Weekly Update – September 9th – Mosquitoes Slow Down, but Hot Spots Remain
September 16, 2025
VIDEO: Mosquito Bite Games – Habitat Edition
September 26, 2025
Overall mosquito numbers stayed about the same this week in the penultimate week of surveillance.
The mosquito graph stayed pretty level this week as we head into the end of the 2025 surveillance season.
Every Monday night starting in mid-May through September, the Metropolitan Mosquito Control District sets out a variety of mosquito and black fly traps throughout the district and employs a network of sweep net collections done by employees and volunteers. Any insects collected are brought back to our lab on Tuesday to be identified throughout the week with maps published to show current mosquito and black fly activity.
Today is the first day of autumn and likely the last night of widespread surveillance for mosquitoes in the Twin Cities. During the penultimate week of surveillance last week the overall number of human-biting mosquitoes remained about steady as it had been the previous two weeks. Like last week there are a few hot spots where traps collected high numbers of mosquitoes including along the Minnesota River in Eagan, Burnsville, Shakopee, and Eden Prairie.
Temperatures this week are likely to stay above average and the heavy rain over the weekend offered plenty of opportunity for more breeding. However, with sunset coming earlier in the day, most mosquito species will begin to enter diapause and cease their activity for the season.
Below are maps showing all human-biting mosquitoes (left) and Culex mosquitoes (right) collected in CO2 and Gravid traps on September 15th-16th:
Deer ticks re-emerge in the Fall - Check for Ticks
As we write this the temperature is close to 90 degrees outside in mid-September and it doesn't feel like fall, but cooler temperatures will be coming. When mosquitoes and other insects tend to enter diapause and cease their activity for the year, it's easy to let your guard down. However, it's important to remember that ticks will remain active until temperatures are consistently below freezing, which may not be until November or December.
As you head out for hunting excursions, leaf-peeping, or just enjoying a nice fall hike, be sure to check yourself, your kids, and your pets for ticks when you get home!
Below is an example of the deer tick life cycle from the CDC:
