Caterpillar, or Eruca, a genus of insects, comprehending many species, of which that most generally known is the common, or garden-caterpillar. The natural food of these creatures consists of the leaves and verdure of vegetables ; but, harmless as they appear, there are some species among them which destroy one another, whenever an opportunity offers : the generality of caterpillars, however, are very peaceable, and many species live together in the same place, without molesting each other. These would breed and multiply to an incredible degree, were they not devoured by other insects, which prey upon them, both externally and internally, and literally consume them alive.

Caterpillars are very destructive in gardens and fields, especially those denominated the black, and the black-canker caterpillar, which prey principally on .turnips. The former insect is of the colour of scot; and, when full grown, about three quarters of an inch in length. It commences its depredations towards the end of August, or the beginning of September, and is particularly numerous, when the north or easterly winds prevail. To counteract the devastation occasioned by this insect, it has been recommended, at the first ploughing, to irrigate the furrows with lime-water, which will effectually destroy it; as few insects like the smell of any thing that has been burned.

The black-canker caterpillars are principally found in the county of Norfolk, where, from the great numbers of inserts which have been washed upon the beach, by the tide, it is generally believed that they are not natives, but wafted across the ocean. These cankers are supposed to be the caterpillar state of the yellow fly, which is particularly destructive in fields planted with turnips and cabbages ; for they have been observed regularly to assume the appearance of those flies. For this evil, there appears to be no other remedy, but to pull the creatures off their nests, and to watch the flies, which during the hot weather are daily depositing their eggs on those plants.

There is also another variety, called by gardeners the grub, the skin of which is very tough, and of a brown colour. This insect is particularly injurious, usually depositing its eggs in the very heart of the plants, through all the blades of which it eats its way, leaving behind a great quantity of its excrement, which is hurtfud to vegetation. Grubs likewise burrow under the surface of the ground, and do great damage to young plants, by eating off their tender stalks, and drawing them into subterraneous holes. This mischief' is principally done in the night 5 but, if the earth be stirred about an inch deep, where a plant is found to be thus injured, the insect will be discovered : and this is the only certain way of exterminating these noxious vermin.

When caterpillars attack fruit trees, the most efficacious way to destroy them is the following: Make a strong decoction of equal quantities of rue, wormwood, and common tobacco, and sprinkle this liquor on the leaves and young branches every night and morning, while the fruit is ripening.

Various other experiments have been made with a view to extirpate these mischievous vermin. We shall, however, mention only the following methods, which have been attended with peculiar success :— Take three quarts of water, and one quart of vinegar; let them be heated till they nearly boil; then put one pound or more of pure soot into the mixture, and stir it with a whisk till the whole is duly incorporated. Sprinkle the plants with this preparation every morning and evening : in a few days all the caterpillars will disappear. This has also been effected by sprinkling plants (and more especially gooseberry-bushes, which are remarkably subject to the depredations of these insects) with a preparation consisting of one quart of tobacco-liquor, in which an ounce of alum has been dissolved. As soon as the plants or bushes appear to be in the least degree corroded, or any eggs are observed on the leaves, a brush should be dipped into the liquor, which, by drawing the hand gently over its hairs, is carefully sprinkled on them. If any eggs be there deposited, they never come forward after this application; and if those eggs have already been changed into worms, they either die, or sicken, so as to fall off the bush ; in which case they may be easily killed.

When the trunk and boughs of trees abound with the eggs of caterpillars, especially in the early spring, it is advisable to rub the bark of all the affected places with a sponge dipped in soap-water ; and, where the height of the tree renders it necessary, this operation may be facilitated, by fastening pieces of flannel to a lath or pole, after soaking them in a similar liquor.

About the middle of the last century, experiments were made to manufacture paper from the cods which caterpillars spin, andin which they undergo their transformations from a worm to a nymph, or chrysalis, and thence to a butterfly. These cods, after being cleared of the leaves that adhered to them, and well beaten, were reduced to a kind of pulp, which, when spread in water, was collected into the form, and made into sheets of paper of a coarse brown colour; but as some of them were much whiter than others, it was supposed, that by being beaten and . washed a longer time in the mortar of the mill, they would acquire a greater degree of whiteness. At the present period, when the materials for manufacturing paper are exceedingly scarce, we would recommend a repetition of this experiment ; for, if the result should be successful, considerable advantage may be derived from the cods of those insects, which occasion often irreparable damage to the industrious cultivator. - See also, Insect.