ICHNEUMON, (Encycl.) One distinguishing and
striking character of these species of flies is the almost continual agitation of their antennæ. The name of ichneumon has been applied to them from the service they do us by destroying caterpillars, plant-lice, and other insects, as the ichneumon or mangouste destroys the crocodiles. The variety to be found in the species of ichneumons is prodigious: among the smaller species, there are males who perform their amorous preludes in the most passionate and gallant manner. The posterior part of the females is armed with a whimble, visible in some species, nowise discoverable in others; and that instrument, though so fine, is able to penetrate through mortar and plaster: the structure of it is more easily seen in the long-whimbled fly. The food of the family to be produced by this fly is the larva of wasps or mason-bees; for it no sooner espies one of those nests, but it fixes on it with its whimble, and bores through the mortar of which it is built. The whimble itself, of an admirable structure, consists of three pieces: two collateral ones, hollowed out into a gutter, serve as a sheath, and contain a compact, solid,
Ichneumon solid, dentated stem, along which runs a groove that conveys the egg from the animal, who supports the whimble with its hinder legs, lest it should break; and by a variety of movements, which it dexterously performs, it bores through the building, and deposits one or more eggs, according to the size of the ichneumon, though the largest drop but one or two. Some agglutinate their eggs upon caterpillars; others penetrate through the caterpillar's eggs, though very hard, and deposit their own on the inside. When the larva is hatched, its head is so situated, that it pierces the caterpillar, and penetrates to its very entrails. These larvæ pump out the nutritious juices of the caterpillar, without attacking the vitals of the creature; who appears healthy, and even sometimes transforms itself to a chrysalis. It is not uncommon to see those caterpillars fixed upon trees, as if they were sitting upon their eggs, and it is afterwards discovered that the larvæ, which were within their bodies, have spun their threads, with which, as with cords, the caterpillars are fastened down, and so perish miserably. The ichneumons performed special service in the years 1732 and 1733; by multiplying in the same proportion as did the caterpillars, their larvæ destroyed more of them than could be effected by human industry. Those larvæ, when on the point of turning into chrysalids, spin a silky cocoon. Nothing is more surprising and singular, than to see those cocs leap, when placed on the table or hand. Plant-lice, the larvæ of the curculionids, spiders' eggs, are also sometimes the cradle of the ichneumon-fly. Carcases of plant-lice, void of motion, are often found on rose-tree leaves: they are the habitation of a small larva, which, after having eaten up the entrails, destroys the springs and inward economy of the plant-louse, performs its metamorphose under shelter of the pellicle which enfolds it, contrives itself a small circular outlet, and sallies forth into open air. There are ichneumons in the woods, who dare attack spiders, run them through with their sting, tear them to pieces, and thus avenge the whole nation of flies of so formidable a foe: others, destitute of wings, (and those are females) deposit their eggs in spiders' nests. The ichneumon of the bedeguar (or sweet-briar sponge), and that of the rose-tree, perhaps only deposit their eggs in those places, because they find other insects on which they feed. The genus of the ichneumon flies, might with propriety be termed a race of diminutive cannibals.