No-see-ums (family Ceratopogonidae) are tiny biting flies that often live near water. No-see-ums are less than a quarter of an inch long. You often see them swarming together in a cloud. Females no-see-ums bite and suck blood. They need the protein from blood to make their eggs. No-see-ums will take blood from mammals, birds, and reptiles. Male no-see-ums are nectar feeders and do not bite.