The house mouse (Mus musculus) is a small mammal of the order Rodentia, but introduced worldwide through association with humans. The house mouse is the most commonly encountered and economically important of the rodents. It is one of the most abundant species of the genus Mus, having a pointed nose, large rounded ears, and a long and hairy tail. House mice are distributed worldwide and can be found throughout the United States despite their Central Asian origin.
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. Being highly adaptive, they are able to survive in buildings and aboard ships, and have a tendency to move into agricultural fields and move out when the habitat changes. They have a very rapid rate of reproduction and can adapt quickly to changing conditions. In fact, a female house mouse can give birth to a half dozen babies every three weeks and can produce up to 35 young per year.
House mouse has a small, slender body 7.5–10 cm (3–4 in) and a tail length of 5–10 cm (2–4 in), equal to its body length. The weight is generally 12 to 30 g (0.4 to 1.1 ounces). It’s fur ranges in color from grey and light brown to black, and they generally have white or buffy belly. On the other hand introduced feral populations have dark, grayish brown upperparts paling to gray on the sides and underparts are similar to the sides and sometimes tinged with buff, and the tail is uniformly dark gray. Among different populations of house mouse around the world, these dimensions can vary in weight and sizes and color of it’s fur.
A mouse’s head or their feet will be proportionally larger to its body. Mouse can be identified by the size of the head and the thin whiskers, narrow hind feet. It has sharp claws; prominent, thinly furred ears that appear naked, but on the rest of the body the fur is short and soft. House mouse has a long tail that has very little fur and has circular rows of scales. The animal has a distinctive strong, musky odour.
On close examination, newborn mice can be distinguished as the anogenital distance in males is about double that of the female. About age 10 days and onwards, female mice have five pairs of mammary glands and nipples; whereas male mice have no nipples. When they reach the age of sexual maturity, the presence of testicles on the male mice are the most striking and obvious difference. These are large compared to the rest of the body and can be retracted into the body.
For balance, a house mouse uses its tail. The tail has only a thin covering of hair as it is the main peripheral organ of heat loss in thermoregulation along with the hairless parts of the paws and ears. Tail length varies according to the environmental temperature of the mouse during postnatal development, so mice living in colder regions tend to have shorter tails. The tail is also used for balance when the mouse is climbing or running, or as a base when tripoding (when the animal stands on its hind legs).
House mice usually run, walk, or stand on all fours. They can stand on the hind legs, as well, and are supported by the tail while eating, fighting, or orienting itself, a behavior known as “tripoding”. Mice are good jumpers, climbers, and swimmers, and are generally considered to be thigmotactic, i.e. usually attempt to maintain contact with vertical surfaces.
They are excellent climbers and can run up any rough vertical surface. They will run horizontally along wire cables or ropes and can jump up 13 inches from the floor onto a flat surface. however, they are colorblind and cannot see clearly beyond six inches.
Very inquisitive in nature, the house mouse will spend the day roaming its territory, exploring anything new or out of the ordinary. They can be seen during the daylight hours but are active mostly at night. The average sleep time of a captive house mouse is reported to be 12.5 hours per day.
When the temperatures outdoors begin to fall, they begin searching for a warmer place to live. Often they enter into homes, attracted by the smell of food and the warmth of a structure. The house mouse can use any opening, such as utility lines, pipe openings, and gaps beneath doors.
Generally mice due to smaller size are afraid of rats which often tend to kill and eat them (a behavior known as muricide). In contrast to this, forest areas in New Zealand, North America, and elsewhere, free-living populations of rats and mice do exist together.
House mice being poor competitors, cannot survive away from human settlements in areas where other small mammals, such as wood mice, are present. However, in some areas (such as Australia), mice are able to coexist with other small rodent species.
The social behavior of the house mouse is species-specific but is also adaptable to the environmental conditions, such as the food and space availability. This adaptability allows house mice to inhabit diverse areas ranging from sandy dunes to apartment buildings worldwide. The size of the House Mouse territory varies, based on the availability of food and water
House mice have two forms of social behaviour, the expression of which depends on the environmental context.
House mice living near humans habitats e.g., in buildings and other urbanized areas are known as Commensal House Mice. Due to access of excessive food sources, Commensal mice are in high population densities with small homes. The social unit of commensal house mouse populations generally consists of one male and two or more females, usually related. These groups breed cooperatively, with the females communally nursing. This cooperative breeding and rearing by related females helps increase reproductive success. When no related females are present, breeding groups can form from non-related females.
House mice living in open areas such as shrubs and fields are known as Non Commensal House Mice. These populations often have access to limited water or food supply, whereas having large territories. Female-female and Male-Male aggression in the Non Commensal house mouse populations is much higher than Commensal House Mice.
Both populations, Commensal and Non Commensal house mouse, males are socially compatible with related mice, but they are hostile and aggressively defend their territory, don’t tolerate intruders and act to exclude all intruders. House Mouse Males mark their territory by scent marking with urine, like many other animals. House mice show a male-biased dispersal; males generally leave their birth sites and migrate to form new territories whereas females generally stay and are opportunistic breeders rather than seasonal.
House mice generally live in close association with humans, structures, houses, apartments, barns, granaries, etc. but they can survive outdoors, too. In the outdoors, they occupy cultivated fields, fencerows, and even wooded areas, but they seldom stray far from buildings. House mice prefer to nest in dark, secluded areas.
House mice often build nests out of paper products, cotton, packing materials, wall insulation and fabrics. They are very moussing and tend to curiously explore changes in their habitats. They will often change their established channels for this reason.
House Mice spend their summers in open fields but with the onset of autumn they move into barns and houses. Normally, the house mice make homes in farm fields, grassy and wooded areas, building nests in areas that are dark and protected and are not far away from a readily available food source. Outdoors, they excavate tunnels to build nests of dry grass, but they will also nest among rocks and crevices. Indoor omnivorous house mice are also considered pests; they construct nests in comfy and dark places such as in walls, under sinks etc. and can contaminate food and damage property.
Indoor house mice prefer seeds, cereal grains, sweets or nuts in its diet, but will eat almost anything available. Whereas house mice living outdoors eat insects and seeds, including grains, which makes them pests in some areas. Some house mice primarily feed on plant matter, but are omnivorous. To acquire nutrients produced by bacteria in their intestines, they eat their own feces. They do not need much water; they fulfil most of their water requirements from their food. To eat large quantities of seeds and grains, Mice often infests farms and granaries.
Mice nibble on food all day long, eating only small amounts of food at a time. They eat many times and eat at different locations. However, they generally feed at dusk and before dawn. Mice also store food as supply permits.
Senses and communication
Mice vision is basically similar to that of humans but the difference lies in their formation of eyes. House Mice are dichromats and have only two types of cone cells whereas humans are trichromats and have three. This means that mice are color blind in the human visual spectrum.
In house mice pheromones are used for social communication, some of which are produced by the preputial glands of both sexes. The tear fluid and urine of male mice also contains pheromones, such as major urinary proteins. Mice detect pheromones mainly with the vomeronasal organ, located at the bottom of the nose.
The urine of house mice, especially that of males, has a characteristic strong odor. At least 10 different compounds, such as alkanes, alcohols, etc., are detectable in the urine. Among them, five compounds are specific to males, namely 3-cyclohexene-1-methanol, aminotriazole (3-amino-s-triazole), 4-ethyl phenol, 3-ethyl-2,7-dimethyl octane and 1-iodoundecane.
Mice can sense surfaces and air movements with their whiskers which are also used during thigmotaxis. If mice are blind from birth, super-normal growth of the vibrissae occurs presumably as a compensatory response. Conversely, if the vibrissae are absent, the use of vision is intensified. The house mouse has a sharp sense of hearing and communicates with other house mice through squeaks. Some of these squeaks are audible to humans, while others extend into the ultrasonic range.
Life cycle and reproduction
Estrous cycle lasts for about four to six days in female house mice, whereas estrus itself lasts no longer than a day. Under crowded conditions, where several female mice are kept together, they will often not have an estrus at all. Under such conditions if exposed to male urine, they will come into estrus after 72 hours.
Male house mice court females by emitting characteristic ultrasonic calls in a specific range. The calls are most frequent during courtship when the male is sniffing and following the female; however, the calls continue after mating has begun, at which time the calls are coincident with mounting behavior. Males can be induced to emit these calls by female pheromones. The vocalizations appear to differ between individuals and have been compared to bird songs because of their complexity. While females have the capability to produce ultrasonic calls, they typically do not do so during mating behavior.
Female mice will normally develop a copulation plug following copulation, to avoid further copulation. It is not necessarily for pregnancy initiation, as this will also occur without the plug. This plug stays in place for some 24 hours. The gestation period is about 19–21 days, and they give birth to a litter of 3–14 young (average six to eight).
One female can have 5 to 10 litters per year, so the mouse population can increase very quickly. Breeding occurs throughout the year. However, in the wild animals do not reproduce in the colder months, even though they do not hibernate.
Female pups reach sexual maturity at about six weeks of age and male pups at about eight weeks, but both can copulate as early as five weeks.
In outdoor, harsh environments house mice usually live less than 1 year. Whereas indoors, houses and apartments, where they find protected environments, they often live 2 to 3 years.
House Mouse and humans
Human domestication led to numerous strains of “fancy” or hobby mice with a variety of colors and a docile temperament. Domestic varieties of the house mouse are bred as a food source for some carnivorous pet reptiles, birds, arthropods, and fish.
Mice as pests
Mice are one of the most common rodents to infest human buildings and are widespread pest organisms. During summer and spring they commonly forage outdoors, but as soon as autumn approaches they retreat into buildings to seek warmth and food. They typically feed on unattended food, leftovers and garden produce. Their foraging risks the contamination and degradation of food supplies, and can also spread other pests such as fleas, ticks and lice.
Mice and diseases
House mice can sometimes transmit diseases, contaminate food, and damage food packaging.
They carry lots of diseases but barely some are potentially contagious.
Lymphocytic choriomeningitis (LCMV) can be transmitted by mice, but is not a commonly reported infection in humans, though most infections are mild and are often never diagnosed. Some concern exists that women should not be infected with LCMV during pregnancy.
House mice are not usually a vector of human plague (bubonic plague) because they have fewer infestations with fleas than do rats, and because the fleas which house mice normally carry exhibit little tendency to bite humans rather than their natural host.
Rickettsialpox, caused by the bacterium Rickettsia akari and similar to chickenpox, is spread by mice in general, but is very rare and generally mild and resolves within two or three weeks if untreated. No known deaths have resulted from the disease.
Murine typhus (also called endemic typhus), caused by the bacterium Rickettsia typhi, is transmitted by the fleas that infest rats. While rat fleas are the most common vectors, cat fleas and mouse fleas are less common modes of transmission. Endemic typhus is highly treatable with antibiotics. The U.S. CDC currently does not mention rickettsialpox or murine typhus on its website about diseases directly transmitted by rodents (in general).
Leptospirosis is carried by a variety of wild and domestic animals including dogs, rats, swine, cattle, mice in general, and can be transmitted by the urine of an infected animal and is contagious as long as the urine is still moist.
House mice can pose serious health threats. House mice can carry diseases and contaminate stored food that they eat in the home. Mouse urine can cause allergies in children. House mouse feces in the home carries bacteria. Inhaling dust that contains dried feces may cause allergies or asthma flare ups. Furthermore, mice can also bring fleas, mites, ticks and lice into your home. If you suspect that your symptoms are associated with rodent infestation, seek medical attention. Be sure to tell your doctor if you suspect contact with rodents or rodent droppings.
As a model organism
Due to their relatively close relationship, and associated high homology, with humans, mice are the most commonly used mammalian laboratory animal. Also due to their ease in maintenance and handling, and their high rate of reproduction. Laboratory mice typically belong to standardized inbred strains selected for the stability or clarity of specific harmful mutations. This allows research with laboratory mice to easily restrict genetic and biological variables, making them very useful model organisms in genetic and medicinal research.
House Mouse Inspection
House mice will gnaw making clean holes about 1-1/2 ” in diameter. Mice will gnaw on paper and boxes, using it for nesting material. House mice will also gnaw on bar soaps. They gnaw various materials to file down their growing teeth and keep the length under control. Common damage includes gnawed electrical wires, marks on wooden furniture and construction supporting elements, and textile damage. Their droppings(feces)are rod-shaped, about 1/8-1/4 inch long. Mouse tracks, mouse droppings, and recent gnawing show locations where mice have been active. When infesting homes, house mice may pose a risk of damaging and compromising the structure of furniture and the building itself.