Mosquito season in Spokane County, WA: when it starts and ends

Mosquito months in Spokane County

In a normal year mosquito season in Spokane County, WA starts around April 26 and ends around October 10, about 24 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 Spokane County, and when

• Start tipping out standing water weekly by April 12.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 10.
• 12 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to July, and check WA spray notices.

Spokane County against the rest of WA

Spokane County has the 26th longest season of 39 WA counties, at 167 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 48.4°F.

• Okanogan County: April 24 to October 8 (167 days, 1 WNV)
• Kittitas County: April 25 to October 9 (167 days, 0 WNV)
• Snohomish County: April 29 to October 12 (166 days, 0 WNV)
• Clallam County: April 30 to October 13 (166 days, 1 WNV)

West Nile in Spokane County

From 1999 to 2025, CDC ArboNET counted 14 human West Nile cases in Spokane County (13 neuroinvasive) across 4 years. The worst was 2017 with 8; the latest was 2022.

Background: reading the West Nile counts; how the dates are worked out.