Ichneumon Wasps

More than 5,000 species in North America


image of an Ichneumon Wasp on tree trunk
Most ichneumon wasps are harmless, although the long ovipositor of the female is intimidating. Their larvae live as parasites inside caterpillars and other larval insects, many of which are considered injurious to human interests.
Donna Brunet

Ichneumonidae (ichneumon wasps) in the order Hymenoptera (ants, bees, wasps)


Ichneumons are much like their cousins, the stinging wasps, only slenderer and with longer antennae (usually at least half the length of the body, with 16 or more segments). The females usually have dramatically long ovipositors (a needlelike or filament-like appendage at the tip of the abdomen used for laying eggs) — it’s often longer than the entire body.

There are thousands of species of ichneumons in North America, and many are hard to tell apart. Colors vary, with some being drab and others brightly colored or patterned. Some have black and yellow bands like stinging wasps.


Length: to about 1½ inch (not including appendages; varies with species; many are much smaller).


image of Black Giant Ichneumon Wasp on tree trunk
Black Giant Ichneumon Wasp (Female)
The black giant ichneumon wasp, Megarhyssa atrata, belongs to a genus called the giant ichneumons. The female’s body can be 1½ inches long, and her ovipositor 5 inches long.


image of female Long-Tailed Giant Ichneumon Wasp on tree trunk
Long-Tailed Giant Ichneumon Wasp (Female)
The long-tailed giant ichneumon wasp, Megarhyssa macrurus, belongs to a genus called the giant ichneumons. Using her 4-inch-long ovipositor, the female of this species drills through decaying wood to deposit eggs onto a larval pigeon tremex, a type of horntail wasp.
Habitat and conservation

Ichneumons are the largest family of any of the animals, with some 60,000 to 100,000 species worldwide. They are common and can be found in nearly all habitats. The name “ichneumon” comes from Greek words meaning “tracker” and “footprint,” and the females of these parasitic wasps certainly do hunt for, and track down, their various host species.


The young of ichneumons are mostly internal parasites of the larvae in the families comprising the beetles; the butterflies and moths; and the ants, bees, and wasps; plus flies and spiders. The mother ichneumon typically inserts her eggs into the body of the host — usually a grub or caterpillar — and the hungry larval ichneumons, devouring their hosts from the inside, usually end up killing their hosts by the time they are ready to pupate and become adult ichneumons.

image of Ichneumon Wasps Distribution Map
Distribution in Missouri




Life cycle

The mother ichneumon uses her ovipositor to inject eggs into a host’s body — usually a grub, caterpillar, or pupa. Many ichneumons need a certain species of insect as a host. Female ichneumons can be seen wandering over tree trunks, using their antennae to seek the larvae of wood-boring insects below the bark; detecting one, the female inserts her long ovipositor through the wood and lays eggs in the larva. Her young hatch and devour their host, pupate, and emerge to begin the cycle again.

Human connections

Most people consider ichneumons beneficial, as they play a huge role in controlling insects, including many considered pests or injurious (such as tomato hornworms, boll weevils, and wood borers).

Ecosystem connections

Ichneumons help control insect numbers by eliminating many insects before they reach an adult, reproductive stage. Despite the wasplike patterns of some, ichneumons themselves are eaten by other predators. Many young ichneumons are no doubt eaten when their hosts are snatched by other predators.