Black-flies belong to the family Simuliidae and have a worldwide distribution. There are approaching 2000 species in about 26 genera. However, only four genera – Simulium, Prosimulium, Austrosimulium and Cnephia – contain species that 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.

External morphology

The Simuliidae are commonly known as black-flies, but in some areas, especially Australia, they may 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 also sometimes called sand-flies, while flies in the subfamily Phlebotominae are regarded as the true sand-flies.

Adult black-flies are quite small, about 1.5–4 mm long, relatively stout-bodied 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.