Things had been in this state since the previous evening, when I heard the larva scratching in the box. On opening, I found my captive busy scratching the cardboard walls with the tips of its mandibles, its body half out of the bag. Already it had made considerable progress, and a heap of little fragments were piled before the opening of the hammock, to be utilised later. For lack of other [[255]]materials it would doubtless have used these scrapings for its constructions, but I thought it better to provide according to its tastes and give it sand. Never did Bembex larva build with such sumptuous material. I poured out for my prisoner sand for drying writing,—sand well sprinkled with gilded grains of mica,—before the opening of the bag, which was in a horizontal position, suitable to the work which would follow. The larva, half out of its hammock, chose its sand almost grain by grain, routing in the heap with its mandibles, and, if one too bulky presented itself, it was seized and cast aside. The sand being sorted, the larva introduced a certain quantity with its mouth into the silken fabric, then retired into its sack and began spreading the materials in a uniform layer on the inner surface, then glued together various grains and inlaid them in the fabric, with silk for cement. The outer surface was constructed more slowly. These grains were carried singly and fixed on with silk gum.
This first deposit of sand only concerns the anterior part of the cocoon—that half which ends in the opening. Before turning round to work at the back part, the larva renews its store of materials and takes certain precautions, so as not to be embarrassed in its masonry. The sand heaped before the entrance might slip inside and hinder the builder in so narrow a space. The grub foresees this, and glues some grains together, making a coarse curtain of sand, which stops up the orifice, imperfectly indeed, but enough for the purpose. These precautions taken, the grub labours at the back part of the cocoon. From time to time it turns round to get [[256]]fresh materials from outside, tearing away a corner of the protecting curtain, and through this window grasping the materials needed. The cocoon is still incomplete—wide open at the upper end and without the spherical cap needed to close it. For this final bit of work the grub provides itself abundantly with sand, and then pushes away the heap before the entrance. A silken cap is now woven and fitted close to the mouth of this primitive basket. On this silken foundation are deposited, one by one, the sand grains kept in the interior and cemented with silk-spittle. This lid completed, the larva has only to give the last finish to the interior of the dwelling and glaze the walls with varnish, to protect its tender skin from the roughness of the sand.
The hammock of pure silk and the cap which later closes it are evidently only scaffolding intended to support the masonry of sand and to give it a regular curve. One might compare them to the constructions used by builders when making an arch or vault. The work being completed, the silken support disappears, partly lost in the masonry, and partly destroyed by contact with rough earth, and no trace remains of the ingenious method employed to put together a construction perfectly regular, yet made of a material so little coherent as is sand. The spherical cap which closes the original basket is a separate work, adjusted to the main body of the cocoon. However well the two pieces are fitted and soldered, the solidity is not such as the larva would obtain had it built the whole dwelling continuously. Thus, on the circumference of the cover there is a circular line less capable of resistance, but this is not [[257]]a fault of construction. On the contrary it is a fresh perfection. The insect would experience grave difficulty in issuing from its strong box, so thick are the walls, did not the line of junction, weaker than the rest, apparently save much effort, as it is usually along this line that the cover is detached when the perfect Bembex emerges.
I have called the cocoon a strong box. It is indeed a solid article, both from its shape and the nature of its materials. Landslips or falling sand cannot alter its form, since the strongest pressure of one’s fingers cannot always crush it. Thus it matters little to the larva if the ceiling of its burrow, dug in loose soil, should sooner or later fall in, and it need not fear, even should a passing foot press down the thin covering of sand; it runs no risks when once enclosed in its stout shelter. Nor does damp endanger it. I have immersed Bembex cocoons for a fortnight in water without finding any trace of damp inside them. Ah! why cannot we have such waterproof for our dwellings? To sum up: the cocoon, of graceful oval shape, appears rather the product of patient art than the work of a grub. For any one not behind the scenes, the cocoons which I saw in process of construction with the sand from my inkstand might well have been precious articles of some unknown industry—great beads starred with golden dots on a ground of lapis lazuli, destined for the necklace of some Polynesian belle. [[258]]
XIX
THE RETURN TO THE NEST
The Ammophila digging her well late in the day leaves her work after stopping the entrance with a stone, flits away from one flower to another, goes into a new neighbourhood, and yet next day can return with a caterpillar to the abode hollowed out the evening before, notwithstanding her want of acquaintance with the locality—often new to her; the Bembex, loaded with prey, alights with almost mathematical precision on the threshold of a dwelling blocked by sand and rendered uniform with the rest of the sandy surface. Where my sight and memory are at fault, theirs have a certainty verging on infallibility. One would say that the insect possessed something more subtle than mere recollection—a kind of intuition of locality with which nothing in us corresponds—in short, an indefinable faculty which I call memory for lack of any other expression by which to designate it. The unknown cannot be named. In order to throw if possible a little light on this point in the psychology of animals I instituted a series of experiments, which I will now describe.
The first had for its subject Cerceris tuberculata, [[259]]which hunts the Cleonus. About 10 a.m. I took a dozen females busy at the same bank and of the same colony, either hollowing or storing burrows. Each was enclosed in a twist of paper, and all were put into a box. About two kilometres from the nests I freed my captives, first marking them with a white dot in the middle of the thorax by means of a straw dipped in an indelible colour, in order to recognise them later. They flew on every side—some here, some there, but only a few paces, alighting on blades of grass and passing their forelegs over their eyes for a moment, as if dazzled by the bright sunshine to which they were suddenly restored. Then they took flight—some earlier, some later; and one and all took unhesitatingly a straight line south, i.e. in the direction of their home. Five hours later I returned to the common territory of the nests. Almost directly I saw two of my white-dotted Cerceris working at their burrows. Soon a third came in, with a weevil between her feet. A fourth soon followed—four out of twelve in a quarter of an hour was enough for conviction; I judged it useless to wait longer; what four could do, the others could, if indeed they had not already done it, and one may very well suppose that the eight absentees were out hunting, or perhaps had retired into the depths of their burrows. Thus, carried to a distance of two kilometres, in a direction and by a way which they could not possibly perceive from the depths of their paper prison, the Cerceris—at all events part of them—had returned home.
I do not know to what distance they go hunting; possibly they know the country round for some two kilometres. In that case they would not have been [[260]]far enough away, and came home by their local knowledge. The experiment had to be tried again at a greater distance, and from a point which the Cerceris could not possibly know.