Black Fly

• GeneralIts larvae live fixed to the stones of the river; its bite tears the skin and bleeds.
• The larva anchors itself to the substrate with a crown of hooks and filters the water with two folding fans on its head.
• It does not bite like a mosquito, which pierces: it cuts the skin with its mouthparts and laps up the blood that wells out, which is why the wound is more painful and longer-lasting.
• Its proliferation in some Spanish rivers has been linked to flow regulation by dams, which stabilises the conditions its larvae need.
• The larva is a filter feeder: it anchors itself to stone with silk and unfurls head fans to strain particles from the current, which is why it lives only in moving water.
• The pupa encloses itself in a silk cocoon glued to the substrate, and the adult emerges through a slit and rises to the surface inside a bubble of air.
• Only the adult stage is terrestrial; egg, larva and pupa all develop in the water.
• In Europe it is a competent vector of Onchocerca lienalis and O. gutturosa, nematodes that cause bovine onchocerciasis. Human onchocerciasis, river blindness, is transmitted by other species of the genus in Africa and the Americas.
• The larvae are used as bioindicators because they are highly sensitive to degradation of the watercourse.

Habitat & environment

The banks of fast rivers and irrigation channels

Sources consulted: Adler y McCreadie (2019); Science of the Total Environment (2024); Organización Mundial de la Salud

Best time: Spring and early summer, beside fast-flowing rivers