Mice and rats

Mouse and Rat Facts

Classification:

Kingdom: Animalia

Subkingdom: Bilateria

Phylum: Chordata

Subphylum: Vertebrata

Class: Mammalia

Subclass: Theria

Infraclass: Eutheria

Order: Rodentia

Suborder: Myomorpha

Family: Muridae, with fifteen subfamilies, 241 genera, and 1,383 species

Geographical location: Worldwide, through introduction by humans

Habitat: Occurs in highly varied habitats, usually in association with humans

Gestational period: Nineteen to twenty-two days, although this may be lengthened in nursing females due to delayed implantation

Life span: Around one year in the wild, laboratory rats and mice may live three to four years or longer

Special anatomy: The scantily-haired tail helps to distinguish house mice and Norway rats from most other types of mice and rats

Although there are many types of mice and rats, the words most often are used to refer to the house mouse, Mus musculus, and the Norway rat, Rattus norvegicus. These two species belong to a family of rodents known as the Muridae, the Old World mice and rats, and there are over 1,380 species within this group. Both species underwent their early evolution in the wilds of Asia. As humans appeared and settled in farms and villages, mice and rats became associated with them. As humans migrated to other parts of the world and as commercial exchanges took place around the world, mice and rats went along for the ride and became established in the Old World and the New World, and today may be found almost any place on Earth where humans are found.

At birth, mice and rats are unimposing animals, as the pups are born in an altricial state—naked, sightless, and helpless. They develop rapidly, however, and by three weeks of age, are weaned from their mother. By one and a half to two months of age for the mouse and two to three months of age for the rat, they are sexually mature. Their powers of reproduction are phenomenal, and many litters, some containing more than a dozen young, can be produced in a single year. A single female mouse may produce over one hundred young in one year.

As adults, mice and rats still are not imposing. They have a long, scaly, scantily-haired tail and are a grayish brown color, which is somewhat paler in the belly. Although they have poor sight, their senses of smell, hearing, and taste are all excellent.

The Good and Bad of Mice and Rats

All of the other mammalian species combined, as well as all other animals, do not cause as much damage and destruction to humans as do mice and rats. The two species have been able to adjust to living with and near humans and their habitations. Their diets are omnivorous and include all types of foods, grains, and grain products. They can climb, burrow, and swim and can invade nearly all buildings, houses, barns, warehouses, and other structures. As a result, they cause billions of dollars worth of damage each year around the world. Human food is eaten or destroyed by contamination with urine and feces. The urine may contain bacteria, causing diseases such as leptospirosis. Food poisoning may be caused by salmonellosis in their feces. Many children and some adults are bitten each year by rats, especially in rundown urban areas. Even those mice and rats that live under semiwild conditions may affect humans in their effect on other wildlife. Ground-nestingbirds and the young of other animals are susceptible to predation by mice and rats. The costs of these pests to humans are tremendous.

Some consolation for having to deal with the extensive bad side of mice and rats may be found in their beneficial use as laboratory animals. Both species are used widely in medical and genetic research. The mouse has been used to elucidate many basic principles of genetics, and today, its many genetic variants serve as models for many human disorders, including genetic diseases and cancer. As studies define the human genome, similar studies define the mouse and rat genomes. The laboratory rat, although not as genetically well known as the mouse, has been used extensively in physiological and psychological research.

It is unlikely that humans will ever be able to completely eliminate mice and rats and control their destruction. Still, it also is unlikely that their importance to both basic and applied science will ever be diminished, at least in the foreseeable future.

Principal Terms

Altricial: born in a helpless state and completely dependent on the parent(s)

Commensal: living in close association with humans; the word means “sharing the table”

Omnivorous: eating all kinds of food, both plant and animal

Rodents: the gnawing mammals characterized by specialization of the incisor teeth into gnawing teeth

Bibliography

“About Rats and Mice.” Environmental Protection Agency, 27 Oct. 2022, www.epa.gov/rodenticides/about-rats-and-mice. Accessed 11 July 2023.

Barnell, S. A. The Rat: A Study in Behavior. Rev. ed. Chicago: University of Chicago Press, 1975.

Chapman, Joseph A., and George A. Feldhamer, eds. Wild Mammals of North America: Biology, Management, and Economics. Baltimore: The Johns Hopkins University Press, 1982.

Crowcroft, Peter. Mice All Over. Chester Springs, Pa.: Dufour Editions, 1966. .

Silver, Lee M. Mouse Genetics: Concepts and Applications. New York: Oxford University Press, 1995.

U.S. National Research Council. Urban Pest Management. Washington, D.C.: National Academy Press, 1980.