ICHNEUMON, is also the name of a genus of flies of the hymenoptera order. It has no tongue; the antennæ have above 30 joints; the abdomen, in most of the species, is petiolated; and it has a sting in the tail inclosed in a double-valved cylindrical sheath. There are 77 species, principally distinguished by their colour.—These flies are sometimes at great pains to destroy and carry the caterpillars in whose bodies they intend to lay their eggs, to places where it is proper those eggs should be hatched. There is one species, whose worm produced from the egg can never succeed, unless it is both bred in the body of a caterpillar, and also have that habitation buried under ground. For this purpose, the parent-fly, when the time of laying her eggs is come, forms a hole in the ground, which she covers with a little clod of earth, that no dust may fall in to fill it up; when this is done, she goes out in quest of a caterpillar proper for her
purpose. Dr Lister assures us, that he has often seen one of these flies seize a caterpillar much larger than herself; and though this has been at a considerable distance from her hole, she has with great labour dragged the creature to it. As soon as she has arrived there with her load, she takes off the little pellet of earth from the mouth of the hole, and going down to see that all is ready for the reception of the new guest, she returns out of it and draws in the caterpillar, which she leaves there after giving it such wounds as, though they do not cause immediate death, yet disable the creature so as to make its escape impracticable. When the creature is thus lodged, she deposits her eggs in the flesh; after which she stops up the orifice of the hole very firmly with several pellets of dirt, and with dust carefully rammed in between, and will even fly up into gummy and resinous trees in order to get a cement to hold all firmly together. When the hole is thus filled up even with the surface of the rest of the ground, she draws a leaf or two to the place, and laying them over the mouth flies away. There is after this no more care taken; but the young worms are hatched from the eggs, and feed on the flesh of the caterpillar till they are fully grown. They then change into the nymph-state, and come out of that in form of their parent-flies, in which state they usually make their way out of the ground. Some of these ichneumons make the bodies of other smaller flies the places of hatching their eggs. They may be often met with flying with one of these small flies in their legs, the head of it being held close to their bellies. If they are watched on this occasion, they will usually be found to carry those flies to certain holes in the ground resembling worm-holes. The first that they carry serves as a nidus for their eggs: the rest are for food to the young ones while in the state of worms; these being too voracious to be subsisted long on the body of one fly, and therefore their parents carry them more every day. The old ones on this occasion crawl backwards into the holes, dragging the flies in after them. When their young worms have fed sufficiently, they are converted into nymphæ; the cases of which are made up of the wings, legs, and other hard parts of the flies they had been feeding upon.