Black flies in Canada
Black fly bites can be avoided by wearing light-coloured clothing that covers the wrists, ankles, and belt line, and by applying commercial insect repellents to the skin and clothing. North American Indigenous peopleshave also deterred biting flies using naturally occurring insect repellents found in bracket fungi and in plants such as fireweed and sweetgrass.
They are particularly common in northern temperate and subarctic regions. Because female black flies need to feed on blood to lay eggs, their biting can be a nuisance to humans and other animals. Among the most common and notorious black flies in Canada are Simulium truncatum and Simulium venustum.
Black flies are 1–5 mm-long flies with short legs and broad wings. Females in particular have a slightly humpbacked shape. Although generally dark-coloured, different species may be black, yellowish orange or brownish grey.
Black flies are found worldwide, except in Antarctica. They can be found virtually anywhere there is flowing water to serve as habitat for larvae. In Canada, they are especially abundant in northern wooded areas and near large rivers and lake outlets. Unlike mosquitoes, adult black flies are mainly active during the day.
Black flies can be quite annoying to humans. Species that bite humans are drawn to subtle odours in sweat. They tend to swarm around the head and skin before biting, and will bite any exposed skin, especially on the wrists, ankles, waistline, neck and hairline. Their bites normally leave a small welt and a droplet of blood, and may itch for several days. In North America, black flies are not known to transmit any diseases. However, in Africa, Mexico, Central America, Brazil, Venezuela and Yemen, they can transmit nematodes (i.e. roundworms) causing river blindness (onchocerciasis) in humans.
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