Megan Hennessy of South Portland slaps at a mosquito Tuesday while gardening at the community garden at Hinckley Park in South Portland. Shawn Patrick Ouellette/Staff Photographer

Megan Hennessy was trying to make quick work of picking produce from her 17-by-8-foot plot in the community garden at Hinckley Park in South Portland.

But as she plucked her first “perfect” zucchini of the season Tuesday evening, along with a fistful of beet greens and a few string beans, she swatted away mosquito after mosquito.

“They’re definitely worse this year,” Hennessy said. “With the water that collects here after it rains, it’s just a breeding ground, really. I can’t stand still or they bite me.”

With plenty of rain in the early summer to help them breed and the arrival of warm and humid weather this week, mosquitoes are out in daunting numbers. And state authorities are urging residents to be on guard.

The Maine Center for Disease Control and Prevention has warned that widespread standing water and increasing heat are ideal conditions for mosquito breeding and biting, and ideal conditions also for the illnesses they transmit, including Eastern Equine Encephalitis virus (EEE), Jamestown Canyon virus and West Nile virus. Because mosquitoes are cold-blooded creatures, they are unable to internally regulate their body temperature and fare best in conditions above 60°F.

Heat, however, isn’t the only piece of this itchy puzzle. According to Jim Dill, a pest management specialist at the University of Maine, weeks of record summer rainfall meant lots of standing water, which is where mosquitoes lay their eggs.

“For some species of mosquitoes, it really only takes about a tablespoon of water, or you can think of a bottle cap full of water, and they can breed mosquito larvae,” Dill said.

Last summer was extremely dry and mosquito populations were reduced as a result. Not so this year.

A mosquito lands on Megan Hennessy’s shoulder as she works in the community garden at Hinckley Park in South Portland on Tuesday. Shawn Patrick Ouellette/Staff Photographer

More than 10 inches of rain have fallen in Portland since June 1, about 5 inches more than normal for the period, according to the National Weather Service. The first three weeks of July brought 5 inches of rain, nearly 3 inches more than normal.

One adult female mosquito can lay 100 eggs in spots where water collects, such as a container, an old tire, or even a puddle. While the eggs can survive months, they can also quickly develop into larvae and produce new adult mosquitoes in as little as eight to 10 days. After finding a blood meal, female mosquitoes will look for wet spots to lay more eggs.

The ideal conditions for breeding and biting also mean more risk of mosquito-borne illnesses.

Mosquitoes are “bridge vectors,” a term scientists use for creatures that carry illnesses between species. With more bridge vectors around, Dill said, the likelihood of disease transmission from animal to human populations goes up.

Each summer, the DHHS collects weekly arboviral surveillance data – data concerning mosquito activity and infection rates –starting in July. Of all the mosquitoes tested last summer, none were found to be carrying the illnesses the DHHS tests for, including EEE and West Nile.

Arboviral surveillance data for 2023 has yet to be published. According to Dill, it’s hard to know what this data will look like because there is “not necessarily a direct correlation” between ideal mosquito conditions and infection rates. This, he says, has more to do with how many infected animals there are in the wild.

Despite an incomplete picture of transmission risks, he’s urging residents to protect themselves and their neighbors from mosquito-borne illness by eliminating sources of standing water where they can breed.

“Anything that will hold water, make sure you empty them at least at least once a week,” he said, noting wheelbarrows, five-gallon buckets, and birdbaths as common culprits.

The Maine CDC recommends that people wear high-coverage clothing, use insect repellant, and minimize time spent outdoors during dusk and dawn to keep the critters at bay.

Hennessy, the South Portland gardener, said she usually wears insect repellent, but she skipped it Tuesday evening.

“I just forgot because I went to the gym before coming here,” she said. “But even with bug spray, you can’t keep ’em away.”