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

Mosquito months in Humboldt County

In a normal year mosquito season in Humboldt County, CA starts around March 27 and ends around November 7, about 32 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Humboldt County, and when

• Start tipping out standing water weekly by March 13.
• Book any yard treatment for late March, ahead of the August peak.
• Repellent can go away after November 7.
• 1 West Nile case since 2016 (last 2018): you should use repellent at dusk August, more so if over 60.

Humboldt County against the rest of CA

Humboldt County has the 43rd longest season of 58 CA counties, at 225 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 54°F.

• San Diego County: March 14 to November 14 (245 days, 36 WNV)
• Inyo County: March 31 to November 12 (226 days, 4 WNV)
• Placer County: April 3 to November 10 (221 days, 35 WNV)
• Mariposa County: April 4 to November 8 (217 days, 0 WNV)

West Nile in Humboldt County

From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Humboldt County (2 neuroinvasive) across 2 years. The worst was 2018 with 1; the latest was 2018.

See how the dates are worked out, and when the season starts across the US.