Mosquito season in Middlesex County, MA: when it starts and ends
Mosquito months in Middlesex County
In a normal year mosquito season in Middlesex County, MA starts around April 21 and ends around October 18, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Middlesex County, and when
- Start tipping out standing water weekly by April 7.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 18.
- 65 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check MA spray notices.
Middlesex County against the rest of MA
Middlesex County has the 9th longest season of 14 MA counties, at 180 days against 194 in Plymouth County and 163 in Berkshire County. Its mean temperature is 49.9°F.
- Hampden County: April 21 to October 19 (181 days, 7 WNV)
- Dukes County: April 27 to October 25 (181 days, 0 WNV)
- Hampshire County: April 24 to October 16 (175 days, 2 WNV)
- Franklin County: April 25 to October 16 (174 days, 2 WNV)
West Nile in Middlesex County
From 1999 to 2025, CDC ArboNET counted 115 human West Nile cases in Middlesex County (87 neuroinvasive) across 23 years. The worst was 2018 with 17; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.