Social Life in the Insect World

by Jean-Henri Fabre

This phase is of short duration. Here, for instance, a migrating larva shows its head, with its big black eyes, and raises the broken fibres of the entrance. It gradually works itself forward, but so slowly that the magnifying-glass scarcely reveals its progress. At the end of half an hour at the shortest we see the entire body of the creature; but the orifice by which it is escaping still holds it by the hinder end of the body.

Then, without further delay, the coat which it wears for this rough piece of work begins to split, and the larva skins itself, coming out of its wrappings head first. It is then the normal larva; the only form known to Réaumur. The rejected coat forms a suspensory thread, expanding at its free end to form a little cup. In this cup is inserted the end of the abdomen of the larva, which, before allowing itself to fall to earth, takes a sun-bath, grows harder, stretches itself, and tries its strength, lightly swinging at the end of its life-line.

This little flea, as Réaumur calls it, first white, then amber-coloured, is precisely the larva which will delve in the earth. The antennæ, of fair length, are free and waving to and fro; the limbs are bending at their articulations; the fore-limbs, which are relatively powerful, open and shut their talons. I can scarcely think of any more curious spectacle than that of this tiny gymnast hanging by its tail, swinging to the faintest breath, and preparing in the air for its entry into the world. It hangs there for a variable period; some larvæ let themselves fall at the end of half an hour; others spend hours in their long-stemmed cup; some even remain suspended until the following day.

Whether soon or late, the fall of the larva leaves suspended the thread by which it hung, the wrappings of the primary larva. When all the brood have disappeared, the aperture of the nest is thus hung with a branch of fine, short threads, twisted and knotted together, like dried white of egg. Each thread is expanded into a tiny cup at its free end. These are very delicate and ephemeral relics, which perish at a touch. The least wind quickly blows them away.

Let us return to the larva. Sooner or later, as we have seen, it falls to the ground, either by accident or intention. The tiny creature, no bigger than a flea, has preserved its tender newly-hatched flesh from contact with the rough earth by hanging in the air until its tissues have hardened. Now it plunges into the troubles of life.

I foresee a thousand dangers ahead. A mere breath of wind may carry this atom away, and cast it on that inaccessible rock in the midst of a rut in the road which still contains a little water; or on the sand, the region of famine where nothing grows; or upon a soil of clay, too tenacious to be tunnelled. These mortal accidents are frequent, for gusts of wind are frequent in the windy and already severe weather of the end of October.

This delicate organism requires a very soft soil, which can easily be entered, so that it may immediately obtain a suitable shelter. The cold days are coming; soon the frosts will be here. To wander on the surface would expose it to grave perils. It must contrive without delay to descend into the earth, and that to no trivial depth. This is the unique and imperative condition of safety, and in many cases it is impossible of realisation. What use are the claws of this tiny flea against rock, sandstone, or hardened clay? The creature must perish if it cannot find a subterranean refuge in good time.

Everything goes to show that the necessity of this first foothold on the soil, subject as it is to so many accidents, is the cause of the great mortality in the Cigale family. The little black parasite, the destroyer of eggs, in itself evokes the necessity of a large batch of eggs; and the difficulty which the larva experiences in effecting a safe lodgment in the earth is yet another explanation of the fact that the maintenance of the race at its proper strength requires a batch of three or four hundred eggs from each mother. Subject to many accidents, the Cigale is fertile to excess. By the prodigality of her ovaries she conjures the host of perils which threaten her offspring.

During the rest of my experiment I can at least spare the larvæ the worst difficulties of their first establishment underground. I take some soil from the heath, which is very soft and almost black, and I pass it through a fine sieve. Its colour will enable me more easily to find the tiny fair-skinned larvæ when I wish to inform myself of passing events; its lightness makes it a suitable refuge for such weak and fragile beings. I pack it Pretty firmly in a glass vase; I plant in it a little tuft of thyme; I sow in it a few grains of wheat. There is no hole at the bottom of the vase, although there should be one for the benefit of the thyme and the corn; but the captives would find it and escape by it. The plantation and the crop will suffer from this lack of drainage, but at least I am sure of recovering my larvæ with the help of patience and a magnifying-glass. Moreover, I shall go gently in the matter of irrigation, giving only just enough water to save the plants from perishing.

When all is in order, and when the wheat is beginning to shoot, I place six young larvæ of the Cigale on the surface of the soil. The tiny creatures begin to pace hither and thither; they soon explore the surface of their world, and some try vainly to climb the sides of the vase. Not one of them seems inclined to bury itself; so that I ask myself anxiously what can be the object of their prolonged and active explorations. Two hours go by, but their wanderings continue.