THE CIGALE LEAVES ITS BURROW

Social Life in the Insect World by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE CIGALE LEAVES ITS BURROW

CHAPTER II. THE CIGALE LEAVES ITS BURROW

The first Cigales appear about the summer solstice. Along the beaten paths, calcined by the sun, hardened by the passage of frequent feet, we see little circular orifices almost large enough to admit the thumb. These are the holes by which the larvæ of the Cigale have come up from the depths to undergo metamorphosis. We see them more or less everywhere, except in fields where the soil has been disturbed by ploughing. Their usual position is in the driest and hottest situations, especially by the sides of roads or the borders of footpaths. Powerfully equipped for the purpose, able at need to pierce the turf or sun-dried clay, the larva, upon leaving the earth, seems to prefer the hardest spots.

A garden alley, converted into a little Arabia Petræa by reflection from a wall facing the south, abounds in such holes. During the last days of June I have made an examination of these recently abandoned pits. The soil is so compact that I needed a pick to tackle it.

The orifices are round, and close upon an inch in diameter. There is absolutely no debris round them; no earth thrown up from within. This is always the case; the holes of the Cigales are never surrounded by dumping-heaps, as are the burrows of the Geotrupes, another notable excavator. The way in which the work is done is responsible for this difference. The dung-beetle works from without inwards; she begins to dig at the mouth of the burrow, and afterwards re-ascends and accumulates the excavated material on the surface. The larva of the Cigale, on the contrary, works outward from within, upward from below; it opens the door of exit at the last moment, so that it is not free for the discharge of excavated material until the work is done. The first enters and raises a little rubbish-heap at the threshold of her burrow; the second emerges, and cannot, while working, pile up its rubbish on a threshold which as yet has no existence.

The burrow of the Cigale descends about fifteen inches. It is cylindrical, slightly twisted, according to the exigencies of the soil, and always approaches the vertical, or the direction of the shortest passage. It is perfectly free along its entire length. We shall search in vain for the rubbish which such an excavation must apparently produce; we shall find nothing of the sort. The burrow terminates in a cul-de-sac, in a fairly roomy chamber with unbroken walls, which shows not the least vestige of communication with any other burrow or prolongation of the shaft.

Taking its length and diameter into account, we find the excavation has a total volume of about twelve cubic inches. What becomes of the earth which is removed?

Sunk in a very dry, crumbling soil, we should expect the shaft and the chamber at the bottom to have soft, powdery walls, subject to petty landslips, if no work were done but that of excavation. On the contrary, the walls are neatly daubed, plastered with a sort of clay-like mortar. They are not precisely smooth, indeed they are distinctly rough; but their irregularities are covered with a layer of plaster, and the crumbling material, soaked in some glutinous liquid and dried, is held firmly in place.

The larva can climb up and down, ascend nearly to the surface, and go down into its chamber of refuge, without bringing down, with his claws, the continual falls of material which would block the burrow, make ascent a matter of difficulty, and retreat impossible. The miner shores up his galleries with uprights and cross-timbers; the builder of underground railways supports the sides and roofs of his tunnels with a lining of brick or masonry or segments of iron tube; the larva of the Cigale, no less prudent an engineer, plasters the walls of its burrow with cement, so that the passage is always free and ready for use.

If I surprise the creature just as it is emerging from the soil in order to gain a neighbouring bough and there undergo transformation, I see it immediately make a prudent retreat, descending to the bottom of its burrow without the slightest difficulty—a proof that even when about to be abandoned for ever the refuge is not encumbered with rubbish.

The ascending shaft is not a hurried piece of work, scamped by a creature impatient to reach the sunlight. It is a true dwelling, in which the larva may make a long stay. The plastered walls betray as much. Such precautions would be useless in the case of a simple exit abandoned as soon as made. We cannot doubt that the burrow is a kind of meteorological observatory, and that its inhabitant takes note of the weather without. Buried underground at a depth of twelve or fifteen inches, the larva, when ripe for escape, could hardly judge whether the meteorological conditions were favourable. The subterranean climate varies too little, changes too slowly, and would not afford it the precise information required for the most important action of its life—the escape into the sunshine at the time of metamorphosis.

Patiently, for weeks, perhaps for months, it digs, clears, and strengthens a vertical shaft, leaving only a layer of earth a finger's breadth in thickness to isolate it from the outer world. At the bottom it prepares a carefully built recess. This is its refuge, its place of waiting, where it reposes in peace if its observations decide it to postpone its final departure. At the least sign of fine weather it climbs to the top of its burrow, sounds the outer world through the thin layer of earth which covers the shaft, and informs itself of the temperature and humidity of the outer air.

If things are not going well—if there are threats of a flood or the dreaded bise—events of mortal gravity when the delicate insect issues from its cerements—the prudent creature re-descends to the bottom of its burrow for a longer wait. If, on the contrary, the state of the atmosphere is favourable, the roof is broken through by a few strokes of its claws, and the larva emerges from its tunnel.

Everything seems to prove that the burrow of the Cigale is a waiting-room, a meteorological station, in which the larva makes a prolonged stay; sometimes hoisting itself to the neighbourhood of the surface in order to ascertain the external climate; sometimes retiring to the depths the better to shelter itself. This explains the chamber at the base of the shaft, and the necessity of a cement to hold the walls together, for otherwise the creature's continual comings and goings would result in a landslip.

A matter less easy of explanation is the complete disappearance of the material which originally filled the excavated space. Where are the twelve cubic inches of earth that represent the average volume of the original contents of the shaft? There is not a trace of this material outside, nor inside either. And how, in a soil as dry as a cinder, is the plaster made with which the walls are covered?

Larvæ which burrow in wood, such as those of Capricornis and Buprestes, will apparently answer our first question. They make their way through the substance of a tree-trunk, boring their galleries by the simple method of eating the material in front of them. Detached by their mandibles, fragment by fragment, the material is digested. It passes from end to end through the body of the pioneer, yields during its passage its meagre nutritive principles, and accumulates behind it, obstructing the passage, by which the larva will never return. The work of extreme division, effected partly by the mandibles and partly by the stomach, makes the digested material more compact than the intact wood, from which it follows that there is always a little free space at the head of the gallery, in which the caterpillar works and lives; it is not of any great length, but just suffices for the movements of the prisoner.

Must not the larva of the Cigale bore its passage in some such fashion? I do not mean that the results of excavation pass through its body—for earth, even the softest mould, could form no possible part of its diet. But is not the material detached simply thrust back behind the excavator as the work progresses?

The Cigale passes four years under ground. This long life is not spent, of course, at the bottom of the well I have just described; that is merely a resting-place preparatory to its appearance on the face of the earth. The larva comes from elsewhere; doubtless from a considerable distance. It is a vagabond, roaming from one root to another and implanting its rostrum. When it moves, either to flee from the upper layers of the soil, which in winter become too cold, or to install itself upon a more juicy root, it makes a road by rejecting behind it the material broken up by the teeth of its picks. That this is its method is incontestable.

As with the larvæ of Capricornis and Buprestes, it is enough for the traveller to have around it the small amount of free space necessitated by its movements. Moist, soft, and easily compressible soil is to the larva of the Cigale what digested wood-pulp is to the others. It is compressed without difficulty, and so leaves a vacant space.

The difficulty is that sometimes the burrow of exit from the waiting-place is driven through a very arid soil, which is extremely refractory to compression so long as it retains its aridity. That the larva, when commencing the excavation of its burrow, has already thrust part of the detached material into a previously made gallery, now filled up and disappeared, is probable enough, although nothing in the actual condition of things goes to support the theory; but if we consider the capacity of the shaft and the extreme difficulty of making room for such a volume of debris, we feel dubious once more; for to hide such a quantity of earth a considerable empty space would be necessary, which could only be obtained by the disposal of more debris. Thus we are caught in a vicious circle. The mere packing of the powdered earth rejected behind the excavator would not account for so large a void. The Cigale must have a special method of disposing of the waste earth. Let us see if we can discover the secret.

Let us examine a larva at the moment of emerging from the soil. It is almost always more or less smeared with mud, sometimes dried, sometimes moist. The implements of excavation, the claws of the fore-feet, have their points covered by little globules of mortar; the others bear leggings of mud; the back is spotted with clay. One is reminded of a scavenger who has been scooping up mud all day. This condition is the more striking in that the insect comes from an absolutely dry soil. We should expect to see it dusty; we find it muddy.

One more step, and the problem of the well is solved. I exhume a larva which is working at its gallery of exit. Chance postpones this piece of luck, which I cannot expect to achieve at once, since nothing on the surface guides my search. But at last I am rewarded, and the larva is just beginning its excavation. An inch of tunnel, free of all waste or rubbish, and at the bottom the chamber, the place of rest; so far has the work proceeded. And the worker—in what condition is it? Let us see.

The larva is much paler in colour than those which I have caught as they emerged. The large eyes in particular are whitish, cloudy, blurred, and apparently blind. What would be the use of sight underground? The eyes of the larvæ leaving their burrows are black and shining, and evidently capable of sight. When it issues into the sunlight the future Cigale must find, often at some distance from its burrow, a suitable twig from which to hang during its metamorphosis, so that sight is obviously of the greatest utility. The maturity of the eyes, attained during the time of preparation before deliverance, proves that the larva, far from boring its tunnel in haste, has spent a long time labouring at it.

What else do we notice? The blind, pale larva is far more voluminous than in the mature state; it is swollen with liquid as though it had dropsy. Taken in the fingers, a limpid serum oozes from the hinder part of the body, which moistens the whole surface. Is this fluid, evacuated by the intestine, a product of urinary secretion—simply the contents of a stomach nourished entirely upon sap? I will not attempt to decide, but for convenience will content myself with calling it urine.

Well, this fountain of urine is the key to the enigma. As it digs and advances the larva waters the powdery debris and converts it into a paste, which is immediately applied to the walls by the pressure of the abdomen. Aridity is followed by plasticity. The mud thus obtained penetrates the interstices of the rough soil; the more liquid portion enters the substance of the soil by infiltration; the remainder becomes tightly packed and fills up the inequalities of the walls. Thus the insect obtains an empty tunnel, with no loose waste, as all the loosened soil is utilised on the spot, converted into a mortar which is more compact and homogeneous than the soil through which the shaft is driven.

Thus the larva works in the midst of a coating of mud, which is the cause of its dirtiness, so astonishing when we see it issue from an excessively dry soil. The perfect insect, although henceforth liberated from the work of a sapper and miner, does not entirely abandon the use of urine as a weapon, employing it as a means of defence. Too closely observed it throws a jet of liquid upon the importunate enemy and flies away. In both its forms the Cigale, in spite of its dry temperament, is a famous irrigator.

Dropsical as it is, the larva cannot contain sufficient liquid to moisten and convert into easily compressible mud the long column of earth which must be removed from the burrow. The reservoir becomes exhausted, and the provision must be renewed. Where, and how? I think I can answer the question.

The few burrows uncovered along their entirety, with the meticulous care such a task demands, have revealed at the bottom, encrusted in the wall of the terminal chamber, a living root, sometimes of the thickness of a pencil, sometimes no bigger than a straw. The visible portion of this root is only a fraction of an inch in length; the rest is hidden by the surrounding earth. Is the presence of this source of sap fortuitous? Or is it the result of deliberate choice on the part of the larva? I incline towards the second alternative, so repeatedly was the presence of a root verified, at least when my search was skilfully conducted.

Yes, the Cigale, digging its chamber, the nucleus of the future shaft, seeks out the immediate neighbourhood of a small living root; it lays bare a certain portion, which forms part of the wall, without projecting. This living spot in the wall is the fountain where the supply of moisture is renewed. When its reservoir is exhausted by the conversion of dry dust into mud the miner descends to its chamber, thrusts its proboscis into the root, and drinks deep from the vat built into the wall. Its organs well filled, it re-ascends. It resumes work, damping the hard soil the better to remove it with its talons, reducing the debris to mud, in order to pack it tightly around it and obtain a free passage. In this manner the shaft is driven upwards; logic and the facts of the case, in the absence of direct observation, justify the assertion.

If the root were to fail, and the reservoir of the intestine were exhausted, what would happen? The following experiment will inform us: a larva is caught as it leaves the earth. I place it at the bottom of a test-tube, and cover it with a column of dry earth, which is rather lightly packed. This column is about six inches in height. The larva has just left an excavation three times as deep, made in soil of the same kind, but offering a far greater resistance. Buried under this short column of powdery earth, will it be able to gain the surface? If its strength hold out the issue should be certain; having but lately made its way through the hard earth, this obstacle should be easily removed.

But I am not so sure. In removing the stopper which divided it from the outside world, the larva has expended its final store of liquid. The cistern is dry, and in default of a living root there is no means of replenishing it. My suspicions are well founded. For three days the prisoner struggles desperately, but cannot ascend by so much as an inch. It is impossible to fix the material removed in the absence of moisture; as soon as it is thrust aside it slips back again. The labour has no visible result; it is a labour of Sisyphus, always to be commenced anew. On the fourth day the creature succumbs.

With the intestines full the result is very different.

I make the same experiment with an insect which is only beginning its work of liberation. It is swollen with fluid, which oozes from it and moistens the whole body. Its task is easy; the overlying earth offers little resistance. A small quantity of liquid from the intestines converts it into mud; forms a sticky paste which can be thrust aside with the assurance that it will remain where it is placed. The shaft is gradually opened; very unevenly, to be sure, and it is almost choked up behind the insect as it climbs upwards. It seems as though the creature recognises the impossibility of renewing its store of liquid, and so economises the little it possesses, using only just so much as is necessary in order to escape as quickly as possible from surroundings which are strange to its inherited instincts. This parsimony is so well judged that the insect gains the surface at the end of twelve days.

The gate of issue is opened and left gaping, like a hole made with an augur. For some little time the larva wanders about the neighbourhood of its burrow, seeking an eyrie on some low-growing bush or tuft of thyme, on a stem of grass or grain, or the twig of a shrub. Once found, it climbs and firmly clasps its support, the head upwards, while the talons of the fore feet close with an unyielding grip. The other claws, if the direction of the twig is convenient, assist in supporting it; otherwise the claws of the two fore legs will suffice. There follows a moment of repose, while the supporting limbs stiffen in an unbreakable hold. Then the thorax splits along the back, and through the fissure the insect slowly emerges. The whole process lasts perhaps half an hour.

There is the adult insect, freed of its mask, and how different from what it was but how! The wings are heavy, moist, transparent, with nervures of a tender green. The thorax is barely clouded with brown. All the rest of the body is a pale green, whitish in places. Heat and a prolonged air-bath are necessary to harden and colour the fragile creature. Some two hours pass without any perceptible change. Hanging to its deserted shell by the two fore limbs, the Cigale sways to the least breath of air, still feeble and still green. Finally, the brown colour appears and rapidly covers the whole body; the change of colour is completed in half an hour. Fastening upon its chosen twig at nine o'clock in the morning, the Cigale flies away under my eyes at half-past twelve.

The empty shell remains, intact except for the fissure in the back; clasping the twig so firmly that the winds of autumn do not always succeed in detaching it. For some months yet and even during the winter you will often find these forsaken skins hanging from the twigs in the precise attitude assumed by the larva at the moment of metamorphosis. They are of a horny texture, not unlike dry parchment, and do not readily decay.

I could gather some wonderful information regarding the Cigale were I to listen to all that my neighbours, the peasants, tell me. I will give one instance of rustic natural history.

THE CIGALE AND THE EMPTY PUPA-SKIN.

Are you afflicted with any kidney trouble, or are you swollen with dropsy, or have you need of some powerful diuretic? The village pharmacopœia is unanimous in recommending the Cigale as a sovereign remedy. The insects in the adult form are collected in summer. They are strung into necklaces which are dried in the sun and carefully preserved in some cupboard or drawer. A good housewife would consider it imprudent to allow July to pass without threading a few of these insects.

Do you suffer from any nephritic irritation or from stricture? Drink an infusion of Cigales. Nothing, they say, is more effectual. I must take this opportunity of thanking the good soul who once upon a time, so I was afterwards informed, made me drink such a concoction unawares for the cure of some such trouble; but I still remain incredulous. I have been greatly struck by the fact that the ancient physician of Anazarbus used to recommend the same remedy. Dioscorides tells us: Cicadæ, quae inassatae manduntur, vesicae doloribus prosunt. Since the distant days of this patriarch of materia medica the Provençal peasant has retained his faith in the remedy revealed to him by the Greeks, who came from Phocæa with the olive, the fig, and the vine. Only one thing is changed: Dioscorides advises us to eat the Cigales roasted, but now they are boiled, and the decoction is administered as medicine. The explanation which is given of the diuretic properties of the insect is a marvel of ingenuousness. The Cigale, as every one knows who has tried to catch it, throws a jet of liquid excrement in one's face as it flies away. It therefore endows us with its faculties of evacuation. Thus Dioscorides and his contemporaries must have reasoned; so reasons the peasant of Provence to-day.

What would you say, worthy neighbours, if you knew of the virtues of the larva, which is able to mix sufficient mortar with its urine to build a meteorological station and a shaft connecting with the outer world? Your powers should equal those of Rabelais' Gargantua, who, seated upon the towers of Notre Dame, drowned so many thousands of the inquisitive Parisians.

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