Strepsiptera

The strepsiptera are a small (~300 species) order of insects. All of them are parasites in other insects; their hosts include bees, wasps, silverfish, cockroaches, and bugs. There are nine families:

Mengenillidae
Mengeidae
Stylopidae
Bohartillidae
Corioxenidae
Halictophagidae
Callipharixenidae
Elenchidae
Myrmecolacidae

Male Strepsiptera have wings, legs, eyes, and antennae, and look like ordinary insects, though they generally have no useful mouthparts. Females never leave their hosts, except in the Mengenillidae, and have no wings.

Strepsipteran eyes are unlike those of any other insect. Instead of hundreds of ommatidia, each of which sees one pixel, they consist of a few dozen lenses each with its own retina.

The order is named for the hind wings, which are held at a twisted angle when at rest. The forewings are reduced to halteres.

Strepsiptera present an enigma to taxonomists. Some believe they are the sister group to the beetle families Meloidae and Rhipiphoridae, which have similar parasitic development and forewing reduction; some say they are the sister group to the beetles; some say they are the sister group to the flies, which have hindwing halteres.

External link: http://www.strepsiptera.uni-rostock.de/e/strepsiptera.html