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Ichneumon flies are parasitic insects whose larvae feed on caterpillars, pupae and larvae of other insects. With more than 60,000 species spread throughout the world, this family has more species than any other family in the order Hymenoptera.
An adult ichneumon fly looks somewhat like a mosquito, except that it has four wings instead of the mosquito's two. In addition, the antennae of an ichneumon are much longer than those of a mosquito, often half as long as the fly's body.
Some species are the size of a small ant. The largest species grows to 1½ inches in body length.
The female's body ends in a pointed ovipositor, which may be 3 inches long. The three threadlike parts of this organ form a tube. With it, the insect places eggs inside trees or in the bodies of caterpillars.
Natural Pest Controller
The ichneumon fly is often called the "farmer's friend" because it controls a great many plant pests. Species have even been transported by man to colonize areas where artificial pest controls have not been successful.
The female lays her eggs in or on the larvae of the host species. When the maggot-like parasitic larvae hatch out, they feed on the body fats and fluids of the host until they are fully grown. Then the parasitic larvae spin cocoons within which they pupate and from whence the adult fly emerges. In the case of parasitic larvae breeding inside the host, the latter behaves normally until shortly before the uninvited guest larva has fully developed.
There are some ichneumon flies which live on other ichneumon flies and these are called hyperparasitic.
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This page was last updated on September 27, 2018.