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Delaware · Mosquito Season Guide

Is it mosquito season in Delaware?

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II. Delaware Mosquito Season Month by month

Delaware may be the nation's second-smallest state, but its mosquito situation is outsized. The Chesapeake and Delaware Bay watersheds, the Inland Bays, and miles of tidal salt marshes create extraordinary breeding habitat. Southern Delaware in particular — the Rehoboth and Lewes coastal areas — runs one of the most intense seasons on the mid-Atlantic coast.

Northern DE / Wilmington
Wilmington · Newark · Middletown
Southern DE / Delmarva Coast
Dover · Rehoboth Beach · Lewes
Very Low Low Moderate High Very High taller = more active · color = severity
~50
mosquito species recorded in Delaware
Apr–Oct
active season statewide
3
counties — all with WNV and EEE exposure
Delmarva
one of the East Coast's most active mosquito corridors

Northern Delaware: suburban pressure

New Castle County from Wilmington south to Middletown sits in the Philadelphia-Wilmington metro corridor, where Culex pipiens thrives in storm drain systems and suburban standing water. West Nile Virus circulates in the bird population annually, with human cases most common August through October. The Christina River and Brandywine Creek corridors amplify pressure near Wilmington.

The Delmarva coast: tidal marsh intensity

Sussex County — Delaware's southernmost — is home to thousands of acres of salt marsh along the Indian River and Inland Bays. Salt marsh mosquitoes (Ochlerotatus sollicitans and Oc. cantator) emerge in explosive numbers after tidal flooding events. State mosquito control has operated in this region for decades, but pressure can still be extreme in July and August.

Eastern Equine Encephalitis: a real risk

EEE has been detected in Delaware wetlands, particularly in Kent and Sussex counties where freshwater swamp complexes harbor the Culiseta melanura vector. While human EEE cases are rare, the southern Delmarva corridor is part of the active Atlantic Coast EEE belt that stretches from Florida to Massachusetts.

III. Delaware's Key Mosquito Species
Culex pipiens mosquito photograph
Culex pipiens
Northern House Mosquito

The primary WNV vector in Wilmington, Newark, and the New Castle County suburbs — and the reason Delaware's small size doesn't translate to low disease risk. Culex pipiens breeds in the storm drain catch basins and stagnant pooling of older Delaware infrastructure, with the highest densities in the Christina River watershed communities south of Wilmington. Human WNV cases are detected in Delaware most years, concentrated in late summer when pipiens populations peak and bird hosts begin dispersing virus through the suburban landscape.

Aedes vexans mosquito photograph
Aedes vexans
Floodwater Mosquito

Delaware's most noticed species — the one that makes June and July outdoor dining unpleasant across the state. Aedes vexans hatches explosively from the Delaware River floodplains and the agricultural lowlands of Kent County following spring rains and tidal flooding. The flat Delmarva topography means that even modest rainfall events can produce widespread flooding, triggering simultaneous hatch events across large areas. The peak surge typically arrives in late May to early June and can be intense for 10–14 days before populations stabilize.

Aedes albopictus mosquito photograph
Aedes albopictus
Asian Tiger Mosquito

Established statewide and advancing. Aedes albopictus arrived in Delaware's Eastern Panhandle region via the DC-Baltimore corridor and has spread throughout all three counties. The species breeds in the kinds of containers common in Delaware's suburban landscape — discarded tires (still frequent in rural Kent and Sussex), neglected birdbaths, and the ornamental containers common in Wilmington's residential neighborhoods. Its daylight biting habit is what distinguishes it from Delaware's other species: people applying repellent only at dusk are unprotected against the tiger mosquito all day.

IV. Delaware Cities at a Glance
CityPeak SeasonOff-SeasonNotes
Wilmington Apr – Oct Off Nov–Mar Christina and Brandywine River corridors; urban storm drain breeding; WNV pressure Check live
Dover Apr – Oct Off Nov–Mar Central DE; St. Jones River wetlands; EEE detected in county most years Check live
Newark Apr – Oct Off Nov–Mar White Clay Creek corridor; suburban container habitat for Ae. albopictus Check live
Rehoboth Beach Apr – Oct Off Nov–Mar Inland Bays salt marsh; intense coastal season; state mosquito control active Check live
Middletown Apr – Oct Off Nov–Mar Southern New Castle County; Chesapeake and Delaware Canal corridor 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 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 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 →