Mosquito season in Lewis County, WA: when it starts and ends
Mosquito months in Lewis County
In a normal year mosquito season in Lewis County, WA starts around April 21 and ends around October 18, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Lewis County, and when
- Start tipping out standing water weekly by April 7.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 18.
- No West Nile cases since 2016, so bites in Lewis County are a nuisance; check window screens.
Lewis County against the rest of WA
Lewis County has the 14th longest season of 39 WA counties, at 181 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 50.8°F.
- Columbia County: April 18 to October 16 (182 days, 0 WNV)
- Clark County: April 21 to October 20 (182 days, 2 WNV)
- Pacific County: April 24 to October 20 (179 days, 0 WNV)
- Thurston County: April 23 to October 18 (178 days, 1 WNV)
West Nile in Lewis County
CDC ArboNET lists no human West Nile cases for Lewis County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 2 of those years.
Background: when mosquitoes go away for the winter; how the dates are worked out.