The time required for hatching varies with the species and may be 3-5 days or as long as 30 days at low temperatures. Larvae most often are found just beneath the surface of rapidly flowing water. They do not come to the surface to breath like mosquito larvae because the gill filaments of larvae extract oxygen directly from the water. Some species overwinter as larvae, although in northern areas, winter is usually passed in the egg stage. These cocoons are attached to slightly submerged objects such as rocks, logs, roots and other debris.
Pupae also possess respiratory filaments with which they remove dissolved oxygen from the water.
Adults emerge from the pupal case, rise to the water surface, unfold their wings and fly away. Mating usually occurs shortly after the initial flight. The complete life cycle, from egg to adult, varies from 6-15 weeks and the number of generations per year ranges from one to six, depending on species and climatic conditions. Larvae are filter feeders and adult females have mouthparts modified for biting and blood feeding. Although a given species may prefer a particular animal host, most will readily feed upon other host species as well.