Mosquito season in Dauphin County, PA: when it starts and ends
Mosquito months in Dauphin County
In a normal year mosquito season in Dauphin County, PA starts around April 18 and ends around October 23, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Dauphin County, and when
- Start tipping out standing water weekly by April 4.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 23.
- 8 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Dauphin County against the rest of PA
Dauphin County has the 26th longest season of 67 PA counties, at 188 days against 222 in Philadelphia County and 154 in Clinton County. Its mean temperature is 51°F.
- Beaver County: April 17 to October 23 (189 days, 3 WNV)
- Blair County: April 17 to October 21 (188 days, 1 WNV)
- Lawrence County: April 20 to October 25 (188 days, 2 WNV)
- Erie County: April 22 to October 27 (188 days, 1 WNV)
West Nile in Dauphin County
From 1999 to 2025, CDC ArboNET counted 18 human West Nile cases in Dauphin County (12 neuroinvasive) across 10 years. The worst was 2003 with 4; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.