The larval stage can be found in almost every aquatic habitat, including hot springs. Although not a significant problem in the United States, certain biting true flies can serve as vectors of disease such as malaria and river blindness in other parts of the world. Dipterans are important components of aquatic and terrestrial food webs. Aquatic Dipterans have been widely used as pollution indicators and are, in general, fairly tolerant of pollution. Depending on the species, larvae occupy a large variety of feeding niches.
Life cycles range from a few weeks to a few years.
Adults may live from several hours to several months. 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.