Mosquito season in Baltimore County, MD: when it starts and ends
Mosquito months in Baltimore County
In a normal year mosquito season in Baltimore County, MD starts around March 30 and ends around November 9, about 32 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Baltimore 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 9.
- 26 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check MD spray notices.
Baltimore County against the rest of MD
Baltimore County has the 9th longest season of 24 MD counties, at 223 days against 235 in Wicomico County and 175 in Garrett County. Its mean temperature is 56.7°F.
- Somerset County: March 27 to November 13 (231 days, 0 WNV)
- Worcester County: March 29 to November 11 (227 days, 0 WNV)
- Howard County: March 30 to November 8 (223 days, 1 WNV)
- Caroline County: April 1 to November 9 (222 days, 0 WNV)
West Nile in Baltimore County
From 1999 to 2025, CDC ArboNET counted 91 human West Nile cases in Baltimore County (71 neuroinvasive) across 21 years. The worst was 2003 with 17; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.