The Sacred Beetle, and Others

by Jean-Henri Fabre

The Sacred Beetle does not stop there: she becomes a geometrician capable of solving a delicate problem of minimum values. Other conditions being equal, evaporation obviously takes place in proportion to the extent of the evaporating surface. The alimentary mass must [[67]]therefore be given the smallest possible surface, in order to reduce the waste of moisture as much as possible; at the same time, this minimum surface must incorporate the maximum aggregate of nutritive materials, so that the grub may find sufficient nourishment. Now what is the form that encloses the greatest bulk within the smallest superficial area? Geometry answers, the sphere.

The Scarab, therefore, shapes the larva’s ration into a sphere (we will leave the neck of the pear out of the question for the moment); and this round form is not the result of blind mechanical conditions, imposing an inevitable shape upon the worker; it is not the violent effect of the rolling along the ground. We have already seen that, for the purpose of easier and swifter transit, the insect kneads into a perfect sphere the materials which it intends to consume at a distance, without moving that sphere from the spot on which it rests; in short, we have realized that the round form precedes the rolling.

In the same way, it will be seen presently that the pear destined for the grub is fashioned in the burrow. It undergoes no rolling-process, it is not even moved. The Sacred Beetle gives it the requisite outline exactly as a modelling artist might do, shaping his clay under the pressure of his thumb.

With the tools which it possesses, the insect could obtain other forms of a less delicate curve than its pear-shaped piece of work. It could, for instance, make a rough cylinder, the sausage customary among the Geotrupes; or, simplifying the work to the utmost, it could leave the lump without any definite form, just as it happened to find it. Things would proceed all the faster and would leave more time for playing in the sun. But no: the Sacred Beetle never chooses any shape but the sphere, [[68]]though it necessitates such scrupulous accuracy; she acts as though she knew the laws of evaporation and geometry from beginning to end.

It remains for us to examine the neck of the pear. What can be its object, its use? The reply forces itself upon us irresistibly. This neck contains the egg, in the hatching-chamber. Now every germ, whether of plant or animal, needs air, the primary stimulus of life. To admit that vivifying combustible, the shell of a bird’s egg is riddled with an endless number of pores. The pear of the Sacred Beetle may be compared with the egg of the Hen. Its shell is the rind, hardened by pressure, to avoid untimely desiccation; its nutritive mass, its meat, its yolk is the soft ball sheltered under the rind; its air-chamber is the terminal space, the cavity in the neck, where the air envelops the germ on every side. Where would that germ be better off, for breathing, than in its hatching-chamber projecting into the atmosphere and giving free play to the passage of gases through its thin and easily permeable wall?

In the centre of the mass, on the other hand, aeration is not so easy. The hardened rind does not possess pores like an egg-shell’s; and the central kernel is formed of compact matter. The air enters it nevertheless, for presently the grub will be able to live in it: the grub, a robust organism which does not need the same tender flutter of life as the sensitive germ.

Where the adolescent larva thrives, the egg would die of suffocation. Here is a proof of it. I take a small, wide-necked phial and fill it with Sheep-dung, the fare required in this case. I push in a bit of stick and obtain a shaft which shall represent the hatching-chamber. Down this shaft I place an egg carefully moved from its cell. I [[69]]close the orifice and cover up everything with a thickly-heaped layer of the same material. Here, in all excepting the shape, we have an artificial reproduction of the Sacred Beetle’s pellet; only, in this instance, the egg is in the centre of the mass, the place which over-hasty considerations made us but now believe the most suitable. Well, the point which we selected is fatal to life. The egg dies there. What has it lacked? Apparently, proper aeration.

Plenteously enveloped by the clammy mass, which is a bad conductor of heat, it is also deprived of the mild temperature needed for its hatching. In addition to air, every germ requires heat. In order to be as near as possible to the incubator, the germ in the bird’s egg is on the surface of the yolk and, thanks to its extreme mobility, always comes to the top, no matter what the position of the egg may be. Thus the most is made of the maternal heating-apparatus seated upon the brood.

In the insect’s case, the incubator is the earth, which is warmed by the sun. Its germ likewise comes close to the heating-apparatus; it goes as near as it can to the universal incubator, in search of its spark of life; instead of remaining sunk in the middle of the inert mass, it takes up its position at the top of a projecting nipple, lapped on all sides by the warm emanations of the soil.

These conditions, air and warmth, are so fundamental that no Dung-beetle neglects them. The piles of food hoarded vary in form, as we shall have an opportunity of seeing: in addition to the pear, such shapes as the cylinder, the ovoid, the pill and the thimble are adopted, according to the genus of the manipulator; but, amid this diversity of outline, one primary feature remains unchanged, and that is the placing of the egg in a hatching-chamber close [[70]]to the surface which allows free access to air and heat. And the most gifted in this delicate art of knowing just where to place the egg is the Sacred Beetle with her pear.