The house mouse, Mus musculus, is one of the most troublesome and costly rodents in the United States. House mice thrive under a variety of conditions; they are found in and around homes and commercial structures as well as in open fields and on agricultural land. House mice consume and contaminate food meant for humans, pets, livestock, or other animals. In addition, they cause considerable damage to structures and property, and they can transmit pathogens that cause diseases such as salmonellosis, a form of food poisoning.

IDENTIFICATION

 House mice are small rodents with relatively large ears and small, black eyes. They weigh about 1/2 ounce and usually are light brownish to gray. An adult is about 5 to 7 inches long, including the 3- to 4-inch tail.

 Droppings, fresh gnaw marks, and tracks indicate areas where mice are active. Mouse 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. Mice 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, Peromyscus maniculatus, which sometimes invades cabins and outbuildings harbors 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. The deer mouse 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 for information about how to prevent hantavirus exposure.

BIOLOGY

 Native to Central Asia, the house mouse arrived in North America on ships with settlers from Europe and other points of origin. A very adaptable animal, the house mouse often lives in close association with humans, along with Norway rats and roof rats; however, mice are more common and more difficult to control than rats.

 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.

 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.

CONTROLLING HOUSE MICE

 Because house mice are so small, they can gain entry into homes and other buildings much more easily than rats. As a result, house mouse infestations are probably 10 to 20 times more common than rat infestations. Effective control involves sanitation, exclusion, and population reduction. Sanitation and exclusion are preventive measures. When a mouse infestation already exists, some form of population reduction such as trapping or baiting is almost always necessary.

 A key to successful long-term mouse control is limiting shelter and food sources wherever possible. Trapping works well, especially when a sufficient number of traps are placed in strategic locations. Trapping also can be used as a follow-up measure after a baiting program. When considering a baiting program, decide if the presence of dead mice will cause an odor or sanitation problem. If so, trapping may be the best approach. After removing mice, take steps to exclude them so that the problem doesn’t recur.

 Several types of rodenticides are available, which can be purchased as ready-to-use baits that typically are labeled for use against only house mice, Norway rats (Rattus norvegicus), and roof rats (R. rattus). Because all rodenticides are toxic to humans, pets, and wildlife, take special precautions to prevent access to baits by children and nontarget animals.

Sanitation

 Because mice can survive in very small areas with limited amounts of food and shelter, controlling them can be very challenging, especially in and around older structures. Most buildings in which food is stored, handled, or used will support house mice if the mice aren’t excluded, no matter how good the sanitation. While good sanitation seldom will completely control mice, poor sanitation is sure to attract them and will permit them to thrive in greater numbers. Pay particular attention to eliminating places where mice can find shelter. If they have few places to hide, rest, build nests, or rear their young, they can’t survive in large numbers.

Exclusion

 Exclusion is the most successful and permanent form of house mouse control. Build them out by eliminating all gaps and openings larger than 1/4 inch. Stainless steel scouring pads make a good temporary plug. Seal cracks in building foundations and around openings for water pipes, vents, and utility cables with metal or concrete. Doors, windows, and screens should fit tightly. It may be necessary to cover the edges of doors and windows with metal to prevent gnawing. Plastic screening, rubber, vinyl, insulating foam, wood, and other gnawable materials are unsuitable for plugging holes used by mice.