Biting Flies Fact Sheet No. 5.582 Insect Series|Home and Garden by W.S. Cranshaw, F.B. Peairs and B. Kondratieff* Although mosquitoes are the best known birds. Species that historically have been Quick Facts of the flies that bite people, several other most annoying to humans and livestock in species can be locally important as a nuisance Colorado are S. griseum and S. bivittatum. • Several flies found in and can cause public health problems. While Simulium apricorium is a pest species largely Colorado bite people and can all biting flies are blood feeders none, aside restricted to elevations above 7,000 feet, be serious annoyance pests. from mosquitoes, are known to transmit where it develops in clear, cool and often These include black flies, human diseases in Colorado. However, turbulent streams. biting midges and deer flies. some flies can transmit animal diseases. All black flies require cool, running water Most important, bites can be painful (e.g., for development and favor sites with cobbled • Control of some biting flies deer flies) or produce swelling and intense bottoms (pebbles, small rocks) that are is possible by treating areas itching as the result of injected saliva (e.g., largely clear of silt. The black fly larvae attach where they breed. black flies). themselves to rocks or other submerged • Problems can sometimes materials and feed on organic particles they filter from the passing waters. Trailing be avoided by personal Black Flies, “Buffalo Gnats,” vegetation or rotted aquatic plants also are protection measures, such “Turkey Gnats” attractive to black flies, providing sites for the as appropriately colored The most common of the small biting larvae to attach for feeding. Breeding may clothing, insect repellents, flies, adult black flies can produce serious also occur in rivulets formed by the flooding and avoiding times of day annoyance problems and sometimes produce of fields. when biting is most intense. serious effects for people and animals. In The black fly life cycle can be rapid, Colorado, black flies usually feed on birds and taking about three weeks from egg laying some livestock ( e.g., horses) buy may bite to maturation of the adult. Only the female humans. They have been known to contribute bites, the blood meal being used to provide to the death of ostriches, which react severely protein for egg maturation. Adults live to the swarming gnats. Black fly outbreaks are about two weeks. Populations can grow very associated with areas with sustained running rapidly. Two to four generations may be water. For example, unusually heavy and produced annually. Individual females may sustained spring run-off, such as occurred lay several hundred eggs. during 1995 in much of eastern Colorado, Adult black flies are migratory, commonly can contribute to large population increases flying many miles from larval breeding sites. and subsequent biting problems. As an extreme example, migrations of more Adult black flies (Simulium spp.) are than 90 miles are reported in Canada. small with a humpbacked appearance. Black fly attacks on people, cattle, horses Approximately 40 species of black flies and pigs tend to be concentrated around the occur in Colorado. Only a few cause serious ears and head. In addition to the blood loss, injury to people or animals. Simulium effects of the insect saliva can cause a variety vittatum, a species which favors birds and is of problems, with swelling and intense skin sometimes known as a “turkey gnat,” is found irritation most common. Allergenic asthma, statewide, although concentrated in the nausea and more systemic effects can also eastern half of Colorado. The “true” turkey occur, a condition known as “black fly fever.” gnat, S. meridionale, is a foothills-prairie Species that attack birds feed mostly around species in eastern Colorado and attacks the eyes. The intense annoyance can cause © Colorado State University animals to become greatly agitated and Extension. 12/96. Revised 6/13. *W.S. Cranshaw, Colorado State University Extension exhaust themselves in attempts to escape. www.ext.colostate.edu entomologist and professor; F.B. Peairs, Extension Some Colorado species of black flies are entomologist and professor; and B. Kondratieff, known vectors of vesicular stomatitus, a professor; bioagricultural sciences and pest disease that can infect horses, cattle and pigs. management. 6/2013 by the black flies, presumably due to their curtailed. Biting may also be more severe in dark colored bill). Light-colored hats that years following periods of drought. cover the ears are an important precaution. Although the exact habitats where The repellent DEET (diethyl toluamide) is Leptoconops midges breed are unknown, it somewhat effective in preventing black fly is suspected that they develop in seepage bites, although swarming gnats may still be areas of crevices along canyon washes. annoying even when using repellent. Emergence of the adult insects usually To reduce attacks on poultry and follows late spring or early summer rains. ostriches, keep the birds in a darkened barn Emergence may be delayed by drought. during the day. Usually fans or some other Control. Because the breeding Figure 1: Black fly, greatly enlarged. means of cooling the birds is needed. sites are widely dispersed and often Larval control is practiced in some inaccessible, control of larvae is impractical. areas where chronic black fly problems Effectiveness of adult control through occur and breeding areas are known. This areawide insecticide sprays has never been involves metering of Bacillus thuringiensis successfully demonstrated and likely would var. israelensis into the flowing water produce poor results because the adult where larvae occur. Trade names include insects may fly considerable distances from Bactimos and Vectobac, the same products breeding areas. The insect repellent DEET used for larval control of mosquitoes. is effective against these insects. However, as previously noted, the breeding sites can be many miles away from where Culicoides Midges the adult insects are causing problems. Culicoides midges are widely distributed Adult control is problematic, again due in the state. Larvae develop in moist soil Figure 2: Biting midge, greatly enlarged. to the migratory behavior of the insects. It rich in organic matter. Damp areas at is likely that permethrin-based products the edges of ponds, swamps and manure are among the best. These are effective lagoons are the more favored breeding against most fly species and are labeled for sites. Several generations can be produced use in mosquito control and for fly control each year. of livestock. Adult stages rarely fly far from breeding sites. Most biting occurs at dusk with Biting Midges, a secondary peak period of biting at “No-See-Ums,” “Punkies” dawn. Where conditions allow, breeding adult insects can be present and produce (Ceratopogonidae) problems for months. Culicoides variipennis Biting midges are minute insects, often and C. sonorensis are known to vector blue called “no-see-ums” because they are so tongue disease of sheep and cattle. small (usually less than 1/8 inch) that they Control. Control of larvae with Figure 3: Deer fly. can pass through typical porch screening. insecticides is not possible due to their However, despite their size, they can be inaccessible breeding sites. However, some Unlike mosquitoes, black flies are painful biters and highly annoying. Two reduction of breeding is possible through day feeders. Biting attacks tend to show common biting midges that cause problems cultural practices that modify larval habitat. some periodicity. During sunny, warm in Colorado are Leptoconops species and This could include intermittently flooding days peak attacks occur in mid-morning Culicoides species. Each has different habits. and/or alternately thoroughly drying ponds and then have a more intense phase in that serve as breeding sites. Eliminating evening, ending at dusk. However, biting Leptoconcops Midges stagnant water rich in organic matter will greatly intensifies at the onset of storms Within Colorado, problems with help reduce breeding habitat. Careful water and may persist all day when overcast Leptoconops midges are restricted to the quality management of settling ponds conditions occur. West Slope. Historically, areas around associated with dairy operations and the Colorado National Monument have feedlots also will reduce breeding habitats. Control reported problems most frequently and Success of adult control is not likely and Black fly control is difficult due to the the canyon country of western Colorado. has not been demonstrated. Although these highly migratory adult stage and their Adults bite during the day, particularly flies do not disperse great distances, adult extensive breeding habitat. In terms of during midmorning and near dusk. biting midges can range widely. They tend personal protection, choice of clothing Although peak biting usually occurs during to rest on tall grasses during the day. DEET can be important. Black flies are highly a single period of the year, it typically lasts is only marginally effective as a repellent. attracted to dark colors, so wear light about two to three weeks, during which colored clothing. (Note: Male ostriches time outdoor activities can be greatly Deer Flies appear to have been particularly hard hit Deer flies (Chrysops spp., Silvius spp.) Snipe Flies are moderate-sized insects. Most common Snipe flies (Symphoromyia spp.) are species are gray or light brown, sometimes close relatives of deer flies. They are found with patterned bodies and wings, and have near forested areas of higher elevations of large colored eyes. Deer flies are day biters, the state. Snipe flies can be vicious biters produce a painful bite, and frequently draw and feed during the day. blood in the process. Very little is known of the habits of They lay eggs on grasses and other these insects. Larvae of some snipe flies aquatic vegetation around the edge of small develop in moist soils of grassy woodlands. ponds and other permanent standing water.