How To Keep Black Flies Away, According To Experts

If you’ve ever been swarmed by tiny, annoying flies while golfing, fishing, or even when gardening, you’re probably familiar with black flies. “Black flies are stout-bodied flies which are closely related to mosquitoes,” says entomologist Elmer Gray, director of the University of Georgia Black Fly Research and Resource Center, the only black fly colony in the world. “Their intense swarming activity around your head and face creates a significant nuisance if you’re trying to enjoy the outdoors.”

Identifying Black Flies

Black flies (Diptera: Simuliidae) are about 2 to 4 millimeters in size with humped backs and a shiny black, tan, or greenish body. The larval stage develops in the flowing water of rivers and streams before they emerge as adults, says Elmer. Depending on the species and where you live, there may be one or more generations produced each year, typically in spring and sometimes in early summer and fall.

Black flies can travel for miles and can be found anywhere there are running streams or rivers nearby, even in urban areas. They are attracted to hosts by smell, heat, and sight. Female flies feed on nectar but require a blood meal to lay eggs, while males feed only on nectar. Many species that bite people are found in northern parts of the country, while species found in the South often are more of a swarming nuisance, says Gray.  

You may not see many of these pests in some years; in other years, it’s nearly impossible to enjoy time outdoors. “Outbreaks of these flies often occur after heavy rainfall events or wet winters,” says Sonja Swiger, PhD, professor and extension entomologist with Texas A & M University. “They never go away but will expand their territory if conditions are right.” 

Fortunately, black flies do not transmit disease to people in the North America. However, in other parts of the world, such as Africa, black flies can transmit parasitic worms that cause onchocerciasis, a disease that leads to blindness.

Read on to learn how to keep these nuisance pests away from you and your family:

Do Black Flies Bite Animals?

Absolutely. These insects can be a threat to domestic animals, feeding on cattle, horses, sheep, goats, poultry, and dogs, says Swiger. A huge number of bites can be toxic to cattle. Also, poultry can die from blood loss, toxins from the insect’s saliva, or from being suffocated by flies lodged in the animal’s airway.

Black flies also impact wildlife, driving birds such as loons, whooping cranes, and snowy owls off their nests, which can disrupt breeding, says Gray.

How Long Do Black Fly Bites Last?

The female black fly uses her mouth parts to snip the skin, often on the head, ears, neck, or forehead, though they’ll bite any exposed area, says Gray. An anti-coagulant is injected, which causes the blood to run.

These bites can be painful and itchy and last days to weeks. Some people and animals may have swelling or severe reactions. If you have an unusual response, contact your doctor immediately.

How To Keep Black Flies Away from You

Fortunately, black flies only live a few weeks and activity drops when temperatures rise into the 80s. Some municipalities treat rivers and streams to suppress larval development. But your best defense is taking a few steps to limit your personal exposure, says Gray and Swiger.

• Use repellants on exposed skin if you must be outdoors. Oil of lemon eucalyptus, picaridin and higher concentrations of DEET seem to be most effective, says Gray. Natural repellants, such as essential oils, are not effective, nor are ultrasonic devices.
• Wear loose-fitting, light-colored long sleeves, long pants, and a hat with fine netting for outdoor activities during peak season. Clothing that has been treated with permethrin also provides some protection, says Gray.
• Black flies prefer to bite outdoors, so go indoors and bring pets inside if there’s a swarm, says Swiger.
• If you have chickens, keep them housed inside the coop during outbreaks, says Swiger. Black flies rarely enter structures.
• Pay attention to weather conditions that are ideal for black flies to emerge, such as after significant rainfall or a wet spring or fall. This awareness can help you take precautions for your animals, such as keeping horses stabled, says Swiger.
• Keep pets away from streams during peak black fly season, and make sure they’re up-to-date on topical repellants for biting insects, says Swiger. Ask your vet for product recommendations.