The name comes from Greek: ichneuein = to hunt out or hunt up.
The family of the so-called parasitic wasps (e.g., Ichneumon nigritarius) represents the biggest group among the Hymenoptera and among the so-called parasitoids, which also include species from other insect groups. The European wood wasp Rhyssa persuasoria reaches a body length of up to 5 cm and has a similarly sized ovipositor, by the help of which it injects its eggs into larvae of butterflies (Lepidoptera), beetles (Coleoptera), or even eggs of spiders (Arachnida). Since these ichneumonids mostly kill their hosts, they are called parasitoids, since the interest of “true parasites” must be to keep alive their hosts, since they have no more a free-living stage.
I own cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all side of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice.