Mosquito season in Niobrara County, WY: when it starts and ends
Mosquito months in Niobrara County
In a normal year mosquito season in Niobrara County, WY starts around May 5 and ends around October 5, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Niobrara County, and when
- Start tipping out standing water weekly by April 21.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 5.
- No West Nile cases since 2016, so bites in Niobrara County are a nuisance; check window screens.
Niobrara County against the rest of WY
Niobrara County has the 4th longest season of 23 WY counties, at 153 days against 163 in Big Horn County and 75 in Teton County. Its mean temperature is 46.9°F.
- Campbell County: May 5 to October 7 (155 days, 3 WNV)
- Fremont County: May 4 to October 4 (153 days, 12 WNV)
- Sheridan County: May 8 to October 5 (150 days, 3 WNV)
- Converse County: May 8 to October 1 (146 days, 1 WNV)
West Nile in Niobrara County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Niobrara County (1 neuroinvasive) across 1 year. The worst was 2003 with 4; the latest was 2003.
More: how the dates are worked out · when mosquitoes go away for the winter.