The naked mole rat (Heterocephalus glaber, the ‘odd-headed smooth one’) is neither a mole nor a rat. Cousin to the porcupine and the guinea pig, it is a three-inch long rodent, which uses its huge incisors to carve out tunnels in the hard desert soil. Although its skin is completely bald externally, it does have hair in its mouth which serves to keep its mouth clean when it digs with its teeth. It also has whiskers and hairy toes.
In 1974, zoologist Richard Alexander of the University of Michigan predicted the existence of a social mammal living underground but not yet known to science. It turned out that naked mole rats fitted the bill perfectly. They are the only mammals to live in organised colonies, like termites and bees. Only one female breeds, serviced by a harem of three males and supported by as many as 300 ‘workers’ and ‘soldiers’, who divide the tunnelling, childcare, food collection and defence functions between them. This behaviour is called eusocial (‘eu’- means ‘true’) and has evolved in response to the harsh conditions of their home territory in eastern Africa, where a lack of rain and food mean they need to co-operate to survive.
Except for the queen and her harem, digging is all that mole rats do. A quarter of their muscle is in the jaw, and a third of their brain is used to process information from their mouths. Colonies contain miles of tunnels; an individual worker can dig half a mile a month when the soil is softened by rain. Size for size, that’s equivalent to a human digging the 12 miles from central London to Heathrow Airport.
A naked mole rat's four front teeth are located outside its mouth.
Naked mole rats are the longest-lived rodent, probably because they can slow their metabolism to a very low level. Because of their longevity an international effort is being made to sequence their genome. They’re also of interest because they might be resistant to cancer and they feel no pain, as they lack the neurotransmitter chemical called ‘Substance P’ which usually sends pain to the central nervous system. This may be an adaptation helping them cope with the near poisonous levels of carbon dioxide in their stuffy burrows.
Mole rats are practically cold-blooded: when they’re not digging or eating, they sleep heaped together in communal chambers to keep warm. They are unable to regulate their own temperature, so they easily overheat or get hypothermia; to overcome this they huddle. At night they sleep in piles four or more deep. When active, their activity generates heat that makes up for heat loss from not being in a huddle. This mechanism is so finely balanced that a few degrees of temperature change in the climate could mean they become extinct.
Naked mole rats can run just as fast backwards as forwards.
A queen naked mole rat can give birth to between 50 and 100 babies a year.
The naked mole rat is also known as the 'sand puppy'.
In a naked mole rat colony, the queen's urine contains a chemical which prevent other females in the nest from having babies.
The naked mole rat is unique among mammals in that it does not avoid incest.