Also known as buffalo gnats because of their humpbacked appearance, black flies (Simuliidae) are small (up to one-eighth of an inch long) dark flies that typically appear in late spring and early summer when they swarm and bite birds and mammals, including domestic animals and people.

Males and females feed on nectar. Male black flies do not bite, but females of most species must feed on blood to produce eggs. Some prefer to bite one type of host. Some species bite people in certain locales, but do not bite in other parts of the species’ range.

Like horse and deer flies, black flies bite using their mouthparts like scissors to cut into skin and lap up the blood. This results in painful bites that can produce bleeding, itching, inflammation and swelling, as well as allergic reactions that can be life-threatening. The flies may enter noses, ears and mouths, causing further discomfort. Domestic animals, especially poultry and exotic birds, can be killed by black fly attacks.

Black flies are aquatic insects that typically prefer clean, fast-running water. Females lay hundreds of triangular eggs in or near the water. Some crawl beneath the surface to deposit eggs on submerged objects such as rocks. The worm-like larvae hatching from these eggs are typically less than half an inch long and shaped like an hourglass.