A genus of biting gnats or midges, the black flies, humpbacked flies, or buffalo gnats in the dipteran family Simuliidae. The aquatic larvae require swift-flowing streams or highly oxygenated waters for their development, a critical epidemiologic factor in the role of these flies as disease vectors. In Central and South America, Mexico, and across central Africa, various species transmit Onchocerca volvulus, agent of human onchocerciasis. SYN: Eusimulium. [L. simulo, to simulate]