Mammals
House Mouse
Mus musculus · also called common mouse
The house mouse is one of the most successful mammals alive, and it owes almost all of that success to us. For 10,000 years it has followed human grain, human buildings, and human ships to nearly every corner of the planet. It is a household pest, an island menace, and, as the laboratory mouse, the animal behind much of modern medicine.
Overview
Mus musculus is a small rodent, with a body of only 7 to 10 cm and a thin tail about as long again, grey-brown above and paler below, with large ears and a pointed snout. It eats almost anything but prefers seeds and grain, and it lives worldwide alongside people, in homes, farms, and warehouses, as well as in fields and hedgerows.
Built to multiply
A mouse must gnaw constantly because its front teeth never stop growing, which is why mice chew through packaging, wood, and electrical cable. And it breeds at a remarkable rate — a female can have a litter every three weeks, and the young breed at six weeks, so a single pair can found hundreds of mice in a year.
The laboratory mouse
The house mouse is the ancestor of the laboratory mouse, the most widely used mammal in biomedical research, chosen for its small size, fast breeding, and a genome that shares most of its genes with ours. Much of what is known about mammalian genetics, cancer, and immunity comes from work on this animal.
A predator on islands
Where house mice reach seabird islands with no native land mammals, they can turn predator, eating eggs and chicks and, on islands such as Gough and Marion, attacking and killing albatross chicks in the nest.
Status
The house mouse is Least Concern and one of the most numerous mammals on Earth. It is a pest and an invasive species, so the concern is the harm it does to native wildlife, not any threat to the mouse.
House Mouse: common questions
How fast do house mice breed?
Very fast, which is the main reason a small problem becomes a large one so quickly. A female house mouse can breed at around six weeks old, is pregnant for about three weeks, and can mate again within a day of giving birth, so she may raise five to ten litters a year of roughly five to eight young each. Those young mature and start breeding on the same timetable. In a sheltered place with food and no serious predators or control, a single pair can, in theory, be the founders of several hundred mice within twelve months. In practice numbers are held down by predators, disease, food limits, and cold, but the potential for explosive growth is always there.
What is the difference between a house mouse and a young rat?
Proportions are the giveaway. A house mouse has a small, rounded head, large ears, small feet, and a thin tail about as long as its head and body combined, and a full-grown adult body is only 7 to 10 cm. A young brown rat has a noticeably larger, heavier head, a blunter muzzle, ears that look smaller relative to the head, chunky feet, and a thicker tail that is shorter than the head and body. A juvenile rat also feels solid and heavy for its length compared with the light, delicate mouse. Droppings differ too, with mouse droppings the size of a rice grain and rat droppings several times larger.
Why is the house mouse so important to science?
It combines practicality with biological closeness to humans. Mice are small and cheap to house, breed quickly so that many generations can be studied in a short time, and are easy to handle. At the same time they are mammals with essentially the same organs, tissues, immune system, and developmental biology as people, and their genome shares a large majority of its genes with the human genome, often in a similar order along the chromosomes. Over a century, researchers have also built up thousands of specialised mouse strains, including many with specific genes altered, so that a huge amount of what is known about mammalian genetics, cancer, immunity, and disease has come from work on the house mouse.
How do you keep house mice out of a home?
Exclusion works better than trapping alone. A house mouse can pass through a gap about the width of a pencil, so the key steps are to seal cracks and holes around pipes, cables, vents, and doors with steel wool, metal mesh, or hard filler, fit door sweeps, and keep external doors closed. Removing food and shelter matters too, so store dry food and pet food in sealed hard containers, clear spilled seed and crumbs, manage compost and rubbish, and reduce clutter where mice can nest. Snap traps are the most effective way to deal with mice already inside; glue boards are inhumane and poisons risk secondary poisoning of pets and wildlife such as owls.