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

Mosquito months in Worcester County

In a normal year mosquito season in Worcester County, MA starts around April 26 and ends around October 16, about 25 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 Worcester County, and when

• Start tipping out standing water weekly by April 12.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 16.
• 7 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.

Worcester County against the rest of MA

Worcester County has the 13th longest season of 14 MA counties, at 172 days against 194 in Plymouth County and 163 in Berkshire County. Its mean temperature is 47.9°F.

• Franklin County: April 25 to October 16 (174 days, 2 WNV)
• Essex County: April 28 to October 19 (174 days, 14 WNV)
• Berkshire County: April 30 to October 10 (163 days, 1 WNV)

West Nile in Worcester County

From 1999 to 2025, CDC ArboNET counted 25 human West Nile cases in Worcester County (17 neuroinvasive) across 12 years. The worst was 2012 with 5; the latest was 2025.

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