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.
After the black fly finishes feeding, bleeding may continue for some time. At first, the bite site appears as a small, red, central spot surrounded by a reddened, swollen area. Next, the area becomes increasingly itchy, swollen and irritating, sometimes for several days. Partial relief can be found by using anti-itch creams or oral anti-histamines, like benedryl.
Flies usually bite during the day in outdoor shaded or partially-shaded areas. They do not bite indoors or late at night. They are less numerous at higher altitudes due to a lack of breeding sites, cooler temperatures and the presence of breezes. Black flies are attracted to mammals by the carbon dioxide and moisture in exhaled breath, perspiration and perfumes. They are also strongly influenced by color — they find dark hues more attractive than pale ones, and blue, purple, brown, and black more attractive than white or yellow. A light-colored shirt, therefore, is a much better choice of clothing than a dark blue one.
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.
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