Mosquito season in Mason County, WA: when it starts and ends
Mosquito months in Mason County
In a normal year mosquito season in Mason County, WA starts around April 20 and ends around October 20, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Mason County, and when
- Start tipping out standing water weekly by April 6.
- Book any yard treatment for mid April, ahead of the August peak.
- Repellent can go away after October 20.
- No West Nile cases since 2016, so bites in Mason County are a nuisance; check window screens.
Mason County against the rest of WA
Mason County has the 11th longest season of 39 WA counties, at 183 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 51.3°F.
- Island County: April 17 to October 20 (186 days, 0 WNV)
- San Juan County: April 20 to October 22 (185 days, 0 WNV)
- Columbia County: April 18 to October 16 (182 days, 0 WNV)
- Clark County: April 21 to October 20 (182 days, 2 WNV)
West Nile in Mason County
CDC ArboNET lists no human West Nile cases for Mason County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 1 of those years.
See how the dates are worked out, and when mosquitoes go away for the winter.