Photomicrograph of Simulium fly (blackfly) showing the bead like antennae. These small flies belonging to the sub-order Nematocera have been the subject of a huge control campaign in parts of west Africa. This has been in an attempt to eradicate the disease onchocerciasis (river blindness). This disease is caused by the filarial worm Onchocerca volvulus. Certain species of blackfly act as vectors for this disease.