Fossil blackflies are about 170 million years old. Of the approximately 1,600 blackfly species, only about 900 are man-biting species. Only female blackflies suck blood, demoralizing the host by their painful bites. Since the larvae develop only in flowing water, attacks by adults regularly occur there, and after mass attacks by adults, these can even induce panic reactions in herds of cattle. Blackflies transmit protozoan blood parasites to birds but are mainly known as vectors of filarial helminths, especially onchocerciasis (River Blindness).