Weekly Update – September 9th – Fall Slow-Down
September 9, 2026
The story of 2026 has been "below average" for mosquito numbers.
Fall is When MMCD Winds Down 2026 and Prepares for 2027.
The mosquito season is just about over for the Twin Cities metro as we have reached the point of the year where even heavy rain is not likely to make a noticeable impact in mosquito numbers. Temperatures are starting to shift to below 55 degrees in the evening hours, which means most species of mosquitoes will be incapable of flight and will begin to cease activity for the year. This is likely the penultimate Weekly Buzz for 2026.
Most of the Twin Cities received over an inch of rain this week with more forecasted for this coming weekend. However, we are past the point in the season where staff will be checking for floodwater mosquito larvae. Instead the remaining seasonal staff have shifted focus to a mosquito that won't emerge until next summer - Coquillettidia perturbans or the "cattail mosquito." This unique species hatches in the fall and the larvae will attach to the root of vegetation (often cattails, hence the name) where it will stay below the ice all winter. In the spring these mosquitoes will work their way back to the water's surface and they will eventually emerge from the water all at once around the 4th of July (notice the big spike in the graph above).
Right now staff are out searching wetlands for the presence of cattail mosquito larvae and fall treatments to reduce their numbers next summer are beginning this week. Helicopters will be calibrated on Wednesday and take to the skies Thursday and Friday, weather permitting, to treat areas where the numbers are above threshold. Our helicopter activity page will be updated daily with the list of planned cities.
As for current adult mosquitoes...there aren't too many. Even fewer black flies. Black fly surveillance is now done for the year and mosquito surveillance will continue for at least one more week.
Here are this week's maps:
West Nile Virus Risk Ticks Up Slightly This Week
There are few mosquitoes active, but enough of them are carrying West Nile virus that the Vector Index moved up slightly this week. According to Vector Ecologist, Dr. Jordan Mandli, "Over the past week, we've seen an increase in the number of positive WNV pools. Activity is more geographically widespread overall, although several of the same traps continue to detect WNV consistently, particularly within our Central District."
Last week there were nine more positive samples of West Nile virus in our mosquito pools found in Hennepin (4), Anoka (1), Carver (1), Dakota (1), and Ramsey (3) Counties. Here is the current vector index:
Screenshot from a Beta version of the new Vector Index.
Upcoming Events
With the winding down of mosquito season comes a wrap-up of MMCD public events. As we head into fall we transition from public tabling events to school and community presentations. Here are some of our last public events coming this week:
- Thursday, September 17th- Fall Roundup Parade in North St. Paul
- Saturday, September 19th - Vehicle Fair in Crystal
Would you like MMCD to come to your event or speak to your group? E-mail Alex Carlson!
Video of the Week - Cattail Season
A few years ago we put together a video to explain cattail season at MMCD with Field Operations Supervisor Murray Parent. We are working on an update for 2026 that will be out soon on Facebook and Instagram! In the meantime, check out our original cattail mosquito video:
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Here is your chance to win either the new MMCD Attack Larvae T-Shirt or last year's Laser Loon shirt. Sign up for "The Weekly Buzz" newsletter with Weekly Mosquito updates. Each week there will be a trivia question at the end. Two correct answers each week will get a shirt!
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