Social Life in the Insect World Part 18

The precaution is fortunate. If I had tried to continue as I began, and to observe the Balaninus in the liberty of the woods, I should never, even with the greatest good fortune, have had the patience to follow to the end the choice of the acorn, the boring of the hole, and the laying of the eggs, so meticulously deliberate is the insect in all its affairs; as the reader will soon be able to judge.

Three species of oak-tree compose the copse inhabited by the Balaninus: the evergreen oak and the p.u.b.escent oak, which would become fine trees if the woodman would give them time, and the kermes oak, a mere scrubby bush. The first species, which is the most abundant of the three, is that preferred by the Balaninus. The acorn is firm, elongated, and of moderate size; the cup is covered with little warts. The acorns of the p.u.b.escent oak are usually stunted, short, wrinkled, and fluted, and subject to premature fall. The aridity of the hills of Serignan is unfavourable to them. The Acorn-beetles accept them only in default of something better.

The kermes, a dwarf oak, a ridiculous tree which a man can jump over, surprises me by the wealth of its acorns, which are large, ovoidal growths, the cup being covered with scales. The Balaninus could not make a better choice; the acorn affords a safe, strong dwelling and a capacious storehouse of food.

A few twigs from these three trees, well provided with acorns, are arranged under the domes of some of my wire-gauze covers, the ends being plunged into a gla.s.s of water which will keep them fresh. A suitable number of couples are then introduced into the cages; and the latter are placed at the windows of my study, where they obtain the direct sunlight for the greater part of the day. Let us now arm ourselves with patience, and keep a constant watch upon events. We shall be rewarded; the exploitation of the acorn deserves to be seen.

Matters do not drag on for very long. Two days after these preparations I arrive at the precise moment when the task is commenced. The mother, larger than the male, and equipped with a longer drill, is inspecting her acorn, doubtless with a view to depositing her eggs.

She goes over it step by step, from the point to the stem, both above and below. On the warty cup progression is easy; over the rest of the surface it would be impossible, were not the soles of her feet shod with adhesive pads, which enable her to retain her hold in any position.

Without the least uncertainty of footing, the insect walks with equal facility over the top or bottom or up the sides of the slippery fruit.

The choice is made; the acorn is recognised as being of good quality.

The time has come to sink the hole. On account of its excessive length it is not easy to manoeuvre the beak. To obtain the best mechanical effect the instrument must be applied perpendicularly to the convex surface of the acorn, and the embarra.s.sing implement which is carried in front of the insect when the latter is not at work must now be held in such a position as to be beneath the worker.

To obtain this result the insect rears herself upon her hind legs, supporting herself upon the tripod formed by the end of the wing-covers and the posterior tarsi. It would be hard to imagine anything more curious than this little carpenter, as she stands upright and brings her nasal bradawl down towards her body.

Now the drill is held plumb against the surface, and the boring commences. The method is that I witnessed in the wood on the day of the storm. Very slowly the insect veers round from right to left, then from left to right. Her drill is not a spiral gimlet which will sink itself by a constant rotary motion; it is a bradawl, or rather a trochar, which progresses by little bites, by alternative erosion, first in one direction, then the other.

Before continuing, let me record an accident which is too striking to be pa.s.sed over. On various occasions I have found the insect dead in the midst of its task. The body is in an extraordinary position, which would be laughable if death were not always a serious thing, above all when it comes suddenly, in the midst of labour.

The drill is implanted in the acorn just a little beyond the tip; the work was only commenced. At the top of the drill, at right angles to it, the Balaninus is suspended in the air, far from the supporting surface of the acorn. It is dried, mummified, dead I know not how long. The legs are rigid and contracted under the body. Even if they retained the flexibility and the power of extension that were theirs in life, they would fall far short of the surface of the acorn. What then has happened, that this unhappy insect should be impaled like a specimen beetle with a pin through its head?

An accident of the workshop is responsible. On account of the length of its implement the beetle commences her work standing upright, supported by the two hind-legs. Imagine a slip, a false step on the part of the two adhesive feet; the unfortunate creature will immediately lose her footing, dragged by the elasticity of the snout, which she was forced to bend somewhat at the beginning. Torn away from her foothold, the suspended insect vainly struggles in air; nowhere can her feet, those safety anchors, find a hold. She starves at the end of her snout, for lack of foothold whereby to extricate herself. Like the artisans in our factories, the elephant-beetle is sometimes the victim of her tools. Let us wish her good luck, and sure feet, careful not to slip, and proceed.

On this occasion all goes well, but so slowly that the descent of the drill, even when amplified by the magnifying-gla.s.s, cannot be perceived.

The insect veers round perpetually, rests, and resumes her work. An hour pa.s.ses, two hours, wearying the observer by their sustained attention; for I wish to witness the precise moment when the beetle withdraws her drill, turns round, and deposits her egg in the mouth of the orifice.

This, at least, is how I foresee the event.

Two hours go by, exhausting my patience. I call the household to my aid.

Three of us take turns, keeping an uninterrupted watch upon the persevering creature whose secret I intend at any cost to discover.

[Ill.u.s.tration: 1. THE GREY LOCUST.

1'. THE NERVATURES OF THE WING.

2. THE BALANINUS FALLEN A VICTIM TO THE LENGTH OF HER PROBOSCIS.]

It was well that I called in helpers to lend me their eyes and their attention. After eight hours--eight interminable hours, when it was nearly night, the sentinel on the watch calls me. The insect appears to have finished. She does, in fact, very cautiously withdraw her beak, as though fearing to slip. Once the tool is withdrawn she holds it pointing directly in front of her.

The moment has come.... Alas, no! Once more I am cheated; my eight hours of observation have been fruitless. The Balaninus decamps; abandons her acorn without laying her eggs. I was certainly right to distrust the result of observation in the open woods. Such concentration among the oaks, exposed to the sun, wind, and rain would have been an intolerable task.

During the whole of October, with the aid of such helpers as are needed, I remark a number of borings, not followed by the laying of eggs. The duration of the observer's task varies greatly. It usually amounts to a couple of hours; sometimes it exceeds half the day.

With what object are these perforations made, so laborious and yet so often unused? Let us first of all discover the position of the egg, and the first mouthfuls taken by the grub, and perhaps the reply will be found.

The peopled acorns remain on the oak, held in their cups as though nothing had occurred to the detriment of the cotyledons. With a little attention they may be readily recognised. Not far from the cup, on the smooth, still green envelope of the acorn a little point is visible; a tiny needle-p.r.i.c.k. A narrow brown aureole, the product of mortification, is not long in appearing. This marks the opening of the hole. Sometimes, but more rarely, the hole is drilled through the cup itself.

Let us select those acorns which have been recently perforated: that is to say, those in which the perforation is not yet surrounded by the brown ring which appears in course of time. Let us sh.e.l.l them. Many contain nothing out of the way; the Balaninus has bored them but has not laid her eggs in them. They resemble the acorns which for hours and hours were drilled in my laboratory but not utilised. Many, on the contrary, contain an egg.

Now however distant the entrance of the bore may be, this egg is always at the bottom of the acorn, within the cup, at the base of the cotyledonary matter. The cup furnishes a thin film like swan-skin which imbibes the sapid exudations from the stem, the source of nourishment. I have seen a young grub, hatched under my eyes, eat as his first mouthfuls this tender cottony layer, which is moist and flavoured with tannin.

Such nutriment, juicy and easy of digestion, like all nascent organic matter, is only found in this particular spot; and it is only there, between the cup and the base of the cotyledons, that the elephant-beetle establishes her egg. The insect knows to a nicety the position of the portions best adapted to the feeble stomach of the newly hatched larva.

Above this is the tougher nutriment of the cotyledons. Refreshed by its first meal, the grub proceeds to attack this; not directly, but in the tunnel bored by the mother, which is littered with tiny crumbs and half-masticated shavings. With this light mealy diet the strength of the grub increases, and it then plunges directly into the substance of the acorn.

These data explain the tactics of the gravid mother. What is her object when, before proceeding to sink her hole, she inspects her acorn, from above, below, before and behind, with such meticulous care? She is making sure that the acorn is not already occupied. The larder is amply stored, but it does not contain enough for two. Never in fact, have I found two larvae in the same acorn. One only, always only one, digests the copious meal and converts it into a greenish dust before leaving it and descending to the ground. Only an insignificant sh.e.l.l remains uneaten. The rule is, to each grub one acorn.

Before trusting the egg to the acorn it is therefore essential to subject it to a thorough examination, to discover whether it already has an occupant. This possible occupant would be at the base of the acorn, under the cover of the cup. Nothing could be more secret than this hiding-place. Not an eye could divine the inhabitant if the surface of the acorn did not bear the mark of a tiny perforation.

This mark, just visible, is my guide. Its presence tells me that the acorn is inhabited, or at least that it has been prepared for the reception of the egg; its absence tells me that the acorn has not yet been appropriated. The elephant-beetle undoubtedly draws the same conclusions.

I see matters from on high, with a comprehensive glance, a.s.sisted at will by the magnifying-gla.s.s. I turn the acorn between my fingers for a moment, and the inspection is concluded. The beetle, investigating the acorn at close quarters, is often obliged to scrutinise practically the entire surface before detecting the tell-tale spot. Moreover, the welfare of her family demands a far more careful search than does my curiosity. This is the reason for her prolonged and deliberate examination.

The search is concluded; the acorn is recognised as unoccupied. The drill is applied to the surface and rotated for hours; then, very often, the insect departs, disdaining the result of her work. Why such protracted efforts? Was the beetle piercing the fruit merely to obtain drink and refreshment? Was the beak thrust into the depths of the base merely to obtain, from the choicer parts, a few sips of nutritious sap?

Was the whole undertaking merely a matter of personal nourishment?

At first I believed this to be the solution, though surprised at the display of so much perseverance rewarded by the merest sip. The behaviour of the males, however, forced me to abandon this idea. They also possess the long beak, and could readily make such perforations if they wished; yet I have never seen one take up his stand upon an acorn and work at it with his augur. Then why this fruitless labour? A mere nothing suffices these abstemious creatures. A superficial operation performed upon the surface of a tender leaf yields them sufficient sustenance.

If the males, the unoccupied males who have leisure to enjoy the pleasures of the palate, ask no more than the sap of the leaf, how should the mothers, busied with the affairs of the breeding-season, find time to waste upon such dearly bought pleasures as the inner juices of the acorn? No, the acorn is not perforated for the purpose of drinking its juices. It is possible that once the beak is deeply sunk, the female may take a mouthful or two, but it is certain that food and drink are not the objects in view.

At last I begin to foresee the solution of the problem. The egg, as I have said, is always at the base of the acorn, in the midst of a soft cottony layer which is moistened by the sap which oozes from the stalk.

The grub, upon hatching out, being as yet incapable of attacking the firm substance of the cotyledons, masticates the delicate felt-like layer at the base of the cup and is nourished by its juices.

But as the acorn matures this layer becomes more solid in its consistency. The soft tissues harden; the moist tissues dry up. There is a period during which the acorn fulfils to perfection the conditions most conducive to the welfare of the grub. At an earlier period matters would not have reached the desired stage; at a later period the acorn would be too mature.

The exterior of the acorn gives no indication whatever of the progress of this internal cookery. In order not to inflict unsuitable food on the grub, the mother beetle, not sufficiently informed by the look of the acorn, is thus obliged to taste, at the end of her trunk, the tissues at the base of the cup.

The nurse, before giving her charge a spoonful of broth, tests it by tasting it. In the same way the mother beetle plunges her trunk into the base of the cup, to test the contents before bestowing them upon her offspring. If the food is recognised as being satisfactory the egg is laid; if not, the perforation is abandoned without more ado. This explains the perforations which serve no purpose, in spite of so much labour; the tissues at the base of the cup, being carefully tested, are not found to be in the required condition. The elephant-beetles are difficult to please and take infinite pains when the first mouthful of the grub is in question. To place the egg in a position where the new-born grub will find light and juicy and easily digested nutriment is not enough for those far-seeing mothers; their cares look beyond this point. An intermediary period is desirable, which will lead the little larva from the delicacies of its first hours to the diet of hard acorn.

This intermediary period is pa.s.sed in the gallery, the work of the maternal beak. There it finds the crumbs, the shavings bitten off by the chisels of the rostrum. Moreover, the walls of the tunnel, which are softened by mortification, are better suited than the rest of the acorn to the tender mandibles of the larva.

Before setting to work on the cotyledons the grub does, in fact, commence upon the contents and walls of this tiny pa.s.sage. It first consumes the shavings lying loose in the pa.s.sage; it devours the brown fragments adhering to the walls; finally, being now sufficiently strengthened, it attacks the body of the acorn, plunges into it, and disappears. The stomach is ready; the rest is a blissful feast.

This intermediary tunnel must be of a certain length, in order to satisfy the needs of infancy, so the mother must labour at the work of drilling. If the perforation were made solely with the purpose of tasting the material at the base of the acorn and recognising its degree of maturity, the operation might be very much shorter, since the hole could be sunk through the cup itself from a point close to the base.

This fact is not unrecognised; I have on occasion found the insect perforating the scaly cup.

In such a proceeding I see the attempt of a gravid mother pressed for time to obtain prompt information. If the acorn is suitable the boring will be recommenced at a more distant point, through the surface of the acorn itself. When an egg is to be laid the rule is to bore the hole from a point as distant as is practicable from the base--as far, in short, as the length of the rostrum will permit.

What is the object of this long perforation, which often occupies more than half the day? Why this tenacious perseverance when, not far from the stalk, at the cost of much less time and fatigue, the rostrum could attain the desired point--the living spring from which the new-born grub is to drink? The mother has her own reasons for toiling in this manner; in doing thus she still attains the necessary point, the base of the acorn, and at the same time--a most valuable result--she prepares for the grub a long tube of fine, easily digested meal.

But these are trivialities! Not so, if you please, but high and important matters, speaking to us of the infinite pains which preside over the preservation of the least of things; witnesses of a superior logic which regulates the smallest details.

The Balaninus, so happily inspired as a mother, has her place in the world and is worthy of notice. So, at least, thinks the blackbird, which gladly makes a meal of the insect with the long beak when fruits grow rare at the end of autumn. It makes a small mouthful, but a tasty, and is a pleasant change after such olives as yet withstand the cold.

And what without the blackbird and its rivalry of song were the reawakening of the woods in spring? Were man to disappear, annihilated by his own foolish errors, the festival of the life-bringing season would be no less worthily observed, celebrated by the fluting of the yellow-billed songster.

To the meritorious role of regaling the blackbird, the minstrel of the forest, the Balaninus adds another--that of moderating the superfluity of vegetation. Like all the mighty who are worthy of their strength, the oak is generous; it produces acorns by the bushel. What could the earth do with such prodigality? The forest would stifle itself for want of room; excess would ruin the necessary.

But no sooner is this abundance of food produced than there is an influx from every side of consumers only too eager to abate this inordinate production. The field-mouse, a native of the woods, stores acorns in a gravel-heap near its hay-lined nest. A stranger, the jay, comes in flocks from far away, warned I know not how. For some weeks it flies feasting from oak to oak, giving vent to its joys and its emotions in a voice like that of a strangling cat; then, its mission accomplished, it returns to the North whence it came.