What’s the Difference Between Rats and Mice?

Both mice and rats are rodents, and some are even members of the same scientific family. When they are small, or when you only see traces of their presence, they can be difficult to distinguish. However, you can learn how to tell a mouse from a rat by its physical characteristics and (in some cases) its behavior.

Classification

The Eurasian mice and rats (Mus and Rattus) are both of the family Muridae—but there are some species that can be considered outliers. Deer mice, for instance, are of an entirely different genus (Peromyscus) and family (Cricetidae) even though they can appear quite similar to the untrained eye. Likewise, the many species of kangaroo rats (genus Dipodomys) are in the same Heteromyidae family as their fellow North American natives, pocket mice (genus Perognathus).

Characteristics

A house mouse is two to four inches in length with large ears and white, brown, or grey fur. Mice have distinctive triangular snouts and long whiskers. Their tails are long, thin, and hairy. While timid, mice are social and territorial rodents. The most common mice in North America are the cotton mouse, western harvest mouse, white-footed mouse, deer mouse, and house mouse.

In addition to being larger (about seven to nine inches long) rats have blunter noses than mice. Their tails are also usually hairless and scaly. Among the most common rats in North America is the brown rat (or Norway rat), an invasive species that can disrupt natural vegetation for birds and other animals. Both rats and mice are nocturnal and produce dozens of droppings throughout the day—up to 50 for rats, and up to 100 for mice.

Another way to tell the difference between these two rodents is to look for grease marks. Rats are more likely to leave tracks on touched surfaces.

Conservation Status

Habitat loss is the greatest threat to rats and mice, led largely by encroachment on their native habitats by humans and their cats. For example, the habitat of the golden mouse (Ochrotomys nuttalli) of the Florida peninsula is increasingly fragmented due to human land use, making it nearly impossible for it to recolonize any areas where it has been eliminated.

Native species of mice and rats play important roles in their habitats as food for many predators that are themselves endangered. Most of those mice and rats exist in the western United States, primarily California and Arizona, or in the American South, primarily Florida. Of the 80 mammals on the U.S. Fish & Wildlife Service's Endangered Species list, nearly a quarter are either mice or rats.

Unlike more charismatic or photogenic mammals that are endangered, such as the Florida panther or the gray wolf, mice and rats get little public sympathy. Often efforts to protect them are fought by entrenched interests that have reduced their habitat or actively attempted to exterminate them. For example, the New Mexico Meadow Jumping Mouse (Zapus hudsonius) was first designated as endangered in 2014, but only after eight years of legal battles with ranchers was the FWS able to enact a recovery plan.

Still, some endangered mice and rats are receiving protection. The Pacific pocket mouse (Perognathus longimembris pacificus) is threatened by the fragmentation of its historic habitat of sandy dunes and coastal scrub from Los Angeles County to the Mexican border. It appeared to be extinct until a single population was discovered in Orange County in 1994. A captive breeding program at the San Diego Zoo led to reintroductions in 2016, but the species is still considered the most endangered of all the pocket mice species in North America.

Along the Gulf Coast, five species of beach mice are endangered. Their coastal dune homes are threatened not only by human development and recreational beach use but by the increasing frequency and intensity of coastal storms. With efforts to decrease the presence of cats and lights, however, the mice are making a comeback—but not enough to remove them from the endangered list.

Among the native rats, almost all the endangered ones are kangaroo rats, getting by in isolated regions of western Canada, Mexico, and the United States. The giant kangaroo rat (Dipodomys ingens) lives in grasslands along the western edge of California's San Joaquin Valley but is increasingly threatened by expanding agricultural use and urban development.

By contrast, the Stephens' kangaroo rat (Dipodomys stephensi) is doing relatively well. After a habitat conservation plan increased its numbers, the FWS proposed to reclassify it as threatened instead of endangered—and succeeded. The fate of native rats and mice, however, remains precarious.