Mosquito season in Costilla County, CO: when it starts and ends
Mosquito months in Costilla County
In a normal year mosquito season in Costilla County, CO starts around May 13 and ends around September 30, about 20 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Costilla County, and when
- Start tipping out standing water weekly by April 29.
- Book any yard treatment for mid May, ahead of the July peak.
- Repellent can go away after September 30.
- 1 West Nile case since 2016 (last 2016): you should use repellent at dusk July, more so if over 60.
Costilla County against the rest of CO
Costilla County has the 36th longest season of 64 CO counties, at 140 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 44°F.
- Rio Blanco County: May 12 to October 1 (142 days, 4 WNV)
- Jefferson County: May 13 to October 2 (142 days, 132 WNV)
- Conejos County: May 13 to September 29 (139 days, 0 WNV)
- Saguache County: May 15 to September 28 (137 days, 1 WNV)
West Nile in Costilla County
From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Costilla County (2 neuroinvasive) across 2 years. The worst was 2016 with 1; the latest was 2016.
More: how the dates are worked out · when the season starts across the US.