University of Illinois Extension

Wildlife Directory

Mice and Rats

Description and Identification

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.

House Mouse <i>Mus musculus</i>

House mouse (Mus musculus): 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.

Deer mouse (<i>Peromyscus maniculatus</i>)

Deer mouse (Peromyscus maniculatus): 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.

White-footed mouse (<i>Peromyscus leucopus</i>)

White-footed mouse (Peromyscus leucopus): 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.

Norway rat (<i>Ratus norvegicus</i>)

Norway rat (Ratus norvegicus): 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.

Habitat

House mice and Norway rats are common around human residences and industrial and commercial areas. House mice are also common in agricultural fields with ground cover nearby. Deer mice are common in open habitats such as pastures, agricultural fields, and field borders and are sometimes found near buildings. White-footed mice are common in forest edges and may inhabit homes built in or near wooded areas.

Distribution and Abundance

The house mouse and Norway rat were introduced from Europe. Deer and white-footed mice are native to Illinois. All four species are common and abundant throughout Illinois. Populations of deer mice and white-footed mice do not commonly overlap due to their preference for different habitats.

Reproduction

All three species of mice have multiple litters per year and produce an average of four to six young per litter. The young mice mature quickly and are able to reproduce within two months. The Norway rat produces six to eight litters of six to nine young per year. The young are able to breed before they are four months old.

Food

All four species are omnivorous (eat plant and animal material). The main food sources are seeds, nuts, and berries. Insects are also consumed. In a human environment, the rodents will consume almost any food to which they have access. They also often chew on inedible materials such as books, soap, and cans.

Behavior

All four species are nocturnal (active at night) and are not commonly seen. Their presence is typically detected by the presence of their droppings, holes chewed into bags and containers, and chewed nesting materials. Mice and rat droppings are small, dark, and cylindrically shaped. Norway rats leave droppings that are about one-half inch to three-fourths inch long with blunt ends. Mice leave slender, pointed droppings that are about one-fourth inch long.

Longevity

Mice typically live less than one year. Rats may live up to three years, but a lifespan of one and a half years is more common.

Damage Prevention and Control Measures

The house mouse and Norway rat are the rodents most often involved in building infestations, contamination of food, and other public health concerns. Large infestations are best corrected by a professional exterminator. The following websites provide information on controlling mice and rats. The information provided for the house mouse is also applicable to deer mice and white-footed mice. The native deer mice and white-footed mice often move into buildings in late fall or early winter and can be live trapped and released at least one mile away from the building.

Public Health Concerns

Wild mice and rats can be carriers of Hantavirus. The house mouse is not known to carry Hantavirus. Mice and rats can also carry salmonellosis, leptospirosis, and tularemia. White-footed mice are an important host in the lifecycle of the deer tick, a carrier of Lyme disease. Rats can be a carrier of bubonic plague. Although rats can be a carrier of bubonic plague, that disease is not indigenous in Illinois. For more information about plague, read the IDPH Plague Fact Sheet.

Ecological Role

Mice and rats are important food resources for foxes, coyotes, owls, hawks, and other predators.

Legal Status

The Illinois Wildlife Code does not protect house mice, deer mice, white-footed mice, or Norway rats. They may be removed without a permit from the Illinois Department of Natural Resources.