Certain species of blackflies of the genus Simulium are responsible for transmission of the filarial nematode, Onchocerca volvulus , the causative agent of 'river blindness' in central and western Africa. Species can also transmit various forms of cattle onchocerciases. Flies live in the vicinity of streams in woodland and eggs are laid close to or in well-aerated running water. They are daytime biters attacking mammals and birds. The flies have a dark humped thorax and it is only the female that feeds on blood, but she can also supplement her diet by feeding on plant sugars.
Transmission occurs through the mouthparts which are designed to pierce the skin.
Sandflies are pale brown flies that move in a series of flying 'hops'. Flies live in the humid earthen burrows of rodents and other small mammals. In general, the flies feed at night after twilight. Eggs are deposited in warm, humid dark places. The flies have long slender bodies and it is the female that feeds on blood.