Mosquito season in Coos County, NH: when it starts and ends

Mosquito months in Coos County

In a normal year mosquito season in Coos County, NH starts around May 12 and ends around September 30, 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 Coos County, and when

• Start tipping out standing water weekly by April 28.
• Book any yard treatment for mid May, ahead of the July peak.
• Repellent can go away after September 30.
• No West Nile cases since 2016, so bites in Coos County are a nuisance; check window screens.

Coos County against the rest of NH

Coos County has the 10th longest season of 10 NH counties, at 141 days against 170 in Strafford County and 141 in Coos County. Its mean temperature is 40.5°F.

• Carroll County: May 7 to October 3 (150 days, 0 WNV)
• Grafton County: May 8 to October 4 (149 days, 0 WNV)

West Nile in Coos County

CDC ArboNET lists no human West Nile cases for Coos County from 1999 to 2025.

See how the dates are worked out, and when mosquitoes go away for the winter.