent sorties every evening, especially in the greenhouse.

On the 23rd and 24th of February, suddenly the Processionaries stop at home again, for no apparent reason. Of the six nests under cover, only two have a few rare caterpillars out on the pine-branches, while previously, in the case of all six, I used every night to see the leaves bending under the weight of an innumerable multitude. Warned by this forecast, I enter in my notes:

“Some deep depression is about to reach us.”

And I have guessed right. Two days later, [[106]]sure enough, the meteorological record of the Temps gives me the following information: a minimum of 29.2 in., coming from the Bay of Biscay on the 22nd, reaches Algeria on the 23rd and spreads over the Provence coast on the 24th. There is a heavy snowfall at Marseilles on the 25th.

“The ships,” I read in my paper, “present a curious spectacle, with their yards and rigging white. That is how the people of Marseilles, little used to such sights, picture Spitzbergen and the North Pole.”

Here certainly is the gale which my caterpillars foresaw when they refused to go out last night and the night before; here is the centre of disturbance which revealed itself at Sérignan by a violent and icy north wind on the 25th and the following days. Again I perceive that the greenhouse caterpillars are alarmed only at the approach of the wave of atmospheric disturbance. Once the first uneasiness caused by the depression had abated, they came out again, on the 25th and the following days, in the midst of the gale, as though nothing extraordinary were happening. [[107]]

From the sum of my observations it appears that the Pine Processionary is eminently sensitive to atmospheric vicissitudes, an excellent quality, having regard to his way of life in the sharp winter nights. He foresees the storm which would imperil his excursions.

His capacity for scenting bad weather very soon won the confidence of the household. When we had to go into Orange to renew our provisions, it became the rule to consult him the night before; and, according to his verdict, we went or stayed at home. His oracle never deceived us. In the same way, simple folk that we were, we used in the old days to interrogate the Dor-beetle,[3] another doughty nocturnal worker. But, a little demoralized by imprisonment in a cage and apparently devoid of any special sensitive apparatus, performing his evolutions, moreover, in the mild autumn evenings, the celebrated Dung-beetle could never rival the Pine Caterpillar, who is active during the roughest season of the year and endowed, as everything [[108]]would seem to affirm, with organs quick to perceive the great atmospheric fluctuations.

Rural lore abounds in meteorological forecasts derived from animals. The Cat, sitting in front of the fire and washing behind her ears with a saliva-smeared paw, foretells another cold snap; the Cock, crowing at unusual hours, announces the return of fine weather; the Guinea-fowl, with her screeching, as of a scythe on the grindstone, points to rain; the Hen, standing on one leg, her plumage ruffled, her head sunk on her neck, feels a hard frost coming; the pretty green Tree-frog inflates his throat like a bladder at the approach of a storm and, according to the Provençal peasant, says:

“Ploùra, ploùra; it will rain, it will rain!”

This rustic meteorology, the heritage of the centuries, does not show up so badly beside our scientific meteorology.

Are not we ourselves living barometers? Every veteran complains of his glorious scars when the weather is about to break. One man, though unwounded, suffers from insomnia or from bad dreams; another, though a brain-worker, cannot drag an idea out of his impotent head. Each of us, in [[109]]his own way, is tried by the passage of those huge funnels which form in the atmosphere and hatch the storm.

Could the insect, with its exceptionally delicate organization, escape this kind of impression? It is unbelievable. The insect, more than any other creature, should be an animated meteorological instrument, as truthful in its forecasts, if we knew how to read them, as the lifeless instruments of our observatories, with their mercury and their catgut. All, in different degrees, possess a general impressionability analogous to our own and exercised without the aid of specific organs. Some, better-gifted because of their mode of life, might well be furnished with special meteorological apparatus.

The Pine Processionary seems to belong to this number. In his second costume, when the segments bear on their dorsal faces an elegant red mosaic, he differs apparently from other caterpillars only by a more delicate general impressionability, unless this mosaic be endowed with aptitudes unknown elsewhere. If the nocturnal spinner is still none too generously equipped, it must be remembered that the season which he passes in this condition [[110]]is nearly always clement. The really formidable nights hardly set in before January. But then, as a safeguard in his peregrinations, the Pine Processionary cleaves his back with a series of mouths which yawn open to sample the air from time to time and to give a warning of the sudden storm.

Until further evidence is forthcoming, therefore, the dorsal slits are, to my mind, meteorological instruments, barometers influenced by the main fluctuations of the atmosphere. To go beyond suspicions, though these are well based, is for me impossible. I lack the equipment necessary to delve more deeply into the subject. But I have given a hint. It is for those who are better favoured in the matter of resources to find the final solution of this interesting problem. [[111]]

[1] A large carnivorous Beetle.—Translator’s Note. [↑]

[2] The highest mountain in the neighbourhood of Sérignan. Cf. The Hunting Wasps, by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chap. xi.—Translator’s Note. [↑]

[3] Geotrupes stercorarius, a large Dung-beetle. Cf. The Life and Love of the Insect, by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chap. ix.—Translator’s Note. [↑]

[[Contents]]

CHAPTER V

THE PINE PROCESSIONARY: THE MOTH

When March comes, the caterpillars reared in domesticity never cease processioning. Many leave the greenhouse, which remains open; they go in search of a suitable spot for the approaching metamorphosis. This is the final exodus, the definite abandonment of the nest and the pine-tree. The pilgrims are much faded, whitish, with a few russet hairs on their backs.

On the 20th of March I spend a whole morning watching the evolutions of a file some three yards in length, containing about a hundred emigrants. The procession toils grimly along, undulating over the dusty ground, where it leaves a furrow. Then it breaks into a small number of groups, which crowd together and remain quiescent save for sudden oscillations of the hind-quarters. After a halt of varying duration, these groups resume their march, henceforward forming independent processions.

They take no settled direction. This one [[112]]goes forward, that one goes back; one turns to the left and another to the right. There is no rule about their marching, no positive goal. One procession, after describing a loop, retraces its steps. Yet there is a general tendency towards that wall of the greenhouse which faces the south and reflects the sun’s rays with added fervour. The sole guide, it would seem, is the amount of sun which a place obtains; the directions whence the greatest heat comes are preferred.

After a couple of hours of marching and countermarching, the fragmentary processions, comprising each a score of caterpillars, reach the foot of the wall. Here the soil is powdery, very dry, easy to burrow in, although made somewhat firmer by tufts of grass. The caterpillar at the head of the row explores with his mandibles, digs a little, investigates the nature of the ground. The others, trusting their leader, follow him with docility, making no attempts of their own. Whatever the foremost decides will be adopted by all. Here, in the choice of a matter so important as the spot whereat the transformation shall take place, there is no individual initiative. There is only one will, [[113]]the leader’s. There is only one head, so to speak; the procession may be compared with the chain of segments of an enormous worm.

Finally some spot is recognized as propitious. The leading caterpillar halts, pushes with his head, digs with his mandibles. The others, still in a continuous line, arrive one by one and likewise come to a halt. Then the file breaks up into a swarming heap, in which each of the caterpillars resumes his liberty. All their backs are joggling pell-mell; all their heads are plunged into the dust; all their feet are raking, all their mandibles excavating the soil. The worm has chopped itself into a gang of independent workers.

An excavation is formed in which, little by little, the caterpillars bury themselves. For some time to come, the undermined soil cracks and rises and covers itself with little mole-hills; then all is still. The caterpillars have descended to a depth of three inches. This is as far as the roughness of the soil permits them to go. In looser soil, the excavation would attain a much greater depth. The greenhouse shelf, supplied with fine sand, has provided me with cocoons placed at a depth of from eight to twelve inches. I would not [[114]]assert that the interment might not be made still lower down. For the most part, the burial is effected in common, by more or less numerous clusters and at depths which vary greatly, according to the nature of the soil.

A fortnight later, let us dig at the point where the descent underground was made. Here we shall find the cocoons assembled in bunches, cocoons of sorry appearance, soiled as they are with earthy particles held by silken threads. When stripped of their rough exterior, they are not without a certain elegance. They are narrow ellipsoids, pointed at both ends, measuring twenty-five millimetres in length and nine millimetres[1] in thickness. The silk of which they are composed is very fine and of a dull white. The fragility of the walls is remarkable when we have seen the enormous quantity of silk expended on the construction of the nest.

A prodigious spinner where his winter habitation is concerned, the caterpillar finds his glands exhausted and is reduced to the strictly necessary amount when the time comes for making the cocoon. Too poor in silk, he strengthens his flimsy cell with a facing of [[115]]earth. With him it is not the industry of the Bembex[2], who inserts grains of sand in her silky web and makes a solid casket of the whole; it is a summary sort of art, devoid of delicacy, which just casually sticks together the surrounding earthy refuse.

Moreover, if circumstances demand it, the Pine Caterpillar can do without earth. In the very midst of the nest I have sometimes—very rarely, it is true—discovered cocoons which were perfectly clean. Not a scrap of alien matter defiled their fine white silk. I have obtained similar specimens by placing caterpillars under a bell-glass in a pan provided only with a few pine-twigs. Better still: an entire procession, a good-sized one too, gathered at the opportune moment and enclosed in a large box containing no sand nor any material whatever, spun its cocoons with no other support than the bare walls. These exceptions, provoked by circumstances in which the caterpillar is not free to act according to his wont, does not in any way invalidate the rule. To prepare for the transformation, the Processionary buries himself, [[116]]to the depth of nine inches and more, if the soil permit.

Here a curious problem forces itself upon the observer’s mind. How does the Moth contrive to ascend from the catacombs into which the caterpillar has descended? Not in the finery of her perfect state—the big wings with their delicate scales, the sweeping antenna-plumes—dare she brave the asperities of the soil, or she would issue thence all tattered, rumpled and unrecognizable. And this is not the case: far from it. Moreover, what means can she employ, she so feeble, to break the crust of earth into which the original dust will have turned after the slightest of showers?

The Moth appears at the end of July or in August. The burial took place in March. Rain must have fallen during this lapse of time, rain which beats down the soil, cements it and leaves it to harden once evaporation has set in. Never could a Moth, unless attired and equipped with tools for the purpose, break her way through such an obstacle. She would perforce require a boring-tool and a costume of extreme simplicity. Guided by these considerations, I institute a few experiments [[117]]which will give me the key to the riddle.

In April I make a copious collection of cocoons. Of these I place ten or twelve at the bottom of test-tubes of different diameters and, last of all, I fill the apparatus with sandy soil, sifted and very slightly moistened. The contents are pressed down, but in moderation, for fear of injuring the cocoons below. When the month of August comes, the column of earth, damp at the outset, has set so firmly, thanks to evaporation, that, when I reverse the test-tube, nothing trickles out. On the other hand, some cocoons have been kept naked under a metallic cover. These will teach me what the buried cocoons would not be able to show. They furnish me, in fact, with records of the greatest interest. On issuing from the cocoon, the Pine Bombyx has her finery bundled up and presents the appearance of a cylinder with rounded ends. The wings, the principal obstacle to underground labour, are pressed against the breast like narrow scarves; the antennæ, another serious embarrassment, have not yet unfolded their plumes and are turned back along the Moth’s sides. The hair, which later forms a dense [[118]]fleece, is laid flat, pointing backwards. The legs alone are free, fairly active and endowed with a certain vigour. Thanks to this arrangement, which does away with all awkward projections, the ascent through the soil is made possible.

True, every Moth, at the moment of quitting her shell, is this sort of swathed mummy; but the Pine Bombyx has in addition an exceptional aptitude rendered necessary by the fact that she hatches under the ground. While the others, once out of the cocoon, hasten to spread their wings and are powerless to defer their development, she, by virtue of an indispensable privilege, remains in her compact and wrapped-up condition as long as circumstances demand it. Under my bell-glasses I see some who, though born upon the surface, for twenty-four hours drag themselves over the sand or cling to the pine-branches, before untying their sashes and unfurling them as wings.

This delay is evidently essential. To ascend from beneath the earth and reach the open air, the Moth has to bore a long tunnel, which requires time. She will take good care not to spread her finery before emerging, [[119]]for it would hamper her and would itself be rumpled and badly creased. Therefore the cylindrical mummy persists until the deliverance is effected; and, if liberty happen to be acquired before the appointed moment, the final evolution does not take place until after a lapse of time in conformity with usage.

We are acquainted with the equipment for emergence, the tight-fitting jerkin indispensable in a narrow gallery. Now, where is the boring-tool? The legs, though free, would here be insufficient: they would scrape the earth laterally, enlarging the diameter of the shaft, but could not prolong the exit vertically, above the insect’s head. This tool must be in front.

Pass the tip of your finger over the Moth’s head. You will feel a few very rough wrinkles. The magnifying-glass shows us more. We find, between the eyes and higher up, four or five transversal scales, so set as to overlap one another; they are hard and black and are trimmed crescent-wise at the ends. The longest and strongest is the uppermost, which is in the middle of the forehead. [[120]]There you have the centre-bit of your boring-tool.

To make our tunnels in granitic rocks we tip our drills with diamond points. For a similar task the Bombyx, a living drill, wears implanted on her forehead a row of crescents, hard and durable as steel, a regular twist-bit. Without suspecting its use, Réaumur was perfectly aware of this marvellous implement, which he called scaly stairs:

“What does it profit this Moth,” he asks, “that she should thus have the front of her head formed like scaly stairs? That is just what I do not know.”

My test-tubes, learned master, will tell us. By good fortune, of the numerous Moths ascending from the bottom of my apparatus through a column of sand solidified by the evaporation of the original moisture, some are making their way upwards against the side of the tube, enabling me to follow their manœuvres. I see them raising their cylindrical bodies, butting with their heads, jerking now in one direction, now in another. The nature of their task is obvious. The centre-bits, with an alternating movement, are boring into the agglutinated sand. The powdery wreckage [[121]]trickles down from overhead and is at once thrust backward by the legs. A little space forms at the top of the vault; and the Moth moves so much nearer to the surface. By the following day, the whole column, ten inches in height, will be perforated with a straight, perpendicular shaft.

Shall we now form an idea of the total work performed? Let us turn the test-tube upside down. The contents, as I have said, will not fall out, for they have set into a block; but from the tunnels bored by the Moth trickles all the sand crumbled by the crescents of the drill. The result is a cylindrical gallery, of the width of a lead-pencil, very cleanly cut and reaching to the bottom of the solid mass.