Larvae are often found anchored to the substrate in the swift currents of streams and rivers. They have special mouthparts to strain microscopic food particles from the water. Black flies have one to several generations per year. Adults typically live three weeks or less. Adult females are biting pests.
Most species have a one-year life cycle.
Although most species feed on algae, leaves, or woody detritus, some are active predators. Crane flies are good examples of life cycles timed to food source availability or temperature. In temperate regions certain species of crane flies start disappearing from the top sediment and rocks in spring. They burrow deep into the sediment through summer. They then leave the stream to pupate on land, emerge as adults and lay eggs.