Any of about 60 species (genus Peromyscus, family Cricetidae) of small, delicate rodents that are active at night and are found in habitats from Alaska to South America. They often outnumber all other mammals in an area. Deer mice are 3–6.5 in. (8–17 cm) long (excluding the long tail) and have large eyes, soft fur, and relatively large ears. Colours range from white to brown or blackish, with white underparts and feet. They eat plant and animal matter and nest in burrows or trees. Clean, easily cared for, and prolific, they are often used as laboratory animals.