Updated: 1:35 p.m. | Posted: 11:54 a.m.
Faith Perrizo was reading a book on her deck in Maplewood earlier this week and the biting gnats drove her right back inside.
“These aren’t the little tiny ones,” she said. “They’re probably twice, maybe three times the size of a regular gnat. They’re pretty big.” Their bites have proven particularly itchy, she added.
Experts say the black flies aren’t new, but they’ve found new footing in the Twin Cities this year — although northern Minnesota is familiar with the Simulium tuberosum variety of black fly.
“The populations of these in certain streams — Minnehaha Creek, maybe Vermillion, maybe Nine Mile Creek — are really growing,” said John Walz, black fly program coordinator for the Metropolitan Mosquito Control District.
“So our job is to sample these streams, get an idea of what the populations are, see why maybe this is happening.”
Walz said the surge in gnats may be simply a battle for space. The larvae grow in streams and rivers, attaching to rocks and sticks and the like, and Walz suspects the success his agency has had fighting other gnats may have given the black flies more opportunities to expand their range.
The mosquito control agency has been treating running water for black flies since 1984, and has permits from the Department of Natural Resources to battle four different species. Walz thinks the surge in new bugs may simply be that their competitors are being held at bay by treatment efforts — although flooding last year thwarted some of those efforts and brought another batch of nasty gnats last spring.
Walz, by the way, has expertise in the matter: he’s president of the North American Black Fly Association, a trade group of researchers insect control agencies. He said he’s in touch with others around the world, asking what might be behind the recent gnat surge.
Folks who spend time outside in Minnesota — at least some of them — can attest to the pesky nature of the new crop of gnats. Kids and others have lines of welts at their necklines from the bites.
Walz said the flies stay in trees and look for opportunities to swoop down and bite. “They’re a lot more irritating than a mosquito,” he said. “They slice open skin and let blood pool for a meal.”
Black flies are not disease carriers in the U.S., according to the MMCD. They are only at risk of spreading disease in some parts of Africa. In our part of the world, they are mostly just annoying pests.
There is also no evidence that blackfies, mosquitoes, or ticks transmit COVID-19 according to the CDC and WHO.
Walz is consulting with the DNR about what to do about the flies. Once the insects are adults and flying, he said there isn’t a good way to get at them high in tree canopies. And it isn’t clear if the flies will be gone once this batch dies off or if there will be more generations — and possibly the opportunity to get a DNR permit to go after the larvae in rivers and streams.
In the meantime, you’ll have to muddle through and try not to attract the flies’ attention.
“Light-colored clothing, no scents or perfumes on you, that helps a little bit,” he said. For some reason, the flies seem to like some people more than others. “It’s a chemistry thing,” he said. “Or a scent thing.” He said DEET, the traditional insect repellent, works. Sort of.
Perrizo’s advice after the swarm found her: get some netting. Either a hat or something that you can wrap around your head to keep the bugs off.
Correction (May 14, 2020): A previous version of this story misspelled Faith Perrizo’s last name.