Keep swatting: End may be near for the mosquito baby boom

For 20 years, Merlin Koerner hasn't let anything stop him from unwinding after work by tending to his gardens. But this year, he has met his match: mosquitoes.

Now he spends his evenings inside. "I have to spray myself from head to toe [with bug repellent]," the Morris, Minn., resident said. "These are the worst mosquitoes I've ever seen."

He may be right.

Mosquito counts have been running as much as three times the average this summer and, while some of that can be attributed to all the rain, most of it can be traced to timing.

Remember the winter that refused to end? It's coming back to bite us. Winter pushed into spring and spring pushed into summer, forcing mosquito species that normally would have hatched earlier in the year to wait until things warmed up.

"In a normal year, we have progressive hatches starting early in the spring," said Mike McLean, public information officer for the Metropolitan Mosquito Control District. "Their arrival would be spread out over time. But this year, that was all scrunched together."

Mosquito monitors also have spotted new-to-Minnesota species that are more aggressive than the mosquitoes we've swatted for years. The interlopers — the Asian Tiger and Japanese (also called Asia) Rock Pool mosquitoes — bite more and fly farther looking for dinner.

"They're just like invasive species in lakes," McLean said. "The exotic species can displace the native species."

The warmer temperatures associated with climate change have helped the Asian bugs survive in Minnesota, but their arrival was facilitated by humans. Both species are believed to have gotten here via eggs carried in imported tires.

This summer's multiple heavy rains have contributed to the number of mosquitoes, but only marginally, McLean said. Each storm typically results in another brood of bugs showing up within a week or two. But, so far at least, we're within the normal range for hatches.

"In a typical summer, we'll have six to eight broods," he said. "This year, we're on our sixth brood. Last year, the rain stopped in late July and everything dried out in August. We don't know what's going to happen next."

Because the backlog of hatches has caught up, the worst of the bug baby boom is likely behind us. But those bugs aren't going away. We'll merely to return to the normal levels.

Mosquitoes that have spent the first part of the summer biting birds — where West Nile originates — spend the last half of the summer biting humans, which is how the disease is passed on.

"The typical thinking is that the more bugs that are biting you, the higher your chances are of getting a disease, but that's not true," McLean said. "It's not the hordes of mosquitoes biting you in the spring that you have to worry about. It's that old, scraggly mosquito that's still around in August."

That's why McLean urges people to stay diligent about repelling mosquitoes.

"People tend to put on lots of repellent early in the year when the bugs are heavy but then cut back in August," he said. "Don't do that."

Last year saw a startling surge in the West Nile virus, with 70 confirmed cases in the state, compared with only two in 2011.

If that's the case, there actually might be a silver lining to our long wait for summer this year.