Mosquito season in Frederick County, MD: when it starts and ends
Mosquito months in Frederick County
In a normal year mosquito season in Frederick County, MD starts around March 30 and ends around November 5, about 31 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Frederick County, and when
- Start tipping out standing water weekly by March 16.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 5.
- 13 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check MD spray notices.
Frederick County against the rest of MD
Frederick County has the 13th longest season of 24 MD counties, at 220 days against 235 in Wicomico County and 175 in Garrett County. Its mean temperature is 56.2°F.
- Caroline County: April 1 to November 9 (222 days, 0 WNV)
- Queen Anne's County: April 1 to November 8 (221 days, 0 WNV)
- Montgomery County: March 30 to November 5 (220 days, 34 WNV)
- Prince George's County: April 1 to November 5 (219 days, 17 WNV)
West Nile in Frederick County
From 1999 to 2025, CDC ArboNET counted 25 human West Nile cases in Frederick County (16 neuroinvasive) across 8 years. The worst was 2025 with 9; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.