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These insects generally resemble wasps , but they are distinguished by longer, more segmented antennae.

In several species, the abdomen of females ends in a long filament that exceeds the size of their body. This egg-laying organ is called an ovipositor.

The vast group of ichneumons consists of thousands of species that vary widely in size (3 to 50 mm in length) and coloring. Many have a uniform shade, varying from yellowish to black, while others feature two-color patterns: black and brown or black and yellow.

Life cycle

The female lays her eggs on or in living insects. She can choose caterpillars, pupae or chrysalis .

The host serves as a pantry for the young insect emerging from the egg. The ichneumon larva transforms into a pupa after having devoured almost entirely the body of its host. The insect spends some time in this motionless form, then the adult emerges.

Many ichneumons hibernate as adults, hidden under bark or under fallen trees.


These insects are common in several habitats. They are found almost everywhere in the world.

What you need to know

Ichneumons are classified as parasitoids because their larvae complete their development by feeding on a host that eventually dies (in the case of parasites, the host does not die). More precisely, these insects are ectoparasitoids when they live on the body of their host, or endoparasitoids when they live in the body of their host.

There are even ichneumons that parasitize other parasitoid insects inside their host. They are hyperparasitoids.

About 3,300 species of ichneumons are recorded in North America. There are an estimated 60,000 species worldwide.

The largest ichneumons in North America are part of the genus Megarhyssa and can be up to 2 inches long.

Ecological roles

These insects parasitize a wide variety of hosts, usually immature stages (larvae, caterpillars, pupae) of insects, including Lepidoptera, Coleoptera and Hymenoptera. Some also attack spiders and other arthropods .

Ichneumons are considered beneficial because they play an important ecological role in helping to balance arthropod populations .

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