Black flies are found in the US and Canada, Scotland, Northern Queensland in Australia, Africa and many other parts of the world. About 300 of the world’s 1600 black fly species are found in North America. Some South American and African species carry a roundworm parasite which causes human blindness. Some species also transmit waterfowl malaria, which accounts for nearly one half of deaths of ducks, geese, and swans.
Black flies are most commonly found along rivers and streams during late spring and early summer. They have a stout body, hump-backed appearance and measure 1 to 5mm in length. Unlike the mosquito, black flies slash the skin and lap up the pooled blood. Their bite is extremely painful, and the injection of venom into the skin causes intense itching, local swelling and soreness. Severe complications (swelling) from black fly bites are possible in allergic individuals and rare cases of death from toxemia or anaphylactic shock have been reported. Even when they are not biting, however, their buzzing presence and constant crawling is as irritating as the bloodsucking itself. They fly around people’s heads, occasionally getting into eyes, ears and crawling in the hair. Livestock, pets, poultry and wildlife are also severely irritated by these flies.
Only female black flies are bloodsuckers. After mating the females require a blood meal before their first batch of eggs is laid. They are attracted to hosts from a distance by smell, heat and by sight. In some part of the world, the female fly may travel more than forty miles from aquatic breeding sites to find blood meals. Females deposit eggs, 200 to 800 per female, on vegetation just below that water surface. Black flies live as larvae in shallow, clear fast running water in rivers and streams. The black, spindle-shapes larvae live on the river bottom attached to rocks and other submerges objects and feed on tiny bits of organic matter, algae and protozoa. Larvae transform in the water to adult flies that rise to the water surface in a bubble of gas. The adults usually live only for about three weeks.
Black flies are strongly influenced by colour – they find dark hues more attractive than pale ones, and blue, purple, brown and black are more attractive than white or yellow. A light coloured shirt, therefore, is a much better choice of clothing than a dark blue one. Black flies numbers and their tendency to bite, increase as sunset approaches and prefer low wind conditions. They seek their blood meal in open spaces seldom entering buildings and do not attack at night.
Dr Barry Tyler, Ph.D (Mosquito and Black Fly Control specialist, Erin, Ontario, Canada.) conducted a trail on the effectiveness of the Mosquito Management System mosquito trap (now referred to as the Mosquito Slayer) machine, in catching and killing mosquitoes and black flies. “The results were impressive; the traps caught literally thousands of mosquitoes and black flies”. “It doesn’t catch them all but it certainly reduces the numbers dramatically”. Dr Tyler also says that “people who have traps around their homes can rest easier knowing that they have taken extra measure to keep their families safe”.