Pack Rat, or Wood Rat, a North American rodent. Most pack rats build large nests by piling up twigs, leaves, rocks, and other available material. The nests are built in rock crevices, tree trunks, and shrubs; they are up to three feet (1 m) high and four feet (1.3 m) wide. As a pack rat forages for nesting material, it will sometimes drop an object it has been carrying in its mouth and pick up another in its place. Because of this trait, it is sometimes called a trade rat. The pack rat is about 8 inches (20 cm) long, with a hairy tail up to 10 inches (25 cm) long; it has a white belly and grayish back. About 20 species occur in western North America from Canada to Mexico and in the eastern United States from New York to Florida.

The pack rat belongs to the genus Neotoma of the New World mouse and rat family, Cricetidae.