Reithrodontomys megalotis (Baird, 1857)

Introduction to Description

This section provides a physical description of Reithrodontomys megalotis, the western harvest mouse, and compares it to similar species.

Fur Coloration

The western harvest mouse has brownish fur, buff-colored sides, a white belly, and an indistinct white stripe running along its spine.

Body Length

Adult individuals reach a total length of 11 to 17 centimetres (4.3 to 6.7 inches), with a tail length between 5 and 10 centimetres (2.0 to 3.9 inches).

Body Height

Their height, measured from the ground to the highest point of the back, ranges from 1.5 to 2.0 centimetres.

Weight and Dimorphism

Mature western harvest mice weigh between 9 and 22 grams (0.32 to 0.78 oz), and this species shows no sexual dimorphism.

Similar Species Distinction

Several similar species can be distinguished from Reithrodontomys megalotis by key traits: the plains harvest mouse (Reithrodontomys montanus) has a more distinct but narrower stripe along its spine; the fulvous harvest mouse (Reithrodontomys fulvescens) has a longer tail; the salt marsh harvest mouse (Reithrodontomys raviventris) has underbelly fur that ranges from pinkish cinnamon to tawny; and the house mouse (Mus musculus) has ungrooved incisors, unlike the grooved incisors of the western harvest mouse.

Dental Formula

The dental formula of Reithrodontomys megalotis is 1.0.0.3 / 1.0.0.3 = 16 total teeth.

Species Distribution

The distribution of this species spans continuously from southwest British Columbia and southeast Alberta in Canada, south through the United States to west Texas, northeast Arkansas, northwest Indiana, and southwest Wisconsin, and continues into the interior of Mexico as far south as Oaxaca.