Mosquito season in Treasure County, MT: when it starts and ends

Mosquito months in Treasure County

In a normal year mosquito season in Treasure County, MT starts around April 30 and ends around October 7, about 23 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Treasure County, and when

• Start tipping out standing water weekly by April 16.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 7.
• No West Nile cases since 2016, so bites in Treasure County are a nuisance; check window screens.

Treasure County against the rest of MT

Treasure County has the 2nd longest season of 56 MT counties, at 160 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 46.2°F.

• Dawson County: April 28 to October 8 (163 days, 8 WNV)
• Phillips County: April 30 to October 6 (159 days, 4 WNV)
• Valley County: April 30 to October 5 (158 days, 12 WNV)

West Nile in Treasure County

From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in Treasure County (2 neuroinvasive) across 3 years. The worst was 2003 with 3; the latest was 2013.

Background: when mosquitoes go away for the winter; how the dates are worked out.