Bugs Are Back: Understanding the Annoyance of Black Flies and Mosquitoes in Canada As warmer weather approaches, Canadians prepare for the annual onslaught of biting insects. Entomologist Douglas Currie discusses the differences between black flies and mosquitoes, their impact, and the potential influence of climate change on their populations and distribution across Canada. As the warmer months approach, Canadians are bracing for the inevitable arrival of biting insects, with black flies and mosquitoes set to make their presence known. While both pests are a common annoyance, Professor Emeritus Douglas Currie, an entomologist from the University of Toronto, offers a nuanced perspective on their impact. Currie explains that distinguishing between the annoyance levels of black flies and mosquitoes is complex, varying significantly with location and season. However, he identifies mosquitoes as the more serious overall pest due to their widespread presence, extended activity periods throughout the day and night, indoor and outdoor biting habits, and their role as vectors for various diseases affecting humans. In contrast, while black flies are almost as prevalent across Canada as mosquitoes, the species that target humans are more concentrated in northern, forested regions, particularly the Canadian Shield. Their peak adult season, typically in June, can see them become so overwhelmingly abundant that they overshadow even the co-existing mosquito populations. The nature of black fly attacks is often described as far more irritating. They tend to swarm around the head, bombarding facial orifices and exposed skin. Their bites, though initially painless, can weep for hours and remain itchy for days or even weeks. Considering this, Currie suggests that in June, in northern Ontario, black flies could indeed be considered more annoying than mosquitoes. Black flies, belonging to the Simuliidae family, are small, dark-colored insects with over 2,300 species globally, at least 164 of which are found in Canada. Their life cycle is tied to streams, where larvae develop, making them ubiquitous wherever flowing water exists. Female black flies require blood meals for egg production, making them a nuisance to humans and animals. In Canada, they are particularly abundant in northern woodlands and near large rivers and lake outlets. Unlike mosquitoes, adult black flies are primarily diurnal, meaning they are most active during daylight hours. The larvae play a crucial role in aquatic ecosystems, with some river sections supporting hundreds of thousands of larvae per square meter, potentially leading to billions of adults emerging per kilometer daily. These larvae are a food source for fish and aquatic invertebrates, while adult black flies are prey for birds. In their feeding process, black fly larvae transform fine organic matter into nutrient-rich fecal pellets, contributing to nutrient cycling. Doug Currie elaborates on the attraction of black flies to humans. Species that bite humans are drawn to the faint odors present in sweat. They are known to congregate around the head and skin before biting, targeting any exposed areas, particularly the wrists, ankles, waistline, neck, and hairline. Their bites typically result in a small welt and a trickle of blood, accompanied by prolonged itching. Historically, Indigenous peoples in North America utilized naturally occurring insect repellents derived from bracket fungi and plants like fireweed and sweetgrass to deter biting flies, a practice that predates modern commercial repellents and even inspired local folklore such as Wade Hemsworth's well-known song, The Blackfly Song. The question of climate change's influence on biting insect populations is complex. Currie notes a lack of agencies specifically monitoring year-to-year fluctuations in biting fly numbers, making it challenging to definitively link increased populations to climate change. He points out that natural factors like overwintering conditions and spring rainfall can cause significant year-to-year variations, complicating the analysis. Climate change, he explains, can have a dual effect, favoring some species while hindering others. However, Currie is certain about one observed trend: the northward expansion of black fly distribution. This observation is supported by data from the 1948-1962 Northern Insect Survey, which mapped insect distribution in Canada's north. Upon revisiting some of these survey sites between 2010 and 2013, Currie found several black fly species that were not previously recorded. Danielle Nowosad, a Postdoctoral Fellow at the University of Calgary, is continuing and validating this work. She confirms that scientific evidence suggests an increase in black fly diversity in parts of the Arctic and that Inuit land users and harvesters in the Kitikmeot region report a worsening of biting insect issues in recent times, building upon Dr. Currie's foundational surveys.