Onchocerciasis vector, black fly pupating. Footage of a larva of a Simulium black fly pupating. This fly is responsible for spreading the nematode roundworm Onchocerca volvulus that causes onchocerciasis (river blindness). This is a type of filariasis, caused by the tiny worms (microfiliariae) that are the larval stage in the life cycle of this roundworm. The larvae are spread by flies which breed in and around rivers, primarily in Africa. The adult worms (macrofiliariae) grow in the body and mate to produce the microfiliarae that cause an allergic reaction, causing blindness if near the eye. This clip is from a film published in 1967, with contributions by the National Institute of Health and Medical Research in Ghana.