Mosquito season in Southeastern Connecticut Planning Region, CT: when it starts and ends

Mosquito months in Southeastern Connecticut Planning Region

In a normal year mosquito season in Southeastern Connecticut Planning Region, CT starts around April 18 and ends around October 28, about 28 weeks.

What to do in Southeastern Connecticut Planning Region, and when

Start tipping out standing water weekly by April 4.
Book any yard treatment for mid April, ahead of the July peak.
Repellent can go away after October 28.
2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.

Southeastern Connecticut Planning Region against the rest of CT

Southeastern Connecticut Planning Region has the 3rd longest season of 9 CT counties, at 193 days against 200 in Greater Bridgeport Planning Region and 164 in Northwest Hills Planning Region. Its mean temperature is 51.8°F.

Greater Bridgeport Planning Region: April 16 to November 2 (200 days, 2 WNV)
Capitol Planning Region: April 16 to October 25 (193 days, 5 WNV)
South Central Connecticut Planning Region: April 19 to October 29 (192 days, 5 WNV)
Lower Connecticut River Valley Planning Region: April 17 to October 25 (191 days, 1 WNV)

West Nile in Southeastern Connecticut Planning Region

From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Southeastern Connecticut Planning Region (2 neuroinvasive) across 2 years. The worst was 2025 with 1; the latest was 2025.

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