British usage any of various small biting flies: midges; biting midges; black flies; sand flies
A gnat is a very small flying insect that bites people and usually lives near water. Any of various small, biting, two-winged flies, such as a punkie or black fly. a small flying insect that bites. Any member of several species of small dipterans, most of which bite or annoy humans. Midges are also sometimes called gnats. In North America the name is also applied to the blackfly, fruit fly, and other small flies that hover about the eyes of humans and other animals