The strepsipterans, or twisted-winged parasites, are possibly the most enigmatic of insect orders, and the relationship between these tiny, parasitic insects and the remaining insect orders has been debated for over a hundred years.

The larvae and most adult females live as endoparasites in other insects, and their bodies have undergone drastic reductions. The adult male is free living, and possesses both compound eyes, antennae and wings. Its structures deviate strongly from those of other flying insects, though; the antennae are fan-shaped, the eyes have a unique, raspberry-like structure, and the fore wing is reduced to a club-like halter in an evolutionary parallell to the dipteran hind wing. A close relationship between strepsipterans and dipterans has been suggested, but most evidence points to a sister group relationship between strepsipterans and beetles.