The deer mouse is a small rodent with large, protruding, black eyes; large, scantily furred ears; long, coarse whiskers; and a moderately to well-furred tail from one-third to less than one-half of the animal’s total length with a slight tuft at the tip. There are 4 clawed toes and an inconspicuous nailed thumb on each front foot, and 5 clawed toes on each hind foot. The soles of the hind feet are thinly furred from the heel to the 6 pads, or tubercles. Small internal cheek pouches are present. The body fur is long and soft.
There is considerable color variation in individual deer mice, but in general the back and sides of the adults vary from grayish to reddish brown with or without a darker area in the middle of the back. This color is sharply marked off from the lower face and underparts, which are white or sometimes grayish. The base of the hairs on both back and belly is dark gray. The feet are white. The tail is dark like the back above and sharply contrasted to light like the belly below. The ears are dark brown for approximately the outer half with a very slight grayish to whitish margin but are whitish to pinkish for the inner half.
The deer mouse is a widely distributed North American species with great variation in form, behavior, and habitat preferences. The subspecies that occurs in Missouri is Peromyscus maniculatus bairdii.
Similar species: Missouri's four species of Peromyscus mice are similar in appearance and habits. The best way to distinguish between them is by differences in size and characters of the tail. Our other Peromyscus species are
- the white-footed mouse (P. leucopus), which usually is larger and usually has a slightly longer tail that lacks the sharp color contrast between upper and lower surfaces; it lives mostly in wooded areas.
- the cotton mouse (P. gossypinus), which is similar to but slightly larger than the white-footed mouse; it lives in moist, timbered areas, and in Missouri it is restricted to the Mississippi lowlands of the Bootheel.
- the Texas mouse (P. attwateri), which closely resembles the deer mouse but is slightly larger with a longer, strongly two-colored tail that has a fur tuft at the tip; the flanks are paler than those of the deer mouse. In Missouri, it occurs in the southwestern part of the Ozark Highlands, where it is confined to particular habitats in the White and Elk River drainages.
In areas where these species occur together, their sizes can be intermediate, so they can be very difficult to identify to species. For accurate species identification, specimens should be examined by a person familiar with these species.
Also, keep in mind that Missouri has — in addition to members of the genus Peromyscus — about 20 other species of small mice, rats, and voles. Missouri mice that look most similar to the deer mouse are the golden mouse, two species of harvest mice, the house mouse, the meadow jumping mouse, and the plains pocket mouse.