Strepsiptera, the twisted-wing parasites, are a small order of insects that make their living entirely as parasites on other insects.
Male streps have wings and legs, and live for only a few short hours after their metamorphosis. In that time, they must locate a female, who is a legless, grublike animal permanently attached to her host insect. They mate by a process known as traumatic insemination, which is pretty much exactly what it sounds like: instead of looking for appropriate orifices on the lady strep, the male uses his surprisingly pointy junk to make an orifice.
Eggs develop inside of their mum, and the larvae will feed on mum until they’re ready to emerge — normally through that convenient hole that dad made. Once they’re outside of mum, the race is on to find a new host insect; these larvae can’t survive for long without one. Their search is very active, and while most species go for adult hosts, some streps will parasitize the eggs of their target species.
Once they find a host, they dissolve its cuticle, latch on for the long haul, and start feeding on its hemolymph. Males will go on to metamorphose into a lovely, raspberry-eyed animal, while the females are stuck there for the rest of their lives.
Other awesome things about strepsipterans — the adult males have totally unique, raspberry-shaped eyes that look more like trilobite eyes than insect eyes. Figuring out their evolutionary relationships has been problematic, although the current consensus seems to be that they are closely related to beetles. Oh, and we have fossil representatives — females stuck in their hosts, that have then become trapped in amber; the oldest known strep was happily parasitizing other insects back in the Cretaceous.
Photography by Pavel Krásenský; original article can be found here (Czech language).