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

Mosquito months in Montgomery County

In a normal year mosquito season in Montgomery County, MD starts around March 30 and ends around November 5, about 31 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 16.
• Book any yard treatment for late March, ahead of the July peak.
• Repellent can go away after November 5.
• 34 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check MD spray notices.

Montgomery County against the rest of MD

Montgomery County has the 14th longest season of 24 MD counties, at 220 days against 235 in Wicomico County and 175 in Garrett County. Its mean temperature is 56°F.

• Queen Anne's County: April 1 to November 8 (221 days, 0 WNV)
• Frederick County: March 30 to November 5 (220 days, 13 WNV)
• Prince George's County: April 1 to November 5 (219 days, 17 WNV)
• Calvert County: April 2 to November 6 (218 days, 1 WNV)

West Nile in Montgomery County

From 1999 to 2025, CDC ArboNET counted 81 human West Nile cases in Montgomery County (45 neuroinvasive) across 19 years. The worst was 2025 with 10; the latest was 2025.

More: how the dates are worked out · reading the West Nile counts.