Black Fly (Simuliidae) Bites

- Tiny biting flies that occur near flowing water -

Summary: Black flies are small biting flies that develop in streams, rivers and other flowing water. Black flies can be extremely abundant and annoying. Insect repellents are somewhat effective against this pest as are certain traps.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Black flies are small biting flies

Black flies are small (1-3 mm), usually dark colored, biting flies with a distinctive "humpbacked" profile (see photo right). Immature, or larval, black flies develop in fast flowing streams, rivers and creeks where they cling to the undersides of rocks or debris. A few species breed in relatively slow moving water and can even be found in landscape water features.

Black flies are very persistent and fierce daytime biting flies. The bite site often bleeds profusely because of a strong anticoagulant in the saliva of the fly. An itchy skin lesion usually develops at the bite site as well. Like mosquitoes, black fly females require a blood meal in order to lay healthy eggs.

black fly
tiny black fly adult ~ 1-3 mm; common names - buffalo gnats, humpbacked flies; misspellings - black flys, blackfly

Use repellents and/or fine mesh head nets to avoid bites

Black flies can be present in dense swarms that attack people and livestock near flowing streams and rivers. Even a small trickle of water can support a black fly population in some circumstances.

It is impractical for individuals to control black fly larvae in the fresh water streams where larvae live so the best approach is to use insect repellents and mosquito/black fly (fine mesh)) head nets when your activity takes you near black fly habitat. While repellents may not always be effective, especially when the flies are numerous, they are worth trying (see Using Insect Repellents for more details) if a head net is not available. When using head nets be sure to wear a wide-brimmed hat so as to keep the netting away from your face and neck. Finally, the new "personal foggers" such as ThermaCELL (tm) can also be effective against biting midges, mosquitoes and black flies.

Black flies are normally found near flowing water, however some species are able to travel on wind currents and thus may occur some distance from a suitable breeding habitat.

Propane-powered mosquito traps may be useful for black fly control if your home is near a fresh water stream where black flies breed.

Diseases carried by black flies

Black flies are not carriers of human diseases in the US but in some tropical regions of the world a very serious disease called onchocerciasis (river blindness) is transmitted by certain species. Black flies can be found almost anywhere you find permanent flowing water.

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