Mosquito season in Santa Cruz County, CA: when it starts and ends

Mosquito months in Santa Cruz County

In a normal year mosquito season in Santa Cruz County, CA starts around January 3 and ends around December 27, about 51 weeks.

What to do in Santa Cruz County, and when

Start tipping out standing water weekly by December 20.
Book any yard treatment for early January, ahead of the August peak.
Repellent can go away after December 27.
1 West Nile case since 2016 (last 2021): you should use repellent at dusk August, more so if over 60.

Santa Cruz County against the rest of CA

Santa Cruz County has the 5th longest season of 58 CA counties, at 358 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 59.5°F.

San Francisco County: all year (365 days, 2 WNV)
Imperial County: January 2 to December 29 (361 days, 7 WNV)
Riverside County: January 10 to December 31 (355 days, 110 WNV)
San Mateo County: December 31 to December 12 (347 days, 5 WNV)

West Nile in Santa Cruz County

From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Santa Cruz County (2 neuroinvasive) across 2 years. The worst was 2021 with 1; the latest was 2021.

More: how the dates are worked out · where mosquitoes never stop.