Keywords Insects

Range Black flies occur nearly anywhere that rivers and streams are present for immature stages, including arctic regions, and are especially abundant in northern wooded regions. Larvae live in flowing water, gathering fine particulate food by straining the water with their head fans.

Structure Females have biting mouth parts with toothed stylets for cutting skin. Males do not bite and are rarely observed. Both sexes require nectar for flight energy; females use blood for egg development.

Reproduction and Development Eggs (150-600 per female) may be laid on substrates in water or dropped as females fly over water. Larvae attach to rocks or vegetation and complete development in 3-14 days, depending on water temperatures and availability of food. Pupae are inactive and do not feed. Adults may emerge from any water depth, floating upward in a bubble of air generated during emergence. They are ready to fly when they break the surface. Average life span is about 3 weeks.

Interaction with Humans In Central America, tropical S America and Africa, black flies frequently transmit nematodes causing river blindness (onchocerciasis) in humans. In Canada, black flies cause human suffering and are a scourge to livestock. In the ATHABASCA R region of northern Alberta, weight loss in cattle caused by the black fly attacks in one outbreak (1971) amounted to 45 kg per animal; 973 animals were killed in one area alone by Simulium arcticum, a species whose saliva contains a toxin which in large quantities causes anaphylactic shock and sometimes death in cattle. In Saskatchewan, 1100 cattle were killed by this black fly species during the outbreak years of 1944-47. Black flies are a nuisance to humans. For example, forest workers in northern BC and Québec demand black fly control as part of their work contract.

See also FLY.

Black Fly
In Canada, black flies cause human suffering and are a scourge to livestock (artwork by Jan Sovak, 1989).

Author R.A. BRUST

Suggested Reading
M. Laird, Black Flies (1981).

Links to Other Sites
Québec Biodiversity Website
A great information source for all budding biologists. Learn about biodiversity theory, Québec natural history, and conservation issues. From McGill’s Redpath Museum.

The Canadian National Collection of Insects, Arachnids and Nematodes
This website provides information about the scope and contents of the Canadian National Collection of Insects, Arachnids and Nematodes. Check the “Index” link for illustrated descriptions of various taxonomic groups.