Mosquito season in Allegheny County, PA: when it starts and ends
Mosquito months in Allegheny County
In a normal year mosquito season in Allegheny County, PA starts around April 12 and ends around October 27, about 28 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Allegheny County, and when
- Start tipping out standing water weekly by March 29.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 27.
- 23 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check PA spray notices.
Allegheny County against the rest of PA
Allegheny County has the 9th longest season of 67 PA counties, at 198 days against 222 in Philadelphia County and 154 in Clinton County. Its mean temperature is 52.1°F.
- Franklin County: April 8 to October 28 (203 days, 12 WNV)
- Adams County: April 11 to October 27 (200 days, 2 WNV)
- Chester County: April 12 to October 27 (198 days, 23 WNV)
- Fulton County: April 12 to October 27 (198 days, 0 WNV)
West Nile in Allegheny County
From 1999 to 2025, CDC ArboNET counted 67 human West Nile cases in Allegheny County (44 neuroinvasive) across 14 years. The worst was 2002 with 22; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.