Mosquito season in Cass County, IA: when it starts and ends
Mosquito months in Cass County
In a normal year mosquito season in Cass County, IA starts around April 22 and ends around October 12, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Cass County, and when
- Start tipping out standing water weekly by April 8.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 12.
- No West Nile cases since 2016, so bites in Cass County are a nuisance; check window screens.
Cass County against the rest of IA
Cass County has the 77th longest season of 99 IA counties, at 173 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 49.1°F.
- Franklin County: April 23 to October 15 (174 days, 1 WNV)
- Sac County: April 23 to October 14 (174 days, 0 WNV)
- Clay County: April 23 to October 13 (173 days, 0 WNV)
- Webster County: April 23 to October 14 (173 days, 1 WNV)
West Nile in Cass County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Cass County (1 neuroinvasive) across 4 years. The worst was 2002 with 3; the latest was 2013.
See how the dates are worked out, and when mosquitoes go away for the winter.