Black Flies (Simuliidae)

What are black flies?

Black flies are small (1-3 mm), usually dark colored, biting flies with a distinctive "humpbacked" profile (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.

Black flies are very persistant 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 as well. Like mosquitoes, black fly females require a blood meal in order to lay healthy eggs.

How can I avoid black fly bites?

Black flies can be present in enormous swarms that attack people and livestock near flowing streams and rivers.

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 their habitat. Repellents are not always effective but are worth trying.

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