Size: 1 to 5 mm

Black flies are small, blood-sucking insects, found in many parts of the United States and Canada. Common names for this pest include buffalo gnats and turkey gnats, and they are known to fly around people’s heads, occasionally getting into eyes and ears, as well as crawling into the hair. Only the females are blood feeders and will readily bite humans and animals. Black flies may sometimes occur in enormous numbers in the late spring and early summer, particularly in the more northern latitudes.

Black flies breed exclusively in running water, and larvae and pupae develop in flowing, typically non-polluted water, with a high level of dissolved oxygen. The immature stages of black flies develop in oxygenated water sources, therefore adults are usually associated with slow-moving streams, creeks, or rivers where the immature stages develop. Flowing water does not necessarily imply white water rapids, but water must be moving. Water in lakes and ponds that are not flowing is unsuitable for black fly development.