Mosquito season in St. Louis city, MO: when it starts and ends
Mosquito months in St. Louis city
In a normal year mosquito season in St. Louis city, MO starts around March 24 and ends around November 8, about 33 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in St. Louis city, and when
- Start tipping out standing water weekly by March 10.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 8.
- 39 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to September, and check MO spray notices.
St. Louis city against the rest of MO
St. Louis city has the 7th longest season of 115 MO counties, at 229 days against 242 in Pemiscot County and 187 in Crawford County. Its mean temperature is 57.7°F.
- Scott County: March 21 to November 8 (232 days, 0 WNV)
- Mississippi County: March 24 to November 9 (230 days, 0 WNV)
- Taney County: March 26 to November 9 (228 days, 0 WNV)
- Wayne County: March 24 to November 6 (226 days, 0 WNV)
West Nile in St. Louis city
From 1999 to 2025, CDC ArboNET counted 178 human West Nile cases in St. Louis city (155 neuroinvasive) across 21 years. The worst was 2002 with 56; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.