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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 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. The best approach is to use insect repellents when your activity takes you near black fly habitat. Repellents are not always effective but are worth trying (see Using Insect Repellents).

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 especially if your home is near a fresh water stream where black flies breed (see Related Articles below).


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.

Related Articles

Using Insect Repellents

Black Flies In Death Valley National Park!

Using Mosquito/Black Fly Traps

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Jack DeAngelis, PhD,  , email:  [email protected]

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