True flies are minute to large insects, with a single pair of membranous wings. Characteristically, the hindwings are reduced to knobbed, drumstick-like stalks, known as halteres, that function as balancing organs during flight. True flies include many predacious or parasitic species, and these often fulfil an important role as natural enemies of harmful or potentially harmful insects and other invertebrates. Gall midges are small or tiny, delicate insects, with broad, often hairy wings and a much reduced wing venation. Several species of Endaphis are known from various parts of the world, of which one is present in Europe. The northern European gall midge Endopsylla agilis is an endoparasitoid of adult psyllids, including well-known orchard pests such as the apple sucker. The genus Lestodiplosis embraces a group of predacious midges, whose larvae most frequently attack the larvae of other gall midges. Snipe flies form a small group of medium-sized to large, mainly brown and yellow, predacious flies with relatively long, slender legs.