Black fly, or buffalo gnat, is the name applied to any member of the dipterous family Simuliidae, which suck blood from birds and mammals, including man.
About 300 kinds of black fly are known, being widely distributed throughout the world. Only the females bite, causing extreme, sometimes fatal, loss of blood. In tropical America and Africa, black flies may be parasitized by the nematode worm, Onchocerca volvulus, which can be transferred to other victims causing the disease onchocerciasis, resulting in blindness if the worms settle in the eye. In the USA, the black fly plague comes in the summer to New England, and is particularly bad after heavy spring rain.