Since the occasion presents itself, let me say a few more words on the insect’s powers of resisting cold. [[231]]Some years ago, while looking for Scolia-cocoons in a heap of mould, I had made a large collection of the grubs of Cetonia aurata.[1] I placed my loot in a flower-pot with a few handfuls of decayed vegetable matter, just enough to cover the insects’ backs. I intended to draw upon them for certain enquiries which I was making at the time. The pot remained in the open air; and I forgot all about it. A cold snap came, accompanied by sharp frost and snow. Then I remembered my Cetoniæ, so ill-protected against this kind of weather. I found the contents of the pot hardened into a conglomeration of earth, dead leaves, ice, snow and shrivelled grubs. It was a sort of almond-rock, in which the larvæ stood for the almonds. Sorely tried by the cold as they were, the colony ought to have perished. But no: when the thaw arrived, the frozen larvæ came to life again and began to swarm about as though nothing unusual had happened.
The insect’s powers of endurance are less great than the larva’s. As the organization becomes more refined, it loses its robustness. My cages, which went through such a bad time in the winter of 1895, provided me with a striking instance. A few species—Scarabæi, Copres, Pilularii and Onthophagi—were represented at the same time by newcomers and old stagers. All the Geotrupes, without an exception, died in the earthy bed which had turned into a block of stone; the Minotaurs also succumbed, every one of them. And yet both find their way up north and are not afraid of cold climates. On the other hand, the southern species, the Sacred Beetle, the Spanish Copris and Pilularius flagellatus, the younger [[232]]generation as well as the veterans, withstood the winter better than I dared hope. Many of them died, it is true; they formed the majority; but at any rate there were survivors whom I marvelled to see recovering from their icy paralysis, trotting about under the first kisses of the sun. In April, those specimens which have escaped from freezing resume their labours. They teach me that, when at liberty, Copres and Scarabæi have no need to retire to winter quarters at great depths underground. A moderate screen of earth, in some sheltered nook, is enough for them. Less skilful diggers than the Geotrupes, they are better provided with the power to resist a passing spell of cold.
We will end this digression by remarking, as so many others have done, that agriculture cannot reckon on the cold weather to rid it of its dread enemy, the insect. Very hard frosts, lasting a long time and penetrating well beneath the surface of the soil, can destroy various species which are not able to go down low enough; but a great many survive. Moreover, the grub and especially the egg in many cases defy our severest winters.
The first five days of April put an end to the torpor of the larvæ of both Geotrupes, snuggling on the bottom floor of their cylinder, in a temporary cell. Activity returns, bringing with it a last flicker of appetite. The remains of the autumn banquet are plentiful. The grub makes use of them no longer for greedy feasting, but just as a midnight snack between two slumbers, that of winter and the deeper sleep of the metamorphosis. Hence the sides of the sheath are attacked spasmodically. Breaches yawn, sections of wall come tumbling down, and soon the edifice is nothing but an unrecognizable ruin. [[233]]
The lower portion of the original sausage remains, however, with its walls intact for a length of an inch or two. Here, in a thick layer, the grub’s excreta are accumulated, held in reserve for the final work. In the centre of this mass a hollow is dug, carefully polished inside. With the excavated rubbish the grub builds not just a canopy, like that with which the winter alcove was protected, but a solid lid, with a rough outer surface, in appearance not unlike the work of the Cetoniæ when they wrap themselves in a shell of mould. This lid, with what is left of the pudding, forms a habitation which would remind us pretty closely of the Cockchafer’s dwelling, were it not truncated in the upper part, which moreover is most often topped by a few remnants from the destroyed cylinder.
The grub is now shut in for the transformation, motionless, with its body emptied of all dross. In a few days a blister appears on the dorsal surface of the last abdominal segments. This swells, spreads and gradually extends as far as the thorax. It is the work of excoriation beginning. Distended by a colourless liquid, the blister gives an uncertain glimpse of a sort of milky cloud, the first blurred outline of the new organism.
The thorax splits in front, the cast skin is slowly pushed backwards, and at last we have the nymph, all white, half-opaque and half-crystalline. I obtain my first nymphs about the beginning of May.
Four or five weeks later, the perfect insect arrives, white on the wing-cases and belly, while the rest of the body already possesses the normal colouring. The chromatic evolution is quickly completed; and, before the end of June, the Geotrupes, now perfectly matured, emerges from the soil at twilight and flies off to start on [[234]]his scavenger’s job without delay. The laggards, those whose egg has gone through the winter, are still in the white nymphal stage when their elders effect their release. Not before September is nigh will they burst their natal shell and, in their turn, sally forth to aid in the cleansing of the fields. [[235]]
[1] The Rose-chafer, whose grub forms the prey of the Scolia-wasp. Cf. The Life and Love of the Insect: chap. xi.—Translator’s Note. [↑]