Black Fly - Ecology

Ecology

Eggs are laid in running water, and the larvae attach themselves to rocks. Breeding success is highly sensitive to water pollution. The larvae use tiny hooks at the ends of their abdomens to hold on to the substrate, using silk holdfasts and threads to move or hold their place. They have foldable fans surrounding their mouths. The fans expand when feeding, catching passing debris (small organic particles, algae, and bacteria). The larva scrapes the fan's catch into its mouth every few seconds. Black flies depend on lotic habitats to bring food to them. They will pupate under water and then emerge in a bubble of air as flying adults. They are often preyed upon by trout during emergence.

Adult males feed on nectar, while females also feed on blood. Some species in Africa can range as far as 40 mi (64 km) from aquatic breeding sites in search of their blood meals, while other species have more limited ranges.

Different species prefer different host sources for their blood meals, which is sometimes reflected in the common name for the species. They feed in the daytime, preferably when wind speeds are low.

Black flies may be either univoltine or multivoltine, depending on the species. The number of generations a particular pest species has each year tends to correlate with the intensity of human efforts to control those pests.

Work conducted at Portsmouth University by Bob Harris in 1986-1987 indicates Simulium spp. create highly acidic conditions within their midguts. This basic environment provides conditions ideally suited to bacteria that metabolise cellulose. Insects cannot metabolise cellulose independently, but the presence of these bacteria allow cellulose to be metabolised into basic sugars. This provides nutrition to the black fly larvae, as well as the bacteria. This symbiotic relationship indicates a specific adaptation, as fresh-flowing streams could not provide sufficient nutrition to the growing larva in any other way.