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Pest Education: Flies in Ontario

Facts and Information about Flies in Ontario, Canada

Tuesday, December 6, 2022 by Greeny’s Pest Control

Flies are an extremely common insect found throughout Ontario. Although many flies look similar to each other not all flies are built equal, with many different species found within the region. Some of the most common species in this area include Cluster Flies, Black Flies, Deer Flies, Horse Flies and House Flies.

Cluster Flies

Cluster Flies look quite similar to the common house fly, however differ greatly in size. Cluster Flies range from 8-10 mm long when fully grown and are usually dark grey with black and silver checkered stomachs. Another key difference between Cluster Flies and House Flies is that the wings of Cluster Flies overlap when resting. These flies are generally slower moving than house flies and get their name because they tend to "cluster" together after they make their way into houses.

Black Flies

It is approximated that there are more then 160 individual species of Black Fly in Canada. Most species in this region reach adulthood from May to July. Although some species are able to bite humans, it is quite rare. Black Flies tend to develop in moving water and emerge as fully developed adults. Much like mosquitos, females are the only type that requires blood meal. Instead of using a needle-like mouth part to suck blood, Black Flies cut and rupture the skin and soak up the blood of its host. Black Flies thrive in hot humid weather which is why they do so well in the Spring.

Deer and Horse Flies

Both Deer and Horse Flies have developed an infamous reputation for their painful bites to people. Many describe the feeling as the insect taking a "chunk of skin" when they bite. Horse Flies are the darker coloured of the two while Deer Flies can be distinguished by their colourful eyes and dark patterned wings. Both species are most commonly found in mid to late Summer in Ontario. Traditional insect repellent has been found to have little affect in both types.

House Flies

Generally speaking House Flies pose little direct harm to people. They can however carry pathogens on their bodies and transmit them to humans through their feces. Food contamination is one of the most common ways illnesses can be spread to people. Female House Flies can lay up to 100 eggs at a time and generally use decaying organic matter to do so. When ready, these eggs turn to larva (otherwise called Maggots), then pupae, and finally adults. House Flies typically live as adults for 2-4 weeks but are able to hibernate during the winter.


  • Canada, H. (2013, June 4). Government of Canada. Clustering flies - Retrieved December 6, 2022, from

  • Mosquitoes and black flies. The Friends of Algonquin Park. (n.d.). Retrieved December 6, 2022, from

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