Mosquito season in Washington County, ME: when it starts and ends

Mosquito months in Washington County

In a normal year mosquito season in Washington County, ME starts around May 6 and ends around October 11, 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 Washington County, and when

• Start tipping out standing water weekly by April 22.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after October 11.
• No West Nile cases since 2016, so bites in Washington County are a nuisance; check window screens.

Washington County against the rest of ME

Washington County has the 6th longest season of 16 ME counties, at 158 days against 164 in Kennebec County and 133 in Franklin County. Its mean temperature is 44.7°F.

• Cumberland County: May 3 to October 13 (163 days, 4 WNV)
• Knox County: May 8 to October 15 (160 days, 0 WNV)
• York County: May 3 to October 7 (157 days, 0 WNV)
• Sagadahoc County: May 8 to October 11 (156 days, 0 WNV)

West Nile in Washington County

CDC ArboNET lists no human West Nile cases for Washington County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 1 of those years.

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