All about the House Mouse

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They’re giants among men! At the sight of a body weighing only one-and-a-half ounces, mice can make grown people shriek, run and hide!

Why is that? There are theories. One is that it’s just their element of surprise. Their appearance is usually sudden and followed by quick movements, causing a startle-response. Men can be startled, too, but women show more fright. New research may have an explanation: Scientists have found that mice are less stressed by women and tend to linger marginally longer around them; male pheromones are more frightening to mice and they skedaddle faster! Or, so it’s said.

Aside from the startle/fright effect, mice are disliked in general for other reasons. Their “beady” eyes. Their long, bald tail. Their history of carrying diseases. And, they’re pests when they eat stored grains, damage root crops with their burrows and move into homes.

What many people don’t realize, though, is that mice play a vital role in ecosystems, including the one in their own backyards. Take a look at this ecological pyramid. Pyramids like this always show plants at the base and herbivores at the next level up. There’s a reason for that.

Color illustration of a four-tier pyramid with a label for each tier.

Ecological pyramid. (Thompsma – Wiki; CC by-sa 3.0)

Herbivores are food for the higher tiers. Mice, in particular, are the main source of food for numerous other wildlife. Without them, there would be no carnivores (including humans). Mice eat plants to survive and carnivores eat mice to survive. They’re not only important for that, but mice prey on pest insects, helping to keep those populations under control. They also eat weed seeds, an aid to gardeners.

Background
The House Mouse, Mus musculus (MUSS MUSS-kuh-lus), 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.

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)

House mice in recent history have traveled with humans all over the globe and are everywhere, except Antarctica. Hardly any environment is 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 5,416² species of mammals, about 2,200 are rodents.

Mice belong to the suborder Myomorpha and the family Muridae (MYUR-uh-dee). In addition to the House Mouse, Mus musculus, there are a number of subspecies, among them the East European House Mouse (Mus musculus musculus) and the West European House Mouse (Mus musculus domestius), all very similar.

House Mouse vs field mouse
The House Mouse is a field mouse. It’s the best known of a number of mice species that inhabit fields and meadows. There is a specific rodent, however, that’s often called the field mouse. It’s the Meadow Vole, Microtus pennsylvanicus.

Physical description
The adult House Mouse is small, only about 2-1/2 to 3-1/2 inches long (6.4 to 8.9 cm). The tail is 2 to 4 inches long. Adults weigh 1-1/4 to 1-5/8 ounces (40 to 45 g), and they’re slender enough to squeeze through a 1/4-inch (1 cm) opening.

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. The tail is scaly, with sparse, brownish hair. Males and females look alike. 

House Mouse front teeth showing angled edge of top teeth.

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

Among the characteristics that group all species of mice with other rodents is their teeth: a pair of sharp incisors (front teeth) in the upper and the lower jaws. The 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, but it isn’t an option for them. If their teeth overgrow, they won’t be able to chew food properly and will starve to death. 

Senses
The sense of smell is the House Mouse’s strongest sense. It isn’t developed at birth and does so slowly over the first 30 days of their lives, as babies begin to bond with their mothers. Researchers believe having to use smell to find their mother and identify her, as well as their siblings and home is a survival advantage. As adults, they rely on smell for finding food and mates, and for detecting the territorial markings of other mice.

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 and use their whiskers to sense air movement and to feel around like cats do.

Black and white drawing of comparison between mouse and rat, with labels.

Comparison of mouse and rats. (CDC; PD)

Difference between House Mouse and rat
The House Mouse is small, with a small head and small feet. Rats are considerably larger, even young ones. Rats have a more rounded snout. Mice may be white, brown or gray in color; rats are white, brown, gray or black. 

Behavior
House mice are nocturnal, but may sometimes go out in the daytime. 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 (9 m) in diameter.

They leave dark, oblong 1/4-inch (6.4 cm) droppings along their well-traveled path. The droppings are often what alert homeowners to their new “lodgers.” House mice become more of a problem for people in winter because they try to move indoors for warmth and food. Their droppings contaminate surfaces, but on a “personal” level they’re very clean, routinely licking and grooming their hair, as well as keeping their nest clean. House mice are active year around; they don’t hibernate.

Sometimes House 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.

Communication
All mice mainly rely on pheromones for social communication. The pheromones are produced by preputial glands, located in folds of skin in front of their genitals. Their tears, as well as the urine of males also contain pheromones. House mice have a musky odor detectable by humans.

All mice communicate vocally, too, by making soft chittering and squeaking sounds to each other in their nest and when they’re hurt or scared. These sounds are audible to humans. 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 the songs of some species get more complex as a mouse grows older. Listen to a surprisingly melodious bird-like song.

Habitat, nesting and foods
House mice are comfortable living around humans, and will gladly 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. Even then, 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. The home will have several access points, not only as a convenience for entering, but also for providing a quick exit if a predator comes around.

Food Sources

House Mouse standing on an apple, with a bag of apples and some cheese behind it.

The House Mouse is omnivorous. (H. Zell / EOL; cc by-sa 3.0)



House mice are omnivores, meaning they eat both animal and plant foods. They eat every part of a plant — leaves, roots, stems and seeds — as well as fruit, grains and nuts. They supplement that with 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 pantry. This habit may have given 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 do so mostly 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. He follows the 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, tiny, pink and hairless with eyes closed. Standing in palm of open hand.

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

Females have five to 10 litters a year. Frequent litters are a hedge against heavy predation. The gestation period 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 1/3 of an ounce (.9 gr), 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 and at three weeks they’re weaned. At five to eight weeks they’re ready to move to their own territory and mate. Sometimes, young females will live near their mother.

Lifespan
Because they’re prey for so many animals and also face environmental hazards, most House mice don’t live beyond a few months, and at most 12 to 18 months. Even under optimum conditions, mice have short lives. Pet mice live an average of only two to three years. There’s a record of one captive House Mouse that lived just over four years.

Defenses
Speed and agility are the House Mouse’s best defenses. They can run at 8 miles per hour (12.9 km). They can climb nearly any slope with a roughened surface, run along thin wires or ropes, jump 12 inches high (.3 m) and swim very well, too, if they must. They also can bite.

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

How to keep House mice away
Many sites on the web offer sound advice for mouse-proofing a house. As for a yard: Remove resting and nesting places and accessible sources of food, particularly around the perimeter of the house. Seal trash cans tightly, keep clutter away, pick up piles of debris and don’t leave doors standing open. If pets are fed outdoors, then clean up any leftovers.

House Mouse and diseases
House mice (and other rodents) don’t carry rabies. There’s no reason why they can’t, but they never do and aren’t a risk. The risk lies in other viruses and bacteria they may carry. The House Mouse does not carry Hantavirus. According to the U.S. Centers for Disease Control, the House Mouse is associated with the Chorio-meningitis virus, and the Salmonella, Tularemia and Leptospirosis bacteria.

*Top photo: George Shuklin / Wiki; cc by 1.0
¹
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²Mammal Species of the World, 3rd Edition (Wilson and Reeder 2005). The figure changes as new species are described.
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