Gnat, common name loosely applied to any biting two-winged fly. In the United States, the term is most often used for blackflies, fungus gnats, and sandflies. In Great Britain mosquitoes are commonly referred to as gnats.
Scientific classification: Gnats belong to the order Diptera. Blackflies make up the family Simuliidae. Fungus gnats make up the family Mycetophilidae. Sandflies make up the family Psychodidae.