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

Mosquito months in South Central Connecticut Planning Region

In a normal year mosquito season in South Central Connecticut Planning Region, CT starts around April 19 and ends around October 29, about 27 weeks.

What to do in South Central Connecticut Planning Region, and when

Start tipping out standing water weekly by April 5.
Book any yard treatment for mid April, ahead of the July peak.
Repellent can go away after October 29.
5 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.

South Central Connecticut Planning Region against the rest of CT

South Central Connecticut Planning Region has the 4th longest season of 9 CT counties, at 192 days against 200 in Greater Bridgeport Planning Region and 164 in Northwest Hills Planning Region. Its mean temperature is 51.9°F.

Capitol Planning Region: April 16 to October 25 (193 days, 5 WNV)
Southeastern Connecticut Planning Region: April 18 to October 28 (193 days, 2 WNV)
Lower Connecticut River Valley Planning Region: April 17 to October 25 (191 days, 1 WNV)
Naugatuck Valley Planning Region: April 20 to October 23 (187 days, 0 WNV)

West Nile in South Central Connecticut Planning Region

From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in South Central Connecticut Planning Region (2 neuroinvasive) across 3 years. The worst was 2024 with 3; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.