The larva spins a pupal case and changes to a pupal stage within it. The long branching tentacles are used for breathing. Adults emerge from pupae in two to three days when the water is warm and are capable of immediate flight and mating. Although their flight range is usually less than ten miles, some may travel much farther from their place of origin. Some species of black flies do not feed as adults, others require a blood meal in order to produce eggs.
Females live from a few days to more than three months.
They prefer calm sunny days, and will not fly at night or on windy days. Black flies are attracted to their animal or human victims by the carbon dioxide and moisture present in exhaled breath, dark colors, convection currents, perspiration, perfumes and toiletries. They often fly into eyes, nose, ears, and mouth. Bites cause pain and dermatitis at the site of the bite because black fly saliva is toxic. Flies can discourage people from remaining in or visiting certain areas.