Mosquito season in Sanders County, MT: when it starts and ends
Mosquito months in Sanders County
In a normal year mosquito season in Sanders County, MT starts around June 9 and ends around September 18, about 14 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Sanders County, and when
- Start tipping out standing water weekly by May 26.
- Book any yard treatment for early June, ahead of the July peak.
- Repellent can go away after September 18.
- 1 West Nile case since 2016 (last 2019): you should use repellent at dusk July, more so if over 60.
Sanders County against the rest of MT
Sanders County has the 55th longest season of 56 MT counties, at 101 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 39.3°F.
- Beaverhead County: May 30 to September 14 (107 days, 0 WNV)
- Granite County: May 29 to September 12 (106 days, 0 WNV)
- Gallatin County: June 11 to September 8 (89 days, 1 WNV)
West Nile in Sanders County
From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in Sanders County (2 neuroinvasive) across 3 years. The worst was 2009 with 3; the latest was 2019.
See how the dates are worked out, and when the season starts across the US.