Mosquito season in Webster County, IA: when it starts and ends

Mosquito months in Webster County

In a normal year mosquito season in Webster County, IA starts around April 23 and ends around October 14, about 25 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 Webster County, and when

• Start tipping out standing water weekly by April 9.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 14.
• 1 West Nile case since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.

Webster County against the rest of IA

Webster County has the 79th longest season of 99 IA counties, at 173 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 46.4°F.

• Cass County: April 22 to October 12 (173 days, 0 WNV)
• Clay County: April 23 to October 13 (173 days, 0 WNV)
• Cherokee County: April 24 to October 14 (173 days, 3 WNV)
• Lucas County: April 26 to October 16 (173 days, 1 WNV)

West Nile in Webster County

From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in Webster County (5 neuroinvasive) across 5 years. The worst was 2010 with 2; the latest was 2025.

See how the dates are worked out, and when mosquitoes go away for the winter.