Mosquito season in Pierce County, WA: when it starts and ends
Mosquito months in Pierce County
In a normal year mosquito season in Pierce County, WA starts around April 28 and ends around October 17, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Pierce County, and when
- Start tipping out standing water weekly by April 14.
- Book any yard treatment for late April, ahead of the August peak.
- Repellent can go away after October 17.
- 2 West Nile cases since 2016 (last 2022): you should use repellent at dusk August, more so if over 60.
Pierce County against the rest of WA
Pierce County has the 19th longest season of 39 WA counties, at 172 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 50.2°F.
- Adams County: April 23 to October 16 (176 days, 0 WNV)
- Whatcom County: April 25 to October 14 (172 days, 1 WNV)
- Grays Harbor County: April 29 to October 18 (172 days, 0 WNV)
- Skagit County: April 26 to October 14 (171 days, 0 WNV)
West Nile in Pierce County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Pierce County (2 neuroinvasive) across 5 years. The worst was 2006 with 2; the latest was 2022.
More: how the dates are worked out · when mosquitoes go away for the winter.