Common House Mouse

The Common House Mouse (Mus musculus), is the most numerous species of the genus Mus. It is the most common and populous mammalian species on earth, besides humans. House mice almost always live in close proximity to humans. Laboratory mice belong to strains of house mice and are some of the most important model organisms in biology and medicine. They are by far the most commonly used laboratory mammal.

House mice are light brown to black, with short hair and a light belly. The ears and tail have little hair. Adults weigh some 0.4 to 1.4 ounces. Their body (including tail) is about 6 to 7.5 inches long, with the tail usually accounting for a bit more than half of it. Young males and females are not easily distinguished; females have a significantly smaller distance between their anus and genital opening. Females have 5 pairs of mammary glands and nipples; males have no nipples. When sexually mature the most striking and obvious difference is the presence of testicles on the males. These are relatively large compared to the rest of the body and can be retracted into the body.

House mice usually walk, run or stand on all fours, but when eating, fighting or orienting themselves they stand only on the hind legs, supported by the tail. When running, the horizontal tail serves for balance; the end stands up vertically, unless the mouse is frightened. Mice are good jumpers, climbers and swimmers. Mice are mostly active during dusk or night – they do not like bright lights. They live in a wide variety of hidden places that are near food sources and construct nests from various soft materials. Mice are territorial and one dominant male usually lives together with several females and young.

House mice primarily feed on plant matter, but they will also accept meat and dairy products. They will drink water but require little of it, relying mainly on the moisture present in their food. They will eat their feces to acquire nutrients produced by bacteria in their guts. House mice, like other rodents, do not vomit. Mice are also afraid of rats and are often killed and eaten by them. They usually cannot survive unless they are in close proximity to human settlements.