Mosquito season in Lancaster County, PA: when it starts and ends
Mosquito months in Lancaster County
In a normal year mosquito season in Lancaster County, PA starts around April 9 and ends around October 29, about 29 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Lancaster County, and when
- Start tipping out standing water weekly by March 26.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 29.
- 44 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check PA spray notices.
Lancaster County against the rest of PA
Lancaster County has the 5th longest season of 67 PA counties, at 204 days against 222 in Philadelphia County and 154 in Clinton County. Its mean temperature is 53.5°F.
- Berks County: April 9 to October 31 (206 days, 17 WNV)
- York County: April 8 to October 30 (205 days, 14 WNV)
- Bucks County: April 10 to October 31 (204 days, 28 WNV)
- Franklin County: April 8 to October 28 (203 days, 12 WNV)
West Nile in Lancaster County
From 1999 to 2025, CDC ArboNET counted 110 human West Nile cases in Lancaster County (72 neuroinvasive) across 15 years. The worst was 2003 with 39; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.