The Ichneumonidae, also known as ichneumon wasps, ichneumonid wasps, ichneumonids, or Darwin wasps, are a family of parasitoid wasps of the insect order Hymenoptera. They are one of the most diverse groups within the Hymenoptera with roughly 25,000 species described as of 2016. However, this likely represents less than a quarter of their true richness as reliable estimates are lacking, along with much of the most basic knowledge about their ecology, distribution, and evolution. It is estimated that there are more species in this family than there are species of birds and mammals combined. Ichneumonid wasps, with very few exceptions, attack the immature stages of holometabolous insects and spiders, eventually killing their hosts. They thus fulfill an important role as regulators of insect populations, both in natural and semi-natural systems, making them promising agents for biological control.
Image: IC Ichneumonini
Image: Cremastinae wasp
Male ichneumonid wasp
Head (Ichneumon xanthorius). Antennae with many segments
Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causing the death of these hosts. Different species specialise in hosts from different insect orders, most often Lepidoptera, though some select beetles, flies, or bugs; the spider wasps (Pompilidae) exclusively attack spiders.
Megarhyssa macrurus (Ichneumonidae), a parasitoid, ovipositing into its host through the wood of a tree. The body of a female is c. 2 inches (50 mm) long, with an ovipositor c. 4 inches (100 mm) long.
Spider wasp (Pompilidae), an idiobiont, carrying a jumping spider she has just paralysed back to her nest, where she will lay an egg on it.
...but endoparasitic koinobiont wasp larvae eventually fill its body and kill it.
Hornworm with parasitic wasp cocoons