A 'brutally average' year for mosquitoes

If you'll be doing any biking along the Paul Bunyan trail this time of year, or hiking, camping or just sitting in the yard anywhere in the state, you'll be aware of mosquitoes.

Several communities around the region including Grand Forks and Sioux Falls have been spraying for the mosquitoes that carry the West Nile Virus.

In the Twin Cities, Mosquito control officials are saying there have been a couple of recent hatches of mosquitoes.

There's also been an uptick in calls with problem areas, but Mike McLean of the Metropolitan Mosquito Control District says the year has been "brutally average."

McLean spoke with All Things Considered host Tom Crann on Wednesday.

Tom Crann: If it has been an average year, why does it seem this year like there are more mosquitoes?

Mike McLean: The reason is the last few years have been really below average when it comes to mosquito numbers. It's been really quite dry, but this year we're getting really normal precipitation, normal weather fronts that move through, and that really triggers those mosquitoes to start hatching and developing in the water.

Crann: Now you've been logging calls. You've had an uptick from problem areas. Where are those problem areas?

McLean: There's a lot of different places, a lot of pockets of mosquitoes being produced, places like northern Anoka County, western Hennepin County, northern Washington County, in the seven-county metro area, kind of the outlying areas.

We treat a lot of the inner part of the metro area with larvicides that keep the mosquitoes from becoming biting adults. We can't get all the way out to the edge.

Mosquitoes don't respect boundaries, either, so they kind of drift in from some of those outlying areas, too. So there might be some spots in the metro area where people are going to notice mosquitoes maybe for the first time in two or three years, they're going to notice some numbers of mosquitoes.

Crann: We've just had a lot of rain over the past week or so. Do mosquitoes need the standing water to breed?

McLean: We have a lot of different species of mosquitoes in Minnesota, but the ones that really like to go after us really like to lay their eggs in the low spots, the damp places.

When you get a big rainstorm or a big front that moves through, all of those roadside ditches, that low spot in your backyard, they fill up with water, and the water stays there long enough for those mosquitoes to go through their life cycle in the water. And then they emerge as adults and start looking for that blood meal.

It's about a week, week and a half between when the rain stops and when you start to see the mosquitoes.

Crann: Walk us through that life cycle of the mosquito after we have a rainstorm. What can we expect?

McLean: A lot of species like to lay their eggs on the ground. And they wait for those small puddles to become big puddles and to flood their eggs. One of the really remarkable things about mosquitoes is that their eggs are very patient. If we don't get much rainfall, the eggs can stay viable for several years without hatching.

So when you go through several dry years, you really have an excess of mosquito eggs that have built up over the last few years. So when you do get normal rainfall and a lot of precipitation, you can get quite a few mosquitoes hatching, sometimes coming from eggs that have been laying there for two or three years.

Crann: So the bottom line for this summer is [that it's] a normal summer, but we've been lucky the last couple, so we'll be feeling it.

McLean: That's right. It's going to be brutally normal when it comes to the mosquito population this year. And that might seem kind of harsh, considering how good we've had it the last couple years.

(Interview edited by MPR News reporter Madeleine Baran.)

Gallery

Fullscreen SlidePrevious Slide

1 of 1

Next Slide