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Black Fly

Description: 1/16-1/8″ (2-4 mm). Humpbacked, head pointing downward. Grayish brown to shiny black. Antennae thick often with many segments. Wings smoky to clear; veins near front margin heavy, others delicate.

  • Warning Bites; female sucks bird and mammal blood. Not known to transmit diseases to humans in North America.
  • Food Male and female feed on nectar. Female sucks blood from birds and mammals. Larva is filter feeder, eating particles such as diatoms and bacteria.
  • Life Cycle Eggs are laid on stones or leaves at the edge of rapidly flowing streams, or on the water surface itself. Larvae tumble into water. Fully grown larvae pupate in cocoons that coat rocks in water, resembling moss. Adults burst out, rise on a bubble of trapped air, and fly away in late spring and early summer.
  • Habitat Near running water in forests, mountains, and tundra.
  • Range Labrador south to Georgia, west to California and Mexico, north to Alaska.
  • Biting adults are the bane of the North Country and mountain resorts, particularly early in the season. Some species transmit waterfowl malaria, which accounts for up to half of the deaths of ducks, geese, swans, and turkeys.