Mosquito season in Ravalli County, MT: when it starts and ends
Mosquito months in Ravalli County
In a normal year mosquito season in Ravalli County, MT starts around May 22 and ends around September 24, about 18 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Ravalli County, and when
- Start tipping out standing water weekly by May 8.
- Book any yard treatment for late May, ahead of the July peak.
- Repellent can go away after September 24.
- 1 West Nile case since 2016 (last 2018): you should use repellent at dusk July, more so if over 60.
Ravalli County against the rest of MT
Ravalli County has the 43rd longest season of 56 MT counties, at 125 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 41.6°F.
- Madison County: May 22 to September 26 (127 days, 1 WNV)
- Meagher County: May 22 to September 25 (126 days, 0 WNV)
- Lincoln County: May 16 to September 15 (122 days, 0 WNV)
- Jefferson County: May 22 to September 21 (122 days, 1 WNV)
West Nile in Ravalli County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Ravalli County (2 neuroinvasive) across 4 years. The worst was 2018 with 1; the latest was 2018.
See how the dates are worked out, and when mosquitoes go away for the winter.