More than 1550 species of black flies have been identified worldwide, and new species are continually discovered. Black fly larvae develop in running water, from small seepages to large rivers and waterfalls.

In forested areas of the Canadian Shield , they are the most dreaded biting insect, particularly in June and July. In fact, population densities of Simulium venustum can be so high and attack with such veracity that outdoor activity becomes practically impossible during peak abundance.

Biological treatment of larval populations is carried out in rivers and streams, where currents transport the control agent applied upstream.

Quantities of control agent applied are determined according to flow velocities and other parameters such as: water temperature, river morphology, grading of substrate, suspended organic content, vegetation and insect population densities.

Increased robustness and better adaptation to flight contribute to the greater dispersal abilities of black flies and treatment buffer zones are therefore increased to 6-10 kilometres surrounding target areas.