Sylvestris, Wood-caterpillars; the name of a genus of caterpillars which do not live, after the manner of others, on leaves of trees or plants, or open to our observation; but under the bark, in the trunk and branches, and in the roots of trees, and sometimes in the body of fruits.

These are easily distinguished from those worms and maggots which are found in roots and fruits, and owe their origin to flies of another kind; but are liable to be confounded with a sort of animals, called by M. Reaumur, false or bastard caterpillars, which carry a great resemblance in their figure to real caterpillars, but which have more legs than any of the true ones have, and are finally transformed into four-winged flies, which are not true butterflies.

The butterflies which are the parents of those caterpillars that lie immersed in trees or fruits, lay their eggs on the surface; and the young caterpillars, when hatched, eat their way in. What appears something surprising, however, in this, is, that there usually is only one caterpillar in a fruit which is large enough to afford food to a great number; and if there are sometimes found two creatures within, one is usually a caterpillar, the other a worm of some other kind. The whole occasion of which is, that the operation of penetrating into the fruit is so difficult to the young animal, that it seldom succeeds in it; and tho' the butterfly deposits many eggs on each fruit, and these all hatch, yet it is only here and there one on a fruit that can find the way into it.

These creatures, when once lodged in their prison, have nothing to do but to eat up the substances which inclose them, leaving the outer hard shell unhurt, which still serves as a cage for them. This is a very frequent case in the grains of corns, where the farinaceous substance serves as aliment, and the hard outer skin becomes a firm hollow cage afterwards for the animal. The farinaceous substance in this case usually proves enough for the animal in its caterpillar-state; but if it does not, the creature has recourse to a very singular expedient; it eats again its own excrements; and finds its now stronger stomach able to separate nourishment from that very matter which had before passed off from its weaker stomach undigested.

Of these species of caterpillars, some go out of their prison in order to change into their chrysalis, and thence into their butterfly-state; but the greater number remain there, and pass through all their changes within. These caterpillars, like all the other kinds, have certain flesh-eating worms, whose parents are of the fly-kind, for their terrible enemies and destroyers; and it is not unfrequent, on opening one of these spoiled fruits, instead of the expected caterpillar, to find a fly just ready to come out; this has been produced from the chrysalis of a worm, which had before found its way into the fruit, and eaten up the caterpillar, which was the original possessor of the place.