Weekly Update – April 27th – First Round of Larval Treatments Complete

The first round of mosquito treatments by helicopter was completed on Saturday. Monday's rain may bring on more hatching.

After a brief warm-up last week, the Twin Cities is back to mild temperatures this week which will likely mean few adult mosquito species will be active. When temperatures are below 50 degrees, mosquitoes are unable to fly and overnight lows are projected to be in the thirties or forties every day this week.

Right now most mosquitoes are in the larval stage in areas of standing water, waiting for temperatures to warm up before emerging as adults. Last week, staff at the Metropolitan Mosquito Control District checked 2,620 large wetlands and 589 contained mosquito larvae above threshold (about 1 in 5). Most of the species were in the spring Aedes family, which are sometimes called "snowmelt mosquitoes" because they are the first to hatch when the snow melts in early spring.

Last week MMCD staff responded to the active sites by beginning larval treatment for the year. Helicopter treatments began on Wednesday for the first time in 2026, though high winds cut things short on Wednesday afternoon and Thursday. Helicopters returned to the skies Friday to finish all the treatments in all metro counties except for Anoka County which wrapped up on Saturday morning. Altogether, 15,750 acres were treated by helicopter and 219 acres were treated by drone.

Rain on Sunday and Monday of this week could mean more mosquito eggs will be hatching and MMCD staff will be out later in the week to check sites where new larvae may develop.

Adult mosquito surveillance begins in mid-May. Look out for "mosquito imposters."

The Monday night sweep net and trap network to collect adult mosquitoes is expected to begin in mid-May when there will hopefully be warm enough temperatures to start seeing the insects in noticeable numbers. Our weekly updates will begin including graphs and maps after that.

In the meantime, be on the lookout for mosquito imposters like midges, mayflies, and crane flies. This is the time of year when we get reports of people's houses being swarmed by mosquito-like insects and see pictures of an entire garage covered in tiny specks. If there are swarms of bugs, but you're not covered in bites, they probably are not mosquitoes and are most likely one of these other species that emerges in the spring.

Here is an infographic we created several years ago to help differentiate between a mosquito and a midge: