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.
While black flies are not known to transmit disease to humans in the United States, human deaths (presumably from allergic reactions) have been reported.
