Social Life in the Insect World

by Jean-Henri Fabre

These facts being understood, we are able to explain the remarkable arrangement of the eggs. The openings in the rind of the twig are practically equidistant, since each time the Cigale moves upward it is by a given length, namely, that of the ovipositor. Very rapid in flight, she is a very idle walker. At the most you may see her, on the living twig from which she is drinking, moving at a slow, almost solemn pace, to gain a more sunny point close at hand. On the dry twig in which she deposits her eggs she observes the same formal habits, and even exaggerates them, in view of the importance of the operation. She moves as little as possible, just so far as she must in order to avoid running two adjacent egg-chambers into one. The extent of each movement upwards is approximately determined by the depth of the perforation.

The apertures are arranged in a straight line when their number is not very large. Why, indeed, should the insect wander to right or to left upon a twig which presents the same surface all over? A lover of the sun, she chooses that side of the twig which is most exposed to it. So long as she feels the heat, her supreme joy, upon her back, she will take good care not to change the position which she finds so delightful for another in which the sun would fall upon her less directly.

The process of depositing the eggs is a lengthy one when it is carried out entirely on the same twig. Counting ten minutes for each egg-chamber, the full series of forty would represent a period of six or seven hours. The sun will of course move through a considerable distance before the Cigale can finish her work. In such cases the series of apertures follows a spiral curve. The insect turns round the stalk as the sun turns.

Very often as the Cigale is absorbed in her maternal task a diminutive fly, also full of eggs, busily exterminates the Cigale's eggs as fast as they are laid.

This insect was known to Réaumur. In nearly all the twigs examined he found its grub, the cause of a misunderstanding at the beginning of his researches. But he did not, could not see the audacious insect at work. It is one of the Chalcididæ, about one-fifth or one-sixth of an inch in length; entirely black, with knotty antennæ, which are slightly thicker towards their extremities. The unsheathed ovipositor is implanted in the under portion of the abdomen, about the middle, and at right angles to the axis of the body, as in the case of the Leucospis, the pest of the apiary. Not having taken the precaution to capture it, I do not know what name the entomologists have bestowed upon it, or even if this dwarf exterminator of the Cigale has as yet been catalogued. What I am familiar with is its calm temerity, its impudent audacity in the presence of the colossus who could crush it with a foot. I have seen as many as three at once exploiting the unfortunate female. They keep close behind the Cigale, working busily with their probes, or waiting until their victim deposits her eggs.

The Cigale fills one of her egg-chambers and climbs a little higher in order to bore another hole. One of the bandits runs to the abandoned station, and there, almost under the claws of the giant, and without the least nervousness, as if it were accomplishing some meritorious action, it unsheathes its probe and thrusts it into the column of eggs, not by the open aperture, which is bristling with broken fibres, but by a lateral fissure. The probes works slowly, as the wood is almost intact. The Cigale has time to fill the adjacent chamber.

As soon as she has finished one of these midges, the very same that has been performing its task below her, replaces her and introduces its disastrous egg. By the time the Cigale departs, her ovaries empty, the majority of the egg-chambers have thus received the alien egg which will work the destruction of their contents. A small, quick-hatching grub, richly nourished on a dozen eggs, will replace the family of the Cigale.

The experience of centuries has taught the Cigale nothing. With her excellent eyesight she must be able to perceive these terrible sappers as they hover about her, meditating their crime. Too peaceable giantess! if you see them why do you not seize them in your talons, crush the pigmies at their work, so that you may proceed with your travail in security? But no, you will leave them untouched; you cannot modify your instincts, even to alleviate your maternal misfortunes.

The eggs of the common Cigale are of a shining ivory white. Conical at the ends, and elongated in form, they might be compared in shape to the weaver's shuttle. Their length is about one-tenth of an inch, their diameter about one-fiftieth. They are packed in a row, slightly overlapping one another. The eggs of the Cacan are slightly smaller, and are assembled in regular groups which remind one of microscopical bundles of cigars. We will consider the eggs of the common Cigale to the exclusion of the others, as their history is the history of all.

September is not yet over when the shining white as of ivory gives way to the yellow hue of cheese. During the first days of October you may see, at the forward end of the egg, two tiny points of chestnut brown, which are the eyes of the embryo in formation. These two shining eyes, which almost seem to gaze at one, and the cone-shaped head of the egg, give it the look of a tiny fish without fins—a fish for whom half a nut-shell would make a capacious aquarium.