All about the House Mouse

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The most common mouse in the U.S. is the House Mouse (Mus musculus). They’re pests when they eat stored grains, damage root crops with their burrows, move into homes (eek!) or carry diseases. But, the flip side is that mice have their own special role in an ecosystem. And it’s an important one. They feed heavily on weed seeds and insects, helping to keep them under control. And they’re food for many other animals. House mice are a benefit to a backyard wildlife habitat.

It’s easy to be dismissive of mice, but millions of people around the world love them as cute, smart, entertaining animals who become quite tame and can learn tricks. For at least a thousand years they’ve been kept as pets and in some ancient societies mice were seen as important creatures, even worshiped.

Oldest placental mammal fossil (Eomaia scansoria). Dinoguy2 / Wiki; cc by-sa 1.0)

Oldest placental mammal fossil (Eomaia scansoria). (Dinoguy2 / Wiki; cc by-sa 1.0)

A mouse-like fossil found in China is the earliest known ancestor of the House Mouse. It also happens to be the earliest ancestor of all other placental (having a placenta) mammals, including humans. The animal, named Eomaia scansoria, lived 125 million years ago, in the Early Cretaceous Period when dinosaurs roamed and birds began to appear. Mus musculus, the House Mouse, is believed to have originated in Iran, Afghanistan, Pakistan, and northern India around 500,000 years ago, during the Cambrian Period, when most major animals began to appear. 

House mice now have traveled with humans all over the globe and are everywhere, except Antarctica. Hardly any environment seems too forbidding for them as long as there’s a food source.

Mice belong to the scientific order Rodentia (row-DENCH-uh), which includes squirrels, chipmunks, beavers, prairie dogs, gophers, groundhogs, chinchillas and others. A child’s pet hamster, gerbil, guinea pig or rat is also a rodent. Rodents are the largest group and largest population (40 percent) of mammals. Out of 5,416** species of mammals, about 2,200 are rodents.

Rodentia is divided into suborders. Mice belong to the suborder Myomorpha and to the family Muridae (MYUR-uh-dee). In addition to the House Mouse, Mus musculus (MUSS MUSS-kuh-lus), there are a number of subspecies also called “House Mouse,” among them the East European House Mouse (Mus musculus musculus) and the West European House Mouse (Mus musculus domestius), all of them very similar.

(Ryan Somma / Flickr; CC)

(Ryan Somma / Flickr; CC)

Physical description
The adult House Mouse is small, with a body only about 2-1/2 to 3-1/2 inches long, The tail is 2 to 4 inches long. Adults weigh 1/2- to 1 ounce. (They can squeeze through an opening as small as 3/8-inch.) They have a long, pointy snout with long whiskers, small eyes and hairless, relatively large ears. Their hair is short and usually light-brown or gray, with a lighter-colored belly. (Some domestic and lab mice have been bred in other colors, including with spots.) The tail is scaly, with sparse, brownish hair. Males and females look alike. House mice have a musky odor.

House Mouse front teeth. (Magne Flaten / Wiki; cc by-sa 2.0)

House Mouse front teeth. (Magne Flaten / Wiki; cc by-sa 2.0)

Among the characteristics that groups all species of mice with other rodents is their teeth: a pair of sharp incisors (front teeth) in the upper and the lower jaws. These teeth are chisel-shaped with hard enamel on the front and softer dentin on the back, which makes them wear unevenly and maintain the chisel shape. The incisors grow continuously, but they’re kept from growing too long by rodents’ habit of gnawing on hard things, as well as by the tough foods they eat. The need to gnaw can make rodents destructive.

Senses
House mice have excellent vision, but little or no color vision. Their hearing is superior and extends into the ultrasonic range. They have an excellent sense of touch — they use their whiskers to sense air movement and to feel, like cats do. Smell is their strongest sense.They rely on it for finding food and mates, and for detecting the territorial markings of other mice. As their sense of smell develops slowly over the first 30 days of their lives, mice kits begin to bond with their mothers; it isn’t automatic at birth. Researchers believe having to learn to find their mother and identify her, their siblings and home through smell is a survival advantage.

House mice protect themselves by being quick and agile. They’re fast runners (up to 8 miles per hour) and can climb about any slope that has a roughened surface. They can run along narrow wire cables or ropes, jump 12 inches high and swim very well, too, if they must.

Comparison of mouse and rat. (CDC;PD)

Comparison of mouse and rat. (CDC;PD)

 Behavior
House mice are nocturnal, but may sometimes go out in daytime. With no defenses except speed and agility they do their best to stay hidden as they move about. They don’t go farther than they need to obtain food. They don’t stray far from their familiar territory and routinely travel the same route, usually no more than about 30 feet in diameter. They leave small, dark, 1/4-inch droppings along their well-traveled path. Their droppings are often what first alerts homeowners to their new “lodgers.” Their droppings contaminate surfaces, but on a “personal” level mice are very clean, routinely licking and grooming their hair, as well as keeping their nest clean.

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Fragile and vulnerable, mice like to stay hidden. (UC IPM Online)

Sometimes mice live together. When they do, it’s usually in a group of one male, several females and offspring, and they’ll defend their home against outsiders.

House mice are active year around, they don’t hibernate. They can become more of a problem for humans in winter because they try to move inside buildings for warmth and food.

Communication
Mice mainly rely on pheromones for social communication. The pheromones are produced by preputial glands, which are located in folds of skin in front of their genitals. Pheromones are also contained in the tears and urine of males.

Mice communicate vocally, too, by making soft chittering and squeaking sounds to each other in their nest and when they’re hurt or scared, which humans can hear. Listen to mouse sounds. They also emit songs beyond our hearing, in the ultrasonic range. Some songs are produced only by males and others only by females. Different species sing different songs and songs of some species get more complex as a mouse grows older. Listen to a surprisingly melodious bird-like song.

Habitat and nesting
House mice live throughout the U.S. They’re quite comfortable living around humans, and sometimes happily move into our homes and offices. Some spend their entire lives in a building, where they live in walls, under major appliances, in storage boxes and drawers, and in upholstered furniture. Most House mice, though, live in crevices in rocks, woodpiles, piles of debris, and in sheds, barns, crawl spaces and garages, wherever they can hide that’s near a source of food. If there’s no other suitable shelter, they may dig complex burrows. House mice usually live relatively close to buildings. Some live outdoors in summer and move indoors in the fall.

Their home usually has separate areas: a “pantry” for stored food and a place for nesting. Nests are made from soft materials, such as finely shredded paper or cloth. A House Mouse home will have several access points, not only a convenience for entering, but also for providing a quick exit if a predator comes around.

House mice are omnivorous. (H. Zell / EOL; cc by-sa 3.0)

(H. Zell / EOL; cc by-sa 3.0)

Food sources
House mice are omnivores, meaning they eat both plants and meat. They’ll eat every part of a plant — leaves, roots, stems and seeds — as well as fruit, grains and nuts. Also in their diet are insects, carrion, pet food, and just about anything that people will eat. They eat a couple of main meals a day, at dawn and dusk, but they also like to snack periodically throughout the day. So, when they find extra food, they store it in their home. This is probably what gave rise to the origin of the word mouse, which derives from the Latin and Sanskrit mus, meaning “to steal.” Mice drink water, but mostly obtain moisture from the foods they eat.

Reproduction
Males and females can mate any time of the year, but mostly do so between late spring and early fall, particularly in the North. Courtship begins with a male emitting ultrasonic calls in the 30 kHz to 110 kHz range. A male follows a female around, sniffing her. He may continue his calls even while mating. Females produce these sounds, too, but usually don’t make it part of their mating behavior.

One-day-old House Mouse. (ShwSie / Wiki cc by-sa 3.0)

One-day-old House Mouse. (ShwSie / Wiki cc by-sa 3.0)

A female generally has five to 10 litters a year. Frequent litters are a hedge against heavy predation. The gestation time is 19 to 21 days. Females are capable of producing 12 to 15 offspring, but the average is five. The babies are bald at birth, their ears flattened and their eyes closed. Weighing only about 0.03 ounce, they’re completely helpless. They grow rapidly, however, and at about 10 days they’re covered with hair. At two weeks they open their eyes, at three weeks they’re weaned and at five to eight weeks they’re ready to move to their own territory and mate. Sometimes, young females will live near their mother.

Life span
Because they’re prey for so many animals, most wild mice don’t live beyond a few months, although some may live a year or more. Even under optimum conditions, mice have short lives: Pet mice live an average of only two years. House mice that have been wild-captured sometimes live up to four years.

Predators
House mice, as well as all other species of mice, are prey for cats, foxes, hawks, owls, weasels, ferrets, snakes, lizards, other animals and even rats (an act called muricide). Humans kill millions of mice a year in scientific research.

How to keep House Mice away
Numerous sites on the web offer good advice for mouse-proofing a house. As for your yard, it will help to control overpopulation if you: Remove resting and nesting places and easy sources of food, particularly around the perimeter of your house. Seal trash cans tightly, keep clutter away, pick up piles of debris, don’t leave doors standing open, and don’t feed pets outdoors (if you do, then avoid leaving leftovers outside).

House Mouse at a glance

Appearance: Long, pointy face with long whiskers, small eyes, large ears. Hair light-brown to gray; belly lighter.
Size:Body 2 1/2 – 3 in. long. Tail 2 – 4 in. Wt. 1 oz. or less.
Lifespan: Less than 1 yr. in the wild. 2 yrs. in captivity.
Range/habitat: Everywhere there’s a food source, incl. deserts. Likes to stay near humans. Behavior: Shy, non-aggressive. Nocturnal, sometimes seen in daytime. Active year ’round. Has small range, stays near nest.
Foods: Grains, plant parts, nuts, fruit, pet food, carrion, garbage.
Nest: In woodpiles, rock piles, debris, burrows, buildings, crawl spaces.
Reproduction: May mate all year, but usually spring to fall. Gestation 19 – 21 days; avg. 5 offspring.
Predators: Snakes, hawks, owls, cats, weasels, ferrets, lizards, coyotes, foxes, humans.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Myomorpha
Family: Muridae
Subfamily: Murinae
Genus: Mus
Species: musculus
 

*Top photo: George Shuklin / Wiki; cc by 1.0
*Mammal Species of the World, 3rd Edition (Wilson and Reeder 2005). The figure changes as new species are described.

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