Mosquito season in Alameda County, CA: when it starts and ends
Mosquito months in Alameda County
In a normal year mosquito season in Alameda County, CA starts around February 3 and ends around December 6, about 44 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Alameda County, and when
- Start tipping out standing water weekly by January 20.
- Book any yard treatment for early February, ahead of the July peak.
- Repellent can go away after December 6.
- 4 West Nile cases since 2016 (last 2023): you should use repellent at dusk July to August, more so if over 60.
Alameda County against the rest of CA
Alameda County has the 17th longest season of 58 CA counties, at 305 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 60°F.
- Sacramento County: January 29 to December 5 (310 days, 131 WNV)
- Stanislaus County: January 30 to December 5 (310 days, 180 WNV)
- Contra Costa County: February 8 to December 10 (305 days, 35 WNV)
- Sutter County: February 2 to December 3 (304 days, 29 WNV)
West Nile in Alameda County
From 1999 to 2025, CDC ArboNET counted 11 human West Nile cases in Alameda County (9 neuroinvasive) across 10 years. The worst was 2012 with 2; the latest was 2023.
More: how the dates are worked out · reading the West Nile counts.