Among those which feed on vegetables, some sink themselves in the earth, and by destroying the roots of the plants, do considerable injuries to our gardens. The food of others is dry and hard; they pierce the wood, reduce it to powder, and then feed on it; some, as the cossus, attack and destroy the trees, while the food of others more delicate is the leaves. The leaf is eaten in a different manner by different insects; some eat the whole substance, while others feed only on the parenchymous parts, which are contained between its superficial membranes, forming withinside the leaf paths and galleries. These insects are not always content with the leaf, but attack the flower also: even this food is too gross for many; the bee, the butterfly, the moth, as well as several species of flies, feed only on the honey, or finer juices, which they collect from flowers. We are continually finding the larva of some insect in pears, plumbs, peaches, and other fruit; these unwelcome intruders on the produce of human industry divide fruits, grain, and corn with us, often depriving us of large quantities. There is, indeed, no part of a plant which does not serve as food to different insects; some have one kind of plant marked out for them to inhabit and feed on, others have another assigned to them, on which, and no other, they will feed; each has its appropriate food, and though the parent animal eats not at all, or lives upon food entirely different, yet she is guided, as has before been observed, to deposit her eggs on that peculiar shrub or plant that will be food for her young; while some, more voracious than the rest, feed upon all with equal avidity; but in countries less cultivated than our own, their annoyance and devastations are terrible. The gryllus migratorius, a few years since, poured out of Tartary in such quantities, as to lay waste a great part of Europe, producing almost unequalled calamities, swarming in such multitudes as to cloud the air and cover the ground, mocking human power and craft; wherever they settled, all verdure disappeared, and the summer fruitfulness was turned into winter desolation; in Sweden the cattle perished with hunger, and the men were forced to abandon their country, and fly to the neighbouring regions.[87] The far greater part feed only, however, on one species of plant, or at most on those which are similar to it, and the same species may always be found on the same plant. Reaumur says, that the caterpillar which infests and feeds upon the cabbage, destroys in twenty-four hours more than twice its weight. If larger animals required a proportionable quantity, the earth would not afford sufficient nourishment for its inhabitants. [87] Select Dissertations from the Amœnitates Academicæ, vol. I, p. 398.