Black flies belong to the family Simuliidae and have a worldwide distribution. There are more than 2000 species in 25 genera. However, only three genera, Simulium, Prosimulium and Austrosimulium, contain species that commonly bite people.

Medically, Simulium is by far the most important genus as it contains many vectors. In Africa, species in the S. damnosum complex and the S. neavei group, and in Central and South America, species in the S. ochraceum, S. metallicum and S. exiguum complexes, transmit the parasitic nematode Onchocerca volvulus, which causes human onchocerciasis (river blindness). In Brazil, S. amazonicum transmits Mansonella ozzardi, a filarial parasite that is usually regarded as non-pathogenic.

The Simuliidae are commonly known as black flies, but in some areas, especially Australia, theymay be called sand flies. As explained in Chapter 5, this latter terminology is confusing and best avoided because biting flies in the family Ceratopogonidae are sometimes also called sand flies, while flies in the subfamily Phlebotominae are regarded as the true sand flies.

External morphology

Adult black flies are quite small, about 1.5–4mm long, relatively stoutbodied and, when viewed from the side, have a rather humped thorax. As their vernacular name indicates they are usually black in colour (Plate 5), but some species have contrasting patterns of white, silvery or yellowish hairs on their bodies and legs, while others may be predominantly orange or bright yellow.