ICHNEUMON, in natural history, a genus of insects of the Hymenoptera or der : mouth with a straight horny mem branaceous bifid jaw, the tip rounded and ciliate ; mandibles curved sharp ; lip cy lindrical, membranaceous at the tip, and emarg-inate ; feelers four, unequal, fili. form, seated in the middle of the lip ; an tenna setaceous, of more than thirty arti culations; sting exserted, inclosed in a cylindrical sheath, composed of two.. valves, and'not very pungent. There are more than five hundred species enume rated by different authors. These are se parated into two families. A. scutel, white or yellow ; antenna annulate with white. B. scutel, white or yellow ; antenna en. tirely black. C. scutel, the colour of the thorax ; antenna annulate. D. scutel, the colour of the thorax ; antenna black. E. antenna yellow. F. minute ; antenna fili form ; abdomen sessile, ovate.
The whole of this singular genus have been denominated parasitical, on account of the very extraordinary manner in which they provide for the future sup port of their offspring. The fly feeds on the honey of flowers, and when about to lay her eggs, perforatesthe body of some other insect, or its larva, with its sting or instrument, at the end of the abdomen, and there deposits them. These eggs in a few days hatch ; and the young larva, which resemble minute white maggots, nourish themselves with the juices of their foster parent, which however con tinues to move about and feed till near the time of its change to a chrysalis, when the larva of the ichneumon creep out, by per forating the skin in various places, and each spinning itself up in a small oval silken case, changes into a chrysalis, and after a certain period they emerge in the state of complete ichneumons.
I. glomeratus may be given as an ex ample of this process. The caterpillar of the common white or cabbage butterfly, which, in the autumnal season, may be observed to creep up some wall, &c. in order to undergo its own change into a chrysalis : but in the space of a day or two, a numerous tribe of small maggots will be seen to emerge from it, and im mediately proceed to envelope them selves in distinct, yellow, silken cases, the whole forming a group round the cater pillar. These are the ichneumons glo meratus: they are black, with yellow legs, and they usually make their appear ance in about three weeks from the time of their spinning themselves up. Some of the ichneumon genus pierce the skins of newly-changed chrysalises of butter flies and moths, in which their larva re main during their own incomplete state. Others are so minute, that the female pierces even the eggs of moths and but terflies, and deposits her own in each. I. seductor, has a yellow scutel ; tip and pe tiole of the abdomen and crenate band on the fore-part yellow ; legs mostly yel low. This insect is found chiefly in Pavia; it forms a nest of cemented clay, in chim neys and windows, divided into cylindri cal cells, in each of which is contained a cylindrical, brown, lucid follicle, and in this the larva, with frequently the carcase of a spider, in which the insect had de posited her eggs.