Mosquito season in Siskiyou County, CA: when it starts and ends
Mosquito months in Siskiyou County
In a normal year mosquito season in Siskiyou County, CA starts around April 16 and ends around October 25, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Siskiyou County, and when
- Start tipping out standing water weekly by April 2.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 25.
- 1 West Nile case since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Siskiyou County against the rest of CA
Siskiyou County has the 50th longest season of 58 CA counties, at 192 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 53.3°F.
- Trinity County: April 11 to October 29 (201 days, 0 WNV)
- El Dorado County: April 15 to October 29 (197 days, 6 WNV)
- Tuolumne County: May 2 to October 30 (181 days, 3 WNV)
- Nevada County: May 8 to October 25 (171 days, 3 WNV)
West Nile in Siskiyou County
From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Siskiyou County (2 neuroinvasive) across 2 years. The worst was 2025 with 1; the latest was 2025.
More: how the dates are worked out · when mosquitoes go away for the winter.