Thursday, August 25, 2011

The Number One Question About Naked Mole Rats

Everything about naked mole rats is fascinating, and Pacific Science Center’s staff are eager to chat about them. Want to know about eusocial behavior? These mammals are a great example. Excited about the latest pups? So are we! Have you followed the adventures of the dispersing morph and want help finding him? Maybe we can help.

But before we can answer any of these questions, we have to address another question, one more urgent:

“Are some of the animals dead?”

We get this question daily, often several times per day. Adult naked mole rats have long life expectancies, and the death of a grown colony member is an extremely rare event for us. So why do we get so many reports of dead animals, and how can a casual viewer separate the living from the dead?

Naked mole rats’ metabolism is adapted to the low oxygen and stable temperature of an underground tunnel. Their respiration and heart rate are lower than one would expect for such a small animal. Thus, there are fewer signs of life to begin with!

Their greyish skin is a second contributor. To many people, the color has an unhealthy appearance, but pinkish grey is the natural color of a healthy naked mole rat.

Additionally, naked mole rats have a habit of sleeping in very relaxed positions. They often stretch out on their backs, with legs splayed in the air, for a long, motionless, deep sleep. Their favorite snoozing spots are over heat exchange ducts. Sleeping naked mole rats will tolerate other animals walking over them, and even kicking them, often showing little or no response.

Small wonder, then, that a grey, motionless, splayed out form would appear lifeless.

We have a few pointers for observing possibly “dead” mole rats before jumping to conclusions.

• If they are in a tube over a heat duct, watch them closely. Animals go here for their deepest sleep, and often lie motionless. When another animal crawls over them, you may see subtle signs of life – a twitch or flexing of muscle. That’s all you need to know they’re ok

• If they are pink and grey, this is a good sign. In the rare cases where an animal has been found dead, it was discolored, with purple extremities.

• Naked mole rats often rest on their backs and spread their legs out. This is a sign of relaxation. An animal that has died would more likely be rigid, rather than relaxed.

• Colony members are not tolerant of dead mole rats in their chambers. They would not ignore or walk over a dead colony mate, but would attempt to drag the animal to the most remote area of the enclosure. So if you see a mole rat being stepped on, it is probably alive.

• This is not a pleasant subject, but in the warm air of the colony, a naked mole rat that had perished would begin to deteriorate rapidly. Their stomach contents and skin would begin to fill with gases, and the animal would appear bloated.

We are always ready to check out any report of possible unhealthy or dead animals, but we also want to minimize the number of times we disturb animals that are simply resting. With so many people viewing our exhibits, it is often a visitor who sees a problem first and reports it. We hope with these criteria, that you have a better idea of when help is needed, and when a mole rat is just enjoying a nap.


  1. Hello,
    love to read about your colony, it's always very interesting!
    Many greetings from Suzy!

  2. Hello,

    I have a question:

    What do (wild living) Naked mole rats, when one of their colony members dies? Did they have a kind of burial chamber for the dead bodies?

    Greetins to you and thanks from

  3. This is Sarah Posting as Anonymous because I can't acce4ss this any other way.

    Suzy, that's a great question, which will be a little hard to answer. Naked mole-rats are difficult to stuy in the wild. They move freely through large underground tunnel systems, and can easily bury or otherwise disable cameras. A great deal is known about their genetics, social structure and physiology, but less about their ordinary daily lives.

    Much of what we know about their behavior comes from trapping wild colonies periodically to survey their members, and extrapolation of their behavior from how they act in captivity.

    Mole rats in captivity live much longer than their wild counterparts. At least, wild colonies have a larger percent of young workers, and older colony members often dissapear between one survey and the next. So we can guess that they are dying, but there doesn't seem to be much written about how the colony handles them.

    Some of them probably fall victim to predators, in which case cleanup isn't so much of an issue. But for those that die inside the colony, I suspect that they are taken to chambers near the outskirts of the colony and yes, probably buried. In the rare cases where we have had colony members die, that is how our captive colony treated them.

    I don't want to be a teas about the mole rat, but stay tuned for more news about them coming soon!


  4. Hello Sarah,

    thank you for your answer! Yes, I agree, surely it's hard to study NMR in the wild.

    For the "dead" NMR: I like to see them sleeping! When they sleeping they are looking so funny - I always say: like overturned compact cars... :)

    I'm always amazed when I see sleeping mole rats and another, awake mole rats run over them, stepping on stomachs, heads or feet... or they are lying like a stack of wood, one on another. And all that seems don't disturb their sleep, really amazing!

    Many greetings from your reader

  5. Hello Sarah,

    I am very interested in these animals' daily average sleep time in wild(prefernce)There maybe a relationship with their non-cancer metabolism..I check internet but unfortunately there are no informations about it..I hope you can help me..Sorry for the english it is not my native language..Take care and have a nice day...