Mosquito season in Pitkin County, CO: when it starts and ends
Mosquito months in Pitkin County
In a normal year mosquito season in Pitkin County, CO starts around May 23 and ends around September 25, about 18 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Pitkin County, and when
- Start tipping out standing water weekly by May 9.
- Book any yard treatment for late May, ahead of the July peak.
- Repellent can go away after September 25.
- 1 West Nile case since 2016 (last 2019): you should use repellent at dusk July, more so if over 60.
Pitkin County against the rest of CO
Pitkin County has the 44th longest season of 64 CO counties, at 126 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 40.9°F.
- Routt County: May 20 to September 23 (126 days, 0 WNV)
- Larimer County: May 23 to September 26 (126 days, 225 WNV)
- Boulder County: May 25 to September 25 (123 days, 191 WNV)
- Ouray County: May 26 to September 23 (120 days, 0 WNV)
West Nile in Pitkin County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Pitkin County (0 neuroinvasive) across 1 year. The worst was 2019 with 1; the latest was 2019.
Background: when the season starts across the US; how the dates are worked out.