Sep 08

Bizarre Animal of the Week: Naked Mole Rat

It doesn’t matter how weird you think the naked mole rat is; it always turns out to be much weirder. Many animals have one main bizarre feature that is easy to focus on. The naked mole rat, on the other hand, is nothing but bizarre features. Maybe we could start with the fact that acid causes it no pain, or that it’s the only cold-blooded mammal, that it lives in an insect-like society, or perhaps even that it drinks an awful lot of libido-suppressing urine?


Photo: Alamy

But no, first things first. As anyone can see, the naked mole rat is not going to be winning any beauty contests any time soon. Pink, wrinkled, seemingly hairless and almost completely blind, it looks a lot like a flaccid penis. The only upside is that it lives underground in almost total darkness and so cannot be disgusted by the grotesque appearance of its own kind.

All of the naked mole rat’s unusual features have come about because of its extreme subterranean lifestyle. Its loose and almost naked skin allows it to scurry through its tunnels and turn around without its fur being clogged by dirt. It can run just as fast backwards through these passageways as it can forwards, rather like a London tube train. It uses its continually-growing teeth, not its claws, to dig at random, hoping to stumble upon underground plant tubers that it almost exclusively feeds upon. It can close its lips behind its protruding incisors to keep its mouth free of dirt as it gnaws through the baked earth of the arid African grasslands and deserts where it lives.  A quarter of the animal’s entire bodily muscles are located in its jaw, and a staggering third of its brain is dedicated to processing information coming from its mouth.


Photo: Raymond Mendez

But the tunnels in which this rodent lives are very poorly ventilated. High levels of carbon dioxide can build up, which can be extremely painful to the lips, nostrils and eyes. The naked mole rat, however, seems unperturbed by this. It lacks a key neurotransmitter called ‘Substance P’, which is responsible in every other mammal for sending pain signals to the central nervous system. This helps them cope with acidic build up in their body tissues that results from the high levels of carbon dioxide in their burrows, and it also means they feel no pain when they are exposed to acid, as some decidedly cruel experiments have shown.

Mean Queen

The naked mole rat lives in large colonies and almost everyone helps in enlarging and maintaining the tunnels. In this supersociety, only the queen breeds. Her main job is to just sit in the depths of the tunnel system and, every eighty days or so, give birth to a litter of between twenty and thirty youngsters. That might seem like a rather tiring job, but she is supported continuously by as many as 300 ‘sterile’ workers and soldiers, who divide between them the tunneling, childcare and food collection. This type of social order, known as ‘eusociality, is seen in insects such as bees, ants and termites, but hardly ever in higher animals such as mammals.


Photo: Houston Zoo

So long as the queen is alive, no other female will breed. This is not because the other females are truly sterile – in fact, they have all of the biological apparatus needed to breed if they so desired – but because they are highly stressed. Yes, living in a naked mole rat colony is very taxing and draining, not least because all the workers are constantly harassed and intimidated by the queen to the point that their sex hormones are suppressed. When the queen isn’t giving birth or suckling her young, she is patrolling the tunnels, harrying her subjects and nipping them, especially the females, to make sure they don’t get any ideas about breeding for themselves.

The queen also supplements this with a special chemical in her urine that further subdues their libido. Since all members of the colony use the same latrine, it is very easy for everyone to become drenched in the queen’s urine. With their sex drive squashed, the workers can concentrate on more menial tasks, such as enlarging and maintaining the tunnels, which is just to the queen’s liking.

So is that the extent of the naked mole rat’s weirdness? Of course not. I forgot to mention that the naked mole rat is by far the longest-lived rodent (queens can live up to thirty years); they have appallingly slow and deformed sperm; they don’t mind eating their own faeces when times are lean; and they have a remarkable resistance to cancer. Mammals tend to be the ‘norm’ when compared with other types of animals, but the naked mole rat just goes to show that there are one or two exceptions in the world poking their ugly, naked noses out.

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