IsItMosquitoSeasonYet
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Wisconsin · Mosquito Season Guide

Is it mosquito season in Wisconsin?

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Check a Wisconsin city
II. Wisconsin Mosquito Season Month by month

Wisconsin sits at the intersection of the Great Lakes, the Mississippi River flyway, and thousands of glacially carved wetlands — ideal conditions for mosquito populations that are short-season but extremely dense. The combination of spring snowmelt, warm humid summers, and abundant standing water drives one of the Midwest's most intense peak seasons.

Milwaukee / Madison corridor
Milwaukee · Madison · La Crosse
Northern Wisconsin
Green Bay · Wausau · Door Peninsula
Very Low Low Moderate High Very High taller = more active · color = severity
~50
mosquito species recorded in Wisconsin
~15,000
named lakes providing breeding habitat
3
disease-vectoring species of concern
72
counties with seasonal exposure

Milwaukee and the Lake Michigan shore

Milwaukee and the southeastern counties experience intense pressure from the Menomonee, Milwaukee, and Root River corridors. Lake Michigan moderates temperatures slightly, producing a June–September peak that is somewhat later to start than inland areas but extends well into September. Urban populations of Cx. pipiens are dense throughout the metro.

Madison and the Driftless Area

Madison sits between two lakes (Mendota and Monona) and experiences above-average pressure for its size. The Yahara River chain and the surrounding Driftless Area wetlands sustain populations through the season. La Crosse, on the Mississippi River, sees significant floodwater species surges after high-water events on the Upper Mississippi.

Northern Wisconsin and the Door Peninsula

The northwoods region and Door Peninsula experience some of the state's most intense short-season pressure in June and early July, driven by bog and wetland habitat. EEE has been detected in northern Wisconsin in some years — the same Great Lakes wetland corridor that affects Michigan and Minnesota.

III. Wisconsin's Three Species to Know
Aedes vexans floodwater mosquito photograph
Aedes vexans
Floodwater Mosquito

The dominant nuisance species in Wisconsin. Hatches explosively from floodplain soils after snowmelt and summer rains. Responsible for the intense early-June surges that most Wisconsin residents know well — particularly along the Mississippi, Wisconsin, and Fox River corridors.

Culex pipiens northern house mosquito photograph
Culex pipiens
Northern House Mosquito

The primary West Nile Virus vector in Wisconsin's urban and suburban areas. Breeds in stagnant water in gutters, catch basins, and urban drainage. WNV is detected annually in Wisconsin; Milwaukee, Dane, and Waukesha counties have the highest case counts most years.

Eastern treehole mosquito photograph
Aedes triseriatus
Eastern Treehole Mosquito

The primary vector of La Crosse encephalitis in Wisconsin. Breeds in water-filled treeholes and artificial containers in wooded areas. Wisconsin is among the top states for La Crosse virus cases nationally — children in forested areas of the state are at highest risk.

IV. Wisconsin Cities at a Glance
CityPeak SeasonOff-SeasonNotes
Milwaukee Jun – Sep Off Oct–May Three river corridors; dense Cx. pipiens urban populations; consistent WNV activity Check live
Madison Jun – Sep Off Oct–May Lakes Mendota and Monona shoreline; Yahara chain wetlands; above-average pressure for city size Check live
Green Bay Jun – Sep Off Oct–May Fox River and Green Bay shoreline; significant floodwater surges after spring rains Check live
La Crosse May – Sep Off Oct–Apr Upper Mississippi River floodplain; one of Wisconsin's earliest and most intense floodwater zones Check live
Appleton Jun – Sep Off Oct–May Fox River wetlands; lake country proximity; Lake Winnebago shoreline habitat 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 Michigan Site of the 2019 EEE outbreak — the deadliest in decades — 10 human cases and 6 deaths concentrated in SW Michigan Great Lakes wetlands 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 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 →