Biting flies feed on blood, attacking humans and other animals as food sources. Some are capable of transferring disease through these feeding habits. There are many species of biting flies, each with its own habits and ecology.
Nearly everyone has been bitten by a fly of one sort or another. Though there are many types of biting flies, mosquitoes account for most of the biting. This fact sheet focuses on other types of biting flies.
While most winged insects have four wings, flies have only two wings. A fly has mouthparts designed to suck up liquids and for piercing, if the fly is one that bites other animals. Like mosquitoes, biting flies locate humans and other animals by sensing certain substances, including the carbon dioxide and moisture in exhaled breath, dark colors and movement, warmth and perspiration.
Biting flies transmit debilitating diseases to millions of people worldwide. In the United States, one deer fly species (Chrysops discalis) can transmit tularemia. In addition, the bites of black flies (Simuliidae), horse flies (Tabanidae) and stable flies (Stomoxys calcitrans), can produce severe allergic reactions. Deer flies are one of the few types of flies that transmit disease to people in the United States.
Common Biting Fly Species
From large horse flies to nearly microscopic midges, homeowners can encounter a variety of flies that bite. Some of the most common species include:
Read also: Experience Fad's Fine African Cuisine
Deer Flies
A little smaller than house flies, these insects emerge in the spring. They use their scissor-like mouthparts to open skin, so deer fly bites are rather painful.
They are medium-size flies, approximately ¼-inch long, about the size of a house fly. They are typically yellow-brown to black with dark bands on their wings. The maggot-like larvae (immature stage) of deer flies are aquatic. The adult flies are often encountered along trails near streams, lakes, ponds, marshes and swamps. They can be quite bothersome, buzzing around a person’s head, especially where large numbers are present.
Both deer flies and horse flies bite with scissor-like mouthparts that cut into skin, causing blood flow which the flies lap up. Because of this relatively crude means of obtaining blood, the bites can be painful.
Horse Flies
Like deer flies, these pests slice into the skin when they bite, which causes pain and swelling. The large size of a horse fly can also be daunting for some people. Due to their large size and the intensity of their bite, horse fly bites are often considered one of the most painful.
Horse flies can be an inch or more long. Some are entirely black. Others, known as “greenheads,” are light brown with shiny green eyes. Horse flies are strong, fast fliers that feed on the blood of livestock and other animals. Like deer fly larvae, the larvae of horse flies usually live in water or moist locations where they prey on other insects, grow and migrate to dryer soil to undergo the pupal (cocoon) stage. The life cycle may take two years to complete.
Read also: The Story Behind Cachapas
Female horse flies feed on blood, while males seek nectar and sugary liquids. Horse flies tend to be active in warmer temperatures.
Black Flies
These insects love moisture and thrive around rivers or creeks. A black fly’s distinguishing feature is its humped back, when viewed up close or under a dissecting microscope.
Adult black flies are small, no more than 1/8-inch long with broad wings and a humpbacked appearance. Like other flies, black flies are creatures of moist environments. Also known as “buffalo gnats,” they are usually encountered near creeks and rivers where the larvae attach to submerged stones. Black flies will fly up to 10 miles in search of blood.
They generally make their homes in most parts of the United States, but are a particular nuisance in the northern part of America. They do not transmit disease to humans in the United States. However, injury from black fly bites can threaten the lives of livestock and even people when present in very large numbers, typically in late spring and early summer. Deaths have been reported from allergic reactions and blood loss from the bites, and even from inhaling the flies. Black fly bites often cause considerable swelling and bleeding, may be itchy and slow to heal.
Stable Flies
Mainly found in late summer and early fall, these biting flies primarily feed on livestock. They look similar to house flies, but stable flies have a pointed mouthpart used to suck blood.
Read also: Techniques of African Jewellery
The stable fly is about ¼-inch long and gray with four dark stripes on its thorax (behind the head). This fly looks like a house fly, except for the pointed proboscis beneath its head through which it sucks blood. They are most abundant in late summer and fall, and will fly several miles to bite livestock (hence the name), pets and people. They typically bite in early morning or late afternoon and often attack the ankles, inflicting a sharp, stabbing pain. Stable flies lay eggs in piles of rotting vegetable matter, such as haystacks, grass clippings, manure and vegetation along shorelines. Like the adults, stable fly larvae are nearly identical to the larvae of house flies.
Snipe Flies
These pests are close relatives of deer flies. They typically live in damp places located in forested areas. Most species of snipe flies do not bite, but some do use their mouthparts to inflict irritating bites.
Sand Flies
Physically similar to drain flies, this species preys on mammals and reptiles. An adult sand fly is less than 1/8 inch in length with long legs and wings that form a V shape.
Sand fly larvae are tiny and worm-like, living in moist decaying plant matter, moss, mud or in water. Adults are long-legged, no more than 1/8-inch long, hairy and brown to gray with wings that form a “V” shape when the flies are at rest. Most sand fly species feed on the blood of mammals, reptiles and amphibians at night. In many parts of the world, including southern Texas in the United States, certain sand fly species (Lutzomyia) are suspected of transmitting cutaneous leischmaniasis, a disfiguring protozoan disease of humans.
A yellow fly bite results in localized swelling and itching.
Biting Midges
Since they rarely grow larger than 1/32 of an inch long, biting midges, also called no-see-ums, easily get into houses through window and door screens. This ability makes them one of the most pervasive flies that bite.
Biting midges are biting flies commonly found near the coast. Larvae thrive in mud and can sometimes be seen swimming freely in infested waters. Larval biting midges pupate at the water’s edge or on floating sticks and leaves. They breed in salt marsh areas. Biting midges are susceptible to air currents and emerge most commonly on still days.
Biting midges should not be confused with other midges (Chironomidae) that are much larger and resemble mosquitoes but do not bite. The biting midges are much smaller, being no more than 1/32 of an inch long. They are also known as “punkies,” “no-see-ums” or simply “gnats.” Their tiny size allows them to penetrate window and door screens.
Mosquitoes
Perhaps the best known biting fly, the mosquito bites more people each year than most of the other species on this list combined and are the vectors of many diseases.
Black Fly - How To Protect Yourself In The Wilderness
Tsetse Flies
Tsetse flies are large biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus Glossina, which are placed in their own family, Glossinidae. The tsetse is an obligate parasite that lives by feeding on the blood of vertebrate animals. Tsetse flies have been extensively studied because of their role in transmitting disease.
Tsetse are biological vectors of trypanosomes, meaning that in the process of feeding, they acquire and then transmit small, single-celled trypanosomes from infected vertebrate hosts to uninfected animals. Some tsetse-transmitted trypanosome species cause trypanosomiasis, an infectious disease. In humans, tsetse transmitted trypanosomiasis is called sleeping sickness. In animals, tsetse-vectored trypanosomiases include nagana, souma, and surra according to the animal infected and the trypanosome species involved.
Problems Caused by Flies that Bite
In addition to the pain caused by bites, flies can trigger allergies for a number of people. Select species spread diseases to humans as well. Mosquitoes, for example, can transmit the West Nile and Zika viruses, while deer flies carry tularemia.
Even more types of flies that bite can attack livestock. In addition to spreading illnesses to the animals, fly swarms often affect the health of cattle or horses by causing constant agitation.
Tularemia, also known as “rabbit fever,” is a bacterial disease that can be acquired from contact with objects or infected animals, from the bites of ticks and, occasionally, from the bites of the deer fly, Chrysops discalis.
Sand flies (Psychodidae) transmit sand fly fever, bartonellosis and leischmaniasis in many parts of the world.
Area-wide control of biting flies can be difficult due to the hidden habitats in which the larvae are found, and because some adult biting flies may fly miles from their larval habitats.
Controlling Biting Flies
The best way to control biting flies is to remove the pests’ optimal breeding conditions. Mosquitoes need water to lay eggs, so emptying containers and other items around the yard after rainfall will curb their numbers. Other types of flies that bite may breed in rotting organic material, so prompt trash removal and cleaning of moist organic matter can help.
Nevertheless, sanitation can be an important method of controlling some biting flies. The larvae of stable flies, for example, develop in piles of decaying hay, straw and other vegetation, including manure containing plant matter. These potential sites for larval development should be eliminated where practical. Other flies (biting midges and sand flies) may be controlled by disposing of decaying vegetation containing their larvae.
Exclusion also can be employed against biting flies. Stable flies are known to enter structures in search of blood meals, so screens should be installed and maintained on windows and doors. However, the mesh of standard household screens is not fine enough to keep out the tiniest biting flies and should be replaced with finer mesh where these flies are a problem. The use of fly paper is limited as it is not as attractive to biting flies as are warm-blooded animals.
Fans may be a more useful means to help keep small areas free of flies, especially smaller flies whose flight is affected by air currents. Similarly, burning candles and torches that produce smoke and air currents may help keep the smaller species away.
Pesticide application is of limited use in controlling biting flies. Ultra-low volume (ULV) treatments (such as “fogging” for mosquitoes) and space sprays of non-residual pesticides are best used where flies are numerous and concentrated in a relatively small area. These materials kill only on contact and quickly decompose, leaving the treated area unprotected soon after application.
Residual pesticides can be used to spray surfaces where flies are resting, such as vegetation, the walls of barns and the exterior walls of houses. But this method will do little good if flies are not landing on these surfaces.
Another chemical control is larviciding, the application of pesticides designed to kill fly larvae. Formulations containing Bacillus thuringiensis (such as BTI) or growth regulators (such as methoprene) have been widely and successfully used against mosquito larvae living in the stagnant water of ditches, lagoons and catch basins. BTI has been used successfully against black fly larvae in streams.
Repellents are the final line of defense against biting flies. Those containing the active ingredient DEET (N,N-diethyl-meta-toluamide) or picaridin are best. While effective against mosquitoes, repellents have been found to be less effective against some types of biting flies. The use of repellents to combat biting flies should be supplemented with other preventive methods, such as avoiding areas inhabited by the flies, avoiding peak biting times, and wearing heavy-duty, light-colored clothing including long-sleeve shirts, long pants and hats. When black flies, for example, are numerous and unavoidable, netting that covers the head, like the “bee bonnets” used by beekeepers, can provide protection. Smaller biting flies, such as biting midges, may become stuck in heavy coatings of lotions or oils applied to skin.
Despite the use of various control methods, control of biting flies is seldom complete. But by supplementing preventive measures with fly management, bites from these vexing pests can be avoided.
NOTE: When pesticides are used, it is the applicator’s legal responsibility to read and follow directions on the product label.
