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II · Season Timing

Typical season — Baltimore

Historical mosquito activity index by month

Minimal Low Moderate High Peak Index 0–5

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55+

mosquito species recorded in Maryland

May–Sept

active season — Eastern Shore starts earlier

July–Aug

peak pressure months statewide

WNV

West Nile monitored by MDA statewide program

IV · Key Species

Culex pipiens

⚠ WNV Vector — Primary Risk

Northern house mosquito — the dominant West Nile vector in Maryland's urban and suburban areas. Thrives in stagnant, organically enriched water: Baltimore stormwater infrastructure, backyard containers, neglected ponds. Bites dusk through dawn. Baltimore City and Prince George's County have historically recorded the highest WNV trap positivity rates in the state.

Aedes albopictus

Asian Tiger Mosquito

Firmly established across the entire DC-Baltimore corridor and expanding statewide. Aggressive daytime biter — most active in shaded suburban yards and wooded neighborhoods. Breeds in any container holding even a tablespoon of water. DC-area suburbs (Montgomery and Prince George's counties) have among the highest Ae. albopictus complaint volumes in the mid-Atlantic region.

Aedes vexans

Inland Floodwater Mosquito

The primary nuisance species responsible for post-storm biting surges across Maryland. Potomac River and Patuxent River floodplains produce intense population spikes after heavy rains. Frederick County and the western Maryland agricultural areas see the most dramatic floodwater events. Eastern Shore tidal marshes also support significant populations of salt-tolerant Aedes species throughout the season.

V · Maryland Mosquito Context

The Chesapeake watershed changes everything

The Chesapeake Bay and its tributaries give Maryland one of the most productive mosquito environments on the East Coast. Maryland has more tidal wetland per square mile than almost any other state — and tidal marshes produce both freshwater and salt-tolerant mosquito species that don't occur in landlocked states. The Eastern Shore is particularly intense: Dorchester, Wicomico, Somerset, and Worcester counties support dense populations of marsh-breeding species from April through October, and the biting pressure near the shore can be severe during peak season.

The Eastern Shore vs. DC suburbs: two different problems

Maryland's mosquito picture splits sharply across the Bay. The Eastern Shore faces large, highly mobile marsh-breeding species that can travel several miles from breeding sites — biting pressure is less about your specific yard and more about regional marsh conditions and wind direction. The DC suburbs (Montgomery, Prince George's, Howard counties) face the opposite problem: Ae. albopictus that breeds hyper-locally in containers within meters of where it bites. The solution for one is county-scale aerial control; the solution for the other is container elimination in your own backyard.

Maryland's mosquito control program

The Maryland Department of Agriculture (MDA) coordinates one of the most comprehensive state mosquito management programs in the mid-Atlantic, running from May through October. Most counties have dedicated mosquito control programs operating larviciding, trapping, and adult control operations. WNV surveillance traps run weekly through the season in all 23 counties and Baltimore City. Check MDA mosquito program resources →

VI · City-by-City Breakdown

City	Season	Off-season	Notes	Live data
Baltimore	May – Sep	Off Oct–Apr	Urban WNV pressure; Cx. pipiens dominant in stormwater infrastructure and dense row-house neighborhoods; Patapsco River and Inner Harbor waterfront; Baltimore City historically records among the highest WNV trap-positive rates in Maryland; Ae. albopictus expanding rapidly; urban heat island extends effective season; significant standing water in vacant lots and neglected containers	Check live
Annapolis	May – Sep	Off Oct–Apr	Chesapeake Bay and South River junction; tidal marsh and saltwater creek proximity; Cx. pipiens and salt-tolerant Aedes species both active; waterfront locations can experience intense pressure June through August; Naval Academy grounds; Anne Arundel County mosquito control active; boating and marina areas see heightened activity near tidal flats	Check live
Rockville	May – Sep	Off Oct–Apr	Montgomery County DC suburb; heavy Ae. albopictus pressure in wooded residential neighborhoods; Rock Creek watershed; WNV detected in Montgomery County surveillance traps regularly; dense tree canopy creates ideal tiger mosquito habitat; one of the highest suburban mosquito complaint volumes in the DC metro area; container elimination is the primary mitigation lever	Check live
Silver Spring	May – Sep	Off Oct–Apr	Dense urban-suburban transition zone; Ae. albopictus extremely active in tree-lined neighborhoods; adjacent to Rock Creek Park (a significant wildlife reservoir for WNV); high human density amplifies exposure; short distances between wooded habitat and residential areas mean biting pressure extends throughout the day; WNV detected in Prince George's County traps	Check live
Frederick	May – Sep	Off Oct–Apr	Monocacy River floodplain — significant Ae. vexans pressure after thunderstorms; Frederick County agricultural areas have extensive low-lying terrain; Carroll Creek urban flood control area; Ae. albopictus present in residential areas; slightly shorter season than eastern MD due to elevation; WNV detected but at lower rates than Baltimore corridor; post-storm biting surges can be intense	Check live
Bethesda	May – Sep	Off Oct–Apr	Heavily wooded DC suburb; Ae. albopictus dense in mature tree-canopy neighborhoods; proximity to Rock Creek Park and Potomac River corridor; affluent residential areas with landscaping (water features, plant saucers) create significant container breeding; NIH campus surrounded by wooded habitat; WNV present; daytime biting pressure some of the most intense in the DC metro area	Check live
Ocean City	Apr – Oct	Off Nov–Mar	Eastern Shore barrier island; salt marsh adjacent — intense seasonal pressure from coastal marsh species that range widely; Worcester County mosquito control operates active aerial and ground programs; tourism season coincides with peak mosquito activity June through August; evening outdoor dining and beach activities are frequently disrupted; earlier season start than western MD (April common)	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 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 →