A naked mole rat is a very unusual rodent native to the deserts of East Africa. It lives in burrows and has developed a number of traits to exist in its harsh environment. The naked mole rat is hairless and nearly cold-blooded, and its skin does not register pain. Its teeth grow outside the mouth so that it can use them to burrow without ingesting dirt. Most unusual of all, the naked mole rat is eusocial, a trait shared by only one other mammal, the Damaraland mole rat.
Naked mole rats are typically about three to four inches (eight to ten cm) in length and weigh about an ounce (30 g). Each colony has a queen, which is about twice the size of typical mole rats. Colonies consist of about 75 to 80 mole rats living in up to two or three miles (three to five km) of tunnels. Naked mole rats feed mainly on large tubers they find underground. They eat only the inside of the tuber, and the skins they leave behind allow the plants to regenerate.
Eusociality, a social structure more common in insects, notably ants and bees, relies on the majority of females in a population giving up their reproductive capabilities to care for the offspring of a single female, the queen. One to three males mate with the queen, and the rest of the colony are specialized workers who may for example dig tunnels, feed offspring, or defend the colony from predators. The queen naked mole rat lives for about 15 to 18 years and is replaced with another queen upon her death. She produces a litter of typically three to twelve young each year. Other mole rats may live past 20 years in some cases.
In order to live in an oxygen-poor underground environment, naked mole rats have small lungs and their blood is incredibly efficient at absorbing oxygen. They are unable to regulate their body temperature to the point of being virtually cold-blooded, and their metabolism is slow, unlike most mammals of their size, to conserve oxygen. They can also reduce their metabolic rate by up to 25 percent in periods of famine, which perhaps accounts for their longevity.
Naked mole rats also lack a neurotransmitter called Substance P in their skin. This neurotransmitter, common to most mammals, sends pain signals to the central nervous system. It has been proposed that naked mole rats developed this adaptation because their limited oxygen supply causes acids to build up in their tissues, which would cause pain if the animals had Substance P.
