Black Flies, HYG-2167-97

Ohio State University Extension Fact Sheet

Entomology

1991 Kenny Road, Columbus, Ohio 43210-1000

Black Flies

HYG-2167-97

William F. Lyon

Common Name Scientific Name 

Black Fly, Buffalo or Turkey 

Gnat 

Simulium vittatum Zetterstedt 

Simulium venustum Say 

Simulium jenningsi

Prosimulium sp 

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Adult Larva (top) 

Pupa bottom 

Certain species of adult black fly females are fierce biters, whereas others are strictly a 

nuisance by their presence around one's nostrils, ears, arms, hands, and other exposed skin 

areas. These flies can discourage people from remaining in or visiting certain recreational 

areas for fishing, camping, hiking, golf, etc. when the black fly season occurs. Children are 

especially susceptible and may be severely bitten while adults in the same area are scarcely 

aware of the flies. Most complaints in Ohio occur in early spring (April to June) in hilly areas 

with swiftly, flowing streams. Bites may appear where clothing fits snugly against the body, 

leaving a ring of bites just above or below the belt line. 

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 slightly reddened, swollen area. Next, 

the area becomes increasingly itchy, swollen and irritating, sometimes for several days. Some 

black flies readily attack people, whereas others prefer domestic animals or birds, often 

feeding during the daylight hours and sometimes into the night. Flies may become so 

abundant as to be drawn into the air passages of livestock, occasionally resulting in death. It 

is believed that allergic reactions to bites may be caused by histaminic substances in the fly's 

saliva. These flies transmit a disease of filarial worms, onchocerciasis, which causes blindness 

in people in Mexico, Central America and Africa in addition to protozoan parasites, 

leucocytozoonosis to turkeys and wild birds. They may be potential transmitters of 

encephalitis. It is suspected that the expansion of black fly populations in Ohio is likened to 

improvement in stream and river water quality in recent years. As with many aquatic insects, 

black flies are very sensitive to water pollution. 

Identification

Most species of adult black flies are about 1/8-inch long (2 to 5mm), black gray or even yellow 

colored, broad clear winged without hairs or scales with heavy veins near the anterior wing 

margin, have short 11 segmented antennae, large round eyes (no simple eyes) and the thorax 

(middle body region) is strongly convex, giving a humpbacked, gnat-like appearance. 

Small creamy-white eggs (rather triangular) about 1/32-inch long (0.1 to 0.4mm) are 

deposited on the water surface or attached in compact masses to stones and vegetation in 

shallow fast-running water (riffles) in streams and rivers. Larvae, black to light brown colored, 

cylindrical, about 1/4-inch or more long (10 to 15mm), are quite active and abundant, 

sometimes appearing as moss. Pupa are boat or basket-shaped cocoons up to 1/8-inch long (2 

to 5mm) in the water. 

Life Cycle and Habits

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There are four species present in both Ohio and Pennsylvania according to Dr. Peter H. Adler, 

Department of Entomology, 114 Long Hall, Clemson University, Clemson, South Carolina 

29631 - Telephone 803-656-3111 (formerly conducted black fly research in Pennsylvania). 

1. Simulium vittatum Zetterstedt - This species is strictly a nuisance attacking horses and 

cattle, but not humans. It does fly around people's faces. Breeding occurs in rich 

productive streams such as polluted (sewage) areas, at beaver dams, etc. It is dark 

gray to velvety black. (Widely distributed in North America.) 

2. Simulium venustum Say - This species is a nasty biter feared by fishermen and 

campers. The season extends from May to September with greatest numbers in June 

and July. They are usually less troublesome in late summer. It is recognized by its whitemarked tibiae (leg parts). (Widely distributed, especially in New England and Canada.) 

3. Simulium jenningsi - This species breeds in huge rivers (one mile or so wide). In 

Pennsylvania, New England and other states, there is currently a multimillion dollar 

program applying a biological larvicide known as Bacillus thuringiensis Berliner 

subspecies israelensis (B.t.i.) into streams and rivers to control larvae before adult 

emergence. 

4. Prosimulium sp. - This species occurs in early spring (April to May). It is a nuisance by 

both swarming and biting. Larvae occur in small woodland streams. It is the first black 

fly species to appear each year. 

Black flies often occur in enormous numbers in the spring and early summer months, 

especially in the northern latitudes. Bites can be extremely painful, and their mouthparts are 

somewhat similar to those of a horse fly (bladelike and piercing) in the female. Mouth parts 

are rudimentary in the male. On people, they crawl into sleeves, under neckbands, around 

boot tops and other vulnerable places, especially favoring the head just beneath the rim of a 

hat. Bites can cause swelling and numb soreness for many days. There are records of both 

domestic animals and people being killed in a few hours through venomous bites and blood 

loss. Death can result from suffocation as a result of plugged nasal or bronchial tubes and 

allergic reactions. 

Flies usually bite during the day in outdoor shaded or partially-shaded areas. They do not bite 

indoors or late at night. Some fly 7 to 10 miles from the breeding sites, or are blown by wind 

even further to feed on warmblooded animals and people. Flies usually bite for about three 

weeks before they die. Dark blue cloth attracts more flies than white cloth. 

Females deposit from 150 to 500 small, shiny, creamy-white eggs on submerged objects in the 

stream such as on water plants, rocks, twigs, leaves, etc. or simply scatter the eggs over the 

water surface. Eggs darken then hatch in four to five days at water temperatures of 70 deg F. 

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Eggs deposited in the autumn do not hatch until the following spring when the water warms. 

Young larvae attach themselves to submerged objects, molting six times as they grow. They 

are elongate with the hind part of their bodies swollen. A head fan sweeps food material into 

the mouth. They retain their position in the water by means of sucker-like discs and tiny hooks 

at the tip of the abdomen. Also, they may spin a fine thread which aids in anchoring them. 

Winter may be passed as larva. Pupation occurs in a cocoon, open at one end. Adults emerge 

in two to three days when the water is warm. They are capable of immediate flight and 

mating. The entire life history spans about four to six weeks, depending on species, water 

temperature, available food, etc. There may be four generations per year. 

Black flies are attracted to mammals by the carbon dioxide and moisture in exhaled breath, 

dark colors, convection currents, perspiration, perfumes, toiletries, etc. 

Control Measures

There is little that the individual homeowner can do to control black flies. Bites can be treated 

with soothing lotions as well as corticosteroids to relieve pain and itching and help lesions 

resolve. If the reaction is mild, oral antihistamine therapy may suffice, but severe reactions 

involving shock may require epinephrine (consult a physician). 

Prevention

Some avoid outdoor activities during the black fly season. One can purchase hats with fine 

mesh netting extending over the face and shoulders from camping supply and mail order 

houses. Repellents offer some relief depending on the individual, species of fly, temperature, 

humidity, time of day, etc. There are times that flies will bite regardless of the repellent and 

concentration used. Protection sometimes lasts for two to two and half hours. Any of the 

following repellents can be used such as deet (Cutters, Diethyl-toluamide, Off), citronella oil 

(Skin So Soft), ethyl hexanediol or dimethyl phthalate. As a whole, the individual can merely 

resort to household sprays, aerosols, repellents and screens (60 mesh bolting cloth) to cope 

with this pest. Some persons indicate that unpainted aluminum "hard hats" attract black flies. 

A thin film of fuel oil smeared over the outer surface traps flies in the oil, giving the wearer 

much protection. 

The best methods of control are directed toward reducing the number of black fly breeding 

areas. Removal of vegetation and other objects in streams will cut down the number of larvae. 

Temporary damming of water can reduce populations, as immature stages need swift, running 

water. Larvae will die in 10 to 24 hours in calm non-running water. 

Insecticides

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Fogging for black flies provides temporary relief since only those flies that contact the fog are 

killed. Later migrants into the treated area are unaffected. Daily treatments of pyrethrins 

usually is necessary. 

Treatment of breeding areas in rivers, streams, etc. is effective when the application timing is 

correct. Large scale efforts are needed such as by a government agency skilled in coping with 

black flies. It is necessary to treat large areas where larvae occur by helicopter or airplane. 

Also, crews spraying streams and other bodies of water, and fog machines and mist blowers to 

kill the adults, is helpful. 

For example, Pennsylvania's Black Fly Suppression Program (PA. Dept. Of Environmental 

Research, P.O. Box 2357, Harrisburg, PA 17120) relies almost exclusively upon the bacterium, 

Bacillus thuringiensis Berliner var. israelensis (B.t.i.) applied by aircraft to control larvae in 

water sites. This larvicide is nontoxic to nontarget beneficial organisms such as fish, birds, etc. 

Treatment of B.t.i. in New Hampshire for more than 10 years has resulted in less and less 

evidence of regeneration of black flies at certain golf courses. 

Other labeled insecticides for application only by Public Health officials and trained personnel 

of Mosquito Abatement Districts for control of adult black flies in residential and recreational 

areas include permethrin (Biomist, Permethrin), chlorpyrifos (ULV Mosquito Master), and 

hypermethrin (Culicideth). 

All educational programs conducted by Ohio State University Extension are available to clientele on a 

nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, 

gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-1868

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