House mouse. The house mouse (Mus musculus) is a small rodent, a mouse, one of the most numerous species of the genus Mus. As a wild animal, the house mouse mainly lives associated with humans, causing damage to crops and stored food. The house mouse has been domesticated as the pet or fancy mouse, and as the laboratory mouse which is one of the most important model organisms in biology and medicine. It is by far the most commonly used genetically altered laboratory mammal.