The New Student's Reference Work/Ichneumon Flies
Ichneumon Flies, insects with four membranous wings, that have the habit of laying their eggs in or upon other insects. In this way they destroy many insect pests. All are parasites upon other insects; as a rule, upon those injurious to vegetation. Caterpillars are especially subject to their attacks. The eggs are frequently placed in their little cases upon the skin of insects. After hatching, the larvæ bore their way into the insects and feed upon the blood and juices of their host. The insects thus attacked die, and the small flies come out. The ichneumon family includes minute forms and large ones. The largest one in the United States is an insect of remarkable appearance, with a slender body and three long filaments at its hinder end. The body is about two and one half inches long, and the extreme length from tip of antennæ to tip of filament is ten inches. The middle filament is an ovipositor to aid in laying the eggs. It is armed with a file at the tip. With this instrument the insect bores into trees (see illustration) infested by the larvæ of another insect, viz., the pigeon tremex, which does so much harm to shade-trees. When the burrow of one of these is found, an egg is deposited in it. The larva which hatches creeps along the burrow and attaches itself to the tremex larva, which it destroys by sucking its blood.