Mosquito season in Spink County, SD: when it starts and ends

Mosquito months in Spink County

In a normal year mosquito season in Spink County, SD starts around April 30 and ends around October 7, about 23 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 Spink County, and when

• Start tipping out standing water weekly by April 16.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 7.
• 21 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to July, and check SD spray notices.

Spink County against the rest of SD

Spink County has the 39th longest season of 66 SD counties, at 160 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 43.9°F.

• Dewey County: April 30 to October 7 (160 days, 11 WNV)
• Hanson County: April 30 to October 7 (160 days, 5 WNV)
• Grant County: May 1 to October 8 (160 days, 7 WNV)
• Marshall County: May 1 to October 8 (160 days, 10 WNV)

West Nile in Spink County

From 1999 to 2025, CDC ArboNET counted 64 human West Nile cases in Spink County (12 neuroinvasive) across 17 years. The worst was 2003 with 18; the latest was 2025.

Background: reading the West Nile counts; how the dates are worked out.