Mosquito season in Baltimore city, MD: when it starts and ends

Mosquito months in Baltimore city

In a normal year mosquito season in Baltimore city, MD starts around March 25 and ends around November 15, about 34 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 Baltimore city, and when

• Start tipping out standing water weekly by March 11.
• Book any yard treatment for late March, ahead of the July peak.
• Repellent can go away after November 15.
• 18 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to September, and check MD spray notices.

Baltimore city against the rest of MD

Baltimore city has the 2nd longest season of 24 MD counties, at 235 days against 235 in Wicomico County and 175 in Garrett County. Its mean temperature is 58.9°F.

• Wicomico County: March 24 to November 15 (235 days, 1 WNV)
• St. Mary's County: March 26 to November 15 (234 days, 0 WNV)
• Anne Arundel County: March 26 to November 13 (232 days, 12 WNV)

West Nile in Baltimore city

From 1999 to 2025, CDC ArboNET counted 73 human West Nile cases in Baltimore city (60 neuroinvasive) across 20 years. The worst was 2003 with 14; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.