Cool air averted flood-borne mosquito swarm

First the bad news.

Mosquitoes hatched by last month's flooding in the Northwest and West suburbs should be reaching adulthood and beginning to bite this weekend.

But the good news is that the cool temperatures, strong winds and below-average rainfall that followed the heavy storm of April 17 and 18 counteracted the potentially ideal conditions this spring brood might have enjoyed.

“We dodged a bullet there,” said Mike Szyska, director of the Northwest Mosquito Abatement District headquartered in Wheeling. “The numbers that we're finding are below normal for this part of the season. But if we get more rainfall, things are going to change.”

And rain is in the forecast for Saturday and early next week.

While the summer ahead is still up for grabs, the weather helped us as much as it might have hurt with last month's flooding, Szyska said. In fact, the delicate balance among all the factors involved created a lingering dilemma for the mosquito abatement district.

Rainfall in the Northwest suburbs was 8.68 inches during April — 5.3 inches above normal. But during the same time period, average temperatures were 2 degrees below normal.

Cool weather slows the development of the nuisance mosquitoes that are hatched by floodwater, Szyska said. The species lays its eggs in the soil, in anticipation of water to come.

University of Illinois Extension Entomologist Phil Nixon said these eggs can be viable for two years as they wait for floodwaters to reach them. They normally start to arrive around Memorial Day, but last month's floods are bringing them out a little earlier.

“Most of the time, the control of these mosquitoes is done by going after the larvae,” Nixon said.

One thing not to worry about from these mosquitoes, though, is disease.

“For the most part, they're heavy biters that will drive you inside your house,” Nixon said.

They're different from the culex mosquitoes that typically arrive and thrive during the hotter months of the summer when they lay their eggs in stagnant water. It is culex mosquitoes — not those reaching adulthood this weekend — that are responsible for spreading West Nile virus, Szyska said.

While both varieties do bite human beings, culex mosquitoes largely feed on birds — which is why dead birds are often an early indicator of the presence of West Nile.

Culex mosquitoes have a more consistent annual life cycle, whereas every bout of flooding can spawn a new generation of nuisance mosquitoes. Multiple generations are capable of coexisting in a single season, Szyska said.

The slowed development of this spring's batch also was affected by persistent heavy winds that cause water to evaporate more quickly.

“If the water disappears, it's irrelevant,” Szyska said.

The end result is that the numbers of mosquitoes beginning to fly this weekend are lower than normal. Quite the opposite would have been true if this spring's flood levels had been combined with last spring's warm temperatures, Szyska said.

The culex mosquitoes to come may still be able to use some remaining pockets of April floodwater this summer, but by that time it seems like those pockets will be small and rare. During the first half of May, rainfall was an inch below normal levels, Szyska said.

But even with Mother Nature and human agencies like Szyska's conspiring against them, mosquitoes are going to be a part of every spring and summer.

“They've evolved and they're perfect at surviving,” Szyska said.