Mosquitoes and flies make up the insect order, which is called dipterans (Diptera). They have, in contrast to most other insects, only one pair of wings. The second pair of wings is small, knobbed structures modified from the hind wings. These are called halteres and are help the insect balance during flight.
The larvae are legless maggots that live in water or damp places. About 60,000 different kinds of mosquitoes and flies are known.