The deer mouse, P. maniculatus, a species of North American white-footed mice, resembles the European long-tailed field mouse. The house mouse, Mus musculus, is the most widely distributed mammal, other than humans, and has been introduced into almost every place inhabited by humans. Many genetic variations, such as the white, or albino, mouse, are bred and raised throughout the world as laboratory animals or pets.

Mice are small rodents, and like all rodents they possess gnawing teeth. The word mouse, however, has no distinct meaning beyond that in scientific classification systems. It has been applied loosely to many rodents simply because of their size and superficial similarities, such as a somewhat pointed snout, a slender and sparsely haired tail, relatively conspicuous ears, and an elongate body. (The word rat is used in an equally loose way for larger rodents of similar appearance.) In terms of these characteristics, mice are conveniently grouped below into New World and Old World families, although both contain many species other than those called mice. In addition, many small rodents with distinctly different characteristics have also come to be known as mice. Among them are the short-tailed field mice, or field voles, Microtus; the pocket mice, family Heteromyidae; the jumping mice, family Zapodidae; and the squirrel like dormice and related forms, families Gliridae, Platacanthomyidae, and Seleviniidae.

Many of these animals carry a variety of viral, bacterial, and parasitic disease. Mice associated with humans also have considerable economic impact through crop damage, destruction of trees, and food contamination.

New World Mice The family Cricetidae, which also contains hamsters, rats, lemmings, voles, and gerbils, comprises about 177 species of mice, grouped into 30 genera. The best-known native North American forms are the white-footed or deer mice, Peromyscus, represented by approximately 57 species ranging from northern coniferous forests into tropical habitats in Central America. The most widespread species is the deer mouse, P. maniculatus. Other common North American mice are the harvest mice, Reithrodontomys, which generally live in grassy or marshy habitats and commonly construct nests above ground in vegetation, and the grasshopper mice, Onychomys, which occupy plains and deserts and which include a high proportion of insects, scorpions, and other small animals in their diet. The smallest New World form is the pygmy mouse, Baiomys, a full-grown specimen of which may be less than 100 mm (4 in) in length, including the tail. The family Muridae, which also contains rats and gerbil mice, comprises about 130 species of mice, grouped into 30 genera, including Mus, the house mice, and Apodemus, the Old World field mice. These mice are found naturally only in the Eastern Hemisphere, with the greatest variety of species in Southeast Asia. They are common throughout Eurasia and Africa and through the islands of Indonesia into Australia, being absent only on the island of Madagascar on the eastern coast of Africa. As with other rodents, the diet consists mainly of plant materials, although a variety of small animals, such as insects, may be eaten when available. Forms living in association with humans may eat almost any food. Most species are terrestrial, although some, such as the African climbing mice, Dendromus, may spend most of their time in trees or shrubs. Some dig burrows or use those of other animals; some occupy abandoned birds' nests; and many use crevices, hollow logs, or other natural features.

The most widely distributed mammal, other than humans, is the house mouse, Mus musculus, which has been introduced into almost every place inhabited by humans. Many genetic variations, such as the white, or albino, mouse, are bred and raised throughout the world as laboratory animals or pets.

Bibliography: Elton, C. S., Voles, Mice and Lemmings (1942; repr. 1965); Hanney, Peter W., Rodents (1975); Rugh, R., The Mouse: Its Reproduction and Development (1990).

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