Black deer fly

The typical deer flies as today’s black deer fly (Chrysops niger) include about 100 species in North America alone. They are usually smaller than the horse flies, and they often have blotched wings and spotted eyes, which helps if you have to identify them.

Female deer flies are active during the day. These flies apparently are attracted to such things as movement, shiny surfaces, carbon dioxide, and warmth. Once on a host, they use their knife-like mouthparts to slice the skin and feed on the blood pool that is created. Bites can be very painful and especially cattle can be seriously affected by them. Numerous painful bites from large populations of these flies can reduce milk production from dairy cattle and interfere with grazing of cattle and horses because animals under attack will bunch together. Animals may even injure themselves as they run to escape these flies.