There are about 5540 species of biting midges in some 103 genera, but only four genera feed on vertebrates. Medically the most important two genera are Leptoconops, which is mainly found in the tropics and subtropics, including the Caribbean area and parts of the USA, and Culicoides, which contains about 1450 species and has an almost worldwide distribution. In many parts of the world species of Culicoides, and in the Americas also Leptoconops, can constitute serious biting problems. In Africa Culicoides milnei, C. austeni and possibly C. grahamii are vectors of the filarial worms Mansonella perstans, while C. grahamii and possibly C. milnei and C. austeni are vectors of Mansonella streptocerca. Culicoides furens is a vector of Mansonella ozzardi in the Americas. These parasites are usually regarded as non-pathogenic to humans. Although they can be a serious biting nuisance, Leptoconops are not disease vectors.

External morphology

Adults are sometimes known as midges or biting midges, and, especially in the Americas, as ‘no-see-ums’. In Australia and some other countries they are often called sand-flies, but this name is unfortunate and should be avoided because phlebotomines (Chapter 5) and occasionally simuliids (Chapter 4) may also be referred to as sand-flies. The most appropriate common name is biting midges; this terminology serves to distinguish them from other small non-biting flies which are often referred to as midges.

Adult Culicoides (Plate 7) are very small, being only 1–2.5 mm long, and with the phlebotomines constitute the smallest biting flies attacking humans.