Mosquito season in Carter County, MT: when it starts and ends
Mosquito months in Carter County
In a normal year mosquito season in Carter County, MT starts around May 6 and ends around October 1, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Carter 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 1.
- No West Nile cases since 2016, so bites in Carter County are a nuisance; check window screens.
Carter County against the rest of MT
Carter County has the 15th longest season of 56 MT counties, at 148 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 44.2°F.
- Carbon County: May 7 to October 3 (149 days, 5 WNV)
- Golden Valley County: May 7 to October 3 (149 days, 0 WNV)
- McCone County: May 6 to October 1 (148 days, 7 WNV)
- Blaine County: May 6 to September 30 (147 days, 4 WNV)
West Nile in Carter County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Carter County (0 neuroinvasive) across 1 year. The worst was 2003 with 3; the latest was 2003.
See how the dates are worked out, and when mosquitoes go away for the winter.