Black flies are back and biting people and pets in Spokane

Rae Presnell took a break from working in the yard earlier this week. Her husband asked if she had cut herself, because blood was running down her hairline.

Instead, she was among many Spokane residents who have encountered tiny black flies. Presnell considers herself lucky that she only had a few bites.

Black flies, commonly known as “buffalo gnats,” are tiny biting flies found near rivers and streams. The flies bite, but do not spread disease.

They are some of the most irritating biters, said Jeb Owen, associate professor of entomology at Washington State University.

The flies are about 5 to 15 millimeters long, Owen said.

Some species are referred to as “punkies” or “no-see-ums,” according to the Spokane Regional Health District.

The flies’ aquatic larvae develop in fast-moving, clean water, Owen said.

The numbers are dependent on weather. Black fly larvae can spend up to two years on rocks at the bottom of rivers and streams, feeding before going through metamorphosis, Owen said.

Some species develop in cycles, which could explain the large population of black flies in 2017 and this year, if the Spokane species is on a two-year cycle, Owen said.

“They’re just everywhere,” Spokane resident Victoria Shoemaker said.

Shoemaker has a swampy area behind her house, along with a natural stream. Last year, there would be bad days with numerous flies, but there’s no escaping the swarms this year, Shoemaker said.

She can’t keep the flies out of her daughter’s long hair, and the tactic of keeping her hair in a ponytail, which they used last summer, doesn’t seem to be working, Shoemaker said.

The bugs have been biting Shoemaker’s neck and leaving bloody, itchy spots. They also like to bite near ears and eyes.

They’re most active on cloudy, humid days without much wind, said Owen, noting they attack animals, too.

Northwest Counseling Center’s therapy dog, Bentley, had red marks appear all over his stomach and legs on Tuesday. When his caretaker, Terese Medina, called the veterinarian and sent in a photo, she learned the culprits likely were black flies. The vet said they have recently received many similar calls.

Sandy Phillips, technical adviser for the Spokane Regional Health District’s environment program, said she’s seen an uptick in black flies over the past five years.

Black flies are the only flies in which the females need blood for their eggs. They are the only fly to bite for a purpose, Phillips said.

The flies make a slit or cut as they bite and leave their saliva behind, which is what causes an individual’s immune system to respond and cause the itch, Owen said.

Black flies commonly travel 7 to 10 miles, so people don’t have to be close to a body of water to be bitten.

There are a variety of factors that affect black fly populations, such as temperature, the amount of food for larvae in the water supply and precipitation. When those factors intersect, it creates conditions for more black flies, Owen said.