Mosquito season in Missoula County, MT: when it starts and ends
Mosquito months in Missoula County
In a normal year mosquito season in Missoula County, MT starts around May 23 and ends around September 22, about 17 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Missoula County, and when
- Start tipping out standing water weekly by May 9.
- Book any yard treatment for late May, ahead of the July peak.
- Repellent can go away after September 22.
- No West Nile cases since 2016, so bites in Missoula County are a nuisance; check window screens.
Missoula County against the rest of MT
Missoula County has the 46th longest season of 56 MT counties, at 122 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 43.3°F.
- Lincoln County: May 16 to September 15 (122 days, 0 WNV)
- Jefferson County: May 22 to September 21 (122 days, 1 WNV)
- Deer Lodge County: May 25 to September 23 (121 days, 0 WNV)
- Daniels County: May 19 to September 16 (120 days, 0 WNV)
West Nile in Missoula County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Missoula County (1 neuroinvasive) across 2 years. The worst was 2006 with 2; the latest was 2007.
Background: when mosquitoes go away for the winter; how the dates are worked out.