Gnat, a general name for various small, blood-sucking flies related to mosquitoes and houseflies. Several tiny species of gnats are called midges. In England, the word gnat usually means mosquito.

Gnats have two membranous wings; long, jointed legs; large eyes; and small antennae. The fragile bodies often have soft, hairy coverings. The gnat's proboscis, or snout, is adapted for both piercing and sucking. The larvae usually hatch in water.

GnatsGnats are small flies, some of which live on the blood of animals.

The black fly of eastern North America is also called the buffalo gnat because of its humpbacked appearance. It can inflict painful bites on humans, and swarms have been known to bite farm animals to death. The gall gnat, or gall midge, damages plants by laying eggs in them. By feeding on the plants, the larvae cause galls, or diseased lumps, to form. The fungus gnat lays its eggs chiefly in fungi and decaying vegetable matter.

The black fly belongs to the family Simuliidae; gall gnat, Cecidomyiidae; fungus gnat, Mycetophilidae. All belong to the order Diptera.