The caterpillars of the large white cabbage butterfly, and also those of the small white species, attack several valuable crops besides cabbages. They consume in the larvæ stage an enormous amount when their size is considered. Mr. Wood tells us that it has been calculated that one caterpillar alone, a month after birth, has increased to ten thousand times its original weight on leaving the egg, and has devoured in the meantime no less than forty thousand times that weight in food; and although during the winter months it may be frozen into a brittle condition, it survives this frost uninjured and becomes itself the parent of two broods during the ensuing summer.
These particular caterpillars feed also on the leaves of turnip plants and on the pods that are left for seeding; they eat radishes, horse-radish and water-cress.
Some years they show in myriads. Describing a flight of butterflies that arrived on a certain day years ago, the Zoologist says that it was one of the largest flights ever seen in this country. It crossed the Channel from France on a Sunday in July.
“Such was the density and extent of the cloud formed by the living mass that it completely obscured the sun from the people on board our Continental steamers. The decks were strewed with the insects in all directions. The flight reached England about twelve at noon, and dispersed themselves inland and alongshore, darkening the air as they went. During the sea-passage of the butterflies the weather was calm and sunny, with scarcely a puff of wind stirring; but an hour or so after they reached terra firma it came on to blow great guns from the south-west, the direction whence the insects came.” On a calm sea the butterflies are able to settle frequently, as though the water were land, and to rise again; otherwise, that is, in windy weather, these long flights would be of course an impossibility.
Louis Figuier, a French entomologist, has told how a swarm of plant lice once appeared between Bruges and Ghent, “hovering about, in troops” in such numbers as to darken the light of day. The walls of the houses were so covered that they could no longer be distinguished, and the whole road from the one town to the other was rendered black by the legions of this insect. These were called “smother-fly.”
A female Blight, as one creature is termed—a very destructive aphis—which was shut up for observation by another naturalist, brought forth ninety-five little ones in less than three weeks, and she can repeat this as often as twenty times during one summer if the weather be favourable to her. The calculations which have been made by such scientists as Professor Huxley prove that, were it not for our allies and friends, our unpaid and often ill-appreciated bird labourers, “there would be room in the world for nothing else” but those tiny creatures the aphides!
Mole crickets in the south of France and in Germany do great harm to the pea and bean crops. They have been known to destroy one-sixth, and even one-fourth, of a crop of young corn by eating off the roots. Barley and potatoes also they do a vast amount of harm to. The mole devours this insect, as it does many underground enemies of the agriculturist, and yet mole-catchers still receive so much an acre, year by year, from landholders for destroying the mole, whose heaps help to fertilise the soil, even if they do make it uneven, and if not levelled they injure the mowing machines; but their services are worth the extra labour in levelling.
Winged beetles swarm in the end of May, and they attack beans, broad and other beans. Horses fed on Sicilian beans are often injured in their health by the numbers of these creatures that have been contained in their food. One farmer in England wrote that he calculated he had as many of these small hurtful beetles as he had beans. Another farmer complained that he lost two whole sowings of turnips owing to the ravages of earwigs, and a writer in the Field states that he had one September to cover his windows with muslin and to shut all his doors at sunset because of the army of earwigs that invaded his precincts. “They dropped,” he says, “on the supper-table, they swarmed in the pantry, getting into fruit pies after cooking, and running out when the pies were cut. They pushed their way into the bread, so that we frequently cut slices of these wretches in cutting bread and butter. They found their way into the beds, linings of hats, coats, etc. When the doors were opened in the morning they dropped in such numbers that the mats were literally covered with them,” etc., etc.
To stop the ravages of caterpillars in some forests trenches have had to be dug. Into these they fall as they pour forth “in serried columns,” after having devoured one section of a wood, when on their way to attack a sound part. In the trenches they are stifled by numbers of men heaping earth on them. Sometimes great trees in the forest have to be set on fire as the only way of stopping their ravages. Then there are concealed foes who hollow out galleries in trees before their presence is suspected. One little insect has been dubbed by a naturalist with the formidable name of “the great pine-gnawer.” It ravages forests of fir-trees in such wise that not a single tree escapes its attacks.