On a recent afternoon, Krista Altendahl had planned to sit with friends in the backyard of her home in St. Paul's Highland Park neighborhood.

In minutes, mosquitoes chased them inside.

"Terrible," she said Friday as she tended to her front yard garden. "I've got welts all over. In the middle of the afternoon they swarm, all over. I've lived here my whole life and it's never been this bad. The worst I've ever seen."

Mosquitoes are out in full force across the Twin Cities metro area, and numbers may not drop any time soon. Standing water left behind from near-record snowfall and spring flooding has led to a bumper crop of the buzzing creatures, already surpassing numbers from this time last year with peak season just arriving.

"Stock up on bug spray," advised Alex Carlson, a spokesman for the Metropolitan Mosquito Control District (MMCD), the agency tasked with keeping the population down. Weather will be the biggest factor in determining if the rest of the summer will be tolerable or miserable.

"A 1-inch rain is all we need for significant mosquito hatching," Carlson said.

Altendahl's Highland Park, areas of Chaska and Chanhassen near the Minnesota River and the northern sections of Anoka and Washington counties are seeing the highest concentrations of mosquitoes, Carlson said. But the MMCD is getting flooded with calls and emails about high mosquito activity across the seven-county area. The agency received more than 960 calls and emails between May 22 and 28 — including a record 350 in one day. That compares with just 59 during the same week last year.

Mosquitoes have been thick across northern Minnesota, too, said Lynn Heaney, grounds maintenance manager at Breezy Point Resort on Pelican Lake.

"Employees, people around town, guests — everybody's saying the same thing: that they're really thick this year," she said. "It used to be if you went down by the lake, you might run into them, but now they're everywhere."

Carrie Scarfino, marketing manager at Cragun's Resort in Brainerd, joked that mosquitoes seem to be bigger this year.

"They're almost bird-sized," she said with a laugh. "Hopefully this means that they're done early."

Not likely. Despite a dry second half of May and the first heat wave of the season, the National Weather Service is predicting normal precipitation in June, July and August, meaning mosquito numbers likely won't fall off — and could even increase.

That's because the insects can wait for the right conditions to lay their eggs, and then let water lead to a hatch, said Ann Fallon, a professor in the Department of Entomology at the University of Minnesota.

"The pattern of rain is associated with expansion of the population from year to year," she said.

As irritating as the pests can be to humans, they do have a place in the ecosystem, Fallon said. Other creatures such as dragonflies feast on them, and pathogens can make a living off mosquitoes, she said.

To keep mosquitoes from making a living off us, the MMCD this summer is treating more than 200,000 acres in the metro area. Helicopters have flown over wetlands, dropping pellets containing a bacterium called Bacillus thuringiensis israelensis, or Bti, into the water. MMCD crews also continue to wade through swampy areas to spread the pellets, which have a texture resembling Grape-Nuts cereal. Larvae ingest the pellets, killing them on the spot.

Bti has no discernible impact on any other species, according to the MMCD and the U.S. Environmental Protection Agency.

The agency also uses permethrin to rid areas of adult mosquitoes, primarily in some locations in northern Anoka County and in western Hennepin County. The spray has no measurable health risk to humans and animals, the MMCD said, but is toxic to fish and bees.

Rob Schultz, vice president of Audubon Minnesota, said he's noticed the mosquito uptick and understands the desire to spray for them. He said he's not familiar with the particular active ingredients the MMCD is using, but generally speaking, he said he'd prefer less spraying given the stress insects are already under.

"There are so many birds that really, really depend on insects as part of their food chain," Schultz said. Birds are looking for "islands of opportunity," he said, since farmlands are heavily sprayed for insects.

Elaine Evans, a bumblebee researcher at the U's Bee Lab, also voiced concern about insecticides that target insects broadly.

One, the rusty patched bumblebee, is listed as federally endangered. It's also Minnesota's state bee. Pesticide exposure is one of the barriers to the bumblebee's recovery, she said.

"It's hard to know really what can be safe when there's lots of habitat that they use," Evans said.

According to the MMCD, staff treating for adult mosquitoes are trained to avoid areas friendly to pollinators — including the rusty patched bumblebee, which according to a 2020 agency document is unlikely to be affected by mosquito treatments.

"These treatments are non-residual and applied when mosquitoes are active, but bees are not," the agency's website says. "We live in this area and enjoy the outdoors too, so we take a personal as well as professional interest in protecting the environment."

Fallon, the U entomology professor, said the abundance of mosquitoes should not dissuade people from getting outside. Though there are slim odds of contracting a mosquito-borne illness such as West Nile virus, "most of the time they are doing nothing worse than leaving a bite. It's not enough to prevent you from going outside and enjoying life."

Staff writers Jennifer Bjorhus and Jenny Berg contributed to this report.