Mosquito season in Bay County, MI: when it starts and ends
Mosquito months in Bay County
In a normal year mosquito season in Bay County, MI starts around April 28 and ends around October 16, about 24 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Bay County, and when
- Start tipping out standing water weekly by April 14.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 16.
- 4 West Nile cases since 2016 (last 2023): you should use repellent at dusk July to July, more so if over 60.
Bay County against the rest of MI
Bay County has the 31st longest season of 83 MI counties, at 171 days against 189 in Allegan County and 124 in Iron County. Its mean temperature is 47.4°F.
- Isabella County: April 27 to October 15 (171 days, 2 WNV)
- Midland County: April 27 to October 15 (171 days, 0 WNV)
- Gratiot County: April 27 to October 14 (170 days, 1 WNV)
- Ionia County: April 27 to October 13 (170 days, 2 WNV)
West Nile in Bay County
From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in Bay County (3 neuroinvasive) across 5 years. The worst was 2017 with 2; the latest was 2023.
Background: reading the West Nile counts; how the dates are worked out.