Ichneumon Wasp

Ichneumon wasps make up the family Ichneumonidae, among the most species-rich families in the entire animal kingdom, with tens of thousands of described species and likely many more undescribed. They belong to the parasitoid wasp guild, alongside the related braconids, and their larvae develop by consuming a host insect from within or attached to its body.

The family's diversity is matched by its variety of forms, from tiny delicate species barely visible to the naked eye to large, dramatic species like the giant ichneumon (Megarhyssa), whose females possess ovipositors several times the length of their body used to reach wood-boring beetle and horntail larvae deep inside tree trunks.

Ecologically, ichneumon wasps are major regulators of other insect populations, particularly moths, butterflies, beetles, and sawflies, making them an important if largely invisible part of forest and garden food webs.

• Slender, elongated body with a narrow waist and long legs, often resembling a large, delicate wasp or overgrown mosquito-like insect.
• Long, thread-like antennae, typically with many more segments than most other wasps, often held forward and constantly moving.
• Females of many species bear a long, needle-like ovipositor extending from the tip of the abdomen, sometimes many times body length in wood-boring specialists.
• Wings are clear or lightly smoky with a relatively complete, complex network of veins.
• Lookalikes: braconid wasps are generally smaller with simpler wing venation; the ovipositor is often mistaken for a stinger, but it functions for egg-laying, not defense.

Ichneumon wasps occur nearly worldwide, from tropical forests to temperate woodlands and gardens, wherever suitable host insects are found. Many species specialize on hosts living in dead or dying wood, leaf litter, or plant stems, so ichneumons are especially common around forests, hedgerows, and mature gardens. Adults are active from spring through fall in temperate climates, with peak activity often timed to host insect life stages.

Females locate host insects, frequently the larvae of moths, beetles, sawflies, or other wasps, using scent and vibration cues, sometimes detecting hosts hidden deep in wood. The ovipositor is used to lay one or more eggs on or inside the host, and the developing wasp larva consumes the host as it grows. Adults typically feed on nectar or honeydew. Ichneumon wasps do not defend a nest and are not known to be aggressive toward people.

After an egg is laid on or in a host, the larva feeds on the host's tissues, eventually killing it, then pupates either within the host remains or in a nearby cocoon. Development follows complete metamorphosis, and the number of generations per year varies widely by species and host availability. Overwintering commonly occurs as a larva or pupa inside the host or its shelter.