The usual dimensions are four centimetres in length and two in width.[1] The colour is as golden as a grain of wheat. When set alight, the material burns readily and exhales a faint smell of singed silk. The substance is in fact akin to silk; only, instead of being drawn into thread, it has curdled into a frothy mass. When the nest is fixed to a branch, the base goes round the nearest twigs, envelops them and assumes a shape which varies in accordance with the support encountered; when it is fixed to a flat surface, the under side, which is always moulded on the support, is itself flat. The nest thereupon takes the form of a semi-ellipsoid, more or less blunt at one end, tapering at the other and often ending in a short, curved tail.
Whatever the support, the upper surface of the nest is systematically convex. We can distinguish in it three well-marked longitudinal zones. The middle one, which is narrower than the others, is composed of little plates or scales arranged in pairs and overlapping like the tiles of a roof. The edges of these plates are free, leaving two parallel rows of slits or fissures through [[149]]which the young emerge at hatching-time. In a recently-abandoned nest, this middle zone is furry with gossamer skins, discarded by the larvæ. These cast skins flutter at the least breath and soon vanish when exposed to rough weather. I will call it the exit-zone, because it is only along this median belt that the liberation of the young takes place, thanks to the outlets contrived beforehand.
In every other part the cradle of the numerous family presents an impenetrable wall. The two side zones, in fact, which occupy the greater part of the semi-ellipsoid, have perfect continuity of surface. The little Mantes, so feeble at the start, could never make their way out through so tough a substance. All that we see on it is a number of fine, transversal furrows, marking the various layers of which the mass of eggs consists.
Cut the nest across. It will now be perceived that the eggs, taken together, form an elongated kernel, very hard and firm and coated on the sides with a thick, porous rind, like solidified foam. Above are curved plates, set very closely and almost independent of one another; their edges end in [[150]]the exit-zone, where they form a double row of small, imbricated scales.
The eggs are buried in a yellow matrix of horny appearance. They are placed in layers, shaped like segments of a circle, with the ends containing the heads converging towards the exit-zone. This arrangement tells us how the deliverance is accomplished. The new-born larvæ will slip into the space left between two adjoining plates, a prolongation of the kernel, where they will find a narrow passage, difficult to go through, but just sufficient when we bear in mind the curious provision of which we shall speak presently; and by so doing they will reach the middle belt. Here, under the imbricated scales, two outlets open for each layer of eggs. Half of the larvæ undergoing their liberation will emerge through the right door, half through the left. And this is repeated for each layer from end to end of the nest.
To sum up these structural details, which are rather difficult to grasp for any one who has not the thing in front of him: lying along the axis of the nest and shaped like a date-stone is the cluster of eggs, grouped in layers. A protecting rind, a sort of solidified foam, surrounds this cluster, except at the top along [[151]]the median line, where the frothy rind is replaced by thin plates set side by side. The free ends of these plates form the exit-zone outside; they are imbricated in two series of scales and leave a couple of outlets, narrow clefts, for each layer of eggs.
The most striking part of my researches was being present at the construction of the nest and seeing how the Mantis goes to work to produce so complex a building. I managed it with some difficulty, for the laying takes place without warning and nearly always at night. After much useless waiting, chance at last favoured me. On the 5th of September, one of my boarders, who had been fertilized on the 29th of August, decided to lay her eggs before my eyes at about four o’clock in the afternoon.
Before watching her labour, let us note one thing: all the nests that I have obtained in the cages—and there are a good many of them—have as their support, with not a single exception, the wire gauze of the covers. I had taken care to place at the Mantes’ disposal a few rough bits of stone, a few tufts of thyme, foundations very often used in the open fields. My captives preferred the wire network, whose meshes furnish [[152]]a perfectly safe support as the soft material of the building becomes encrusted in them.
The nests, under natural conditions, enjoy no shelter; they have to endure the inclemencies of winter, to withstand rain, wind, frost and snow without coming loose. Therefore the mother always chooses an uneven support for the nest, so that the foundations can be wedged into it and a firm hold obtained. But, when circumstances permit, the better is preferred to the middling and the best to the better; and this must be the reason why the trelliswork of the cages is invariably adopted.
The only Mantis that I have been allowed to observe while engaged in laying does her work upside down, hanging from the top of the cage. My presence, my magnifying-glass, my investigations do not disturb her at all, so great is her absorption in her labour. I can raise the trellised dome, tilt it, turn it over, spin it this way and that, without the insect’s suspending its task for a moment. I can take my forceps and lift the long wings to see what is happening underneath. The Mantis takes no notice. Up to this point, all is well: the mother does not move and [[153]]impassively endures all the indiscretions of which I am guilty as an observer. And yet things do not go quite as I could wish, for the operation is too rapid and is too difficult to follow.