Black Fly, any of a number of species of small humpbacked flies, the females of which are bloodsucking. Black flies are typically dark in color with broad, transparent wings. Adults range in size from 2.5 to 3.5 mm (0.01 to 0.14 in). Black flies are sometimes called buffalo gnats or (improperly) sand flies.
After mating the female deposits the fertilized eggs on rocks in swift streams, and the larvae develop aquatically, feeding on algae and debris. Adult flies first emerge in spring, and several generations may be produced each year.
The northern, or Adirondack, black fly is a common pest in some woods and mountains of the northeastern United States. A related species in the Mississippi Valley, the southern buffalo gnat, is sometimes a serious pest of cattle. The turkey gnat injures poultry. Certain species in Mexico, Central America, and Africa transmit the disease organism that causes onchocerciasis, or river blindess, in humans.
Scientific classification: Black flies are considered true gnats and make up the family Simuliidae, in the order Diptera. The northern black fly is classified as Simulium hirtipes, the southern buffalo gnat as Cnephia pecuarum, and the turkey gnat as Simulium meridionale.