The naked mole rat (Heterocephalus glaber), also known as the sand puppy or desert mole rat, is a burrowing rodent native to parts of East Africa and the only species currently classified in the genus Heterocephalus. It is one of only two known eusocial mammals (the other being the Damaraland mole rat) and has a highly unusual set of physical traits that enables it to thrive in a harsh, underground environment, including a lack of pain sensation in its skin and a very low metabolism.
Typical individuals are 8 to 10 cm (3 to 4 in) long and weigh 30 to 35 grams (1.1 to 1.2 oz). Queens are larger and may weigh well over 50 grams (1.8 oz), the largest reaching 80 grams (2.8 oz). They are well-adapted to their underground existence. Their eyes are quite small, and their visual acuity is poor. Their legs are thin and short; however, they are highly adept at moving underground and can move backward as fast as they can move forward. Their large, protruding teeth are used to dig, and their lips are sealed just behind the teeth to prevent soil from filling their mouths while digging. They have little hair (hence the common name) and wrinkled pink or yellowish skin.
The naked mole rat is well adapted for the limited availability of oxygen within the tunnels that are its habitat: its lungs are very small and its blood has a very strong affinity for oxygen, increasing the efficiency of oxygen uptake. It has a very low respiration and metabolic rate for an animal of its size, about 2/3 that of a mouse of the same size, thus using oxygen minimally. In long periods of hunger, such as a drought, its metabolic rate can be reduced by up to 25 percent.