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

Mosquito months in Franklin County

In a normal year mosquito season in Franklin County, MO starts around March 31 and ends around November 3, about 31 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 Franklin County, and when

• Start tipping out standing water weekly by March 17.
• Book any yard treatment for late March, ahead of the July peak.
• Repellent can go away after November 3.
• No West Nile cases since 2016, so bites in Franklin County are a nuisance; check window screens.

Franklin County against the rest of MO

Franklin County has the 33rd longest season of 115 MO counties, at 217 days against 242 in Pemiscot County and 187 in Crawford County. Its mean temperature is 56.1°F.

• Barton County: March 31 to November 4 (218 days, 0 WNV)
• Douglas County: March 31 to November 3 (217 days, 0 WNV)
• Jefferson County: March 31 to November 3 (217 days, 3 WNV)
• Ripley County: March 31 to November 3 (217 days, 0 WNV)

West Nile in Franklin County

From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Franklin County (2 neuroinvasive) across 3 years. The worst was 2006 with 1; the latest was 2006.

Background: when the season starts across the US; how the dates are worked out.