Some of our machines have extraordinary-looking mechanisms, which remain inexplicable so long as they are seen in repose. But wait until the whole is in motion; then the uncouth-looking contrivance, with its cog-wheels interacting and its connecting-rods oscillating, will reveal the ingenious combination in which all things are skilfully disposed to produce the desired effects. It is the same with certain insects; with certain weevils, for instance, and notably with the Acorn-beetles or Balanini, which are adapted, as their name denotes, to the exploitation of acorns, nuts, and other similar fruits.
The most remarkable, in my part of France, is the Acorn Elephant (Balaninus elephas, Sch.). It is well named; the very name evokes a mental picture of the insect. It is a living caricature, this beetle with the prodigious snout. The latter is no thicker than a horsehair, reddish in colour, almost rectilinear, and of such length that in order not to stumble the insect is forced to carry it stiffly outstretched like a lance in rest. What is the use of this embarrassing pike, this ridiculous snout?
Here I can see some reader shrug his shoulders. Well, if the only end of life is to make money by hook or by crook, such questions are certainly ridiculous.
Happily there are some to whom nothing in the majestic riddle of the universe is little. They know of what humble materials the bread of thought is kneaded; a nutriment no less necessary than the bread made from wheat; and they know that both labourers and inquirers nourish the world with an accumulation of crumbs.
Let us take pity on the question, and proceed. Without seeing it at work, we already suspect that the fantastic beak of the Balaninus is a drill analogous to those which we ourselves use in order to perforate hard materials. Two diamond-points, the mandibles, form the terminal armature of the drill. Like the Larinidæ, but under conditions of greater difficulty, the Curculionidæ must use the implement in order to prepare the way for the installation of their eggs.
But however well founded our suspicion may be, it is not a certitude. I can only discover the secret by watching the insect at work.
Chance, the servant of those that patiently solicit it, grants me a sight of the acorn-beetle at work, in the earlier half of October. My surprise is great, for at this late season all industrial activity is as a rule at an end. The first touch of cold and the entomological season is over.
To-day, moreover, it is wild weather; the bise is moaning, glacial, cracking one's lips. One needs a robust faith to go out on such a day in order to inspect the thickets. Yet if the beetle with the long beak exploits the acorns, as I think it does, the time presses if I am to catch it at its work. The acorns, still green, have acquired their full growth. In two or three weeks they will attain the chestnut brown of perfect maturity, quickly followed by their fall.
My seemingly futile pilgrimage ends in success. On the evergreen oaks I surprise a Balaninus with the trunk half sunk in an acorn. Careful observation is impossible while the branches are shaken by the mistral. I detach the twig and lay it gently upon the ground. The insect takes no notice of its removal; it continues its work. I crouch beside it, sheltered from the storm behind a mass of underwood, and watch operations.
Shod with adhesive sandals which later on, in my laboratory, will allow it rapidly to climb a vertical sheet of glass, the elephant-beetle is solidly established on the smooth, steep curvature of the acorn. It is working its drill. Slowly and awkwardly it moves around its implanted weapon, describing a semicircle whose centre is the point of the drill, and then another semicircle in the reverse direction. This is repeated over and over again; the movement, in short, is identical with that we give to a bradawl when boring a hole in a plank.