Why does it hurt when a black fly bites?

Black fly

First it was ticks and now it’s black flies. They are out. Even though I haven’t seen one YET, I know it’s true because I read it on Facebook!

Mildred: Yes, they are.

Sarah: Aaaaand it’s blackfly season.

Justin: Black flies showed up.

Black flies may not transmit diseases in the United States like deer ticks and mosquitos do, but they sure can be a nuisance. There are 1500 to 1800 known species in the world. We’ve got about 40 in Maine — four to six bite and they’re all females. Males prefer nectar, but the females go for blood — they need a protein-rich blood meal because they need it to lay eggs. Did you know that black flies will fly up to 10 miles in search of blood!

Why a black fly bite can hurt

It can hurt when a black fly bites because she cuts a hole in the skin so she can feast on a pool of blood. GROSS, I know! She also injects an anti-coagulant to prevent the blood from clotting, which can cause a mild to severe allergic reaction in some people. James Dill, who is the pest management specialist with the University of Maine Cooperative Extension, says, “People who move to Maine often have moderate to severe reactions to black fly bites for their first two to three years in Maine. I find it hard ‘to swallow’ that people have died from inhaling large numbers of black flies!!”

When my daughter Katharine was a toddler, her eye became so swollen from a black fly bite we took her to the local emergency department. A little Benadryl and she was fine but what a sight, my poor baby.

Katharine with black fly bite

I’m told that black flies don’t bite at night and depending on the weather, tend to be more active at certain times of the day — usually between 9 and 11 am and again between 4 and 7 pm or until the sun falls below the horizon. They enjoy humid cloudy days and the calm before a storm. Even when they don’t bite, they are SO ANNOYING. Not fun at all when they fly around your head and try to get into your eyes and nose and ears and mouth. And don’t they love to crawl up sleeves, into waistbands, under socks and up pant legs. In a word, tenacious!

Your best defense is to work outside when they’re least active and dress appropriately.

Black fly emergency preparedness

  • Cover up well
  • Wear light-colored clothing
  • Wear a bandana around your neck
  • Wear a shoulder-length head net
  • Work outside in the early morning or late evening when they are supposed to be less active. (Of course, you have to worry about the mosquitoes at night.)
  • Try using a mosquito repellent, although you may need to keep reapplying.

Dill says repellents work well for black flies, “Including Skin so Soft,” he adds. “Probably the greasiness. For gardeners, a silver or white hard hat covered with baby oil works well for black flies. A light-colored, oil-covered hard hat seems to help attract them and they get stuck in the baby oil.”

As for predicting black flies from year to year, Dill says it really hard to do. “Usually populations are pretty much the same from year to year,” he explains. “They breed in clean running water and the habitat doesn’t change much from year to year. In the 60s and 70s we had black fly season essentially in May and June. The reason was our waters were so polluted that only a couple of species were surviving the pollution. Since we cleaned up our rivers, etc., we have many more species, hence, black fly season from May to Nov!!”

Is there anything good to say about black flies?

Sure, there is!

  • They need to breed in fresh running water, so where there are black flies there is probably unpolluted water nearby.
  • They help pollinate flowers.
  • They are a good source of food for certain birds, bats and dragonflies.
  • They are important in the food chain. Predaceous aquatic insects (Bugs that feed on nuisance insect or plant species) feed on black fly larvae in the water and then fish feed on the larger predators. Fish also feed on black fly larvae.

There is even a Black Fly Breeders Association in Maine

If you are ever in Machias, you have GOT TO stop by the Maine Blackfly Breeders Association. “Headquarters” is at the Woodwind Gallery on Main Street. I’ve been and it was worth the visit. You’ll see wonderful art, along with some wicked fun black fly products the association sells (proceeds go to several local charities).

Black fly t-shirt

Association member Marilyn Dowling got in touch with me a few years ago and explained that while they try to promote positive traits possessed by the black fly, they are sympathetic toward the people and animals who have allergic reactions to the bites. “We even participated in a research project to develop a vaccine,” she wrote. “We sent bags of blackflies, painstakingly sorted from other bugs collected in mosquito magnets, to Spectrum Lab in Arizona. So far I don’t think they’ve found a solution, but these things take time.”

Marilyn also shared a limerick written by Monica Grabin, another loyal member.

A blackfly has babies to feed,
She’s fulfilling a primary need.
It’s not personal though,
It’s just nature, and so,
Stop your complaining and BLEED!

One last thing …

The black fly is the unofficial Maine state bird. At least that’s what Tim Sample claims.

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Diane Atwood

About Diane Atwood

For more than 20 years, Diane Atwood was the health reporter on News Center 6. She's now a regular guest on the Morning Report. Before she became a health reporter, Diane was a radiation therapist/dosimetrist at Maine Medical Center. In 2000, she left the world of reporting to manage marketing and public relations for Mercy Hospital. In 2011, she decided to pursue a longtime dream of being a freelance writer and launched her award-winning blog Catching Health with Diane Atwood.