Their biting can disrupt outdoor activities at home, recreation and work areas, as well as impact on livestock production.
Black flies get into the nose, eyes, ears and mouth and crawl into clothing when abundant.
On cattle and horses, the ears seem to be the favorite feeding location. Flies lacerate the skin and suck blood. A strong anticoagulant in the saliva facilitates bleeding of the host. A lesion may form at the bite and the bitten area itches. Black flies serve as vectors of human and animal diseases in some areas of the world.