Black Fly Facts

Black Fly Facts

1. A member of the family Similiidae (Diptera).  There are more than 1,800 known species. They are also known as the Buffalo Gnat, turkey gnat, or white socks.

2. The black fly is 1-5mm in length.  They are misnamed because most of them are gray and others are light tan to yellow in color. Adults are typically robust with a characteristic arched or humped prothorax.

3. They gain nourishment by feeding on the blood of other animals.  They are usually small, black or gray, with short legs, and antennae.

4. They lay their eggs in running water, and the larvae attach themselves to rocks. The breeding success is highly sensitive to water pollution.

5. Both sexes feed on the nectar of flowers. Only the females require a blood meal for ovarian development.

6. Although a given species may prefer a particular animal host, most will readily feed upon other host species as well. Black flies attack man and a wide variety of domestic and wild animals and birds; others feed only on cold-blooded animals.  Many important pest species belong to the genus Simulium.

7. They are annoying and buzz around you. They bite and suck your blood. They spread diseases. But what you don’t know there are many good things about them that make our life easier.

8. Females deposit 150-500 creamy-white eggs that darken until they are almost black just prior to hatching.  The eggs are usually are deposited in masses on some convenient object in or near the edge of flowing water. The water can be slow-moving, but most species prefer rapidly flowing water.

9. Breeding may occur in marshy areas.  The time required for hatching varies with the species and may be 3-5 days or as long as 30 days at low temperatures. Larvae most often are found just beneath the surface of rapidly flowing water. Duration of larval development, like the egg stage, varies with species and temperature; it may range from 10-14 days to 7-10 weeks.

10. Some species overwinter as larvae. Winter is usually passed in the egg stage. The last larvae instar spins a reddish-brown, basket-like cocoon in which pupation occurs. These cocoons are attached to slightly submerged objects such as rocks, logs, roots, and other debris.

11. Pupae also possess respiratory filaments with which they remove dissolved oxygen from the water. The pupal period varies from 4-5 days to as long as 3-5 weeks, depending on water temperature and species. Mating usually occurs shortly after the initial flight.

12. Simulium vittatum Zetterstedt - This species is strictly a nuisance attacking horses and cattle, but not humans. It does fly around people’s faces. Breeding occurs in rich productive streams such as polluted (sewage) areas, at beaver dams, etc. It is dark gray to velvety black. (Widely Distributed in North America.)

13. Simlium venustum Say - This species is a nasty biter feared by fishermen and campers. The season extends from May to September with greatest numbers in June and July. They are usually troublesome in late summer. It is recognized by its white-marked tibiae (leg parts).(Widely distributed, especially in New England & Canada.)

14. As a whole, the individual can merely resort to household sprays, aerosols, repellents and screens (60 mesh bolting cloth) to cope with this pest. Some persons indicate that unpainted aluminum “hard hats” attract black flies.

15. They are good indicators of clean water. They need clean water for breeding, if you have a lot of black flies that means you have clean running water. They are pollinators. The males dine only on plant nectar and sap. They get this food in part from our earliest spring wildflowers, and they pollinate as they go. They may be responsible for pollinating some of our blueberries. They are a good food source, bats, dragonflies, flycatchers and swallows are a few of the critters that eat them.