There are several species of mice and rats in Illinois. The species most likely to cause problems are the house mouse, deer mouse, white-footed mouse, and the Norway rat. The house mouse and Norway rat are not native to Illinois. They have moved along with humans throughout North America and the world.
Mice and Rats
The house mouse is a gray-brown mouse with a nearly hairless tail that is as long as or longer than the body. They are typically 5½ to 7 inches in length including the tail and weigh one-half ounce. This mouse was bred to produce the laboratory mouse.
The deer mouse has a grayish-brown to reddish-brown back and white undersides. The upper surface of the tail is the same color as the back and the underside of the tail is white. The tail is one-third to less than one-half the length of the body. Deer mice have large, black eyes and large, nearly hairless ears. The feet are white. They are typically 6½ to 7½ inches in length including the tail and weigh one-half to one ounce.
The white-footed mouse can be difficult to distinguish from the deer mouse, as the coloring of the two species is the same. White-footed mice are typically slightly larger than deer mice, with a tail that is about half the length of the body. They are typically 6½ to 7½ inches in length including the tail and weigh one-half to one ounce.
Field mice are small mammals that tend to have large heads, compact bodies, and short noses. They have short ears that barely protrude from the fur surrounding them. The meadow vole is a typical representative of this group and has dull fur that is grizzled chestnut to yellowish brown on the upper parts of the body, silvery gray on the lower parts. The tail, about one-third of the total body length, is sparsely haired and scaly.
Norway rats have coarse, brown fur, with lighter fur on the undersides. The ears and tail are nearly hairless. They are typically 12 to 18 inches long including the tail and weigh 10 to 16 ounces.