A mouse (plural: mice) is a small rodent characteristically having a pointed snout, small rounded ears, a body-length scaly tail and a high breeding rate. The best known mouse species is the common house mouse (Mus musculus). It is also a popular pet. In some places, certain kinds of field mice are locally common. They are known to invade homes for food and shelter.
Domestic mice sold as pets often differ substantially in size from the common house mouse. This is attributable both to breeding and to different conditions in the wild. The most well known strain, the white lab mouse, has more uniform traits that are appropriate to its use in research.
The American white-footed mouse (Peromyscus leucopus) and the deer mouse (Peromyscus maniculatus), as well as other common species of mouse-like rodents around the world, also sometimes live in houses. These, however, are in other genera.
Cats, wild dogs, foxes, birds of prey, snakes and even certain kinds of arthropods have been known to prey heavily upon mice. Nevertheless, because of its remarkable adaptability to almost any environment, the mouse is one of the most successful mammalian genera living on Earth today.
Mice can at times be vermin, damaging and eating crops, causing structural damage and spreading diseases through their parasites and feces.
In North America, breathing dust that has come in contact with mouse excrement has been linked to hantavirus, which may lead to hantavirus pulmonary syndrome (HPS).
Primarily nocturnal animals, mice compensate for their poor eyesight with a keen sense of hearing, and rely especially on their sense of smell to locate food and avoid predators.
Mice build intricate burrows in the wild. These burrows typically have long entrances and are equipped with escape tunnels or routes. In at least one species, the architectural design of a burrow is a genetic trait.
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 owing 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 g (0.018–0.053 oz) 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 g (0.35–0.42 oz). If the postpartum estrus is not utilized, the female resumes cycling 2–5 days post-weaning.
Newborn male mice are distinguished from newborn females by noting the greater anogenital distance and larger genital papilla in the male. This is best accomplished by lifting the tails of littermates and comparing perineums.