Black fly (Simulium sp.) larva. Coloured scanning electron micrograph (SEM) of the foot of a black fly larva, showing the hairs it uses to filter food from the water. Most black flies (family Simuliidae) feed on the blood of mammals, including humans, although the males feed mainly on nectar. Their larvae are aquatic and filter food from the water. Magnification: x200, when printed 10 cm wide.