Mouse Facts and Pictures

A mouse (plural mice) is a rodent that belongs to one of numerous species of small mammals. The best known mouse species is the common house mouse (Mus musculus). It is found in nearly all countries and, like the laboratory mouse, serves as an important model organism in biology, and is also a popular pet. The American white-footed mouse (Peromyscus leucopus) and the deer mouse (Peromyscus maniculatus) also sometimes live in houses. These species of mice live commensally with humans.

Although they may live up to two years in the lab, the average mouse in the wild lives only about 5 months, primarily due to heavy predation. Cats, wild dogs, foxes, birds of prey, snakes and even certain kinds of insects have been known to prey heavily upon mice. Nevertheless, due to its remarkable adaptability to almost any environment, and its ability to live commensally with humans, the mouse is regarded to be the third most successful mammalian species living on Earth today, after humans and the rat.

Mice can be harmful pests, damaging and eating crops and spreading diseases through their parasites and feces. In the Western United States, breathing dust that has come in contact with mouse feces has been linked to the deadly hantavirus. The original motivation for the domestication of cats is thought to have been for their predation of mice and their relatives, the rats.

Mice are small rodents, resembling diminutive rats. They usually have pointed snouts and small ears. The body is typically elongated with slender, usually hairless tails, but different types of mice show large variations. Body dimensions vary considerably by species, though some approximate values are available: total length 28-130 mm, mass 2.5 to >34g.

Mice generally live on an herbivore diet, but are actually omnivores; they will eat meat, the dead bodies of other mice, and have been observed to self-cannibalise their tails during starvation. Grasshopper mice are an exception to the rule, being the only fully carnivorous mice. Mice eat grains, fruits, and seeds for a regular diet, which is the main reason they damage crops. They are also known to eat their own feces. Mice are generally thought to enjoy cheese and people sometimes use it as mousetrap bait, but mice actually do not like cheese due to its fatty texture. Instead, they like food that contains high sugar, although chocolate is toxic to them.

Mice are social animals, preferring to live in groups. Male rivalry can become harmful for the animals, especially when a group is confined to a small space. The natural habitats of the mouse are very diverse. Mice can be found in forests, savannahs, grasslands and rocky habitats. In Africa they tend to particularly like forest edge, derived savannah, and (as elsewhere) agricultural areas. Mice build nests for protection and warmth, but species differ in their preferences: M. minutoides nests in shallow burrows; M. caroli and M. cervicolor burrow; and M. shortridgei and M. pahari nest aboveground. Most species will construct nests of grass, fibers, and shredded material. Mice do hibernate.

Mice should be fed a commercial pelleted mouse or rodent diet and water ad lib. These diets are nutritionally complete and do not require supplementation. Food intake is approximately 15g/100g BW/day; water intake is approximately 15 ml/100g BW/day.

Breeding onset is at about 50 days of age in both females and males, although females may have their first estrus at 25-40 days. Mice are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 4-5 days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle. Mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a vaginal smear is also a reliable indicator of mating.

Female mice housed together tend to go into anestrus and do not cycle. If exposed to a male mouse or the pheromones of a male mouse, most of the females will go into estrus in about 72 hours. This synchronization of the estrous cycle is known as the Whitten effect. The exposure of a recently bred mouse to the pheromones of a strange male mouse may prevent implantation (or pseudopregnancy), a phenomenon known as the Bruce effect.

The average gestation period is 20 days. A fertile postpartum estrus occurs 14-24 hours following parturition, and simultaneous lactation and gestation prolongs gestation 3-10 days due to delayed implantation. The average litter size is 10-12 during optimum production, but is highly strain dependent. As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice. The young are called pups and weigh 0.5-1.5 grams at birth, are hairless, and have closed eyelids and ears. Cannibalism is uncommon, but females should not be disturbed during parturition and for at least 2 days postpartum. Pups are weaned at 3 weeks of age; weaning weight is 10-12 grams. If the postpartum estrus is not utilized, the female resumes cycling 2-5 days postweaning.

Newborn male mice are distinguished from newborn females by noting the greater anogenital distance and larger genial papilla in the male. This is best accomplished by lifting the tails of litter mates and comparing perineums.

Mice are the most commonly utilized animal research model with hundreds of established inbred, outbred, and transgenic strains. In the United States, they are not covered under the Animal Welfare Act (AWA) (administered by the USDA, APHIS) as an animal. However, the Public Health Service Act (PHS) as administered by the National Institutes of Health (NIH) does cover their humane treatment.

Mice are common experimental animals in biology and psychology primarily because they are mammals, and thus share a high degree of homology with humans. The mouse genome has been sequenced, and virtually all mouse genes have human homologs. They can also be manipulated in ways that would be considered unethical to do with humans. Mice are a primary mammalian model organism, as are rats.

There are many additional benefits of mice in laboratory research. Mice are small, inexpensive, easily maintained, and can reproduce quickly. Several generations of mice can be observed in a relatively short period of time. Mice are generally very docile if raised from birth and given sufficient human contact. However, certain strains have been known to be quite temperamental.

Mouse-like species are among the oldest mammals. It has been proposed that higher mammals evolved from rodent-like species many millions of years ago.

Mice have been known to humans since antiquity. The Romans differentiated poorly between mice and rats, calling rats Mus Maximus (big mouse) and referring to mice as Mus Minimus (little mouse). In Spanish similar term are in use: ratón for mouse and rata for rat.

Discoloration in mice was supposedly first noticed in China by 1100 BC, where a white mouse was discovered. However, there is sufficient evidence to believe that white mice were first noticed before that, in the times of the Greeks and Ancient Rome.

The word "mouse" and the word muscle are related. Muscle stems from musculus meaning small mouse - possibly because of a similarity in shape. The word "mouse" is a cognate of Sanskrit mush meaning 'to steal,' which is also cognate with mys in Old Greek and mus in Latin.