Mosquito season in Sullivan County, NH: when it starts and ends
Mosquito months in Sullivan County
In a normal year mosquito season in Sullivan County, NH starts around May 5 and ends around October 7, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Sullivan County, and when
- Start tipping out standing water weekly by April 21.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 7.
- No West Nile cases since 2016, so bites in Sullivan County are a nuisance; check window screens.
Sullivan County against the rest of NH
Sullivan County has the 7th longest season of 10 NH counties, at 156 days against 170 in Strafford County and 141 in Coos County. Its mean temperature is 44.4°F.
- Cheshire County: May 2 to October 10 (161 days, 1 WNV)
- Merrimack County: May 3 to October 9 (159 days, 1 WNV)
- 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 Sullivan County
CDC ArboNET lists no human West Nile cases for Sullivan County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 1 of those years.
More: how the dates are worked out · when mosquitoes go away for the winter.