Swarms of mosquitoes have blanketed much of the Milwaukee area over the past several days.
The mosquito uptick has affected many outdoor events, including at American Family Field, where mosquito traps were seen in the Milwaukee Brewers dugout during Tuesday night’s game against the Arizona Diamondbacks. Sunbeam Kids, a nonprofit that conducts community-service projects for children and families, cut short an event over the weekend focused on the removal of invasive species from Havenwoods State Forest due to the massive number of mosquitoes in the area.
July through September usually tends to be the worst time for mosquitoes in Southeastern Wisconsin, but the pesky insects’ presence has been especially bothersome as this summer enters its waning days, leaving some residents hunkered inside their homes. Some neighborhoods have seen a more significant increase in mosquitoes, while others remain at their usual seasonal levels.
Chelsea Cook, assistant professor of biological sciences and pest insect expert at Marquette University, is certain that the swarms of mosquitoes are the direct result of the record-breaking rainfall and devastating flooding in Milwaukee and surrounding communities earlier this month.
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On Wednesday, Gov. Tony Evers formally requested a presidential disaster declaration from President Donald Trump in response to the severe storms and flooding, which displaced families and caused significant property damage in Milwaukee, Washington and Waukesha counties. A formal assessment for those counties determined that 1,500 residential structures were destroyed or sustained major damage, with total damage costs estimated at more than $33 million.
Although standing water is often a breeding ground for certain types of mosquitoes, Cook said highly saturated soil is likely more of an issue in the aftermath of the flooding.
“There are specific mosquito species that are associated with flooding, and those are likely the ones we are seeing in massive numbers,” Cook says.
All mosquitoes need water to reproduce, but so-called “floodwater” mosquitoes need much less of it. “Their eggs can hatch in soil that is really wet instead of an actual pool of water,” Cook says. “So, when the soil got super saturated [after the flooding], the eggs hatched.”
She has witnessed it in her own garden. “I can definitely tell they are coming from the soil and not standing water.”
Mosquitoes have four life stages: eggs, larva, pupa and adult. Adults lay eggs, and the cycle continues. Three of the four stages depend on water: eggs, larva and pupa, the last of which is a transformative stage. The mosquito doesn’t eat in this stage but breathes air through the water’s surface. The population of floodwater mosquitoes can explode after heavy rains, when large numbers of eggs laid earlier – in some cases years before – hatch at once.
So are these mosquito bites just highly annoying or are they a cause for concern for diseases like West Nile?
The answer is complicated, Cook says, but the good news, as she explains, is that the floodwater mosquitoes – those that rise from the soil – are likely just an inconvenience. “Only specific species of mosquitoes carry diseases,” she says. “These specific flood mosquitoes don’t seem to carry any diseases that may impact humans or animals that we know of.”
The City of Milwaukee Health Department noted that they have not received any reports of health concerns related to the mosquitoes.
Wisconsin is home to nearly 60 species of mosquitoes, most of which don’t bite humans. However, the aftermath of the floods could be problematic when it comes to mosquito species that rely on standing water, which could increase the chance of West Nile virus, Cook warned. It’s important, she said, to dump standing water in flower pots, buckets, grill covers, bird baths and any other spots, no matter how tiny the level.
“Mosquitoes will reproduce in even the smallest amounts of standing water,” Cook said.
The Wisconsin Department of Health Services confirmed in late July the first West Nile virus activity in the state this year. A human case was reported at that time in a resident of Barron County, with mosquitoes collected from Milwaukee and Lafayette counties having tested positive for the virus. West Nile, which is spread to humans, birds and other animals through the bite of an infected mosquito, poses a risk to everyone, but especially to people who have weakened immune systems, the department noted at that time.
Regardless of whether the mosquitoes buzzing around flood-stricken communities came from the soil or standing water, it’s prudent to prevent bites, Cook said. It’s important to wear bug spray, especially formulas containing DEET or Picaridin, on clothing for those planning to be outside for a while doing yard work, hiking or camping. “Lemon Eucalyptus oil also works decently if you’re looking for something more natural,” Cook adds. There are also repellent systems that seem to work well. A list of tested repellents and traps can be found here.
Over the long term, mosquito populations can be controlled by supporting local ecosystems so that spiders, bats and other animals that eat the insects can thrive, Cook says.
