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

Mosquito months in Butte County

In a normal year mosquito season in Butte County, SD starts around May 2 and ends around October 8, 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 Butte County, and when

• Start tipping out standing water weekly by April 18.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after October 8.
• 3 West Nile cases since 2016 (last 2018): you should use repellent at dusk July to August, more so if over 60.

Butte County against the rest of SD

Butte County has the 48th longest season of 66 SD counties, at 159 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 45.9°F.

• Moody County: May 1 to October 7 (159 days, 3 WNV)
• Walworth County: May 1 to October 7 (159 days, 17 WNV)
• Brookings County: May 1 to October 6 (158 days, 27 WNV)
• Campbell County: May 1 to October 6 (158 days, 3 WNV)

West Nile in Butte County

From 1999 to 2025, CDC ArboNET counted 68 human West Nile cases in Butte County (11 neuroinvasive) across 11 years. The worst was 2003 with 47; the latest was 2018.

See how the dates are worked out, and when the season starts across the US.