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

Mosquito months in Cass County

In a normal year mosquito season in Cass County, MO starts around April 2 and ends around October 31, about 30 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 Cass County, and when

• Start tipping out standing water weekly by March 19.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 31.
• 1 West Nile case since 2016 (last 2021): you should use repellent at dusk June to August, more so if over 60.

Cass County against the rest of MO

Cass County has the 54th longest season of 115 MO counties, at 212 days against 242 in Pemiscot County and 187 in Crawford County. Its mean temperature is 54.6°F.

• Bates County: April 2 to November 1 (213 days, 0 WNV)
• Wright County: April 2 to November 1 (213 days, 0 WNV)
• Howard County: April 2 to October 31 (212 days, 0 WNV)
• Platte County: April 2 to October 30 (212 days, 3 WNV)

West Nile in Cass County

From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in Cass County (3 neuroinvasive) across 4 years. The worst was 2002 with 2; the latest was 2021.

Background: when mosquitoes go away for the winter; how the dates are worked out.