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 andAustrosimulium, contain species that commonly bitepeople.

Medically, Simulium is by far the most important genus as itcontains many vectors. In Africa, species in the S. damnosumcomplex and the S. neavei group, and in Central and SouthAmerica, species in the S. ochraceum, S.metallicum and S. exiguum complexes, transmit theparasitic nematode Onchocerca volvulus, which causes humanonchocerciasis (river blindness). In Brazil, S. amazonicumtransmits Mansonella ozzardi, a filarial parasite that isusually regarded as non-pathogenic.

The Simuliidae are commonly known as black flies, but in some areas, especiallyAustralia, theymay be called sand flies. As explained in Chapter 5, this latterterminology is confusing and best avoided because biting flies in the familyCeratopogonidae are sometimes also called sand flies, while flies in thesubfamily Phlebotominae are regarded as the true sand flies.

External morphology

Adult black flies are quite small, about 1.5–4mm long, relatively stoutbodiedand, when viewed from the side, have a ratherhumped thorax. As their vernacular nameindicates they are usually black in colour (Plate5), but some species have contrasting patterns of white, silvery or yellowishhairs on their bodies and legs, while others may be predominantly orange orbright yellow.