Mosquito season in Dolores County, CO: when it starts and ends

Mosquito months in Dolores County

In a normal year mosquito season in Dolores County, CO starts around May 2 and ends around October 15, about 24 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 Dolores County, and when

• Start tipping out standing water weekly by April 18.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after October 15.
• No West Nile cases since 2016, so bites in Dolores County are a nuisance; check window screens.

Dolores County against the rest of CO

Dolores County has the 22nd longest season of 64 CO counties, at 166 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 48.8°F.

• Huerfano County: April 29 to October 15 (169 days, 2 WNV)
• Yuma County: April 29 to October 15 (169 days, 3 WNV)
• Otero County: April 29 to October 11 (165 days, 12 WNV)
• Douglas County: May 1 to October 12 (164 days, 49 WNV)

West Nile in Dolores County

CDC ArboNET lists no human West Nile cases for Dolores County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 1 of those years.

See how the dates are worked out, and when mosquitoes go away for the winter.