Black flies

Simulium spp.

1. Identification

• Common name: Black flies
• Scientific name: Simulium spp.
• Order: Diptera
• Family: Simuliidae

2. Pest description

• Small adults (2–5 mm), robust body and dark color.
• Short, broad wings, with characteristic venation.
• Aquatic, elongated larvae, attach to stones and vegetation in watercourses.
• Pupae also aquatic, enclosed in cocoons fixed to submerged substrates.
• Hematophagous adults, with females that feed on the blood of animals and humans.

3. Main hosts

• Domestic mammals: cattle, sheep, goats, horses.
• Wild animals.
• Humans (as occasional hosts).
• Higher incidence in areas near clean, flowing watercourses.

4. Symptoms and damage

• Intense irritation caused by the bites of the females.
• Allergic reactions, edema and inflammation in the bite area.
• Stress in animals, reduced appetite and productivity.
• Possible transmission of pathogenic agents.
• Animal welfare problems and economic impact on livestock farms.

5. Biological cycle

• Larvae and pupae develop exclusively in flowing water.
• Adults emerge and disperse to feeding areas.
• Females require blood for egg maturation.
• Eggs deposited in the water or on nearby substrates.
• Cycle favored by mild temperatures and stable flows.

6. Monitoring

• Direct observation of adults in livestock areas and near rivers.
• Identification of larvae and pupae in watercourses.
• Recording of periods of greatest activity (spring and early summer).
• Assessment of complaints of bites on animals and workers.
• Environmental monitoring of watercourses conducive to larval development.

7. Management measures

• Cultural: temporary removal of animals from riverbanks, management of grazing schedules and improvement of housing conditions to reduce exposure.
• Biological: use of Bacillus thuringiensis israelensis (Bti) in watercourses, when authorized, for larval control.
• Integrated protection: regular monitoring, application of authorized repellents, physical protection of the animals and integration of environmental measures to reduce local populations.

Bibliographic references

• EPPO Global Database – Simulium spp..
• CABI Invasive Species Compendium – Simulium spp..
• Adler, P. H. et al. (2004). The biology of black flies.
• Crosskey, R. W. et al. (2002). Taxonomy and ecology of Simuliidae.