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

Mosquito months in Florence County

In a normal year mosquito season in Florence County, WI starts around May 11 and ends around September 29, about 20 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 Florence County, and when

• Start tipping out standing water weekly by April 27.
• Book any yard treatment for mid May, ahead of the July peak.
• Repellent can go away after September 29.
• No West Nile cases since 2016, so bites in Florence County are a nuisance; check window screens.

Florence County against the rest of WI

Florence County has the 69th longest season of 72 WI counties, at 141 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 40.1°F.

• Marinette County: May 14 to October 3 (142 days, 1 WNV)
• Forest County: May 10 to September 29 (141 days, 0 WNV)
• Oneida County: May 13 to October 1 (141 days, 0 WNV)
• Vilas County: May 12 to September 29 (140 days, 1 WNV)

West Nile in Florence County

CDC ArboNET lists no human West Nile cases for Florence County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 2 of those years.

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