Rodent Identification

Side black silhouettes of four animals. An opossum, a mouse, a rat, and a squirrel

Both wild and commensal rodents may infest homes and other structures, especially in rural areas. These are a few of the most common rodent species that you may see San Mateo County.

Roof Rat

Roof rats are also called black rats, ship rats, or house rats.

Norway Rat

Norway rats are also called brown rats, sewer rats, or street rats.

House Mouse

House mice (Mus musculus) are brown to black with a lighter, but not white, underbelly. They are smaller than rats (2 to 3.5 inch long body with 3 to 4 inch long tail) but similar in appearance. Young rats are sometimes mistaken for mice. House mice are seen both indoors and in agricultural areas.

Sideview of a mouse. The mouse is mostly dark brown, but the belly of the mouse is white. The mouse has light pink feet, large black eyes, and long white whiskers.

Deer Mouse

The western deer mouse (Peromyscus maniculatus) is native to California and distributed throughout wooded areas from Alaska down to central Mexico.

Wood Rats

Dusky-footed wood rats (Neotoma fuscipes) are native to San Mateo County and frequently live in wooded areas near creeks and streams. They make large, elaborate nests, called woodrat houses, of twigs and leaves that can be over three feet high. These houses can be on the ground or in the trees and provide shelter for other species including native mice, lizards, and an incredible variety of…

Side view of a grey squirrel. The squirrel appears to be holding something in its front paws and holding it near its mouth. The face of the squirrel is light brown with black eyes. The body of the squirrel is grey and brown. The tail of the squirrel is very bushy and light brown colored with longer grey hairs as well.

Tree Squirrels

There are multiple species of squirrels common throughout San Mateo County, but only the ones that live up in trees are called “tree squirrels” (squirrels that live underground are called ground squirrels).

Front view of a California ground squirrel, which has a mottled brown and light brown coat of fur on its body. It has a bushy grey tail (but not as bushy as a tree squirrel).

Ground Squirrels

The California ground squirrel (Otospermophilus beecheyi) is native to the United States from western Washington to Baja California.

Side view of a opossum. The opossum has a white face with black eyes and a pointed pink nose. The ears and legs are darker than the rest of its dark grey colored body. The opossum has a long pink colored tail.

Opossums (not a rodent, but often confused!)

Opossums (Didelphis virginiana) are not rodents, but they are often confused as rodents. (They are marsupials – like kangaroos!) Opossums are grey, brown and white with a sharp pointed face and a long, scaled tail. Adult opossums are 2-3 feet long with the tail included and can weigh up to 15 lbs. If you have seen or heard of “a rat as big as a cat,” it was most likely an opossum.

Green grass lawn with small mounds of dark brown dirt pile.

Other small mammals

Gophers, moles, and voles

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