Black fly season occurs from mid-March to mid-July in Ohio, Pennsylvania, New Jersey, north through New York and New England, the Upper Peninsula of Michigan and into Southern Canada. Some backpackers, campers and fishermen avoid outdoor activities during black fly season, but the rest of us soldier on despite the bugs, glad to escape the confines of snow-bound home life.
Like mosquitoes, black flies gain nourishment by sucking the blood of other animals. Actually, it’s just the females who feed on blood: the males feed mainly on flower nectar. Unlike mosquitoes, black fly eggs are laid in moving water where the larvae attach to rocks using tiny hooks and survive under ice, waiting for the spring thaw. There, they pupate under water feeding on passing organic debris and emerge in a bubble of air as flying adults. When they hatch, they are often preyed upon by fish, such as trout. They live about 4-6 weeks, depending on species, temperature, and food supply.
Black flies are small black or grey insects with short legs and antennae. Bites can be extremely painful, and their mouthparts are similar to those of a horse fly. Some species of adult black flies prefer humans whereas others target specific animals or birds. On people, they crawl into sleeves and around boot tops, especially favoring the head just beneath the rim of a hat. Bites can cause swelling and soreness for many days. There are records of both domestic animals and people being killed in a few hours through bites and blood loss. Death can result from suffocation as a result of plugged nasal or bronchial tubes and allergic reactions.
Proper clothing offers good protection against black fly bites. Keep shirt sleeves and front closely fastened and tuck trousers inside socks or high boots. Zippered front shirts will keep flies out better than button shirts. Light colors such as orange, yellow and light blue are less attractive to black flies than dark ones. Shoulder-length head nets are sometimes useful. These can also be impregnated with repellents.