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Most people are eagerly awaiting the arrival of the summer season, which appears to be on the verge of revealing itself.  Comfortable weather conditions are encouraging more and more people to go outdoors and enjoy the mild weather. However, in addition to being a great time for nature walks and other outdoor activities, these conditions also signal the return of biting insects, which include black flies.

Found throughout Quebec and Canada, this species is known to be a nuisance to people who venture into northern woodlands.  However, like most insects, black flies come out at certain times of the year.

Here are some facts about black fly season in Quebec.

A brief overview of the black fly

Before getting to the heart of the matter, it is worth sharing some information about the black fly.

As part of the simulium family, black flies have an arched thorax, a stocky build and a wingspan that can range from 6 to 14 mm. Although their name suggests that all varieties of this insect pest are black, they can sometimes be orange or grey in appearance.

While they mainly feed on nectar, female simulium need to absorb a certain amount of blood for their eggs to develop. That’s why females have short, sharp mouthpieces, allowing them to slit the skin and draw blood. Males do not bite.

The black fly life cycle

It is worth mentioning that mature black flies are the ones known to bother animals and humans. Yet, this insect also passes through the egg, larvae and pupae stages before it can take off. The larvae grow in the running water of rivers and streams, where they collect fine food particles by filtering the water with their head combs.

Shortly after leaving their aquatic environment, the black flies mate and the female begins her quest for blood to bring her eggs to maturity. Once she has absorbed enough blood, she can go and lay eggs and the cycle can start again up to four times a year, depending on the region.

Periods of intense black fly activity

Since black flies overwinter as eggs or larvae, a first cohort can be observed throughout Quebec as early as May, when the temperatures are warming. In June, they flourish on the Canadian Shield, where countless streams and rivers that are essential for their reproduction are located. Areas north of Saint-Jérôme are invaded early in the season. Holidaymakers should therefore avoid pitching their tents in these areas in June or even as early as May.

Although the outbreak occurs in the spring, people travelling to areas with large rivers such as Trois-Rivières can be bothered by black flies until August and even September. This is because high-flow rivers stay cool longer and provide an ideal environment for the development of many larval cohorts per year.


Naturally, there is no way to get rid of these insects. So if you want to avoid being pestered by black flies, you may not want to leave the major urban centres in May and June, since the species is most abundant during this period.

However, if other types of pests are making your life miserable, why not contact Elite Pest Control? Our team’s extensive insect knowledge ranks our pest control services among the best in Quebec!

Pascal Rock
Pascal Rock  
Director, Elite Pest Control
Founder and mainstay of Elite Pest Control, Pascal Rock has embodied expertise and dedication for over a decade. His training, acquired with expert mentors in extermination and pest decontamination, has shaped an outstanding professional. Under his leadership, a team of six seasoned technicians deploys the very best pest control strategies. Together, they ensure the peace of mind and safety of residents and professionals from Montreal to Quebec City, by offering fast, effective interventions, available at all times.