Public Health Vectors and Pests

Black Fly


Common Name Black Fly
Scientific Name Simulium spp
Size Black Fly is 1-5mm
Colour Blackish, brown, grey and yellow
Description Black flies are humped back, biting flies. It is possible that they may have a high population in the spring and early summer, especially in pasture areas along the streams. The immature stages are found in flowing water pupation occurs under the water and the adults float to the surface, ready to flight, feeding and mating.  Black flies only feed during daylight hours.
Habitat The outlets of ponds and lakes are particularly favoured and productive habitats.
  • After mating the female deposits the fertilised eggs on rocks or other substrate in swift water. Larvae emerge from eggs and develop aquatically, feeding on algae and organic matter flowing by the moving water for 7-10 days, then develop into pupae. Adults emerge from pupal case through a slit and float to the surface on a bubble of air.
  • Emerging adults live from 2-3 weeks. They are usually found from spring through fall, with the greatest numbers appearing in the late spring and summer.

Disease Transmitted River blindness
Symptoms There maybe no symptoms manifested by an infected person. One of the three can be noticed from those who show the symptoms: skin rash, eye lesions, and/or subcutaneous bumps under the skin.
Type of Damage
  • Anaemia is possible in areas were there is a high population of black fly.
  • Bites may cause severe reactions such as toxaemia and anaphylactic shock.
  • The files bite by cutting into the skin and feeding on the pool of blood that forms in the hole they make.
Sources / Breeding Males form hovering swarms and in some cases mating occur when females fly into or near the swarms.
In some cases mating occurs accidentally by becoming in contact with the ground or else where.
Prevention The manipulation of water flows can be done so as to kill immature black flies since they require running water. Black fly control is difficult due to the highly migratory adult stage and their extensive breed habitat. Personal protection is the most effective way of preventing black fly bite. Black flies are so attracted to colours, so it is better to wear light colours. Light coloured hats that cover the ears are an important precaution. The repellent DEET (diethyl toluamide) is effective in preventing black fly bites.

Larval control can be practiced in areas were chronic black fly problems occur and breed areas are known. This involves metering of Bacillus thuringiensis namely. Israelensis into flowing water were larvae occurs.

Adult black flies can be controlled with the use of permethrin-based products.
Control Monitoring:
Take the observational walk and search for the areas that are used by the black flies as breeding sites and decide what control measures are necessary.

Install screens on windows and doors to prevent entry and reduce the amount of light around your property.

There are some predators like fish, spiders, bats and birds that feed on biting flies.

Some insects repellents are used, but they should be registered and labelled.

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