Mosquito season in Big Horn County, WY: when it starts and ends
Mosquito months in Big Horn County
In a normal year mosquito season in Big Horn County, WY starts around April 27 and ends around October 6, about 23 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Big Horn County, and when
- Start tipping out standing water weekly by April 13.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 6.
- 1 West Nile case since 2016 (last 2017): you should use repellent at dusk July to August, more so if over 60.
Big Horn County against the rest of WY
Big Horn County has the 1st longest season of 23 WY counties, at 163 days against 163 in Big Horn County and 75 in Teton County. Its mean temperature is 45.6°F.
- Campbell County: May 5 to October 7 (155 days, 3 WNV)
- Fremont County: May 4 to October 4 (153 days, 12 WNV)
West Nile in Big Horn County
From 1999 to 2025, CDC ArboNET counted 10 human West Nile cases in Big Horn County (3 neuroinvasive) across 5 years. The worst was 2003 with 4; the latest was 2017.
More: how the dates are worked out · when mosquitoes go away for the winter.