name given by some authors to a species of worms bred in the body of the caterpillar, and which eat its flesh: these are owing to a certain kind of fly that lodges her eggs in the body of this animal, and they, after their proper changes, become flies like their parents.

Mr Reaumur has given us, in his history of insects, some very curious particulars in regard to these little worms. Every one of them, he observes, spins itself a very beautiful case of a cylindric figure, made of a very strong sort of silk; these are the cases in which this animal spends its state of chrysalis; and they have a mark by which they may be known from all other animal productions of this kind, which is, that they have always a broad stripe or band surrounding their middle, which is black when the rest of the case is white, and white when that is black. Mr Reaumur has had the pains and patience to find out the reason of this singularity, which is this: the whole shell is spun of a silk produced out of the creature's body; this at first runs all white, and towards the end of the spinning turns black. The outside of the case must necessarily be formed first, as the creature works from within: consequently this is truly white all over, but it is transparent, and shows the last spun or black silk through it. It might be supposed that the whole inside of the shell should be black; but this is not the case: the whole is fashioned before this black silk comes; and this is employed by the creature, not to line the whole, but to fortify certain parts only; and therefore is all applied either to the middle, or to the two ends omitting the middle; and so gives either a black band in the middle, or a blackness at both ends, leaving the white in the middle to appear. It is not unfrequent to find a sort of small cases, lying about garden-walks, which move of themselves; when these are opened, they are found to contain a small living worm. This is one of the species of these caterpillar-eaters; which, as soon as it comes out of the body of that animal, spins itself a case for its transformation long before that happens, and lives in it without food till that change comes on; and it becomes a fly like that to which it owed its birth.