Black Flies


These pests are outside the authority of the Vector Control Program. We offer educational information but do not control or regulate these pests. 

Black Fly Facts

Black flies, also known as buffalo gnats, are small humpbacked flies with many different colors.  Their colors include shades of black, brown, gray and yellow. Their abdomens often have dark, spotted areas on the middle segment.  Wings are unmarked and spear-shaped with all major support veins on the edge.  There are more then 1,200 different types of black flies.

Black flies feed on flower nectar and animals. Certain types of black flies prefer a specific host, but most will prey on a range of hosts.  Black flies attack humans, and a number of domestic and wild animals.  Some feed on cold-blooded animals as well.

Black Flies And Livestock
In the United States, as well as in other countries, livestock deaths along river basins occur from black fly attacks.  Large numbers of cattle, horses, mules, hogs, turkeys, chickens, sheep, dogs and cats have been killed. Death normally occurs due to a large number of bites, or because of an allergic reaction. 
Black Flies Around a Cow's Eye

The Black Fly Life Cycle

Eggs: Female black flies deposit 150 to 500 small, shiny, creamy-white eggs on submerged objects in streams such as plants, rocks, twigs, or leaves.  Some simply scatter the eggs over the water's surface. When the water temperature is around 70o F, the eggs hatch in 4 to 5 days.

Larvae: Upon hatching, the larvae attach themselves to submerged objects, where they will most likely stay until they are fully developed.  This normally lasts one to several weeks.

Pupae: Next they turn into pupae which attach themselves  to the underside of objects that stick out of the water and continue to get oxygen. They can take anywhere from several days to weeks depending on the fly and water temperature to move to the next stage.

Adults: Adults leave the pupal case and rise to the water's surface.  They unfold their wings and fly away.  Mating usually happens shortly after the first flight.  The complete life cycle from egg to adult can last from 6 to 15 weeks.

Where You Find Them 
Black flies can normally be found in swarms in the late spring and early summer where streams provide enough running water for their development.   

Black Fly Bites
Most females are bloodsuckers and are often vicious.  There are some types of flies that can not break through the skin of vertebrates.  The females need blood for their ovarian development.  The males, on the other hand, do not bite humans or animals.

Black Fly Mating 
Males form hovering swarms and in some cases mating may occur when females fly into or near the swarms.  At other times it appears that mating occurs by accidental contact on the ground or elsewhere.

Black Fly Control   
Controlling black flies is difficult due to the number and extent of breeding sources.  Approved insecticides have been applied to rivers, stream and canals where breeding occurs.  Pupae are not destroyed however and insecticides that could kill them have bad effects on natural areas.  Fly repellents applied to the chest, stomach and ears are somewhat effective, but need daily use.  When outdoors around areas where black flies breed, it is best to wear long-sleeved pants and shirts.


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