In proportion as they increase in age and in strength—especially in their last year—do they attack also ligneous vegetation. When they have gnawed away the lateral roots of a young tree, the new shoots corresponding to them dry up. The larvæ then attack the principal root, and thus bring about the death of the tree. There will be found round the roots of trees thus attacked immense numbers of these worms. M. Deschiens relates that he had seen six hectares of acorns, sown three times in the space of five years with a perfect result, entirely destroyed as many times by the larvæ of the cockchafer. A nurseryman of Bourg-la-Reine suffered, in 1854, from the ravages of these terrible larvæ, losses which he estimated at 30,000 francs. Others only preserved about a hundredth part of their plants. In Prussia they destroyed, in 1835, a considerable nursery of trees in the Institut Forestier. In the forests of Kolbetz more than a thousand measures of wild pines were destroyed in the same way.
We shall not, then, be surprised to learn that the thunders of excommunication were formerly launched at the cockchafers, as they were also at the caterpillars and the locusts. We do not know whether this had much impression upon them. In 1479, the cockchafers having occasioned a famine in the country, were cited before the ecclesiastical tribunal of Lausanne. The advocate (Fribourg) who defended them, did not find, doubtlessly, in the resources of his eloquence arguments powerful enough in their favour; for the tribunal, after mature deliberation, condemned the accused troop, and sentenced them to be banished from the territory. But it is not enough to pass a sentence—there must also be the means of putting it in execution; and these were wanting to the tribunal of Lausanne. And so the condemned cockchafers continued to live on Swiss land, without appearing mindful of the condemnation which had been fulminated against them.
The larvæ of the cockchafer are not easily destroyed. They successfully resist those scourges which one fancies must harm them. Thus, the inundation which devastated the banks of the Saône, fifteen years ago, had no effect on them. The land and meadows, which had remained for from four to five weeks under water, were none the more rid of them. The only circumstance which is really hurtful to them, and to the adult cockchafer, is late frost in the months of April and May. When these frosts come after mild weather, they surprise the larvæ at the surface of the soil, and kill them. Unfortunately, the same causes do harm to the plants which have already begun to spring up. Nature has not, then, sufficiently provided the means of destroying these mischievous beings. One would say that she had not foreseen their extraordinary multiplication, which has been, we must confess, encouraged by agriculture and by the cultivation of the land.
Animals do not contribute much towards limiting the number of cockchafers, although the latter are not wanting in natural enemies. Among insects, it is the large species of Carabus which search after the larvæ as well as the adult cockchafers. The Carabus auratus attacks them with great coolness. M. Blanchard saw a carabus seize a cockchafer in the middle of the road, open its belly with its mandibles, and devour its intestines. The cockchafer tossed about from one side to the other, and even walked, while it was undergoing its cruel punishment; and the Carabus followed it without interrupting its work. Some reptiles, many carnivorous animals, such as the shrew-mouse, pole-cats, weasels, rats, and certain birds, especially the night-birds, prey upon the cockchafer and its larvæ. Ravens and magpies, which are seen going from clod to clod, make savage but insufficient war against them. In fact, all these animals together do not destroy the hundredth part of the cockchafers which are born every year.
As an example which will show the extent of the evil, a field of 29 acres was ploughed up into 72 furrows. At the first ploughing were gathered 300 larvæ per furrow; at the second, 250; at the third, 30 more; which amounted to 600 per furrow, and to 43,200 in all. Man, who is the victim of these ravages, has been necessarily obliged to think of a means of destroying this enemy. Many infallible means have been proposed, which have, however, given no result. Prizes have been offered, but the evil has not diminished. Here are a few of the processes recommended.
Immediately after the ploughing, you must turn into the field infested by the larvæ a flock of turkeys, to whom it will be a great treat to devour them, or else you must sow in the field rape-seed, very thickly, which you must then bury by a very deep ploughing, when it is as high as your hand. Colewort, it is said, kills the larvæ, while it at the same time manures the soil. Or again, you must plough up the land on the approach of hard frosts, to expose the worms to the cold. Lastly, you can water the field with oil of coal, or sprinkle it with ashes of boxwood. All these are expensive. The simplest means are here the best. It is better to depend upon labour than destructive substances, whose employment always presents inconveniences. Considering the difficulties which oppose themselves to us in our search after larvæ, we had better collect them in their adult state by violently shaking the branches of the trees on which they doze during the day, and then kill them in some way or other, thus destroying from twenty to forty eggs with each female. A general cockchafer hunt, rendered obligatory by a law, and encouraged by prizes, would be the only efficacious means of opposing a pest which costs agriculture many millions. This means would also be less costly than the turning up of the land concealing the larvæ, when it is remembered that they prefer land in full bearing.
In 1835 the General Council of La Sarthe voted a sum of 20,000 francs for a cockchafer hunt. Nearly 600,000 litres were delivered in, thanks to a prize of three centimes per litre. As a litre contains about 500 cockchafers, there were thus destroyed about 300,000,000 of them. It is true that M. Romieu, then Prefect of La Sarthe, who was the principal promoter of this excellent measure, became food for the wit of the newspapers, and was represented dressed like a cockchafer in the Charivari. Derision and ridicule are too often the reward of useful ideas. In Switzerland were taken, in 1807, more than 150,000,000 of these insects. But these isolated measures were useless in producing a durable result.
It has been tried to make use of cockchafers in industrial arts. According to M. Farkas, they have succeeded, in Hungary, by boiling them in water, in extracting from them an oil, which is used to grease the wheels of carriages; and, according to M. Mulsant, the blackish liquid which is contained in the œsophagus may be used for painting. But the produce arising from these industrial occupations is not considerable enough to ensure them a certain extension, which is to be regretted, for agriculture would thus be rid of one of its most formidable scourges. Poultry are sometimes fed on these insects; pigs are also very fond of them.
The Melolontha Hippocastani differs from the common species in having black legs. The Melolontha fullo, twice as large as the common species, is variegated with tawny and white. It is met with on the sea-coasts, and on the downs of the north and south of France, as its larvæ feed on the roots of maritime plants.
Among the genera very near to the cockchafer we will mention the little Rhizotrogus, light-coloured and hairy, which flies in the evening in the meadows, and the Euchloras, or Anomalas, of splendid metallic colours. The Anomala vitis is an insect of about half an inch long, of a beautiful green, bordered by yellow, with the elytra deeply furrowed. It sometimes causes extensive ravages in the vineyards.