Mosquito season in Shelby County, IA: when it starts and ends
Mosquito months in Shelby County
In a normal year mosquito season in Shelby County, IA starts around April 17 and ends around October 19, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Shelby County, and when
- Start tipping out standing water weekly by April 3.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 19.
- 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.
Shelby County against the rest of IA
Shelby County has the 31st longest season of 99 IA counties, at 185 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 49.4°F.
- Clinton County: April 17 to October 19 (186 days, 3 WNV)
- Henry County: April 17 to October 20 (186 days, 2 WNV)
- Washington County: April 17 to October 19 (185 days, 1 WNV)
- Adams County: April 18 to October 19 (185 days, 2 WNV)
West Nile in Shelby County
From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in Shelby County (6 neuroinvasive) across 7 years. The worst was 2004 with 2; the latest was 2025.
More: how the dates are worked out · when the season starts across the US.