Mice Rats and Relatives: Muridae

Rats, mice, and relatives, sometimes called murids (MYOO-rids; 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.