The coupling takes place towards the end of May, after which the males die; the females only surviving them from the time necessary to ensure the propagation of the species. The number of eggs which a female lays is from twenty to thirty. With her front leg she hollows out a hole in the ground from two to four inches in depth, and deposits her eggs, of a yellowish white and of the size of hemp-seed, therein. Her instinct leads her to choose soft, light, and well-manured soils, which are, at the same time, the best ventilated and the most fertile. We may conclude from this that cultivation and labour have made the cockchafer more common than it was formerly. It is the child of civilisation, the parasite of agriculture. In from four to six weeks after being laid, the little larvæ are hatched ([Fig. 433]), and immediately attack the roots of vegetables. They have a hard and horny head, and slender black legs, longer than in any other species of Scarabæides. Their body is composed of a whitish pulp under a transparent skin; the head and the mouth have a reddish tinge. The length of their existence in this state is three, sometimes four years. From the egg laid in the month of June is hatched a larva, in the month of July. It increases in size during the last six months of the year, and continues to do so during the two following years, changing its skin many times during the period. Towards the end of the third year it changes into a pupa, after having surrounded itself with a cocoon consolidated with a glutinous froth and some threads of silk. The pupa ([Fig. 434]) is of a pale russety yellow, with two little points at the extremity of its body; the elytra and the wings, lying down, cover the legs and the antennæ.
Fig. 433.—Larva of the Cockchafer (Melolontha vulgaris).
Fig. 434.—Pupa of the Cockchafer (Melolontha vulgaris).
Towards the end of October the perfect insect is already marked out, but it is still soft and weak. It passes the winter in its hiding-place, hardens and becomes coloured at the end of the winter, and shows itself by degrees on the surface of the ground. In the month of April, three years after its birth, the cockchafer emerges from the earth, and commences its attack on the leaves of trees. This long duration of the development of the insect explains why we do not see them every year in the same number. When they have once appeared in great quantities, it is not for three years afterwards that we need expect to see their progeny again in proportionate numbers. It is, then, every three years that we have a cockchafer year like 1865, but in the intermediate years they are never very abundant. For the first year the little larvæ do not eat much. They feed then principally on fragments of dung, and on vegetable detritus, and keep together in families. In winter they bury themselves deeply, so as to be secure against frost and floods. Next spring the want of a greater abundance of food forces them to disperse. They then make subterranean galleries in all directions, without, however, going far from the place where they were hatched. They begin attacking the roots which they find within their reach; the damage they do increasing with their size and the strength of their mandibles. Among roots, they seem to prefer those of the strawberry and of rose-trees; but they do not despise other vegetables, and attack legumes and cereals as well as bushes and plants. The ravages which they occasion are sometimes incalculable; market gardens are sometimes entirely devastated. Fields of lucerne have been seen partially destroyed by them; meadows of great extent lose their pasturage; oat fields die off before they have come to maturity; and many of the ears of corn fall before they are cut.