At the end of the gallery again there is nothing to remind us of the spacious hall, the workshop where Copres, Scarabæi and Gymnopleuri fashion their artistic pears and ovoids, but a mere cul-de-sac of the same diameter as the nest. A veritable drill-hole, if we make allowances for the occasional knots and twists inevitable in boring through stuff that offers more resistance at some places than at others; a winding channel: that is what the Geotrupes’ burrow is.
The contents of the crude dwelling take the form of a sort of sausage or pudding, which fills the lower part of the cylinder and fits it exactly. Its length is not far short of eight inches and its width about an inch and a half, when the thing belongs to the Stercoraceous Geotrupes. The dimensions are a little smaller in the work of the Mimic Geotrupes. In either case, the sausage is nearly always irregular in shape, now curved, now more or less dented. These imperfections of the surface are due to the accidents of a stony ground, which the insect does not always excavate according to the canons of its art, which favours the straight line and the perpendicular. The moulded material faithfully reproduces all the irregularities of its mould. The lower end is rounded off like the bottom of the burrow itself; the upper end is slightly concave, through being packed more closely in the middle. [[206]]
The voluminous object is put together in layers rather suggestive, as regards curve and arrangement, of a pile of watch-glasses. Each of them obviously corresponds with a load of materials gathered in the heap above the burrow, carried down separately, placed in position on the previous layer and then vigorously trampled flat. The edges of the disk, which adapt themselves less well to this work of compression, remain at a higher level; and all this tends to form something like a concave lens. These same less-compressed edges give a sort of rind, which is soiled with earth owing to its contact with the walls of the tunnel. Altogether, the structure tells us the method of manufacture. The Geotrupes’ sausage, like our own, is obtained by moulding in a cylinder. It results from layers introduced one after the other and duly compressed, especially in the middle, which is more easily accessible to the manipulator’s legs. Direct observation will presently confirm these inferences and supplement them with details of considerable interest, which we should never suspect from simply examining the work.
Before continuing, let us note how well inspired the insect is in always boring its burrow under the heap whence the materials for the sausage are to be extracted. The number of loads successively carried down and pressed is considerable. Allowing a thickness of a sixth of an inch for each layer—a figure which is near enough—I see that some fifty journeys are needed. If the provisions had each time to be fetched from a distance, the Geotrupes would be unable to cope with her task, which would be too long and tiring. Her sort of work is incompatible with all that travelling, after the fashion of the Sacred Beetle’s. She is wise to settle beneath the heap. She has only to climb up from her well to find under her [[207]]feet, at her very door, enough to make her black-pudding, however large she may wish it to be.
This, it is true, presupposes a copiously supplied workyard. When toiling on behalf of her grub, the Geotrupes keeps a look-out for one of this kind and accepts no purveyors except the Horse and the Mule, never the Sheep, who is too niggardly. It is not a question here of the quality of the foodstuffs; it is a question of quantity. My cages, in fact, tell me that the Sheep would have the preference, if she were more generous. What she does not give normally I create artificially by piling sheaf upon sheaf. Beneath this extraordinary treasure, the like of which is never offered by the fields, my captives work with a zest that shows how well they appreciate the windfall. They enrich me with more sausages than I know what to do with. I arrange them in strata in great pots, so that, when winter comes, I may study the actions of the larva; I lodge them separately in glass tubes and test-tubes; I pack them in tins. The shelves of my study are crammed with them. My collection reminds me of an assortment of potted meats.
The unfamiliarity of the material involves no change in the structure. Because of its finer grain and greater plasticity, the surface is more regular and the inside more homogeneous; and that is all.
At the lower end of the sausage, which end is always rounded off, is the hatching-chamber, a circular cavity which could hold a fair-sized hazel-nut. The respiratory needs of the germ demand that the side-walls should be thin enough to allow the air to enter freely. Inside, I catch the gleam of a greenish, semifluid plaster, a simple exudation from the porous mass, as in the Copris’ ovoids and the Sacred Beetle’s pears. [[208]]
In this round hollow lies the egg, without adhering in any way to the surrounding walls. It is a white, elongated ellipsoid and is of remarkable bulk in proportion to the insect. In the case of the Stercoraceous Geotrupes, it measures seven to eight millimetres in length by four at its widest point.[1] The egg of the Mimic Geotrupes is a little smaller.
This little hollow contrived in the substance of the sausage, at the lower end, does not agree at all with what I have read about the Geotrupes’ nest-building. Quoting an old German writer, Frisch,[2] an author whom the poverty of my library does not allow me to consult, Mulsant,[3] speaking of the Stercoraceous Geotrupes, says:
‘At the bottom of her perpendicular gallery, the mother builds, usually with earth, a sort of nest, or egg-shaped shell, open at one side. On the inner wall of this shell she glues a whitish egg, the size of a grain of wheat.’