Mosquito season in Douglas County, SD: when it starts and ends
Mosquito months in Douglas County
In a normal year mosquito season in Douglas County, SD starts around April 21 and ends around October 16, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Douglas 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 16.
- 11 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check SD spray notices.
Douglas County against the rest of SD
Douglas County has the 3rd longest season of 66 SD counties, at 178 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 49°F.
- Yankton County: April 21 to October 16 (179 days, 20 WNV)
- Tripp County: April 22 to October 18 (179 days, 4 WNV)
- Charles Mix County: April 22 to October 17 (178 days, 18 WNV)
- Union County: April 22 to October 15 (176 days, 13 WNV)
West Nile in Douglas County
From 1999 to 2025, CDC ArboNET counted 30 human West Nile cases in Douglas County (6 neuroinvasive) across 13 years. The worst was 2003 with 13; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.