Mosquito season in Laramie County, WY: when it starts and ends

Mosquito months in Laramie County

In a normal year mosquito season in Laramie County, WY starts around May 9 and ends around October 1, about 21 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 Laramie County, and when

• Start tipping out standing water weekly by April 25.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after October 1.
• 11 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July, and check WY spray notices.

Laramie County against the rest of WY

Laramie County has the 9th longest season of 23 WY counties, at 145 days against 163 in Big Horn County and 75 in Teton County. Its mean temperature is 46.7°F.

• Weston County: May 9 to October 2 (146 days, 0 WNV)
• Goshen County: May 9 to October 1 (145 days, 15 WNV)
• Platte County: May 9 to October 1 (145 days, 6 WNV)
• Sweetwater County: May 12 to October 2 (144 days, 0 WNV)

West Nile in Laramie County

From 1999 to 2025, CDC ArboNET counted 52 human West Nile cases in Laramie County (16 neuroinvasive) across 12 years. The worst was 2003 with 29; the latest was 2025.

Background: reading the West Nile counts; how the dates are worked out.