Black flies are small, dark-coloured insects belonging to the family Simuliidae. Of the world’s more than 2,300 species, at least 164 are found in Canada. Black flies reproduce in streams and are found all across Canada. 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.