Black flies are small, persistent insects and a common outdoor nuisance, especially in many northern regions. Known for their biting habits, these tiny flies can significantly impact outdoor activities. Understanding their lifecycle and preferred conditions helps anticipate their emergence and mitigate their presence.
Understanding Black Fly Season
Black fly season typically begins in late spring and extends through early summer in many temperate regions. The exact start and end dates can vary annually and between different species of black flies.
Their activity often peaks during daylight hours, particularly in the morning and early evening. Some species are most active between 9:00 AM and 11:00 AM, and again from 4:00 PM to 7:00 PM. Their presence can be influenced by weather conditions, with higher activity noted on humid, cloudy days or just before storms.
Factors Driving Emergence
The emergence and population size of black flies are closely tied to environmental conditions, particularly water temperature. Black fly larvae develop in flowing water, and their growth rate is highly dependent on water temperature. Eggs of some species hatch when water temperatures rise in spring.
Heavy snowmelt and increased water flow in spring, combined with warming temperatures, can lead to robust black fly seasons. Larval development can take anywhere from a week to several months, depending on the species and water temperature. Warmer temperatures generally lead to faster development.
Where Black Flies Thrive
Black flies are particularly abundant in northern temperate and subarctic regions, including much of Canada and the northern United States. Their presence is dictated by the availability of clean, flowing fresh water, which is essential for their larval and pupal stages.
Larvae attach themselves to submerged objects in fast-flowing streams, rivers, and lake outlets, where they filter feed on organic matter. While prevalent near running water, they are less common in stagnant water bodies like ponds or lakes. They are often encountered in wooded areas adjacent to these water sources.
Protecting Yourself from Black Flies
Protecting against black flies involves several strategies to minimize exposure. Wearing appropriate clothing is a primary defense. Light-colored, loose-fitting long sleeves, long pants, and a hat are recommended, as black flies are attracted to dark colors and cannot bite through fabric. Tucking shirts into waistbands and pant cuffs into socks can further prevent access. In areas with heavy infestations, a head net can offer significant protection for the face.
Insect repellents are also effective, with active ingredients such as DEET, picaridin, and oil of lemon eucalyptus. Applying these repellents to exposed skin and clothing can deter bites. Avoiding outdoor activities during peak black fly times, such as morning and early evening, and staying away from their preferred habitats like stream banks, can reduce encounters. If bitten, cleaning the area with soap and water, applying a cold compress, and using over-the-counter antihistamines or anti-itch creams can help alleviate symptoms like swelling and itching.