Rats, mice, and relatives, sometimes called murids (MYOOrids; members of the family Muridae), are divided into seventeen subfamilies, including voles and lemmings, hamsters, Old World rats and mice, South American rats and mice, and many others. As a result of the large number of species, there is much variation in the physical characteristics of murids.

Voles and lemmings are small rodents with a broad, rounded head; small eyes and ears; thick, cylindrical body; and short legs and tail. Most species’ fur is some shade of brown with paler underparts. Lemmings look a lot like voles, but most species are stockier, with heavier bodies and shorter tails. Adults are 3.5 to 24.5 inches (8.5 to 62 centimeters) long and weigh between 0.5 ounces and 4 pounds (15 grams to 1.8 kilograms).

Hamsters are mouse-like Old World rodents with large cheek pouches used to carry food; stout body; short legs; wide, (sometimes) furry feet; and short, furry tails. They have front paws with four digits and a short thumb, and hind feet with five digits. Their soft, thick fur varies in color (depending on the species) from gray to reddish brown, and their underparts can be white, gray, or black. They have excellent senses of hearing and smell, but poor eyesight (even though they have large, round eyes). Adults are 2 to 13.4 inches (5 to 34 centimeters) long and weigh between 0.9 and 31.7 ounces (25 to 900 grams).

Old World rats and mice have long tails (sometimes longer than the body) that are either furry or scaly; strong feet; long hind feet; and opposable digits on their front feet. Adults have a length of 1.9 to 14.7 inches (5 to 36 centimeters) and a weight of 0.2 to 52.9 ounces (5 grams to 1.5 kilograms).

South American rats and mice are small- to medium-sized rodents with brownish or blackish upper coats; very small or no external ears; grayish or whitish underparts; thinly haired tails that sometimes have a penciled tip; and relatively small feet. They have a head and body length of 2.4 to 11.4 inches (6.1 to 29.0 centimeters); tail length of 1 to 6.3 inches (3 to 16 centimeters); and weight of 0.4 to 18 ounces (12 to 510 grams).

All other rats, mice, and relatives vary widely in physical characteristics. Most species are small, usually with somewhat long tails and brownish fur.


Rats, mice, and relatives are found throughout the world except for the extreme polar regions of Earth.


Rats, mice, and relatives live in many different habitats including open flatlands, savannas (flat grasslands), grasslands, prairies, steppes (treeless plains that are often somewhat dry and grass-covered), woodlands, forests, deserts, scrublands, foothills, jungles, rainforests, wetlands, cultivated lands and fields, and along waterways and water bodies. They are found from dry temperate (mild) climates to wet tropical environments.


Most species of rats, mice, and relatives eat at least a few of the following foods: grasses, seeds, grains, root vegetables such as bulbs and tubers, green plant parts, conifer needles, nuts, berries, fruits, insects and insect larvae (LAR-vee), fish, lizards, frogs, baby birds, crabs, tadpoles, salamanders, fungus, lichens, mosses, other small vertebrates (animals with a backbone) and invertebrates (animals without a backbone), and carrion (decaying animals).


Rats, mice, and relatives are active during the day, at night, or both night and day (depending on the species). For their size, they can be very aggressive to predators and even to other members of their species. The rodents can be vocal, with various communicative sounds such as chattering, screaming, and whistling. They set up territories and defend them vigorously.

Murids are sometimes found alone, but often are social, and are found traveling and sleeping together. They use nests for shelter and to raise their young. Some species breed throughout the year but others only during certain seasons. Murid rodents generally have high reproduction rates (lots of offspring) and large populations. Litters (groups of young born at the same time from the same mother) have one to seventeen offspring. Young are born blind and naked, although they develop fast, are weaned (stop drinking their mother’s milk) quickly, and are able to reproduce within weeks or months.


Rats, mice, and relatives are generally considered pests in agricultural and forested lands. Large species are often trapped for their fur. Some species carry diseases that can sicken and kill people. Rats, mice, and relatives are frequently used as laboratory research animals. Some, such as hamsters and gerbils, are kept as pets. They are often important in maintaining a healthy ecosystem in their natural habitats.


Almost 450 species of murids are listed on the World Conservation Union’s (IUCN) Red List. Of these, twenty-one are Extinct, died out; fifty are Critically Endangered, facing an extremely high risk of extinction in the wild; seventy-four are Endangered, facing a very high risk of extinction in the wild; and 110 are Vulnerable, facing a high risk of extinction in the wild.