Mosquito season in Washtenaw County, MI: when it starts and ends
Mosquito months in Washtenaw County
In a normal year mosquito season in Washtenaw County, MI starts around April 27 and ends around October 16, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Washtenaw County, and when
- Start tipping out standing water weekly by April 13.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 16.
- 3 West Nile cases since 2016 (last 2018): you should use repellent at dusk July to July, more so if over 60.
Washtenaw County against the rest of MI
Washtenaw County has the 27th longest season of 83 MI counties, at 172 days against 189 in Allegan County and 124 in Iron County. Its mean temperature is 48°F.
- Eaton County: April 26 to October 15 (172 days, 2 WNV)
- Livingston County: April 26 to October 15 (172 days, 3 WNV)
- Genesee County: April 27 to October 15 (171 days, 9 WNV)
- Isabella County: April 27 to October 15 (171 days, 2 WNV)
West Nile in Washtenaw County
From 1999 to 2025, CDC ArboNET counted 15 human West Nile cases in Washtenaw County (8 neuroinvasive) across 8 years. The worst was 2012 with 4; the latest was 2018.
More: how the dates are worked out · when mosquitoes go away for the winter.