Michigan · Mosquito Season Guide

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II. Michigan Mosquito Season Month by month

Michigan's mosquito season is shorter than most of the Midwest — roughly June through September — but punches above its weight in disease risk. The state's vast Great Lakes wetlands, cattail marshes, and glacially carved swamps create ideal habitat for the species that carries Eastern equine encephalitis. In 2019, Michigan recorded its worst EEE outbreak in decades.

Very Low Low Moderate High Very High taller = more active · color = severity

Chart reflects southeast Michigan / Detroit baseline. Northern Lower Peninsula (Traverse City, Petoskey) starts 2–3 weeks later and ends earlier. Upper Peninsula season runs roughly July–August only.

~60

mosquito species recorded in Michigan

2019

year of Michigan's worst EEE outbreak in decades — 6 deaths

Jun–Sep

typical active season — shorter than most Midwest states

counties — all with MDHHS mosquito surveillance

The 2019 EEE outbreak: Michigan's wake-up call

In the summer and fall of 2019, Michigan recorded 10 confirmed human EEE cases and 6 deaths — making it the deadliest EEE outbreak in the US in decades and one of the worst in Michigan's recorded history. The outbreak was concentrated in southwestern and south-central Michigan, particularly in counties bordering swampy terrain: Calhoun, Kalamazoo, Van Buren, and Barry. Several counties issued emergency advisories closing parks and canceling outdoor evening events. The Michigan Department of Health and Human Services (MDHHS) expanded surveillance and aerial mosquito spray operations in response. EEE activity in Michigan has remained elevated in subsequent years, and the MDHHS publishes weekly EEE risk maps from June through October.

Why Michigan's wetlands create unique EEE risk

Eastern equine encephalitis circulates primarily in birds in freshwater swamp environments, transmitted by Culiseta melanura, a deep-wetland specialist that rarely bites humans. The human (and horse) cases occur when "bridge vector" species — primarily Coquillettidia perturbans, the cattail mosquito — pick up EEE virus from infected birds and then bite mammals. Michigan's extensive cattail marshes, glacial swamps, and Great Lakes coastal wetlands create ideal habitat for both. Van Buren, Allegan, and Barry counties in the southwest have the highest historical EEE burden.

West Nile and urban exposure

Culex pipiens drives WNV transmission in the Detroit metro and other urban centers. Wayne, Oakland, and Macomb counties record WNV in mosquito surveillance pools annually. The Great Lakes climate moderates temperatures, limiting the summer season relative to Ohio or Illinois, but July and August deliver conditions — warm, humid nights following afternoon thunderstorms — that sustain high Culex activity.

III. Michigan's Three Species to Know

Culex pipiens

Northern House Mosquito · ⚠ West Nile Vector

The dominant mosquito across the Detroit metro and other urban/suburban areas. Breeds in standing water — storm drains, catch basins, birdbaths. Feeds at dusk and overnight, preferring birds but shifting to humans in late summer. The primary WNV vector statewide; MDHHS monitors Cx. pipiens trap counts as an early-warning indicator across Wayne, Oakland, and Macomb counties. Eliminating standing water cuts local populations immediately.

Aedes vexans

Inland Floodwater Mosquito

The most abundant mosquito across rural Michigan and a significant nuisance after summer rain events statewide. Eggs survive dry conditions in low-lying areas for years, hatching en masse when flooded — populations can explode within 5–7 days of a significant storm. Bites aggressively during daylight. Not a primary disease vector in Michigan, but responsible for the bulk of the summer outdoor biting misery, particularly in agricultural and river corridor areas. The EEE-carrying bridge vector Coquillettidia perturbans inhabits cattail marshes in southwestern Michigan — avoid dusk activity near swampy terrain in EEE advisory counties.

Aedes albopictus

Asian Tiger Mosquito

Established in the southeastern Lower Peninsula — Detroit metro and outward — and continuing to expand northward as winters moderate. Visually distinctive: black with bold white stripes. Bites aggressively during daylight, especially morning and late afternoon. Breeds in tiny water volumes: bottle caps, saucers, gutters, any standing water. Less dominant than in southern states but increasingly significant in Michigan's southern tier. The shift toward daytime biting catches residents off guard who are accustomed to only worrying about dusk.

Michigan EEE risk is real and present every season. EEE has a fatality rate above 30% in humans. When MDHHS posts elevated EEE risk maps for your county — especially in southwestern Michigan — avoid outdoor activities at dusk and dawn near wooded wetland areas, and use repellent with DEET or picaridin. Check current MDHHS EEE risk maps →

IV. City-by-City Reference

City	Active Season	Off-Season	Notes	Live data
Detroit	Jun – Sep	Near-zero Oct–May	Wayne County runs active WNV surveillance; Culex pipiens dominant; Ae. albopictus established in metro suburbs; Detroit River corridor and city park standing water are primary breeding sites; county mosquito control programs larvicide catch basins seasonally	Check live
Grand Rapids	Jun – Sep	Off Oct–May	Kent County; Grand River corridor amplifies floodwater species; proximity to southwestern MI EEE counties — check MDHHS EEE risk maps seasonally; Culex pipiens and Ae. vexans dominant; Ae. albopictus present and expanding	Check live
Lansing	Jun – Sep	Off Oct–May	Ingham County; Grand River corridor; state capital — MDHHS surveillance data published from here; WNV detected most seasons; within range of south-central MI EEE pressure; Ae. albopictus present in metro area	Check live
Ann Arbor	Jun – Sep	Off Oct–May	Washtenaw County; Huron River corridor; University of Michigan campus has extensive park/water habitat; WNV detected annually; Ae. albopictus well established; suburban yard containers are primary daytime biting source	Check live
Traverse City	Jul – Aug	Off Sep–Jun	Northern LP — shorter season (2–3 weeks later start, earlier end); Grand Traverse Bay wetlands provide spring breeding habitat; EEE risk lower than southwestern MI; prime tourist season coincides exactly with peak mosquito activity; Ae. vexans dominant after rainfall	Check live
Kalamazoo	Jun – Sep	Off Oct–May	Kalamazoo County — within the southwest Michigan EEE core zone; one of the higher EEE-risk counties in the state; extensive wetland habitat on city outskirts; Kalamazoo River corridor; MDHHS historically flags this region for elevated EEE risk most seasons	Check live
Flint	Jun – Sep	Off Oct–May	Genesee County; Flint River corridor; WNV detected in county surveillance traps regularly; Culex pipiens and Ae. vexans dominant; Ae. albopictus expanding; EEE risk lower than southwestern counties but not zero	Check live

More State Guides

Florida Year-round activity in the south — 80+ species including invasive Ae. aegypti and the Asian tiger mosquito across all 67 counties Texas ~85 species across four climate zones — Gulf Coast active March through November, with year-round pressure in the Rio Grande Valley California Central Valley is the #1 West Nile corridor in the US — invasive Ae. aegypti and Ae. albopictus now established in 20+ counties Georgia Atlanta metro leads the Southeast in Asian tiger mosquito density — active statewide March through November New York Ground zero for West Nile in the US (1999 Queens outbreak) — NYC metro and Long Island see the highest Northeast seasonal pressure Illinois Home of the 2002 Cook County West Nile outbreak — the deadliest urban WNV event in US history — peak season June through September Ohio Lake Erie to the Ohio River — WNV active in Franklin and Cuyahoga counties, with floodwater species surging after summer storms Pennsylvania Philadelphia WNV corridor meets rural EEE risk in western PA — the densest human population in the mid-Atlantic mosquito belt New Jersey Oldest organized county mosquito control in the US (1914) — Pine Barrens EEE corridor and fierce salt marsh Shore species Virginia Tidewater season runs April–October — the longest mid-Atlantic window — with the Great Dismal Swamp as an active EEE hotspot North Carolina The coastal plain runs one of the longest seasons in the Southeast — NC leads the nation in La Crosse encephalitis cases from the Appalachian foothills Maryland Chesapeake Bay watershed creates extraordinary mosquito habitat — tidal marshes, Eastern Shore wetlands, and the DC-Baltimore corridor combine for dense seasonal pressure Tennessee Memphis and the Mississippi River corridor historically record the highest WNV case counts in the mid-South — Ae. albopictus has colonized all 95 counties Indiana Indiana sits at the crossroads of the Great Lakes EEE belt — Lake Michigan wetlands in the north and the Wabash River floodplain drive intense seasonal pressure Louisiana The Gulf Coast's most intense pressure — coastal marshes and summer rains keep Cx. quinquefasciatus and Ae. aegypti active from March through November Alabama Mobile Bay to the Tennessee Valley — Ae. albopictus has reached all 67 counties and peak WNV season runs June through September South Carolina Low Country marshes produce some of the Southeast's densest Anopheles and Culex populations — season runs March through November Minnesota 10,000 lakes means 10,000 breeding sites — the Northwoods sees intense but short July–August peaks, while the Twin Cities face a longer June–September window Wisconsin Great Lakes wetlands and the Mississippi River backwaters drive strong WNV pressure in the Milwaukee corridor — peak season July through August Missouri At the confluence of the Missouri and Mississippi rivers — St. Louis historically ranks among the highest WNV cities in the US — season May through October Arkansas Delta rice-field flooding and the Arkansas River bottomlands create some of the highest rural mosquito pressure in the mid-South — active April through October Washington Western WA stays mild and damp year-round; the Yakima Valley and Columbia Basin face the highest WNV risk in the Pacific Northwest — peak July through September Arizona Monsoon season (July–September) drives sudden mosquito explosions across the Valley of the Sun — WNV detected annually Colorado Front Range WNV corridor stretches Denver to Fort Collins — eastern plains carry the state's highest risk Connecticut Connecticut River valley WNV pressure meets EEE risk in inland freshwater wetlands — active May through October Delaware Chesapeake and Delaware Bay marshes create outsized pressure for the nation's second-smallest state Hawaii Year-round activity at sea level — no native species, but Ae. aegypti and tiger mosquitoes established statewide Idaho Snake River Plain irrigation districts fuel summer WNV pressure — season June through September Iowa Mississippi River corridor and prairie wetlands drive intense June–September pressure — WNV active statewide Kansas Great Plains WNV corridor — Wichita and Kansas City see peak pressure July–August; floodwater species surge after storms Kentucky Ohio River corridor and Kentucky Lake wetlands sustain a long April–October season across all 120 counties Maine Short but intense July–August season — EEE detected in some years in the southern coastal plain Massachusetts EEE fatality rate exceeds 30% — the Plymouth County swamp complex is the active epicenter — season May through October Mississippi Gulf Coast near-year-round pressure meets Delta rice-field flooding for one of the South's most intense mosquito environments Montana Yellowstone and Missouri River corridors drive a compressed June–August season — WNV detected most years in eastern MT Nebraska Platte River valley and eastern Nebraska are among the Great Plains' most active WNV zones — peak July–August Nevada Las Vegas monsoon season drives July–September activity; Reno irrigation districts fuel a parallel northern peak New Hampshire EEE detected most years — the southern lakes and coastal plain are in the active Northeast EEE corridor New Mexico Monsoon season (July–September) creates sudden breeding habitat; WNV circulates in the Rio Grande valley annually North Dakota Red River Valley flooding produces some of the Great Plains' most extreme floodwater mosquito events — peak June–August Oklahoma One of the South-Central's most intense seasons — the Arkansas and Red River corridors sustain populations April through October Oregon Eastern Oregon Columbia Basin is the state's WNV hotspot; western Oregon runs a mild coastal season June through September Rhode Island New England's densest coastal pressure — Narragansett Bay salt marshes and WNV active in all five counties South Dakota Missouri River and James River valleys drive summer WNV activity — eastern SD sees the most intense pressure Utah Salt Lake Valley WNV corridor and irrigation districts sustain a July–September peak — drier areas see limited activity Vermont Champlain Valley runs Vermont's longest season — EEE detected in the Lake Champlain lowlands in some years West Virginia Kanawha and Ohio River valleys sustain a May–October season — Ae. albopictus now established statewide Wyoming The shortest meaningful season of any contiguous US state — North Platte valley WNV window is just 6–8 weeks

West Nile, dengue, and EEE: US disease risk by region → Asian tiger mosquitoes: why you're getting bitten during the day → Eliminating standing water: the highest-leverage yard move →