The three species of murids are all introduced from the Old World. All three occur in the Southwest, but apparently only two in any one place. All three often are associated with human communities, though Mus may occur well away from human structures.

Mus musculus—House Mouse. This small mouse occurs throughout the lower elevations of New Mexico and Trans-Pecos Texas. "They have the distribution of a typical grassland rodent, occurring commonly in weedy grasslands, disturbed roadside communities in grasslands, and also in better developed grasslands, along with such native rodents as Sigmodon, Peromyscus, Reithrodontomys, and Perognathus" (Findley et al. 1975). They often are found around human structures. They seem ill adapted to colder areas in the Southwest, and Findley et al. note that they've not taken House Mice in well developed woodland or above.

Those that live with humans differ both morphologically and behaviorally from wild populations in the same region (Findley 1987). Those living in houses and farm building have longer tails and darker coloration than those living in the wild. The social setup also differs between the two.

Mus musculus originally was an inhabitant of central and southern Asia, but has spread nearly worldwide in association with man. In North America, arrival apparently was with the earliest colonists (with possibly those from the Northeast having come from Britain and northern Europe, while those in the southern U.S. and into Central and South America may have originated from populations of the Iberian Peninsula.

Rattus norvegicus—Norway Rat. Nearly 600 species of Rattus have been named—of these, two have become closely associated with man: the Norway Rat and the Black Rat. The Norway Rat arrived in both Europe and the New World later than the other species, apparently getting to Europe in the early 1700s. It is believed to have gotten to North America about 1775 and arrived at the West Coast about 1850. As it spread, it slowly displaced the Black Rat except in the southern portions of the U.S. It is more aggressive than the Black Rat. In some areas, both species occur, generally dividing up the area into ground level and basements for the Norway Rat and multistory building for the Black Rat; this fits the generally differences between the two, with the Norway Rat being a burrower and the Black Rat a climber. There are a few records of the Norway Rat in the more northern portions of the state, such as Albuquerque.

Rattus rattus—Black Rat. The Black Rat entered Europe around the 12th Century and probably entered the New World with Columbus or very shortly thereafter. After becoming widespread in North America, it became mostly limited to the southern portions of the U.S. as it was outcompeted by the Norway rat in colder climes.

In our area, it occurs in the Rio Grande Valley in the vicinity of Las Cruces and also has been recovered from the Lower Valley of the El Paso area. It seems mainly associated with farms or agriculture-associated entities such as cotton gins.


Last Update: 1 Feb 2008

Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso