Mosquito season in Calvert County, MD: when it starts and ends

Mosquito months in Calvert County

In a normal year mosquito season in Calvert County, MD starts around April 2 and ends around November 6, about 31 weeks.

What to do in Calvert County, and when

Start tipping out standing water weekly by March 19.
Book any yard treatment for early April, ahead of the July peak.
Repellent can go away after November 6.
1 West Nile case since 2016 (last 2018): you should use repellent at dusk June to August, more so if over 60.

Calvert County against the rest of MD

Calvert County has the 16th longest season of 24 MD counties, at 218 days against 235 in Wicomico County and 175 in Garrett County. Its mean temperature is 56.8°F.

Montgomery County: March 30 to November 5 (220 days, 34 WNV)
Prince George's County: April 1 to November 5 (219 days, 17 WNV)
Charles County: April 2 to November 6 (218 days, 2 WNV)
Kent County: April 2 to November 6 (218 days, 2 WNV)

West Nile in Calvert County

From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Calvert County (1 neuroinvasive) across 3 years. The worst was 2018 with 1; the latest was 2018.

See how the dates are worked out, and when mosquitoes go away for the winter.