Mosquito season in Rio Grande County, CO: when it starts and ends
Mosquito months in Rio Grande County
In a normal year mosquito season in Rio Grande County, CO starts around May 19 and ends around September 26, about 19 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Rio Grande County, and when
- Start tipping out standing water weekly by May 5.
- Book any yard treatment for mid May, ahead of the July peak.
- Repellent can go away after September 26.
- 1 West Nile case since 2016 (last 2025): you should use repellent at dusk July, more so if over 60.
Rio Grande County against the rest of CO
Rio Grande County has the 40th longest season of 64 CO counties, at 130 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 40.5°F.
- Saguache County: May 15 to September 28 (137 days, 1 WNV)
- Alamosa County: May 16 to September 27 (134 days, 2 WNV)
- Archuleta County: May 23 to September 30 (130 days, 4 WNV)
- Routt County: May 20 to September 23 (126 days, 0 WNV)
West Nile in Rio Grande County
From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in Rio Grande County (2 neuroinvasive) across 3 years. The worst was 2003 with 3; the latest was 2025.
More: how the dates are worked out · when mosquitoes go away for the winter.