Mosquito season in Teller County, CO: when it starts and ends
Mosquito months in Teller County
In a normal year mosquito season in Teller County, CO starts around May 27 and ends around September 24, about 17 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Teller County, and when
- Start tipping out standing water weekly by May 13.
- Book any yard treatment for late May, ahead of the July peak.
- Repellent can go away after September 24.
- 6 West Nile cases since 2016 (last 2025): you should use repellent at dusk July, more so if over 60.
Teller County against the rest of CO
Teller County has the 47th longest season of 64 CO counties, at 120 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 40.9°F.
- Boulder County: May 25 to September 25 (123 days, 191 WNV)
- Ouray County: May 26 to September 23 (120 days, 0 WNV)
- Custer County: May 28 to September 20 (115 days, 1 WNV)
- Eagle County: May 31 to September 18 (110 days, 1 WNV)
West Nile in Teller County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Teller County (4 neuroinvasive) across 3 years. The worst was 2023 with 4; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.