Mosquito season in Nevada County, CA: when it starts and ends
Mosquito months in Nevada County
In a normal year mosquito season in Nevada County, CA starts around May 8 and ends around October 25, about 24 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Nevada County, and when
- Start tipping out standing water weekly by April 24.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 25.
- 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk July, more so if over 60.
Nevada County against the rest of CA
Nevada County has the 52nd longest season of 58 CA counties, at 171 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 50.3°F.
- Siskiyou County: April 16 to October 25 (192 days, 1 WNV)
- Tuolumne County: May 2 to October 30 (181 days, 3 WNV)
- Modoc County: May 11 to September 25 (137 days, 0 WNV)
- Plumas County: May 17 to October 1 (137 days, 0 WNV)
West Nile in Nevada County
From 1999 to 2025, CDC ArboNET counted 10 human West Nile cases in Nevada County (5 neuroinvasive) across 6 years. The worst was 2005 with 4; the latest was 2025.
More: how the dates are worked out · when the season starts across the US.