From Wikipedia:
Limoniidae is a family of flies closely related to the crane flies Tipulidae although they can usually be distinguished by the way the wings are held at rest. Limoniids usually hold the wings along the back of the body whereas tipulids usually hold them out at right angles. Members of the genus Chionea (snow flies) have no wings at all. Limoniids are also usually smaller than tipulids, although there are exceptions. Limoniidae is a very large family with nearly 11000 described species in 150 genera. These flies are found in damp places throughout the world and many species form dense swarms in suitable habitats.
Mostly, larvae are aquatic or semi-aquatic, unlike tipulids which are mostly terrestrial. Various species have evolved to feed on different food sources so there are phytophagous, saprophagous, mycetophagous and predatory species.