Colored scanning electron micrograph (SEM) of Black fly adult male (Simulium hippovorum). Simulium hippovorumis a blood-sucking insect closely related to mosquitoes. The head possesses two compound eyes, short segmented antennae and skin piercing mouthparts. Note the split compound eye (holoptic) possesses two sizes of ommatidia. Black flies are considered a human pest in some areas of the US and Canada. Adult females of certain species are fierce biters, whereas others are strictly a nuisance by their presence around exposed skin areas. Female black flies require a blood meal; males feed mainly on nectar. Also shown is the prothoracic proleg is used to pull or hold threads of silk, as well as to grasp the silk pad it forms on a substrate in moving water. Black flies can transmit filarial worms to humans resulting in a disease called onchocerciasis, which cause blindness. Magnification: x12 when shortest axis printed at 25 millimeters.