Rattus norvegicus

Brown Rat
(*Rattus norvegicus*)
Brown Rat (Rattus norvegicus)
Range
Taxonomic classification
Order:	Rodentia
Suborder:	Supramyomorpha
Infraorder:	Myomorphi
Superfamily:	Muroidea
Family:	Muridae
Subfamily:	Murinae
Tribe:	Rattini
Subgenus:	Rattus
Binomial details
	Rattus norvegicus (J. Berkenhout, 1769)
Other resources
	Full taxonomic details at MDD

The Brown Rat (Rattus norvegicus) is a large rat that is found in a wide range of human-made habitats. Despite being a biomedically and economically important species, its distribution is not generally well understood. The range map to the right should be used to generally understand the range of the species in North America and should not be used to make determinations about the species presence or absence on small islands or at the northern limit of its estimated range. This is a wide-ranging species and its range will likely continue to expand with human expansion and climate change.

Description

From Best & Hunt (2020): "The brown rat is a large rat with coarse pelage. Pelage is usually grayish-brown on upperparts with scattered black hairs, somewhat darker down the center of the back, and pale gray or grayish-brown on the ventrum. However, color may be black, white, brown, or combinations of these. The tail is nearly hairless, scaly, and less than 50% of total length. Ears are medium-sized and covered with short hairs, and eyes are small and dark. Feet are gray or white."

From Armstrong et al. (2010): "The Norway rat is a large, heavy-bodied rat with a long, sparsely haired, scaly tail. The upperparts are usually brown to brownish black whereas the underparts are paler in color. Occasionally some individuals show a high degree of spotting or splotching with white. The pelage is somewhat coarse. The ears are conspicuous and covered with short hairs."

External measurements

Length measurements are in millimeters (mm) and weight measurements are in grams (g), unless stated otherwise. If available, the sample size (n=) is provided. If a range is not provided and n= is not given, then the listed measurement represents an average.

Part of range	Reference	Total length	Tail length	Hindfoot length	Ear length	Mass
Alabama	Best & Dusi (2014)	362 (290–434) (n=15)	168 (135–206) (n=15)	41 (35–56) (n=15)		189.3 (87.5–357.0) (n=5)
California	Jameson & Peeters (2004)	300–475	120–215	32–44	19–24	300–525
Carolinas, Virginia, Maryland	Webster et al. (1985)	320–480	150–220			300–540
Colorado	Armstrong et al. (2010)	300–480	150–255	30–44	18–21	150–540
Minnesota	Hazard (1982)	360–415	160–183	40–43	19–21	200–270
North Dakota	Seabloom et al. (2020)	390	175	41	20	up to 485
Texas	Schmidly & Bradley (2016)	440	205	46		400–500
Virginia	Linzey (1998)	325–475	150–215			280–335

Skull

From Armstrong et al. (2010): "The skull is long and narrow with conspicuous temporal ridges. The length of the first upper molar is lover than the combined length of molars 2 and 3." Additionally, "the cheekteeth of woodrats [Neotoma] are prismatic whereas those of Norway rats have well-defined cusps arranged in 3 parallel rows."

FMNH186612. Rattus norvegicus. Dorsal view of the skull.
FMNH186612. Rattus norvegicus. Lateral view of the skull.
FMNH186612. Rattus norvegicus. Dorsal view of the lower jaw.
Rattus norvegicus. Upper molars.
Rattus norvegicus. Lower molars.
Rattus norvegicus. Upper incisors.

Footprint

Rattus norvegicus. Front right footprint.
Rattus norvegicus. Hind right footprint.

Similar species

Comparison with Neotoma

From Armstrong et al. (2010): "Although superficially similar in size and appearance, Norway rats can be distinguished from woodrats (Neotoma) by their naked tail, poorly haired ears, and relatively coarser hair."

Brown Rat (Rattus norvegicus)
Eastern Woodrat (Neotoma floridana) shown, representing members of the genus Neotoma.
Brown Rat (Rattus norvegicus). Dorsal view of the skull. The zygomatic arches are broken in this individual.
Eastern Woodrat (Neotoma floridana) shown, representing members of the genus Neotoma. Dorsal view of the skull.
Brown Rat (Rattus norvegicus). Upper molars.
Eastern Woodrat (Neotoma floridana) shown, representing members of the genus Neotoma. Upper molars. Black arrows point to a character that can be helpful for differentiating species of Neotoma, but can be ignored in this comparison. Notice that the upper molars are E-shaped, unlike in Rattus norvegicus.

Comparison with Rattus rattus

From Best & Hunt (2020): "Brown rats are similar in appearance to roof rats [Rattus rattus], but roof rats generally are smaller and have a tail greater than 50% of total length. The rostrum of brown rats is blunter than that of roof rats, and the overall shape of the body is broader in brown rats."

Brown Rat (Rattus norvegicus)
Roof Rat (Rattus rattus). Note that the tail length is much longer than the length of the head and body in this species.
Brown Rat (Rattus norvegicus). Dorsal view of the skull. The zygomatic arches are broken in this individual.
Roof Rat (Rattus rattus). Dorsal view of the skull.
Brown Rat (Rattus norvegicus). Upper molars.
Roof Rat (Rattus rattus). Upper molars.

References

Armstrong DM, Fitzgerald JP, Meaney CA. 2010. Mammals of Colorado, Second Edition. Denver (CO, USA): University Press of Colorado.

Best TL, Hunt JL. 2020. Mammals of the southeastern United States. Tuscaloosa (AL, USA): University Alabama Press.

Hazard EB. 1982. The mammals of Minnesota. Minneapolis (MN, USA): University of Minnesota Press.

Jameson EW, Peeters HJ. 2004. Mammals of California (No. 66). Berkeley (CA, USA): University of California Press.

Linzey DW. 1998. The mammals of Virginia. McDonald & Woodward Publishing.

Schmidly DJ, Bradley RD. 2016. The mammals of Texas. Austin (TX, USA): University of Texas Press.

Seabloom R, Hoganson JW, Jensen WF. 2020. The mammals of North Dakota. Fargo (ND, USA): North Dakota State University Press.