Mosquito season in Plymouth County, MA: when it starts and ends

Mosquito months in Plymouth County

In a normal year mosquito season in Plymouth County, MA starts around April 20 and ends around October 31, about 28 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 Plymouth County, and when

• Start tipping out standing water weekly by April 6.
• Book any yard treatment for mid April, ahead of the July peak.
• Repellent can go away after October 31.
• 5 West Nile cases since 2016 (last 2022): you should use repellent at dusk July to August, more so if over 60.

Plymouth County against the rest of MA

Plymouth County has the 1st longest season of 14 MA counties, at 194 days against 194 in Plymouth County and 163 in Berkshire County. Its mean temperature is 52.1°F.

• Suffolk County: April 19 to October 29 (193 days, 18 WNV)
• Norfolk County: April 15 to October 23 (191 days, 6 WNV)

West Nile in Plymouth County

From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in Plymouth County (6 neuroinvasive) across 5 years. The worst was 2019 with 2; the latest was 2022.

Background: reading the West Nile counts; how the dates are worked out.