The prohibition is understood; the tempting fruit is left almost untouched. For my part, I inspect the nuts assiduously. All my trouble is unavailing: I do not succeed in surprising a Balaninus engaged in her patient task of boring. At the utmost, at sunset, I happen to see one who, hoisted to her full height, is trying to insert her drill. The little that I observe teaches me nothing new; the Acorn-weevil has already shown me as much.
In any case, it is only a brief attempt. The insect is casting about and has not yet found what [[101]]suits her. Perhaps the perforator of hazel-nuts works at night.
In another respect I have been more fortunate. Some nuts, some of the first colonized, are laid by in my study and subjected to frequent inspections. My diligence is rewarded with success.
At the beginning of August, two larvæ leave their coffers before my eyes. They have no doubt long been chipping with the points of their mandibles, that patient chisel, at the hard wall. The exit-hole is just finished when I take note of the coming departure. A fine dust is falling by way of shavings.
The window of release is distinct from the narrow aperture of the entrance. Perhaps it will not do to obstruct this grating, which ventilates the house, while the grub is still at work. The window aforesaid is situated at the base of the fruit, close to the rough surface by which the nut adheres to its cupule. In this region, where the incipient materials are elaborated until the nut is perfectly ripe, the density is a little less than elsewhere. The point to be perforated is excellently chosen therefore: it is here that the least resistance will be encountered.
Without any preliminary auscultation, without exploratory soundings, the recluse knows the weak point of his prison. Confident of success, he works away with a will. Where the first blow of the pick is struck the others follow; no time is wasted on [[102]]experiments. Persistence is the strength of the weak.
It is done: daylight enters the coffer. The window is opened, round, widening a little inwards and carefully polished over the whole circumference of its embrasure. Under the burnisher of the mandibles any roughness that might presently increase the difficulty of the emergence has disappeared. The holes in our steel draw-plates are scarcely more accurate.
The comparison with a draw-plate comes in quite aptly here: the larva actually frees itself by a wire-drawing-operation. Like a length of brass wire which is reduced by being passed through an orifice too narrow for its diameter, it escapes through the window in the shell by decreasing its girth. The wire is drawn by an exertion on the part of the workman’s pincers or by the rotation of the machine; it subsequently retains the reduced thickness which the operation has given it. The grub knows another method: it lengthens and thins itself by its own efforts; and, directly it has passed through the narrow orifice, it returns to its natural size. Apart from these differences the resemblance is striking.
The exit-aperture is precisely the same width as the head, which, being rigid, with a horny cap, does not lend itself to deformation. Where the head has passed, the body has to pass, however fat it may be. When the liberation is completed, [[103]]it is most surprising to see how bulky a cylinder, how corpulent a grub has contrived to make its way through the tiny opening. If we had not witnessed the exodus, we should never have suspected such a feat of gymnastics.
The orifice, we were saying, is exactly fitted to the diameter of the head. Now this inelastic head, by whose size that of the hole has been calculated, represents at most one-third of the width of the body. How does a threefold thickness pass through a single calibre?