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Texas Invasive Species Institute

Texas Invasive Species Institute

Norway rat

Rattus norvegicus

Class: Mammalia
Order: Rodentia
Family: Muridae

Rattus norvegicus

Photographer: unknown Source:www.wittpm.com Copyright: CC BY


The Norway rat (Rattus norvegicus) is a member of the family Muridae and is very similar to the nonnative roof rat (Rattus rattus). The Norway rat can be distinguished by a larger and fuller body size. Body color of the Norway rat is sandy to gray in color, with a yellow to white patch ventrally, and patches of black or dark coloring dorsally. Adult Norway rats are an average of 440 mm in length and weigh 400-500 g.

Field Identification of the Norway rat vs. a house mouse - provided by Internet center for Wildlife Damage Management

Ecological Threat

There are multiple known predators of the Norway rat, but its high fecundity prevents effective population control with predators alone. After Norway rats become established in higher population densities destruction to property is frequent. Norway rats are known to eat young chickens, chicken eggs, and in some cases even young pigs and sheep. Further concern of Norway rat populations arises from the number of known diseases they carry such as bubonic plague (transmitted from fleas to humans), endemic typhus fever and ratbite fever,.


Norway rats are known for their prolific breeding with gestation periods lasting only 21-23 days and an average of 8 offspring per litter. Newborn Norway rats are highly dependent on their parents because they are born naked and blind. After a period of two weeks young rats open their eyes and are weaned following 3-4 weeks of age. The life expectancy of the average Norway rat is 3-4 years. Breeding seasons are not specified with copulation occurring regularly, but decreases during winter months.


Introduction of the Norway rat to the United States occurred in 1775. A preference to lower elevations exists, but the rat effectively became established throughout 48 states.

Native Origin

Native Origin: Norway

Current Location

U.S. Habitat: Norway rats live in close proximity to humans in basements of homes or hole in foundations, but also live in marshy areas or fields where no human contact occurs. Primarily, Norway rats feed on vegetation, but will eat chicken eggs, young chickens, and garbage in areas where humans are present. Norway rats build nests on the ground and are most comfortable there, but have the ability to climb buildings and walk across electric wires to access other structures.

U.S. Present: All contiguous 48 states.


Early detection and prevention is vital to preventing these prolific breeders from becoming established in your home or farm.Norway rat populations can be prevented by removing possible food sources such as garbage. Make sure to secure garbage cans to prevent rats from feeding. Closely observe house foundations and basements for evidence of rat nests. Rat poison can be used for eradicating new populations of Norway rats, but should be used with extreme caution if household pets are present. Snap traps can be laid out near areas where rat droppings or gnawing has been observed indicating a regular path taken by Norway rats.   

More information - Fact sheet provided by Illinois Department of Health



Brooks, J. E. 1973. A review of commensal rodents and their control. CRC Critical Reviews in Environ. Control. 3(4):405-453.

Davis, D. E. 1981. Environmental control of rodents. Pages 493-498 in D. Pimentel, ed. CRC Handbook of pest management in agriculture, Vol. 1. CRC Press, Inc., Boca Raton, Florida.

Emlen, J. T., Jr., A. W. Stokes, and C. P. Winsor. 1948. The rate of recovery of decimated populations of brown rats in nature. Ecology 29:133-145.

Gutteridge, N. J. A. 1972. Chemicals in rodent control. Chem. Soc. Rev. 1:381-409.

Kaukeinen, D. E. 1982. A review of the secondary poisoning hazard potential to wildlife from the use of anticoagulant rodenticides. Proc. Vertebr. Pest Conf. 10:151-158.

Bjornson, B. F., K. S. Litting, H. D. Pratt. 1973. Control of domestic rats and mice. Public Health Serv. US Dep. Health, Educ. Welfare, Pub. No. (CDC) 77-841. 47 pp.

Weber, W.J. 1982. Diseases transmitted by rats and mice. Thomson Pub. Fresno, California. 182 pp.

Internet Sources





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