Midges are a group of insects that include many kinds of small flies. They are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid zones. The term "midge" does not define any particular taxonomic group, but includes species in several families of Nematoceran Diptera. Some midges, such as many Phlebotominae (sand fly) and Simuliidae (black fly), are vectors of various diseases. Many others play useful roles as prey items for insectivores, such as various frogs and swallows. Others are important as detritivores, participating in various nutrient cycles. The habits of midges vary greatly from species to species, though within any particular family midges commonly have similar ecological roles.
Examples of families that include species of midges include:
The Ceratopogonidae (biting midges) include serious blood-sucking pests, feeding both on humans and other mammals. Some of them spread the livestock diseases blue tongue and African horse sickness – other species though, are at least partly nectar feeders and some actually suck insect bodily fluids.
Most other midge families are not bloodsuckers, but it is not possible to generalise rigidly because of the vagueness of the term "midge". There is for example no objective basis for excluding the Psychodidae from the list, and some of them (or midge-like taxa commonly included in the family, such as Phlebotomus) are blood-sucking pests and disease vectors.
Most midges, apart from the gall midges (Cecidomyiidae), are aquatic during the larval stage. Some Cecidomyiidae (e.g., the sorghum midge) are significant plant pests. The larvae of some Chironomidae contain haemoglobin and are sometimes referred to as bloodworms.
Non-biting midge flies are a common nuisance around man-made bodies of water, and are frequently mistaken for mosquitos.