Weekly Update – August 5th – West Nile Risk Remains Elevated, Nuisance Mosquitoes Continue Decline
August 11, 2025
Weekly Update – August 19th – Nuisance Mosquitoes and Disease Vectors Decline
August 25, 2025
Mosquito numbers continue to decline this week, in line with the 10-year average.
Human-biting mosquitoes are down again this week as we head into the waning months of summer.
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.
With strange weather all summer long and several years of either excessive rain or drought, "normal" isn't something we've seen very often in terms of mosquito numbers. However, for the past 4 weeks that's exactly where we've been - the number of human biting mosquitoes collected in CO2 traps has been right in line with the 10-year average. After an initial spike in early July, thanks to the highest number of cattail mosquitoes we've seen in five years, mosquito numbers are back down to where they were in early June. Only two traps this week collected more than 300 mosquitoes and most collected fewer than 100.
As mentioned in last week's update, however, the end of the summer is not a time to ignore safety precautions and put away the bug spray. While nuisance mosquitoes like cattail mosquitoes and summer floodwater mosquitoes typically decline at the end of the summer, disease vectors like Culex tarsalis often increase and are often more likely to be carrying West Nile virus. Culex tarsalis mosquito numbers declined from their peak a few weeks ago, but they are still above average and the risk for West Nile virus remains elevated.
According to MMCD Vector Ecologist, Dr. Jordan Mandli, "Our WNV positivity rate in Culex mosquito pools continues to decline. District-wide, the Minimum Infection Rate (MIR) decreased from 17.6 to 15.3, based on 33 positive pools out of 119 total." There continues to be positive pools of mosquitoes in every metro county with the highest activity in recent weeks occurring in Ramsey County, northern Dakota County, and Hennepin County. MMCD continues to monitor the situation and remind everyone to wear insect repellent, empty standing water, and avoid outdoor exposure during peak mosquito feeding times of dawn and dusk.
Below are maps showing all human-biting mosquitoes (left) and Culex mosquitoes (right) collected in CO2 and Gravid traps on August 11th-12th:
Preparations Underway for the Minnesota State Fair!
We are one week away from the best event of the summer - the Minnesota State Fair! Starting on Thursday, August 21st, MMCD will have a booth setup in the Dairy Building at the corner of Judson and Underwood. We will have live mosquito larvae, tattoos, sunglasses, and other giveaways, educational materials, coloring sheets, tick specimens, and much more!
New this year will be our educational tick dog, Babe, who will help fairgoers learn how to check their pets for ticks (pictured below on the left). We've also been busy helping the fairgrounds stay mosquito-free during the time of year when West Nile virus risk is at its highest (pictured below on the right).
While we get ramped up, here are 10 reasons to stop by the MMCD Booth at the Minnesota State Fair!
Babe the Tick Dog will be at the Fair.
Caleb helped do treatments on the fairgrounds.
