AFRICAN MOLE-RATS: Bathyergidae

PHYSICAL CHARACTERISTICS

African mole-rats are small to medium-sized rodents with streamlined bodies 3.2 to 11.0 inches (83 to 281 millimeters) in length and with a weight of 1.2 to 31.0 ounces (34 to 896 grams). African mole-rats bodies are covered in hair that is thick and short, except for one species. They have robust heads, small eyes, very small ears, and flattened pig-like noses. The stiff hairs are thicker on the front of the face and around the eyes. Their necks are muscular so there is not much change in size from their head to body and their limbs are short giving their bodies an overall cylindrical appearance. On the outer edges of their hind feet and on their short tail they also have stiff hairs, except for one species. They also have stiff hairs that are used for touching that are scattered all over their bodies. Under their loose skin they have long, strong muscles. The African mole-rats have large, ever growing, white incisors, sharp-edged teeth which are flat, in the front of the mouth used for cutting and tearing food.

GEOGRAPHIC RANGE

African mole-rats are found in sub-Saharan Africa.

HABITAT

African mole-rats inhabit dry regions such as savannas, or flat grasslands, and open woodlands. The rodents are not found in dense forests. They are usually found in areas with plants that provide an underground food source such as bulbs, tubers, and rootstalks. African mole-rats live in burrow systems consisting of a complicated network of foraging tunnels. The tunnels usually include a deeper nest complex with an area for relieving bodily waste, and usually one or more food storage areas. The surface opening is sealed except when dug-out soil is taken out.

DIET

They eat bulbs, tubers, and corms, the underground stem base of plants such as the crocus or gladiolus. Food is either eaten when it is found or brought back to a central storage area near the nest. Large food sources are often left to grow, and eaten on from time to time.

BEHAVIOR AND REPRODUCTION

African mole-rats are considered by experts to show the widest range in social structure of all mammals. They are solitary rodents, and spend much of their time underground. Almost all species dig by biting the soil with their large incisor teeth or in one genus (JEE-nus), a group of animals with similar characteristics, by loosening soil with strongly developed forefeet. Muscular lips with strong hairs keep soil out of the mouth. The loosened soil is pushed under their bodies with their forefeet and then collected and kicked behind them with their hind feet until it is kicked out of the surface opening.

Courtship and mating activities are short encounters between a male and female. Pups at about two months of age begin to make their own burrows. Colonies of social African mole-rats have divisions of labor for reproductive activities. A single female, the queen, and a few chosen males do the mating. Remaining members, who are related to the breeders, are helpers. They remain members of the colony unless environmental conditions allow them to go out on their own or if a breeder dies. If the breeding female dies, some of the oldest females in the colony become sexually active and often fight for the highest position of breeding female. The gestation period, the amount of time the offspring is in the womb, is forty-four to 100 days. Litter, a group of young animals born at the same time from the same mother, size is from less than four up to twenty-eight, depending on the species.

AFRICAN MOLE-RATS AND PEOPLE

African mole-rats are considered pests in farmlands and in urban developments. Their burrows often damage roads, airport runways, and other such structures. They can also chew through underground cables, irrigation pipes, and other human-made objects.

CONSERVATION STATUS

One species of African mole-rat is listed as Vulnerable, facing a high risk of extinction in the wild, and six species are listed as Data Deficient, meaning there is not enough information available to decide their status.

DAMARALAND MOLE-RAT (Cryptomys damarensis): SPECIES ACCOUNTS

Physical characteristics: Damaraland mole-rats have either grayish yellow-brown or dark brown coat colors. In either case, they have a large white patch on the top of the head. Damaraland mole-rats have a flattened nose; very small eyes; two large incisor teeth on top and another set of large incisors on the bottom of the mouth; five thin claws on each foot; and a stubby tail. They weigh about 4.6 ounces (130 grams), with males a little larger than females. Weight varies depending on social status.

Geographic range: They are widely found in Namibia, most of Botswana, and extending into western Zimbabwe and northwestern South Africa.

Habitat: They inhabit dry regions with an average annual rainfall of under 15.6 inches (40 centimeters). They prefer red Kalahari desert arenosols, sandy soils featuring very weak or no soil development; loose deposits of rivers and streams; and sands.

Diet: They eat geophytes (JEE-oh-fites), plants with underground organs such as bulbs, tubers, and rootstalks. Large geophytes are eaten at the place they grow, while the smaller ones are carried back to a communal storage area. The animals dig together as a group in search for food.

Behavior and reproduction: Damaraland mole-rats are highly organized and social creatures. They use their incisor teeth for digging. These rodents live in colonies of up to forty animals. The colony consists of a single breeding female, her several male partners, and their non-breeding offspring. The breeding animals control the colony. Pups of breeders remain as non-breeding helpers. Breeding occurs throughout the year. The gestation, pregnancy, period is seventy-eight to ninety-two days. The litter size is one to five, but averages three. The breeding female can have up to four litters in one year. Breeders can live more than ten years.

Damaraland mole-rats and people: There is no known significance between people and Damaraland mole-rats.

Conservation status: Dameraland mole-rats are not threatened. ∎

NAKED MOLE-RAT (Heterocephalus glaber): SPECIES ACCOUNTS

Physical characteristics: Naked mole-rats, sometimes called sand puppies, are the smallest of the mole-rats. Even though they are called both moles and rats, they are much more closely related to porcupines, chinchillas, and guinea pigs. They are nearly hairless except for scattered sensory hairs. They lack the fur typically found on rodents have underdeveloped eyes and pinkish brown to pinkish gray wrinkled skin, long buck teeth, and long tails. Adults have an average length of 3 inches (7.6 centimeters), and an average weight of about 1.2 ounces (34 grams). Males and females look alike but size varies with social status; and dominant individuals can weigh up to 2.8 ounces (80 grams).

Geographic range: They are widely found in the regions of the Horn of Africa; that is, the east-central Africa area that includes Ethiopia, Somalia, and Kenya.

Habitat: Naked mole-rats inhabit dry regions with an average annual rainfall of under 15.6 inches (40 centimeters). They like fine sandy soils that become very hard in dry seasons.

Diet: Their diet consists of geophytes that are found through the coordinated foraging, searching for food, of colony members. They almost constantly dig tunnels in search of irregular food supplies and to escape snakes, their primary predator. The animals also eat feces, solid bodily waste; in fact, the breeding female and the weaning pups often beg for feces from colony members.

Behavior and reproduction: Naked mole-rats are highly social animals, living in complex underground colonies, which is unique among mammals, and much more common among insects, with 20 to 300 animals, but with an average of 75. They live almost their entire lives in the total darkness of underground burrows, living in the same home range for many years. The rodents have very underdeveloped eyes so, instead, use highly accurate sensitivities to vibrations in the ground. They show a very highly developed division of labor that is centered on reproduction. One breeding female mates with several males, often one to three; all such animals are called the breeders. All other members are non-breeding worker and soldier animals that are offspring of the breeders and do all the jobs necessary within their territory in order to ensure the success of the group.

The breeding female stops non-breeding members from breeding with aggressive behaviors. Most non-breeders never leave the colony or breed. Odors separate friends from enemies, which is achieved by all members from rolling about in the burrow's toilet chamber, and coating their bodies with the familiar scent of the colony's feces and urine. Naked mole-rats will fiercely attack unfamiliar intruders, such as when another colony breaks into another colony's burrow system. Some breeding occurs outside the colony from animals that are highly sexed and attracted to animals from other colonies.

The breeding female has a distinctive elongated body and up to seven pairs of nipples. Her breeding occurs throughout the year. The gestation period is sixty-six to seventy-four days. The average litter size is one to twenty-eight, but the average size is twelve. Up to four litters are born each year. They live long lives, and females are able to reproduce into old age.

Naked mole-rats and people: There is no known significance between people and naked mole-rats.

Conservation status: Naked mole-rats are not threatened. ∎

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. Vol. 2. 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, DC and London: Smithsonian Institution Press, 1993.