If the haricot pest were ever to threaten us seriously it would not be very difficult to wage a war of extermination against it. Its habits teach us what tactics we ought to follow. It exploits the dried and gathered crop in the granary or the storehouse. If it is difficult to attack it in the open it would also be useless. The greater part of its affairs are managed elsewhere, in our storehouses. The enemy establishes itself under our roof and is ready to our hand. By means of insecticides defence should be relatively easy.
CHAPTER XX
THE GREY LOCUST
I have just witnessed a moving spectacle: the last moult of a locust; the emergence of the adult from its larval envelope. It was magnificent. I am speaking of the Grey Locust, the colossus among our acridians,[10] which is often seen among the vines in September when the grapes are gathered. By its size—and it grows as long as a man's finger—it lends itself to observation better than any other of its tribe.
The larva, disgustingly fat, like a rude sketch of the perfect insect, is commonly of a tender green; but it is sometimes of a bluish green, a dirty yellow, or a ruddy brown, or even an ashen grey, like the grey of the adult cricket. The corselet is strongly keeled and indented, and is sprinkled with fine white spots. As powerful as in the adult insect, the hind-leg has a corpulent haunch, streaked with red, and a long shin like a two-edged saw.
The elytra, which in a few days will extend far beyond the tip of the abdomen, are at present too small triangular wing-like appendages, touching along their upper edges, and continuing and emphasising the keel or ridge of the corselet. Their free ends stick up like the gable of a house. They remind one of the skirts of a coat, the maker of which has been ludicrously stingy with the cloth, as they merely cover the creature's nakedness at the small of the back. Underneath there are two narrow appendages, the germs of the wings, which are even smaller than the elytra. The sumptuous, elegant sails of to-morrow are now mere rags, so miserly in their dimensions as to be absolutely grotesque. What will emerge from these miserable coverings? A miracle of grace and amplitude.
Let us observe the whole process in detail. Feeling itself ripe for transformation, the insect climbs up the wire-gauze cover by means of its hinder and intermediate limbs. The fore-limbs are folded and crossed on the breast, and are not employed in supporting the insect, which hangs in a reversed position, the back downwards. The triangular winglets, the sheaths of the elytra, open along their line of juncture and separate laterally; the two narrow blades, which contain the wings, rise in the centre of the interval and slightly diverge. The proper position for the process of moulting has now been assumed and the proper stability assured.
The first thing to do is to burst the old skin. Behind the corselet, under the pointed roof of the prothorax, a series of pulsations is produced by alternate inflation and deflation. A similar state of affairs is visible in front of the neck, and probably under the entire surface of the yielding carapace. The fineness of the membrane at the articulations enables us to perceive it at these unarmoured points, but the cuirass of the corselet conceals it in the central portion.