Mosquito season in Montgomery County, PA: when it starts and ends

Mosquito months in Montgomery County

In a normal year mosquito season in Montgomery County, PA starts around April 12 and ends around October 27, about 28 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Montgomery 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.
• 41 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check PA spray notices.

Montgomery County against the rest of PA

Montgomery County has the 12th longest season of 67 PA counties, at 198 days against 222 in Philadelphia County and 154 in Clinton County. Its mean temperature is 53°F.

• Chester County: April 12 to October 27 (198 days, 23 WNV)
• Fulton County: April 12 to October 27 (198 days, 0 WNV)
• Lebanon County: April 12 to October 26 (197 days, 14 WNV)
• Washington County: April 12 to October 25 (196 days, 3 WNV)

West Nile in Montgomery County

From 1999 to 2025, CDC ArboNET counted 72 human West Nile cases in Montgomery County (44 neuroinvasive) across 18 years. The worst was 2018 with 13; the latest was 2025.

Background: reading the West Nile counts; how the dates are worked out.