The Life of the Grasshopper

by Jean-Henri Fabre

Until now, with a little patience, observation [[158]]has been practicable and has given satisfactory results. It becomes impossible when we come to the very complex structure of that middle zone where exits are contrived for the emergence of the larvæ under the shelter of a double row of imbricated plates. The little that I am able to make out amounts to this: the tip of the abdomen, split wide from top to bottom, forms a sort of button-hole whose upper end remains almost fixed while the lower end, in swinging, produces foam and immerses eggs in it. It is that upper end which is undoubtedly responsible for the work of the middle zone. I always see it in the extension of that zone, in the midst of the fine white foam collected by the caudal filaments. These, one on the right, the other on the left, mark the boundaries of the band. They feel its edges; they seem to be testing the work. I can easily imagine them two long and exquisitely delicate fingers controlling the difficult business of construction.

But how are the two rows of scales obtained and the fissures, the exit-doors, which they shelter? I do not know. I cannot even guess. I leave the rest of the problem to others. [[159]]

What a wonderful mechanism is this which emits so methodically and swiftly the horny matrix of the central kernel, the protecting froth, the white foam of the median ribbon, the eggs and the fertilizing fluid and which at the same time is able to build overlapping plates, imbricated scales and alternating open fissures! We are lost in admiration. And yet how easily the work is done! The Mantis hangs motionless on the wire gauze which is the foundation of her nest. She gives not a glance at the edifice that is rising behind her; her legs are not called upon for assistance of any kind. The thing works of itself. We have here not an industrial task requiring the cunning of instinct; it is a purely automatic process, regulated by the insect’s tools and organization. The nest, with its highly complicated structure, proceeds solely from the play of the organs, even as in our own industries we manufacture by machinery a host of objects whose perfection would outwit our manual dexterity.

From another point of view, the Mantis’ nest is more remarkable still. We see in it a superb application of one of the most beautiful principles of physics, that of the conservation [[160]]of heat. The Mantis anticipated us in a knowledge of non-conducting bodies.

We owe to Rumford,[2] the natural philosopher, the following curious experiment, which fittingly demonstrates the low conductivity of the air. The illustrious scientist dropped a frozen cheese into a mass of foam supplied by well-beaten eggs. The whole was subjected to the heat of an oven. The result in a short time was an omelette soufflée hot enough to burn the tongue, with the cheese in the middle as cold as at the beginning. The air contained in the bubbles of the surrounding froth explains the strange phenomenon. As an exceedingly poor thermal conductor, it had arrested the heat of the oven and prevented it from reaching the frozen substance in the centre.

Now what does the Mantis do? Precisely the same as Rumford: she whips her white of egg into an omelette soufflée, to protect the eggs collected into a central kernel. Her aim, it is true, is reversed: her coagulated foam is intended to ward off the cold, not the heat. But a protection against [[161]]one is a protection against the other; and the ingenious physicist, had he wished, could easily with the same frothy wrapper have maintained the heat of a body in cold surroundings.

Rumford knew the secrets of the stratum of air thanks to the accumulated knowledge of his ancestors, his own researches and his own studies. How is it that for no one knows how many centuries the Mantis has beaten our natural philosophers in the matter of this delicate problem of heat? How did she come to think of wrapping a blanket of foam around her mass of eggs, which, fixed without any shelter to a twig or stone, has to endure the rigours of winter with impunity?

The other Mantidæ of my neighbourhood, the only ones of whom I can speak with full knowledge, use the non-conducting wrapper of solidified foam or do without it, according as the eggs are destined to live through the winter or not. The little Grey Mantis, who differs so greatly from the other owing to the almost entire absence of wings in the female, builds a nest not quite so big as a cherry-stone and covers it very cleverly with a rind of froth. Why this beaten-up envelope? [[162]]Because the nest of the Grey Mantis, like that of the Praying Mantis, has to last through the winter, exposed on its bough or stone to all the dangers of the bad weather.

On the other hand, in spite of her size, which is equal to that of the Praying Mantis, Empusa pauperata, who is the most curious of our insects, builds a nest as small as that of the Grey Mantis. It is a very modest edifice, consisting of a small number of cells set side by side in three or four rows joined together. Here there is no frothy envelope at all, though the nest, like those mentioned above, is fixed in an exposed situation on some twig or broken stone. This absence of a non-conducting mattress points to a difference in climatic conditions. The Empusa’s eggs, in fact, hatch soon after they are laid, during the fine weather. Not having to undergo the inclemencies of winter, they have no protection but the slender sheath of their cases.

Are these scrupulous and rational precautions, which rival Rumford’s omelette soufflée, a casual result, one of those numberless combinations turned out by the wheel of fortune? If so, let us not shrink from any absurdity, but recognize straightway that the [[163]]blindness of chance is endowed with marvellous foresight.