Fortunately, though, the rest of the summer might not be so bad. A Madison entomologist says early indications suggest this season may end up being no worse than usual, and that standard precautions might be enough to keep the pesky critters away.
Some hardware stores up north have been having trouble keeping bug repellent on the shelves, and some residents say they can't remember a summer with such abundant swarms.
PJ Liesch, who studies insects at the University of Wisconsin-Madison, was in northern Wisconsin over Memorial Day weekend. That Friday and Saturday were pleasantly mosquito-free, but hordes of the blood-sucking pests appeared as if out of nowhere that Sunday, he said.
"It was like someone flipped the switch," Liesch said. "They all seemed to come out at the same time."
Their sudden appearance might lead people to fear that this season will be unusually bad, but conditions point to a generally average mosquito season, Liesch said.
That's good news to Ed Hammer, who runs Wisconsin River Outfitters in Lake Tomahawk. For the last week or so, the swarms have been so thick that he turned away at least half a dozen customers who wanted to paddle down the Wisconsin River.
"If people don't have a good time, they're not going to want to come back," he explained.
How bad is the problem? Hammer said he pulled into his driveway recently, and as soon as he shut off his truck he could hear the low hum of their buzzing outside. The 64-year-old, who lived in Michigan's Upper Peninsula for 30 years, said it's one of the worst mosquito seasons he can remember.
There are more than 50 species of mosquitoes in Wisconsin, and there are variations in when, where and how frequently they lay their eggs. Most lay them on or near water, and the eggs hatch when temperatures rise into the 70s and 80s.
Temperatures usually rise gradually, and hatching occurs accordingly. But parts of northern Wisconsin went from having snow on the ground to 80-degree temperatures in the unusually short span of three to four weeks, which likely explains the flurry of mosquito hatchings.
If temperatures remain high through the summer and moisture is abundant, species that lay eggs several times per season can produce several hatches. In another bit of good news for mosquito-haters, though, this summer is expected to be a bit cooler than average, which could limit the number of hatchings.
Bob McMahon, a meteorologist with the National Weather Service, said long-term forecasts predict that there is a 40 percent chance that temperatures from June through August will be below average. The models don't say how far below average, but every bit of coolness helps, he said.
Even though the long-range models also predict more rain than usual, the cooler temperatures might help limit mosquito numbers, he said.
Liesch advises residents to avoid mosquitoes by using the same tried-and-true methods that work every year: Wear long-sleeved shirts and long pants, avoid being outside around dawn and dusk when mosquitoes are more active, and use repellent that contains DEET.