The ratio of vertical diameter of eye and height of gena (face index) is widely used in identification of individual species.

They may be differentiated by short thoracic segments (like the abdominal ones) and by the absence of a ventral arch linking the mouth hooks.

Imago are phytophagous, sometimes feeding on microscopic algae and bacteria (Paracoenia, Ephydra), or predatory (Ochthera, Ephydrinae).

As larvae, many are phytophagous, grazing on aquatic plants (including cultivated rice), others are algal grazers or saprophagous.

For example, Ephydra brucei lives in hot springs and geysers where the water temperature exceeds 45 degrees Celsius; some Scatella live in hot sulphur springs; Helaeomyia petrolei develops in pools of crude oil; and Ephydra cinerea, the brine fly proper, in pools with very high concentrations of salt.