Mosquito season in Butler County, MO: when it starts and ends

Mosquito months in Butler County

In a normal year mosquito season in Butler County, MO starts around March 20 and ends around November 9, about 33 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 Butler County, and when

• Start tipping out standing water weekly by March 6.
• Book any yard treatment for mid March, ahead of the July peak.
• Repellent can go away after November 9.
• 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to September, more so if over 60.

Butler County against the rest of MO

Butler County has the 4th longest season of 115 MO counties, at 234 days against 242 in Pemiscot County and 187 in Crawford County. Its mean temperature is 58.6°F.

• Dunklin County: March 19 to November 13 (239 days, 0 WNV)
• New Madrid County: March 19 to November 10 (236 days, 1 WNV)
• Scott County: March 21 to November 8 (232 days, 0 WNV)
• Mississippi County: March 24 to November 9 (230 days, 0 WNV)

West Nile in Butler County

From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Butler County (3 neuroinvasive) across 2 years. The worst was 2025 with 2; the latest was 2025.

More: how the dates are worked out · when mosquitoes go away for the winter.