Naked mole-rats: They're not just for scientists anymore

Paul Sherman with a naked mole-rat.

Slavishly devoted to a charismatic figure, wearing more hair on their toes than on their wrinkled heads, living in the underground among scores of near-identical gang members with really gross personal hygiene — they're the kind of cult parents pray their children won't join.

Which is why Cornell biologist Paul Sherman, co-author of two new books about naked mole-rats for children and young adults, expects one of the world's weirdest animals will appeal to kids and spark their scientific curiosity.

Naked Mole-Rats (Carolrhoda Books, 1996) and The Naked Mole-Rat Mystery: Scientific Sleuths at Work (Lerner Publications, 1996), co-written with Ithaca children's book author Gail Jarrow, focus on subterranean dwellers of eastern Africa that have puzzled scientists for some 150 years. Sherman hopes the books will appeal to young readers' sense of adventure — not to mention their affinity for the absurd -- while illustrating the exciting aspects of research in behavioral ecology.

First at the University of California at Berkeley and then at Cornell, Sherman established one of the first laboratory colonies of Heterocephalus glaber (or "different-headed hairless') and edited the first scientific book (Biology of the Naked Mole-Rat) about rodents that burrow through rock-hard soil of Ethiopia, Kenya and Somalia. Now that naked mole-rats are displayed at many zoos, the Cornell professor of neurobiology and behavior attempts to tell the skeptical public why biologists find beauty in such an ugly animal.

"Naked mole-rats are unique among mammals because of the way they look and act, the way their bodies work and the way they live. They give birth and nurse like mammals, they keep warm like reptiles, they live in colonies like social insects," Sherman said. "For scientists, the big mystery question is why -- why have these animals become eusocial (truly social) living in large, family groups where only a few of the colony members reproduce and all the others work to raise the young?

Working with naked mole-rats for 17 years, Sherman has heard all the descriptions of their appearance. Some labels are merely unkind while others are downright obscene, he said, adding, "Probably the most charitable thing you can say is that they look like hot-dogs that were left in the microwave too long."

The mole-rat's protruding teeth make it look like a miniature walrus, but they come in handy for the animal's life work: excavating labyrinths of tunnels and chambers beneath the surface of the sun-baked surface and gnawing the plant roots that comprise its diet. The few hairs on its otherwise naked body have a purpose, too: Between the toes the hairs serve as tiny whisk brooms to sweep excavated dirt from the burrow, while lip hair helps keep soil out of the mole-rat's mouth. Facial hair enables the animal to navigate as it runs, with tiny eyes closed, through the dark tunnels — when it's not running backward at equal speed, that is.

As if bizarre appearance weren't enough, the naked mole-rat has adopted some odd habits. It regularly rolls in feces and urine of the underground toilet chamber, for example, to refresh the colony's scent on its body. The scent of the colony, which can have up to 300 related members, tells who's family and who's foe when territorial disputes erupt.

Under the insect-like division of labor that prevails in naked mole-rat colonies, one female queen and no more than three male breeders are responsible for reproduction, while all other colony members are workers who help raise as many as five litters a year. Naked mole-rat colonies are so inbred, Sherman and Cornell biologists H. Kern Reeve and Charles F. Aquadro discovered several years ago, that all colony members' DNA fingerprints are virtually identical. Therefore, solving a naked mole-rat crime with DNA evidence alone would be difficult.

Without giving away the solution to the mystery, it can be divulged that the reason for mole-rats' eusociality and for most of their strange traits has something to do with the environment. And with snakes that don't care how funny-looking the overcooked hot-dogs are.

Young readers who reach the end of the books shouldn't despair that all the mole-rat puzzles have been solved. Some questions may be answered with certainty by generations of scientists who follow in the biologists' footsteps, Sherman said. "But others will stay unsolved mysteries for a long time. Maybe forever."

Eleven really weird things about naked mole-rats

From Naked Mole-Rats and The Naked Mole-Rat Mystery by Gail Jarrow and Paul Sherman

  • NAME GAME. Naked mole-rats are neither moles nor rats. Like rats, they are rodents, but they're more closely related to porcupines and chinchillas. And they're not totally naked. They have fine hairs over most of their bodies, with concentrations on their heads, tails and between their toes. Thirty-seven species of rodents worldwide are called mole-rats because they burrow underground and have rat-like teeth and tails; all except Heterocephalus glaber (which means "different-headed hairless') have fur.
  • ROLE MODELS. Naked mole-rats could be animal role models for little old, bald men with poor eyesight and bad hygiene who don't go out much. Rarely venturing beyond their underground burrows, the gerbil-sized rodents roll in the colony's toilet chamber to affix the group scent. There's no advantage to good vision in the dark burrows, but naked mole-rats have a keen sense of smell . Their almost-hairless skin does not harbor parasites, a potential problem in crowded conditions, and all the wrinkles add surface area to collect and dissipate heat.
  • MOTOR MOUTHS. Designed for digging, 25 percent of the naked mole-rat's muscle mass is in its jaw -- the same percentage humans have in each leg. These rodents could easily out-chew humans; we have only 1 percent of muscle mass in the jaws. Naked mole-rats produce at least 18 vocal sounds -- including grunts, chirps, squeaks, squeals, trills and hisses -- more than any other known rodent.
  • SWIVEL HIPS. Naked mole-rats' skins are so loose the animals can wriggle half-way around inside.
  • CONSERVATIONISTS. Some roots eaten by naked mole-rats are the size of beach balls and weigh up to 50 pounds. But the rodents aren't gluttons; they often consume just the roots' fleshy centers, then plug the holes with soil. When the plants regenerate, the mole-rats return to dine again.
  • CONVEYOR BELTS. When they excavate burrows, naked mole-rats line up head-to-tail with a large, "digger" at the lead and a big "volcanoer" kicking dirt out the opening to the surface. Smaller "sweepers" kick dirt backward toward the volcanoer, then return to the head of the line by walking tiptoe over the other sweepers.
  • SUPERBOWL. A naked mole-rat colony can occupy the area of 20 football fields.
  • NOT SO STUFFY. Burrows are sealed except during excavation, so fresh air is scarce and the carbon dioxide level would suffocate most animals. The gerbil-sized H. glaber compensates for the lack of oxygen with a metabolic rate less than half that of other rodents and with highly efficient hemoglobin that captures more oxygen for the bloodstream.
  • EUSOCIAL TOO? Like ants, termites and some bees and wasps, these mammals are considered "eusocial" because they live in large colonies with a single reproductive female, or queen, producing all the young. All other colony members labor in maintenance or defense activities. Naked mole-rats are the most extreme case of eusociality in mammals.
  • QUEEN FOR LIFE. Once a female naked mole-rat wins the weeks-long battle to become her colony's queen, her body becomes one-third longer to accommodate large litters of pups -- in one documented case 900 in a lifetime, including 27 in one super litter. No other known mammal increases in length after reaching adulthood.
  • SNIFF CHECK. For animals that revel in feces, they have a discriminating sense of smell. Mole-rats inside Plexiglas of the Cornell laboratory colonies become uneasy when Paul Sherman changes his brand of bath soap.