The body structure of ichneumon wasps is generally similar to that of other narrow-waisted wasps. Their body is divided into three parts: the head (cephalon), thorax, and abdomen. The initial segments of the abdomen are strongly constricted into a narrow petiole, sharply separating the thorax from the abdomen. The head features a pair of compound eyes, three simple ocelli, filamentous antennae, and mandibulate mouthparts for chewing. The thorax consists of three segments, each bearing a pair of legs. The middle (mesothorax) and rear (metathorax) thoracic segments each support a pair of membranous, sparsely veined wings. The forewings are larger than the hindwings, and the two pairs are connected by small hooks. The abdomen lacks legs.

The ovipositor is elongated and tubular, designed for egg-laying. Along with the eggs, the ovipositor can also inject venom to immobilise the host. In some ichneumon species, the ovipositor can be extremely long, sometimes measuring several centimetres and exceeding the length of the body.

Ichneumon wasps comprise the largest family of Hymenoptera, with approximately 25,000 described species. They are found on all continents except Antarctica, inhabiting virtually all terrestrial ecosystems. All ichneumon wasps are parasitoids, meaning their larvae develop inside a host, ultimately killing it at the end of their development. The larvae’s hosts are most often the larvae of other holometabolous insects. Predominant hosts include the larvae of moths, beetles, flies, and other Hymenoptera. Some ichneumon wasps also parasitise spiders.

In most cases, the female lays her eggs directly inside the host’s body by piercing its outer wall with her ovipositor. Often, she must also penetrate the substrate in which the host resides. For instance, in the case of beetle larvae living within tree trunks, the ichneumon wasp must pierce several centimetres of wood, in addition to the larva’s body wall. One such example is the pimpline ichneumon wasp (Dolichomitus mesocentrus), which parasitises the larvae of longhorn beetles (Cerambycidae).

Adult ichneumon wasps are free-living and feed on various food sources. They most commonly consume plant sap and nectar. Females of some ichneumon species also feed on host body fluids that escape through the host’s body wall during egg-laying. Parasitism by ichneumon wasps plays a significant role in regulating the population sizes of certain arthropods that serve as their hosts. As a result, some ichneumon species are employed in biological control to manage harmful insect populations.