Fabre's Book of Insects

by Jean-Henri Fabre

The barricade—a door which the larva builds as a protection from danger—is twofold, and often threefold. Outside, it is a stack of woody refuse, of particles of chopped timber; inside, a mineral lid, a concave cover, all in one piece, of a chalky white. Pretty often, but not always, there is added to these two layers an inner casing of shavings.

Behind this threefold door the larva makes its arrangements for its transformation. The sides of the chamber are scraped, thus providing a sort of down formed of ravelled woody fibres, broken into tiny shreds. This velvety stuff is fixed on the wall, in a thick coating, as fast as it is made. The chamber is thus padded throughout with a fine swan’s-down, a delicate precaution taken by the rough grub out of kindness for the tender creature it will become when it has cast its skin.

Let us now go back to the most curious part of the [[221]]furnishing, the cover or inner door of the entrance. It is like an oval skull-cap, white and hard as chalk, smooth within and rough without, with some resemblance to an acorn-cup. The rough knots show that the material is supplied in small, pasty mouthfuls, which become solid outside in little lumps. The animal does not remove them, because it is unable to get at them; but the inside surface is polished, being within the grub’s reach. This singular lid is as hard and brittle as a flake of limestone. It is, as a matter of fact, composed solely of carbonate of lime, and a sort of cement which gives consistency to the chalky paste.

I am convinced that this stony deposit comes from a particular part of the grub’s stomach, called the chylific ventricle. The chalk is kept separate from the food, and is held in reserve until the right time comes to discharge it. This freestone factory causes me no astonishment. It serves for various chemical works in different grubs when undergoing transformation. Certain Oil-beetles keep refuse in it, and several kinds of Wasps use it to manufacture the shellac with which they varnish the silk of their cocoons.

When the exit way is prepared, and the cell upholstered in velvet and closed with a threefold barricade, the industrious grub has finished its task. It lays aside its tools, sheds its skin, and becomes a pupa—weakness personified, in the swaddling-clothes of a cocoon. The [[222]]head is always turned towards the door. This is a trifling detail in appearance; but in reality it is everything. To lie this way or that in the long cell is a matter of great indifference to the grub, which is very supple, turning easily in its narrow lodging and adopting whatever position it pleases. The coming Capricorn will not enjoy the same privileges. Stiffly encased in his horny armour, he will not be able to turn from end to end; he will not even be capable of bending, if some sudden curve should make the passage difficult. He must, without fail, find the door in front of him, or he will perish in the transformation-room. If the grub should forget this little matter, and lie down to sleep with its head at the back of the cell, the Capricorn would be infallibly lost. His cradle would become a hopeless dungeon.

But there is no fear of this danger. The “bit of intestine” knows too much about the future to neglect the formality of keeping its head at the door. At the end of spring the Capricorn, now in possession of his full strength, dreams of the joys of the sun, of the festivals of light. He wants to get out.

What does he find before him? First, a heap of filings easily dispersed with his claws; next, a stone lid which he need not even break into fragments, for it comes undone in one piece. It is removed from its frame with a few pushes of the forehead, a few tugs of the claws. [[223]]In fact, I find the lid intact on the threshold of the abandoned cell. Last comes a second mass of woody remnants as easy to scatter as the first. The road is now free: the Capricorn has but to follow the wide vestibule, which will lead him, without any possibility of mistake, to the outer exit. Should the doorway not be open, all that he has to do is to gnaw through a thin screen, an easy task. Behold him outside, his long antennæ quivering with excitement.

What have we learnt from him? Nothing from him, but much from his grub. This grub, so poor in organs of sensation, gives us much to think about. It knows that the coming Beetle will not be able to cut himself a road through the oak, and it therefore opens one for him at its own risk and peril. It knows that the Capricorn, in his stiff armour, will never be able to turn round and make for the opening of the cell; and it takes care to fall into its sleep of transformation with its head towards the door. It knows how soft the pupa’s flesh will be, and it upholsters the bedroom with velvet. It knows that the enemy is likely to break in during the slow work of the transformation, and so, to make a protection against attack, it stores lime inside its stomach. It knows the future with a clear vision, or, to be accurate, it behaves as if it knew the future.

What makes it act in this way? It is certainly not taught by the experiences of its senses. What does it [[224]]know of the outside world? I repeat—as much as a bit of intestine can know. And this senseless creature astounds us! I regret that the philosopher Condillac, instead of creating a statue that could smell a rose, did not gift it with an instinct. How soon he would have seen that the animals—including man—have powers quite apart from the senses; inspirations that are born with them, and are not the result of learning.

This curious life and this marvellous foresight are not confined to one kind of grub. Besides the Capricorn of the Oak there is the Capricorn of the Cherry-tree. In appearance the latter is an exact copy of the former, on a much smaller scale; but the little Capricorn has different tastes from its large kinsman’s. If we search the heart of the cherry-tree it does not show us a single grub anywhere: the entire population lives between the bark and the wood. This habit is only varied when transformation is at hand. Then the grub of the cherry-tree leaves the surface, and scoops out a cavity at a depth of about two inches. Here the walls are bare: they are not lined with the velvety fibres dear to the Capricorn of the Oak. The entrance is blocked, however, by sawdust, and a chalky lid similar to the other except in point of size. Need I add that the grub lies down and goes to sleep with his head against the door? Not one forgets to take this precaution.