Wild species 2010: chapter 16

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Insects: Black flies

Simuliidae - Family of insects in the Diptera order. This family includes any small blackish stout-bodied dipterous fly, which sucks the blood of human, mammals, and birds.

Quick facts

• There are over 1250 known species of black flies worldwide, of which 162 have been found in Canada.
• When excluding species ranked as Extinct, Extirpated, Undetermined, Not Assessed, Exotic or Accidental, the majority (91%) of black flies in Canada have Canada General Status Ranks (Canada ranks) of Secure, while 9% have Canada ranks of Sensitive.
• Black flies are found on all continents except Antarctica and are established in all of Canada’s Provinces and Territories.
• Larvae live in flowing water. They strain fine particulate food matter from the water as it flows by using specially formed “fans” on their head.
• Only females bite; males feed mainly on plant nectar and are rarely observed.
• The average life span of a black fly is three weeks.

Background

Black flies are insects belonging to the order Diptera, family Simuliidae. They are small (1-5 mm long) biting flies that are black, or yellowish orange, or brownish grey in colour. There are more than 1250 species known worldwide and 162 have been identified in Canada. Black flies occur almost anywhere that rivers and streams are present as they require moving water for the immature stages of their development. They are found throughout Canada, including the arctic regions.

Females have specialized mouths that include toothed “stylets” which are used for cutting skin when in search of a blood meal. Males do not bite and are rarely observed. Both the male and female depend on nectar from plants for their flight energy whereas females require blood for egg development.

Black flies lay their eggs in moving water. The female will produce 150-600 eggs which are laid directly on substrates in the water (e.g. rocks, vegetation) or dropped in the water as the female flies over (where they settle into the sediment). The larvae will attach to rocks or vegetation in the moving water using specialized hooks. The larvae have foldable “fans” around their mouths which expand to catch passing debris in the water such as bacteria, algae and small organic particles. The larva scrapes the debris caught in the fan into its mouth, repeating this process every couple of seconds. The larvae develop into pupae, an inactive phase of development during which time they do not feed. The pupae develop into adults and will float upward to the surface of the water in a bubble of air that is produced when they emerge from the pupae stage. The adults are ready to fly when they emerge from the water. The adult females will quickly go in search of a blood meal and soon after will lay their eggs. The average life span of a black fly is three weeks.

The bite of black flies causes suffering to humans and wild and domestic animals. The saliva of some species contains a toxin which in large quantities can cause anaphylactic shock and in rare cases, death. Farmers are particularly aware of the potentially devastating impacts of some black fly species. A study in northern Alberta found that an outbreak of the black fly Simulium arcticum in 1971 led to the death of 973 cows and an average weight loss 45 kg per animal in those that survived.

The breeding success of black flies is greatly affected by water pollution. Accordingly, measures to control black fly populations typically involve the dispersal of insecticides upstream of the area of the river or stream that is known to be a productive breeding ground. Similarly, because of the larvae’s susceptibility to both organic and inorganic pollution, black flies are often used in studies related to the environmental monitoring of freshwater contamination.

Status of knowledge

Globally, the Simuliidae are a poorly researched and relatively unknown family. The situation is very much the same in Canada. For example, a research trip in the Northwest Territories in 2006 organized by Doug Currie of the Royal Ontario Museum identified 43 species of black flies, nearly doubling the previous estimate of 22 species for the region. Much survey work remains to be done if we are to confirm which black fly species are established in Canada as well as their abundance and distribution.

The work of Roger W. Crosskey and Theresa M. Howard was until recently considered the taxonomic standard. Since the release of this publication however, taxonomic disagreement among black fly experts is increasing, leading to new challenges in the field of Simuliidae research.

Richness and diversity in Canada

British Columbia is the province with the most number of species of black flies (81 species, figure 16), followed by Alberta (72 species), Quebec (66 species) and Ontario (63 species). The province with lowest number of species of black flies is Nova Scotia (13 species).

Species spotlight - Simulium giganteum

Simulium giganteum is known in North America from just one specimen that was collected near Arviat, Nunavut. It is difficult to determine if this and other “rare” black fly species are indeed “rare” owing to the great challenges of conducting comprehensive surveys in Canada’s subarctic and arctic regions. Immense areas of land coupled with a lack of roads leads to high survey costs. Much research is necessary before we can confirm the distribution and abundance of Simulium giganteum. This species has a general status Canada rank of Undetermined.

Results of general status assessment

Most species of black flies had a Canada rank of Secure (72%, 116 species, figure 16 and table 23). However, 12 species were ranked as Sensitive (7%) and 34 species were ranked as Undetermined (21%).

Threats to Canadian black flies

The biggest known threat to black fly populations is water pollution caused by industrial and agricultural activity. Organic and inorganic chemicals released into streams and rivers can harm and/or destroy black fly larvae downstream. These pollutants include pesticides, fertilizers and effluent from mining and pulp and paper operations.

Conclusion

This report presents the first general status assessment of Canada’s black fly species. Though important progress has been made in the field of Simuliidae research, much survey work, particularly in Canada’s northern regions, is needed in order to confirm the richness and diversity of Canada’s black flies.

Further information

Adler, P. H., Currie, D. C. and Wood, D. M. 2004. The black flies (Simuliidae) of North America. Cornell University Press: 960 pp.

Blackflies Info. 2009. Taxonomy and Systematics of Simuliidae. (Accessed March 8, 2010).

Currie, D. C. and Adler, P. H. 2000. Update on a survey of the black flies (Diptera: Simuliidae) from the Northwest Territories and Nunavut Project. Arctic Insect News 11: 6-9.

The Canadian Encyclopedia Online. 2010. Black flies. (Accessed March 4, 2010).

References

Biological Survey of Canada. 2006. A preliminary assessment of Subarctic black fly diversity (Diptera: Simuliidae) in Norman Wells and environs, Northwest Territories. Newsletter of the Biological Survey of Canada (Terrestrial Arthropods) 25. (Accessed March 8, 2010).

Crosskey, R. W. and Howard, T. M. 2004. A revised taxonomic and geographical inventory of world blackflies (Diptera: simuliidae). Department of Entomology, The Natural History Museum, Cromwell Road, London.

Currie, D. C. and Adler, P. H. 2008. Global diversity of black flies (Diptera: Simuliidae) in freshwater. Hydrobiologia 595: 469-475. (Accessed March 8, 2010).

Fauna Europaea. 2009. Simulium (Schoenbauria) giganteum. (Accessed March 9, 2010).

The Red Path Museum. 2010. The Canadian Biodiversity Website. Insects – Black flies / Family Simuliidae. (Accessed March 8, 2010).