This spring's relentless rains may be nearing an end, with at least a few days of sun and warm temperatures expected this week, but experts say the effects of the soggy start to the season will likely be with us into the summer.

Entomologists warn that the heavy rainfall and resulting stagnant water around the South Shore could lead to an uptick in the spring mosquito population just as T-shirt weather and warm evening temperatures are arriving. Massachusetts annually sees 51 different species of mosquitoes, the state says, and they breed most quickly when they have access to standing fresh water, such as the puddles that form after frequent rain.

"The water has to be stagnant for seven to 14 days, at least," said Kimberly Foss, the Northeast Massachusetts Mosquito Control and Wetlands Management District's entomologist. "The summer mosquitoes that we have will go lay eggs in that stagnant water, and our spring mosquitoes have eggs that have already been in the soil."

The spring mosquitoes that lay eggs in soil need ample water to be able to hatch, and Foss said the state is coming out of a three-year drought that has kept that from happening.

"But with a wet spring like this, it gives the potential for those eggs in the soil to now be flooded and hatched," she said. "A lot of the hatching has been delayed, and with this rain we're getting now it's been all or nothing. Some places have a lot and some don't have any. We're seeing pockets of them pop up and we're seeing a lot of breeding on the salt marshes as well."

April was a historically rainy month in the Boston area, with 21 days of measurable rainfall, the most days in a month since at least 1872, according to the National Weather Service. May has had more than 2 inches of rain so far, and the forecast predicts showers again Friday.

With all that rain comes flooding and standing water, and Norfolk County Mosquito Control District entomologist Kaitlyn O'Donnell said her office has been taking additional steps to control the mosquito population. The control district always does aerial spraying of bacterial control agents in river areas, she said, but this year it also sprayed floodplain habitats that may become breeding grounds due to overflowing rivers.

"We had a lot of rain and we had some flooding in our river areas, but even so it's always hard to tell what's going to happen," she said.

O'Donnell said the cool temperatures have mostly kept mosquitoes at bay, but that this week's warm weather will likely bring them out for the first time this year. She said she hasn't observed particularly high or low numbers of larva in the field, and she's taking a wait-and-see approach.

The Norfolk County Mosquito Control District will inspect standing water on private property by request. O'Donnell said people can check around their homes themselves for larva breeding in areas such as birdbaths and pool covers.

"Checking areas that usually accumulate standing water is always good," she said. "We definitely recommend wearing bug repellent, and if mosquitoes are really bad, people can avoid being outside during peak biting times, which is around dusk."

The state Department of Public health has not confirmed any cases of West Nile virus this year, but cases of the mosquito-borne virus aren't usually reported until mid-summer. The state had confirmed 25 human cases as of late September last year, including one in Norfolk County.

Reach Mary Whitfill at mwhitfill@patriotledger.com.