Mosquitoes have emerged in swarms throughout northern Illinois within the last few weeks following heavy rainfall, and marking a late arrival for the pesky bloodsuckers, according to entomologists.
A dry May with drought-like conditions delayed these common pests, aptly named “nuisance” mosquitoes, from hatching, said entomologist Patrick Irwin. But after more than 7 inches of rainfall was recorded in June, Chicagoans may have noticed an upswing in mosquitoes — or the itchy red welts that accompany their bites — because they thrive in swampy conditions, he said.
“People thought this was going to be a mosquito-free year, and all of the sudden they all come out at once,” Irwin said. “But the good thing about nuisance mosquitoes is they pretty much all come out at once, but they all die at once too.”
Irwin, the assistant director of the Northwest Mosquito Abatement District, said nuisance mosquitoes breed in stagnant water and lay their eggs near bodies of water or damp soil. Rainfall coats the eggs, allowing them to hatch. However, this year’s drought conditions allowed mosquito eggs to stockpile, and once rain broke the dry spell, heaps of mosquitoes emerged, he said.
“We saw a dramatic increase (in mosquitoes),” he said. “Before the last two weeks, we were well below our historical average for nuisance mosquitoes, but that has definitely gone up.”
Nuisance mosquitoes are more prevalent in forested areas where soil traps moisture. Irwin said his abatement team has collected about 500 mosquitoes per trap per day in forested or wooded areas — much higher than typical averages for July. In residential areas, that number is less than 50, he said.
Similarly, in the North Shore Mosquito Abatement District, researchers have observed about 46 mosquitoes per trap each night, identical to data from May of last year, which surpassed records for the wettest May since meteorologists started keeping records in Chicago in 1871.
The North Shore abatement group’s executive director, Mark Clifton, said it is unusual for the numbers to be this high late into the summer.
“Their first appearance got pushed into July when people are more likely to be wearing shorts or short-sleeved shirts, so they are more exposed and they notice (mosquitoes) more,” he said. “That heightens people’s awareness.”
The good news: Nuisance mosquitoes have a brief five to seven-day life cycle, and just as populations begin to peak, they will quickly die off, Irwin and Clifton said.
“This too shall pass,” Irwin said. “The mosquito numbers will go down — this isn’t something people are going to have to deal with for the rest of summer.”
Nuisance mosquitoes do not pose a health hazard to humans, aside from the welts and an itchy sensation left behind from their bites, Irwin said. However, entomologists anticipate rising levels of another type of mosquito capable of spreading West Nile virus in late July and into August.
The threat of West Nile virus in Cook County was rated “low,” according to a June report by the county Department of Public Health. Only one of 406 mosquito pools tested positive for West Nile as of late June, the report said. The Illinois Department of Health has not reported any cases of West Nile virus in humans this year, according to its surveillance data.
People can best protect themselves from mosquitoes by applying insect repellent approved by the Environmental Protection Agency and dress in long pants and a long-sleeved shirt if outside for long stretches of time, according to public health directives.
Mosquitoes are not strong flyers, so Irwin and Clifton additionally recommended people use box or oscillating fans when sitting outside to keep them at bay. People should also dump out any standing water, like buckets, traps or birdbaths, regularly, they said.
Clifton said the drought may have delayed the emergence of West Nile vectors and may keep the numbers well below the area’s 10-year averages. Irwin added that the mosquitoes capable of transmitting West Nile virus typically feed on birds, but they may turn to humans if they are “looking for a quick meal and it’s opportunistic.”
“There will be more West Nile later in the year, I think that’s probably certain. But I’m hopeful that we avoid a severe West Nile season,” Clifton said.
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Mosquitoes emerge later in summer season - Chicago Tribune
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