Mosquito season in Mercer County, PA: when it starts and ends
Mosquito months in Mercer County
In a normal year mosquito season in Mercer County, PA starts around May 3 and ends around October 13, about 23 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Mercer County, and when
- Start tipping out standing water weekly by April 19.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 13.
- No West Nile cases since 2016, so bites in Mercer County are a nuisance; check window screens.
Mercer County against the rest of PA
Mercer County has the 57th longest season of 67 PA counties, at 163 days against 222 in Philadelphia County and 154 in Clinton County. Its mean temperature is 48.4°F.
- Wyoming County: May 1 to October 13 (165 days, 0 WNV)
- Forest County: May 2 to October 13 (164 days, 0 WNV)
- Cambria County: May 4 to October 12 (161 days, 4 WNV)
- Elk County: May 3 to October 10 (160 days, 0 WNV)
West Nile in Mercer County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Mercer County (3 neuroinvasive) across 2 years. The worst was 2003 with 5; the latest was 2003.
See how the dates are worked out, and when the season starts across the US.