Mosquito season in Blaine County, MT: when it starts and ends
Mosquito months in Blaine County
In a normal year mosquito season in Blaine County, MT starts around May 6 and ends around September 30, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Blaine 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 September 30.
- 4 West Nile cases since 2016 (last 2023): you should use repellent at dusk July, more so if over 60.
Blaine County against the rest of MT
Blaine County has the 17th longest season of 56 MT counties, at 147 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 43.1°F.
- Carter County: May 6 to October 1 (148 days, 0 WNV)
- McCone County: May 6 to October 1 (148 days, 7 WNV)
- Broadwater County: May 7 to October 1 (147 days, 1 WNV)
- Musselshell County: May 7 to October 1 (147 days, 0 WNV)
West Nile in Blaine County
From 1999 to 2025, CDC ArboNET counted 20 human West Nile cases in Blaine County (11 neuroinvasive) across 6 years. The worst was 2007 with 7; the latest was 2023.
See how the dates are worked out, and reading the West Nile counts.