Heterocephalus glaber
naked mole rat

Naked mole-rats are found only in parts of Kenya, Ethiopia and Somalia.

Naked mole-rats live underground in arid savannah and grasslands near the equator. Their population density is highest where their food plants are most abundant.

Although, as their name indicates, naked mole-rats do not have fur, they are not completely hairless. They have sensory whiskers on their faces and on their tails (they move both backwards and forwards through their tunnel systems), and they have hairs between their toes that allow their feet to function as brooms with which they sweep soil. Their skin is pink and somewhat translucent on the underside and light purplish brown on their backs and tails. This countershading appears to be lost with advanced age. There is no sexual dimorphism between males and females. The queen and breeding males are generally among the heaviest individuals in a colony, and the queen is the longest individual. When a female becomes a queen she actually grows longer, even though she is already an adult, by increasing the distance between the vertebrae in her spine.

Maximum longevity in this species is as yet unknown, since animals that have been in captivity for as long as 20 years are still currently living. This life span is unprecedented among small rodents.

Naked mole-rats are eusocial, meaning that they live in large colonies in which only one female breeds and the majority of workers (both males and females) spend their entire lives working for the colony. Colony size averages 70 individuals, but colonies of up to 295 have been observed. The animals in these groups are very closely related. Workers are generally raising their siblings, since a single queen may reign for many years. Dispersal is quite rare and inbreeding is common, which results in a high degree of genetic similarity among colony members. If a queen dies or is removed from a colony, a few females may fight to the death in order to become the new queen. Naked mole-rats live in complex underground burrow systems. The tunnels are about 4 cm in diameter. Some tunnels run just under the surface of the ground, while others can be up to 2 m deep. There is a great deal of branching and interconnection of tunnels, with the result that a colony's total tunnel length can add up to 4 km. Tunnels connect nest chambers, toilet areas, and food sources. Burrowing is the only way these animals find food, since they do not travel above ground.

Workers dig through the hard-packed soil with their powerful ever-growing incisors, aided by the fact that 25% of an individual's muscle mass is involved in jaw closure. A mole-rat's lips actually close behind its incisors, such that it can dig without getting dirt in its mouth. They work assembly-line style, with the front animals actually breaking through the dirt while a string of workers sweeps the soil through the tunnel system to an opening to the surface, where another worker kicks the dirt up onto the ground above its head, forming a mole hill. Mole-rats seem to do the majority of a year's digging just after the rainy season, when the normally hard ground is softened.

These eusocial rodents also cooperate to thermoregulate. Unlike most other mammals, they cannot maintain a steady body temperature. Their temperatures fluctuate with the ambient temperature, making naked mole-rats essentially cold blooded. By huddling together in large masses, they slow their rate of heat loss. They also behaviorally thermoregulate by basking as needed in their shallow surface tunnels, which are warmed by the sun.

The small eyes of these subterranian animals are nearly sightless. They also have small pinnae, but their hearing is acute, as evidenced by their large repertoire of social vocalizations. Their sense of smell is very important, and they are also very sensitive to vibrations in the ground and the movement of air currents.

These exclusively fossorial rodents eat the underground parts of plants, particularly the succulent tubers that are formed by many of the plant species that grow in arid areas. They obtain all the water they need through their food; they do not drink. In captivity they will readily consume sweet potatoes, various fruits, baby cereal and dog biscuits. When a group of mole-rats finds a large tuber (sometimes more than a foot in diameter) in the wild, they generally bore through it, eating mainly the interior flesh while leaving the thin epidermis intact. This behavior may allow the plant to remain healthy for some time, indeed even to continue growing, thereby providing a long-term food resource for the colony. This diet is high in cellulose, which is difficult to digest. Naked mole-rats have high densities of gut fauna that aid in digestion. They also regularly practice coprophagy, the reingestion of feces, which allows them to maximize their uptake of nutrients from their food.

If a naked mole-rat colony finds a farmer's crop, it can quickly destroy much of the yield by eating the roots of the plants. They are a problem especially for sweet potato farmers.

In the United States naked mole-rats are becoming very popular in zoos and in the popular press. The fascination that people tend to have for them makes them an excellent educational tool, since they provide an outstanding example of some of the myriad ways in which animals have adapted to exploit various environments.

Although this unique animal has a limited geographic distribution, it can be quite numerous where it does occur.