Mus musculus
house mouse

Mus musculus may have originally been distributed from the Mediterranean region to China, but it has now been spread throughout the world by humans and lives as a human commensal.

House mice generally live in close association with humans-- in houses, barns, granaries, etc. They also occupy cultivated fields, fencerows, and even wooded areas, but they seldom stray far from buildings. Some individuals spend the summer in fields and move into barns and houses with the onset of cool autumn weather. Because of their association with humans, house mice have been able inhabit inhospitable areas (such as tundra and desert) which they would not be able to occupy independently.

House mice are from 65 to 95 mm long from the tip of their nose to the end of their body, their tails are 60 to 105 mm long. Their fur ranges in color from light brown to black, and they generally have white or buffy bellys. They have long tails that have very little fur and have circular rows of scales (annulations). House mice tend to have longer tails and darker fur when living closely with humans. They range from 12 to 30 g in weight. Many domestic forms of mice have been developed that vary in color from white to black and with spots.

If a house mouse is a pet, the average life span is about 2 years, but mutant and calorie-restricted captive individuals have lived for as long as 5 years. Wild-derived captive Mus musculus individuals have lived up to 4 years in captivity. In the wild, most mice do not live beyond 12-18 months.

In the wild state, house mice generally dwell in cracks in rocks or walls or make underground burrows consisting of a complex network of tunnels, several chambers for nesting and storage, and three or four exits. When living with humans, house mice nest behind rafters, in woodpiles, storage areas, or any hidden spot near a source of food. They construct nests from rags, paper, or other soft substances and line them with finer shredded material. House mice are generally nocturnal, although some are active during the day in human dwellings. House mice are quick runners (up to 8 miles per hour), good climbers, jumpers, and also swim well. Despite this, they rarely travel more than 50 feet from their established homes.

Mus musculus is generally considered both territorial and colonial when living commensally with humans. Territoriality is not as pronounced in wild conditions, however. Dominant males set up a territory including a family group of several females and their young. Occasionally, subordinate males may occupy a territory or males may share territories. Females establish a loose hierarchy within the territories, but they are far less aggressive than males. Aggression within family groups is rare, but all the individuals in a territory will defend an area against outsiders. Young mice are generally made to disperse through adult aggression, although some (especially females) may remain in the vicinity of their parents.

House mice have excellent vision and hearing, a keen sense of smell, and use their whiskers to feel air movements and surface textures. House mice often squeak to each other in the nest. They use pheromones and other smells to communicate with each other about social dominance, family composition, and reproductive readiness. It was recently discovered that male mice produce complex, ultrasonic songs in response to female sex pheromones. (Holy and Guo, 2005)

In the wild, house mice eat many kinds of plant matter, such as seeds, fleshy roots, leaves and stems. Insects (beetle larvae, caterpillars, and cockroaches) and meat (carrion) may be taken when available. In human habitation, Mus musculus consumes any human food that is accessible as well as glue, soap, and other household materials. Many mice store their food or live within a human food storage facility.

House mice are eaten by a wide variety of small predators throughout the world, including cats, foxes, weasels, ferrets, mongooses, large lizards, snakes, hawks, falcons, and owls. House mice try to avoid predation by keeping out of the open and by being fast. They are also capable of reproducing very rapidly, which means that populations can recover quickly from predation.

Where house mice are abundant they can consume huge quantities of grains, making these foods unavailable to other (perhaps native) animals. House mice are also important prey items for many small predators.

House mice do not cause such serious health and economic problems as do Rattus norvegicus and Rattus rattus. Mice are agricultural pests in some areas, however, and they do consume and contaminate stored human food with their droppings. They also destroy woodwork, furniture, upholstery, and clothing. In addition, they contribute to the spread of diseases such as murine typhus, rickettsial pox, tularemia, food poisoning (Salmonella), and bubonic plague. Recent research has also shown that they carry a virus--the mouse mammary tumor virus (MMTV)--that may contribute to breast cancer in humans. (Indik et al., 2005; Stewart et al., 2000)

Domesticated forms and albinos have been developed which are commonly used as laboratory animals (especially in medicine and genetics), and as pets. Mus musculus also has a small role as an insect destroyer, but this is minimal.

Commensal populations of Mus musculus are generally stable and densities can be as high as 10 mice per square meter. In the wild, populations are less stable and densities may be less than 1 mouse per 100 square meters. Overall, populations are flourishing and are in fact aided by human construction of houses, barns, and other structures.

Mus musculus often refers to several fairly distinct kinds of mice. As many as seven separate species may be placed under Mus musculus, such as Mus domesticus, western European house mice, and Mus castaneus, southeastern Asian house mice. "Dancing" and "singing" mice are other names for house mice. The former refers to a genetic strain with inner ear defects, causing the mice to weave, turn in circles, and wobble when they walk. The latter refers to a pathological condition causing mice to twitter constantly with a "song" resembling that of a cricket. (Sage, Atchley, and Capanna, 1993)