House Mouse Facts & How to Identify Them

In Pennsylvania and many other states throughout the U.S., the house mouse is identified as one of the most troublesome and costly rodents. They thrive under a variety of conditions and can be found in and around homes and commercial structures as well as in open fields and on agricultural land. They are small rodents with relatively large ears and small, black eyes. They weigh about 1/2 ounce and typically are light brown to gray in color. An adult is about 5 to 7 inches long, nose to tail. They reproduce quickly. In a single year, a female may have 5 to 10 litters of about 5 or 6 young. Young are born 19 to 21 days after conception, and they reach reproductive maturity in 6 to 10 weeks. The life span of a mouse is usually 9 to 12 months.

House mice consume and contaminate food and cause considerable damage to structures and property, and they can transmit pathogens that cause diseases such as salmonellosis, a form of food poisoning. Although house mice usually prefer to eat cereal grains, they are nibblers and will sample many different foods. Mice have keen senses of taste, hearing, smell, and touch. They also are excellent climbers and can run up any rough vertical surface. They will run horizontally along wire cables or ropes and can jump up to 12 inches from the floor onto a flat surface. Mice can squeeze through openings slightly larger than 1/4 inch across. House mice frequently enter homes in autumn, when outdoor temperatures at night become colder.

Droppings, fresh gnaw marks, and tracks indicate areas where mice are active. Their nests are made from finely shredded paper or other fibrous material, usually in sheltered locations. House mice have a characteristic musky odor that reveals their presence. They are active mostly at night, but they can be seen occasionally during daylight hours.

While the house mouse hasn't been found to be a carrier of hantavirus, the deer mouse can harbor the Sin Nombre virus, which causes a rare but often fatal illness known as hantavirus pulmonary syndrome (HPS). The house mouse is distinguished from the deer mouse by its overall gray coat. It has larger eyes and a white underside with a distinct line of demarcation between the dark coloration on top and the white underside. In addition, the tail on the house mouse has almost no fur on it, whereas the tail of the deer mouse is moderately to well furred and is light underneath and dark on top.

Before attempting to clean up premises where deer mice have been present, contact your county health department or see the Centers for Disease Control and Prevention Web site If you think you have a mouse problem, contact us at 717-384-8210.