Midge, name given to several groups of small, slender-bodied flies. In Canada, nonbiting midges (chironomids), biting midges (ceratopogonids) and gall midges (cecidomyiids) are most important.
About 500 species of chironomids are known in Canada; many more await discovery. They reach the northern limit of land, forming an increasingly large component of insect fauna in northern latitudes. Larval stages are mostly aquatic and may form much of the diet of fish.
Minute ceratopogonids (no-see-ums) can be a scourge in midsummer and seem undeterred by chemical repellents. They are transmitters of bluetongue virus of cattle and sheep, and of protozoan bird diseases. In Canada, 180 species are reported; not all are pestilential. Their predatory larvae inhabit mud or moist soil.
Cecidomyiids are known as gall midges, although not all larvae form plant galls (see Plant Disease). The notorious Hessian fly, whose larvae bore into wheat stems, is a cecidomyiid. Some larvae are fungus feeders, including some serious pests of commercial mushrooms. Others are predatory. Canadian cecidomyiid fauna has been little investigated, with only 100 species recorded of a fauna estimated to exceed 1000.