Delaware mammals

Norway Rat in Delaware

Rattus norvegicus

Introduced to Delaware

Delaware's Rattus norvegicus records are of an introduced species; it does not occur here as a wild native population.

IUCN Red List status

LC – Least Concern

Widespread and abundant; not at risk.

Photo: Charles J. Sharp · CC BY-SA 4.0Live Norway rat beside shallow waterPhoto: Sciadopitys from UK · CC BY-SA 2.0Brown rat crossing stones in a streamPhoto: AnemoneProjectors (talk) · CC BY-SA 2.0Norway rat feeding in short vegetationPhoto: Chuck Homler d/b/a Focus On Wildlife · CC BY-SA 4.0Brown rat standing beside rocks in an urban parkPhoto: Steve Milsom · CC0Live Norway rat walking through debris beside human structures

Photo: Charles J. Sharp · CC BY-SA 4.0Live Norway rat beside shallow waterPhoto: Sciadopitys from UK · CC BY-SA 2.0Brown rat crossing stones in a streamPhoto: AnemoneProjectors (talk) · CC BY-SA 2.0Norway rat feeding in short vegetationPhoto: Chuck Homler d/b/a Focus On Wildlife · CC BY-SA 4.0Brown rat standing beside rocks in an urban parkPhoto: Steve Milsom · CC0Live Norway rat walking through debris beside human structures

Norway Rat in Delaware, by the numbers

Occasional in Delaware 24th most recorded of 62 mammals logged in Delaware

25 occurrence records

25 with iNaturalist photos

Jan 31, 2026 Last seen in Delaware

Records from 2000–2026.

When to look for the Norway Rat in Delaware

Most sightings fall in January.

25 Delaware occurrence records (iNaturalist and GBIF) by month of year, 2000–2026. Shows when the species is recorded, not a guarantee of presence. Based on a small number of dated records; the seasonal pattern may not be representative.

Monthly Delaware records (table)

Month	Records
January	6
February	1
March	3
April	3
May	4
June	1
July	0
August	1
September	1
October	0
November	3
December	2

Monthly norway rat occurrence records (iNaturalist and GBIF) in Delaware, 2000–2026.

Seasonality

Year-round in Delaware, with recorded sightings peaking in January, with a smaller rise in May.

Occurrence map

Where Norway Rat has been recorded in Delaware

25 records mapped · zoom and drag to explore

25 Delaware records mapped

Notable places to look

Park, forest, or monument	iNaturalist records
First State National Historical Park	2

Protected places with the most norway rat sightings, from the USGS Protected Areas Database plus named mountain ranges, good spots to look, not a full breakdown, so they don't sum to the total.

Where it's recorded in Delaware

County	Records
New Castle County	9
Sussex County	8
Kent County	6
Other localities	2

The complete county distribution, spread across 3 Delaware counties. Every occurrence record falls in one county, so these sum to the total. Counties from GBIF and US Census boundaries.

Norway Rats are introduced in Delaware and most closely associated with buildings, ports, farms, refuse, and hardened shorelines. Records near natural areas can reflect nearby human infrastructure rather than a preference for intact marsh or forest, so refuge dots are not wildlife-viewing recommendations.

They occur in any month, with limited observations spread across the year. Reduce attractants by securing food, feed, and waste and closing entry points around structures.

Occurrence data from iNaturalist and GBIF.

Full species profile Norway Rat Rattus norvegicus Size 15–28 cm5.9–11 in Weight 140–500 g0.3–1.1 lb Lifespan Up to 3.8 yr View the full profile

More mammals in Delaware in the atlas

Data & sources

The data and visualizations on this page draw on these open sources:

GBIFCC-BY 4.0occurrence records behind the range map, elevation, and record counts
iNaturalistCC0 / CC-BY / CC-BY-SAobservations, photos, and audio recordings
NatureServe ExplorerCC-BYthe state conservation rank
IUCN Red Listattributed factthe global conservation status
USGS NASpublic domainnative / introduced status
Natural Earthpublic domainthe relief basemap
USGS Protected Areas Databasepublic domainthe named parks, forests, and refuges behind "notable places to look"