RATS, MICE, AND RELATIVES: Muridae

PHYSICAL CHARACTERISTICS

Rats, mice, and relatives, sometimes called murids (MYOO-rids; members of the family Muridae), are divided into seventeen subfamilies, including voles and lemmings, hamsters, Old World rats and mice, South American rats and mice, and many others. As a result of the large number of species, there is much variation in the physical characteristics of murids.

Voles and lemmings are small rodents with a broad, rounded head; small eyes and ears; thick, cylindrical body; and short legs and tail. Most species' fur is some shade of brown with paler underparts. Lemmings look a lot like voles, but most species are stockier, with heavier bodies and shorter tails. Adults are 3.5 to 24.5 inches (8.5 to 62 centimeters) long and weigh between 0.5 ounces and 4 pounds (15 grams to 1.8 kilograms).

Hamsters are mouse-like Old World rodents with large cheek pouches used to carry food; stout body; short legs; wide, (sometimes) furry feet; and short, furry tails. They have front paws with four digits and a short thumb, and hind feet with five digits. Their soft, thick fur varies in color (depending on the species) from gray to reddish brown, and their underparts can be white, gray, or black. They have excellent senses of hearing and smell, but poor eyesight (even though they have large, round eyes). Adults are 2 to 13.4 inches (5 to 34 centimeters) long and weigh between 0.9 and 31.7 ounces (25 to 900 grams).

Old World rats and mice have long tails (sometimes longer than the body) that are either furry or scaly; strong feet; long hind feet; and opposable digits on their front feet. Adults have a length of 1.9 to 14.7 inches (5 to 36 centimeters) and a weight of 0.2 to 52.9 ounces (5 grams to 1.5 kilograms).

South American rats and mice are small- to medium-sized rodents with brownish or blackish upper coats; very small or no external ears; grayish or whitish underparts; thinly haired tails that sometimes have a penciled tip; and relatively small feet. They have a head and body length of 2.4 to 11.4 inches (6.1 to 29.0 centimeters); tail length of 1 to 6.3 inches (3 to 16 centimeters); and weight of 0.4 to 18 ounces (12 to 510 grams).

All other rats, mice, and relatives vary widely in physical characteristics. Most species are small, usually with somewhat long tails and brownish fur.

GEOGRAPHIC RANGE

Rats, mice, and relatives are found throughout the world except for the extreme polar regions of Earth.

HABITAT

Rats, mice, and relatives live in many different habitats including open flatlands, savannas (flat grasslands), grasslands, prairies, steppes (treeless plains that are often somewhat dry and grass-covered), woodlands, forests, deserts, scrublands, foothills, jungles, rainforests, wetlands, cultivated lands and fields, and along waterways and water bodies. They are found from dry temperate (mild) climates to wet tropical environments.

DIET

Most species of rats, mice, and relatives eat at least a few of the following foods: grasses, seeds, grains, root vegetables such as bulbs and tubers, green plant parts, conifer needles, nuts, berries, fruits, insects and insect larvae (LAR-vee), fish, lizards, frogs, baby birds, crabs, tadpoles, salamanders, fungus, lichens, mosses, other small vertebrates (animals with a backbone) and invertebrates (animals without a backbone), and carrion (decaying animals).

BEHAVIOR AND REPRODUCTION

Rats, mice, and relatives are active during the day, at night, or both night and day (depending on the species). For their size, they can be very aggressive to predators and even to other members of their species. The rodents can be vocal, with various communicative sounds such as chattering, screaming, and whistling. They set up territories and defend them vigorously. Murids are sometimes found alone, but often are social, and are found traveling and sleeping together. They use nests for shelter and to raise their young. Some species breed throughout the year but others only during certain seasons. Murid rodents generally have high reproduction rates (lots of offspring) and large populations. Litters (groups of young born at the same time from the same mother) have one to seventeen offspring. Young are born blind and naked, although they develop fast, are weaned (stop drinking their mother's milk) quickly, and are able to reproduce within weeks or months.

RATS, MICE, RELATIVES, AND PEOPLE

Rats, mice, and relatives are generally considered pests in agricultural and forested lands. Large species are often trapped for their fur. Some species carry diseases that can sicken and kill people. Rats, mice, and relatives are frequently used as laboratory research animals. Some, such as hamsters and gerbils, are kept as pets. They are often important in maintaining a healthy ecosystem in their natural habitats.

CONSERVATION STATUS

Almost 450 species of murids are listed on the World Conservation Union's (IUCN) Red List. Of these, twenty-one are Extinct, died out; fifty are Critically Endangered, facing an extremely high risk of extinction in the wild; seventy-four are Endangered, facing a very high risk of extinction in the wild; and 110 are Vulnerable, facing a high risk of extinction in the wild.

MUSKRAT (Ondatra zibethicus): SPECIES ACCOUNTS

Physical characteristics: The muskrat has dark brown upperparts and light grayish brown underparts. Adult head and body length is 15.5 to 24.5 inches (40 to 62 centimeters) and weight is 1.1 to 4 pounds (0.55 to 1.82 kilograms).

Geographic range: They range in the western part of North America, and have also been introduced into Europe, Asia, and South America.

Habitat: Muskrats are found around water, specially rivers, lakes, marshes, and lagoons.

Diet: They eat aquatic plants, invertebrates, and small vertebrates.

Behavior and reproduction: Muskrats either dig burrows in earthen banks or build large floating lodges of vegetation. They sometimes live in families of several generations. Females have a gestation, pregnancy, period of twenty-five to thirty days, and then have a litter of four to eight young. Five or six litters are possible each year.

Muskrats and people: People hunt and raise muskrats for fur. They are often considered pests in some regions.

Conservation status: Muskrats are not threatened. ∎

NORWAY LEMMING (Lemmus lemmus): SPECIES ACCOUNTS

Physical characteristics: Norway lemmings have brown to black fur. Adult head and body length is 3 to 7 inches (8 to 17.5 centimeters) and weight is 0.5 to 4.5 ounces (20 to 130 grams).

Geographic range: They are found in Scandinavia (the northern European region of Norway, Sweden, Denmark, Finland, Iceland, and the Faroe Islands).

Habitat: These lemmings inhabit open tundra and subarctic bog areas.

Diet: Their diet consists of mosses, lichens (LIE-kenz), bark, and some grasses.

Behavior and reproduction: Norway lemmings are mostly nocturnal (active at night). They travel long distances in mass migrations, and are active year-round, remaining mostly beneath snow cover. The gestation period is about sixteen days, with a litter of up to thirteen young and up to six litters produced each year.

Norway lemmings and people: Scandinavian people have made lemmings a popular animal in their myths and legends.

Conservation status: Norway lemmings are not threatened. ∎

BLACK-BELLIED HAMSTER (Cricetus cricetus): SPECIES ACCOUNTS

Physical characteristics: Black-bellied hamsters have a short hairless tail; a thick fur that is reddish brown above with white patches on the flanks, nose, cheeks, and throat; and black underparts. Males are larger than females. Adults are 8 to 12 inches (20 to 34 centimeters) long and weigh between 4.5 and 36.3 ounces (112 to 908 grams).

Geographic range: These hamsters are found in central and eastern Europe, from Belgium to the Altai region of Siberia.

Habitat: Black-bellied hamsters live in lowlands such as steppes, agricultural lands, and along riverbanks.

Diet: Their diet includes grains, beans, roots, green plant parts, insect larvae (especially beetle larvae), frogs, earthworms, and field mice. They often store cereal grains, seeds, peas, and potatoes in winter burrows.

Behavior and reproduction: Black-bellied hamsters generally live alone; are active at night; and hibernate in winter. Winter burrows can extend more than 6 feet (2 meters) below the soil surface. Older females with young have the most complex burrows with several entrance tunnels, numerous chambers for nesting and food storage, and a dead-end tunnel for waste disposal. Breeding takes place from June to August. A courting male enters a female's territory by marking an area with his secretions, running after the female, and making loud sniffing noises. The female drives away the male after mating. The gestation period is eighteen to twenty days, with a litter of four to twelve pups. Two litters are raised each year. They sometimes live to the age of eight years old.

Black-bellied hamsters and people: People hunt black-bellied hamsters for food and trap them for clothing. They are considered pests when around cornfields, but do help to control other pests such as mice and insects. The rodents are also used as laboratory animals.

Conservation status: Black-bellied hamsters are protected under European Community Habitats Directive as a threatened species in Belgium, Germany, the Netherlands, France, and Austria. They are also protected in Croatia, Bulgaria, and Slovenia. ∎

EGYPTIAN SPINY MOUSE (Acomys cahirinus): SPECIES ACCOUNTS

Physical characteristics: Egyptian spiny mice have large ears; gray-brown to sandy spiny hairs covering its back; gray to white bellies; and scaly, hairless tails. Adults have a body length of 2.7 to 6.7 inches (7 to 17.0 centimeters); tail length of 1.9 to 4.7 inches (5 to 12 centimeters); and weight of 1 to 2.4 ounces (30 to 70 grams).

Geographic range: These mice are distributed through Africa and the Middle East.

Habitat: Egyptian spiny mice live in arid (dry) and semi-arid environments like deserts and savannas, often preferring to be around rocks. They live in burrows and are sometimes found in trees, but are considered to be terrestrial, ground-living, animals.

Diet: They eat mostly arthropods, along with snails, plant materials, grains, and grasses.

Behavior and reproduction: Egyptian spiny mice are fairly social animals, living in small groups with a dominant male who fights to maintain his control. They are good jumpers, and build simple nests. The gestation period is five to six weeks, with a litter of one to five pups. Young are well developed when born, having thin hair, open eyes (within a few days), and are able to breed almost immediately. Females help each other with the birthing process.

Egyptian spiny mice and people: People keep Egyptian spiny mice as pets.

Conservation status: Egyptian spiny mice are not threatened. ∎

AUSTRALIAN JUMPING MOUSE (Notomys alexis): SPECIES ACCOUNTS

Physical characteristics: Australian jumping mice have light sandy brown to gray upperparts; white to light gray bellies; long tails with fine fur; large ears; narrow, large hind feet; and sebaceous (secretion) glands that are used for territorial marking. Adults have a body length of 3.9 to 5.9 inches (10 to 15 centimeters); tail length of 3.5 to 8.2 inches (9 to 21 centimeters); and weight of 0.7 to 1.7 ounces (20 to 50 grams).

Geographic range: They are found throughout central Australia.

Habitat: They inhabit arid desert environments; living around dunes and grasslands so that they can easily dig large, complicated burrows.

Diet: Their diet consists of berries and other vegetation. They can live without water as long as they receive enough moisture from their food.

Behavior and reproduction: Australian jumping mice are nocturnal, social creatures. As a group, they groom, huddle, walk over and crawl under each other, and sleep together. Their large hind feet allow them to jump higher than 3.2 feet (1 meter). When angry with another animal, they rush and leap at it, and punch it with their forelegs. They generally walk on all four limbs, but when necessary will leap with their hind legs. The gestation period is about one month. Females produce a litter with an average of three pups that are born naked and blind, but open their eyes within three weeks. They are weaned after five weeks and ready to reproduce within three months.

Australian jumping mice and people: People keep these animals as pets.

Conservation status: The Australian jumping mouse is not threatened. ∎

HISPID COTTON RAT (Sigmodon hispidus): SPECIES ACCOUNTS

Physical characteristics: Hispid cotton rats have a gray streaked coat with blackish or dark brownish hairs; pale to dark grayish underparts; dark tail; and five pairs of nipples, although some have four or six pairs. Adults have a total length of 8.8 to 14.4 inches (22.4 to 36.5 centimeters); tail length of 3.2 to 6.5 inches (8.1 to 16.6 centimeters); and weight of 3.5 to 8 ounces (100 to 225 grams).

Geographic range: They are found from southeast and southcentral United States through the interior and eastern part of Mexico, into Central America, and to northern Colombia and Venezuela.

Habitat: Hispid cotton rats usually live in grasslands.

Diet: Their diet consists mostly of grasses.

Behavior and reproduction: Hispid cotton rats are active during the day and night, and are able to swim. They breed throughout the year. The gestation period is about twenty-seven days. Litter size is from one to fifteen pups, with northern populations having larger litters. Young are well developed at birth; eyes open within thirty-six hours of birth; and are weaned in ten to fifteen days. Males are able to reproduce within sixty to ninety days, and females within ten to forty days.

Hispid cotton rats and people: Scientists observe hispid cotton rats to help them determine how environmentally healthy an area is.

Conservation status: The hispid cotton rat is not threatened, though two subspecies, populations that live in specific areas, are Near Threatened (likely will be threatened in the future). ∎

GAMBIAN RAT (Cricetomys gambianus): SPECIES ACCOUNTS

Physical characteristics: Gambian rats are fairly large rodents with short fur that can range from soft to coarse. Some species are mottled, or splotched, with darker colors or may have an indistinct white line running across the shoulders. They have large ears; dark rings around the rather small eyes; a long and narrow head and face; cheek pouches to collect food and other materials; smooth incisor teeth; dark or grayish brown upperparts with red tinges; creamy underparts; and a long, scaly tail that is hairless and completely white for the last half of the length. They have good senses of smell and hearing, but have poor eyesight. Adults have a body length of 9.4 to 17.7 inches (24 to 45 centimeters); tail length of 14.3 to 18.1 inches (36.5 to 46.0 centimeters); male weight of about 6.1 pounds (2.8 kilograms); and female weight of about 3 pounds (1.4 kilograms).

Geographic range: Gambian rats are found in Africa, specifically from Senegal and Sierra Leone in the west to Sudan and Uganda in the east and as far south as Angola, Zambia, and northern South Africa.

Habitat: They inhabit forests, forest edges, thickets, and sometimes grasslands.

Diet: Their diet consists of insects, fruits (especially palm fruits and kernels), seeds, roots, nuts, leaves, snails, and crabs.

Behavior and reproduction: Gambian rats are mostly nocturnal although sometimes active during the day. They climb and swim well, and are usually seen alone. The rodents sometimes dig a simple burrow that has long passageways with side chambers for bedding and storage and is covered by dense vegetation. At other times, they use burrows of other animals, termite mounds, or natural crevices in rocks and hollow trees. Breeding occurs throughout the year. Up to ten litters per year are possible for females. The gestation period is twenty-seven to thirty-six days, with one to five pups born, although four pups in a litter is average. Young develop quickly and are able to breed as early as twenty weeks old.

Gambian rats and people: People buy and sell Gambian rats within the pet trade. These animals transmit diseases, such as monkeypox, to humans. Some people hunt them.

Conservation status: Gambian rats are listed as Rare in South Africa. Otherwise, they range from common to less common in their other ranges, and are not listed as threatened by the IUCN. ∎

FOR MORE INFORMATION

Books:

Feldhemer, George A., Lee C. Drickamer, Stephen H. Vessey, and Joseph
F. Merritt. Mammalogy: Adaption, Diversity, and Ecology. Boston: WCB McGraw-Hill, 1999.

Nowak, Ronald M. Walker's Mammals of the World, 6th ed. Baltimore and London: The Johns Hopkins University Press, 1999.

Vaughan, Terry A., James M. Ryan, and Nicholas J. Czaplewski. Mammalogy, 4th ed. Philadelphia: Saunders College Publishing, 2000.

Whitfield, Philip. Macmillan Illustrated Animal Encyclopedia. New York: Macmillan Publishing Company, 1984.

Wilson, Don E. and DeeAnn M. Reeder, eds. Mammal Species of the World, 2nd ed. Washington, D.C. and London: Smithsonian Institution Press, 1993.