Black flies serve as vectors of human and animal diseases in some areas of the world. An important protozoan parasite of poultry, Leucocytozoon simondi , is transmitted by black flies in the United States. Because of their distinct humpbacked shape, they are sometimes called buffalo gnats. The wings are broad and the antennae are about as long as the head. Male black flies have larger eyes than females.
Some species have white markings.
Egg - Black fly eggs are 0.18 to 0.46 mm long and somewhat irregular in shape although they are oval in some aspects. Pale white at first, the eggs darken as the embryo matures. The head has slender antennae and two brushlike structures called cephalic fans. Pupa - Black fly pupae are 2 to 3 mm long with a respiratory organ on the thorax which protrudes from the open end of the cocoon. If removed from the cocoon, the wing pads, legs and other features of the adult fly can be seen, although these structures are closely appressed to the body.