The naked mole rat (Heterocephalus glaber) is a burrowing social rodent found in the grasslands of East Africa, mainly in Ethiopia, Kenya and Somalia. The unusual anatomy and social life of this bizarre animal was first studied by the German naturalist, Eduard Rüppell in 19th century, although he thought them to be mutated and deformed individuals.
Anatomy. Normally the individuals are 3 to 4 inches long but the dominant queen is larger and has longer body. Fertile males are also larger than the workers and possess abdominal testes. All individuals possess almost hairless and wrinkled pinkish to yellowish skin, hence the name, naked mole rat. Very little scattered hairs and some whiskers are present on the body. They have lost hairs because of underground life, where they do not need hairs to protect them from sun rays. Eyes are quite small or rudimentary as they are not needed in dark tunnels where they spend their entire lives. Their sense of smell and touch are very well developed to compensate for the loss of eyes. Legs are thin and short but are well adapted to move backward as well as forward with ease. The prominent organs of their body are oversized incisors that are used to dig underground tunnels. Their lips close tight just behind the teeth to prevent soil from entering mouth while digging. Their jaw muscles are strong and large as they spend most of their time digging burrows. They have no external ear pinna.
Naked mole rat has long life for a rodent as it can survive up to 30 years, while the other rodents survive only 3 years. This unusual longevity is attributed to the social structure and protected life of this species in tunnels. They escape excessive heat of the surface by remaining in cool, moist burrows and when it is very cold in night, they huddle together in a pile to conserve one another’s body heat.
Social system. The naked mole-rat is the only mammal that exhibits social life similar to termites in which members of the colony are anatomically modified into different castes to perform various duties and also spend their entire lives underground. Only one female called the queen is fertile that breeds and dominates and controls the activities of the colony. One to three males are fertile to fertilize the queen, while the rest of the members of colony of both sexes are sterile and function as workers. There are two types of workers; the smaller ones focus on gathering food, tunnelling and maintenance of the nest, while the larger workers defend the nest from intruders and predators. Larger individuals do less tunnelling work and food gathering but spend their time in scouting and defending the colony from invaders. Smaller individuals are more active and do all the household duties. Colony of 75 to 80 individuals is normal but up to 300 members can be found in some healthy colonies that live in a complex system of tunnels which may reach a cumulative length of up to 3-5 kilometres.
Tunnelling system. The naked mole rats spend all their lives underground in dark tunnels and never come out to see the light of the day. Their tunnel system is intricate and often spreads to several kilometres, two to three feet below the surface. It has several chambers for queen, juveniles, breeding males and workers for feeding, sleeping, reproducing and other activities of the colony. There are also chambers where food collected during burrowing is stored for future use by the colony. There is also a separate isolated communal defecation area in the tunnels to prevent infectious diseases. Tunnel systems are sealed from the outside world for protection of the colony and to keep the intruders away, but this causes the burrows to be oxygen deficient. However, the naked mole-rat is well adapted for low oxygen environment found within the tunnels. Mole rats expand their burrows after rains when the soil becomes soft for easy tunnelling.
Food. Naked mole rats feed on the underground portions of plants that include large tubers, bulbs and rhizomes that are exposed during tunnelling. As their diet is composed of chiefly cellulose, they possess symbiotic bacteria in their gut to digest it, as in termites. Vertebrates cannot digest cellulose and must take the services of micro-organisms to digest it. The young individuals must feed on the faeces of other individuals to get the cellulose digesting bacteria in their guts.