Naked Mole-rat

About the naked mole-rat

The naked mole-rat, also known as the sand puppy, is a burrowing rodent native to the Horn of Africa and parts of Kenya, particularly Somali regions, and is the only species in its genus, Heterocephalus. It's a genuinely strange mammal: it's the only known mammalian thermoconformer, meaning its body temperature largely tracks the temperature around it rather than being internally regulated the way most mammals' bodies are, and it's one of only two known eusocial mammals, the other being the closely related Damaraland mole-rat. Eusociality here means a colony structure built around a reproductive division of labor, with separate breeding and non-breeding castes and cooperative care of young — a social system otherwise associated with insects like ants and termites.

Physically, typical individuals measure 8 to 10 cm (3 to 4 in) long and weigh 30 to 35 grams (1.1 to 1.2 oz), though breeding females run larger, sometimes well over 50 grams and up to 80 grams (2.8 oz). The animal has small eyes and poor eyesight, thin short legs that let it move backward as fast as forward, and large protruding teeth used for digging, with lips that seal behind the teeth to keep soil out of its mouth while it works — about a quarter of its muscle mass is devoted just to closing its jaw. It has little hair, giving it its name, and loose, wrinkled pink or yellowish skin with no insulating layer beneath.

The naked mole-rat was once grouped with the blesmols, but more recent classification places it in its own family, Heterocephalidae, separate from the other African mole-rats.

Behavior and diet

Naked mole-rats live almost entirely underground in constant darkness, which shapes much of their unusual biology. Their lungs are underdeveloped and their hemoglobin binds oxygen unusually efficiently, letting them survive on very little of it — the species can withstand air containing just 5% oxygen for at least five hours without visible distress, tolerate an atmosphere of 80% carbon dioxide and 20% oxygen, and even survive up to 18 minutes with no oxygen at all, during which its heart rate drops from about 200 to 50 beats per minute and it loses consciousness. Given a choice, naked mole-rats actually prefer low-oxygen air to normal air, a preference not seen in most mammals.

Because they don't regulate body temperature internally, naked mole-rats rely on behavior instead: when cold, they huddle together or move to shallow, sun-warmed parts of the burrow; when too warm, they retreat to cooler, deeper tunnels. Their skin also lacks the neurotransmitters needed to feel pain from acid or capsaicin exposure, likely an adaptation to living in carbon-dioxide-rich, poorly ventilated tunnels where acid buildup in tissue would otherwise be constantly painful.

Colony life is organized around a single breeding female, the queen, and one to three breeding males, while the rest of the colony works as functionally sterile helpers. Smaller workers gather food and maintain the nest; larger workers dig tunnels and respond most aggressively to threats. Workers cooperate to groom, warm, and guard the queen's pups. The queen is pregnant for about 70 days and typically produces a litter of 11 to 12 pups (up to 28 in the wild), which she nurses for the first month before other colony members take over feeding them fecal pap until they can eat solid food. In the wild, colonies usually breed once a year; in captivity, they can breed year-round, producing a litter roughly every 80 days.

Range and habitat

The naked mole-rat is native to the drier tropical grasslands of East Africa, primarily southern Ethiopia, Kenya, and Somalia. It lives in extensive underground burrow systems that it digs and maintains itself, spending essentially its entire life below ground rather than on the surface. The record doesn't describe any recent change in the species' range.

Conservation status

The naked mole-rat is listed as Least Concern (LC). It has drawn scientific attention less for conservation risk and more for its extraordinary physiology: it can live over 37 years, far longer than any other rodent (the next longest-lived, the African porcupine, reaches about 28 years), and its mortality rate doesn't rise with age the way it does in most mammals. It also shows strong resistance to cancer, credited to a combination of genetic "over-crowding" mechanisms that halt cell division once cells touch, and to an unusually large sugar molecule in its tissue that appears to suppress tumor growth. These traits led the journal Science to name it "Vertebrate of the Year" in 2013. The first documented cancers in the species, reported in 2016, occurred in two zoo-born animals kept in normal atmospheric oxygen levels far higher than the 2–9% oxygen typical of their natural burrows — a difference that may have contributed to those cases.