Mosquito season in Eau Claire County, WI: when it starts and ends

Mosquito months in Eau Claire County

In a normal year mosquito season in Eau Claire County, WI starts around April 28 and ends around October 8, about 23 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Eau Claire County, and when

• Start tipping out standing water weekly by April 14.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 8.
• 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.

Eau Claire County against the rest of WI

Eau Claire County has the 30th longest season of 72 WI counties, at 163 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 44.2°F.

• Outagamie County: April 29 to October 11 (164 days, 5 WNV)
• Brown County: April 30 to October 12 (164 days, 7 WNV)
• Polk County: April 29 to October 9 (163 days, 0 WNV)
• Waushara County: April 30 to October 10 (163 days, 0 WNV)

West Nile in Eau Claire County

From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in Eau Claire County (5 neuroinvasive) across 4 years. The worst was 2013 with 2; the latest was 2025.

Background: when mosquitoes go away for the winter; how the dates are worked out.