Mosquito and tick season in Michigan: what the state has counted

Two seasons that do not line up

Mosquitoes and ticks are lumped together on pest control websites, and in Michigan they run on different clocks with different public data. West Nile virus risk concentrates in the late summer, and blacklegged ticks, the ones that carry Lyme disease, are active whenever outdoor temperatures are above 40 degrees Fahrenheit. This guide uses the Michigan Department of Health and Human Services (MDHHS) and county health pages, says when a number is provisional and leaves out anything we could not source, including a current Lyme count.

Mosquito season and what the state has counted

MDHHS says West Nile outbreaks have occurred in Michigan every summer since 2002, that Macomb, Oakland and Wayne counties and Kent County have historically seen the most activity, and that people over 60 face the greatest risk of severe illness. Oakland County’s health division says risk is highest from late July through September and says over 50. About 8 in 10 infected people have no symptoms and about 1 in 150 develop serious neurologic illness, according to MDHHS.

The numbers for 2026, from MDHHS’s weekly arbovirus summary updated October 16, 2026, are provisional and the page is overwritten weekly. It lists 31 human arbovirus cases this year, 29 of them West Nile, one eastern equine encephalitis (EEE) case in Roscommon County and one Jamestown Canyon case, plus 120 West Nile-positive mosquito pools. Human West Nile cases include Wayne 6, Oakland 6, Macomb 5, Kent 4, Detroit 3 and Ottawa 2, with Emmet, Ingham and Newaygo also listed. For earlier years, MDHHS reported 13 human cases in 2019, 32 in 2020, 46 in 2021 including seven deaths, 12 in 2022 and, provisionally, 24 in 2023; its five-year table and its year-end summaries differ slightly for 2021 and 2022, so treat the figures as approximate.

EEE is rarer and more severe. MDHHS says about 30 percent of people ill with EEE die, many survivors have permanent neurologic damage and there is no vaccine or specific treatment for people. Suspected human cases are reported to MDHHS at 517-335-8165 and horse cases to MDARD at 800-292-3939. The 2026 summary lists two EEE-positive horses.

A new mosquito, and what counties do

A September 2025 notice on the City of Livonia’s website, quoting a Wayne County Health Division advisory, says the Asian tiger mosquito is new to Michigan, has a black-and-white striped body and bites during the day. It asks residents to report unusual daytime biting to Wayne County Environmental Health at (734) 727-7400, and says current disease risk in Michigan is low.

Public mosquito control is uneven. The EPA says adult mosquitoes are controlled by aircraft or truck-mounted sprayers, typically under 3 ounces per acre, with malathion, naled and pyrethroids commonly used by state and local agencies. We did not find a county or city adult-mosquito spraying program in Wayne, Oakland, Macomb, Kent, Washtenaw or Ingham counties. Macomb County describes mosquito and tick surveillance and lists 586-469-5236, and says West Nile is endemic in the county. Treat “not found” as that, not as a statement that none exists. MDHHS retired its disease mapper on January 31, 2025, so any page that sends you there is out of date.

Ticks: the seasons and the map

MDHHS names five common ticks likely to bite people in Michigan. The American dog tick is active early May to November. The blacklegged tick is widespread and carries Lyme disease, anaplasmosis and babesiosis. The lone star tick is sometimes found across the state. The woodchuck tick carries Powassan virus, and the brown dog tick can survive and breed indoors. Oakland County says the American dog tick is the tick most often identified in Michigan and that ticks are found in nearly every county.

Lyme disease is the most common vector-borne disease in Michigan, according to MDHHS. Infected blacklegged ticks were first confirmed in the Lower Peninsula in 2002 along the west coast and have been spreading north and across it; they are established in the Upper Peninsula and the western Lower Peninsula. MDHHS counted 424 Lyme cases in 2019 and 1,146 in 2023, the latter provisional, with 970 locally acquired. The 2023 figures are the latest we cite. MDHHS also says milder winters and longer, hotter summers contribute to a longer tick season, and that Powassan is rare, with the state’s most recent resident case reported in 2001 in a 2016 to 2020 report. MDHHS will identify a tick from a photo or specimen at no charge, which is the sensible first step before any treatment.

What a company can and cannot do

For mosquitoes, a company hired for your yard works under MDARD category 7F, which covers managing mosquitoes in an outside environment, and Michigan’s drift rules apply to outdoor applications. A yard treatment is a pesticide application like any other, so MCL 324.8313(12) bars calling it necessary for a pest that is not present or likely to occur. Ask for the months and number of visits in the price, the product and the label. See the mosquito page.

For ticks, the sourced actions are to identify the tick, report it and talk to a health professional if you are bitten. Yard treatment is a separate question to put to the company. The season calendar puts the dates above in month order.

Where the data lives now

When MDHHS shut down its disease mapper, it pointed people to three places: the Arbovirus Weekly Summary, the current-year rabies map and the MiTracking tick and rabies data. MiTracking’s tick page also says more than 20 tick species are known in Michigan and that residents can report ticks through its data portal. If a pest control page quotes a case count without a date and a link to one of those, assume it is stale.

What to do, in order

Check the current MDHHS arbovirus summary rather than an old page. Note the months a company is proposing to treat and compare them with the late July through September window. Send ticks to MDHHS for identification. Report unusual daytime biting in Wayne County. If a company sells a seasonal plan, ask what pest it is targeting and what makes it likely at your address.