A Surprisingly Strong Animal

Mother sloth and tiny baby in Costa Rica


Dear Readers, on Fridays I try to share something that I’ve read that has cheered me up, and so this week I am turning my attention to the sloth, that ‘languid dangler’ of Central and South American forests. I was lucky enough to have a trip to Costa Rica a few years ago and fell in love with these animals, partly because they always seemed so relaxed. I especially loved this one. The only view that we got of her baby was this little limb poking out, but it could not have been more adorable.So it was with some delight that I read that sloths have been found to have a pound-for-pound grip stronger than humans, chimps or even gorillas. Researcher Melody Young, who was working at the Sloth Sanctuary in Costa Rica, noticed how strong (and sometimes painful) the grip of the sloths was when they clasped on to the side of her torso, and she got to thinking. She invented what sounds like a rather Heath Robinson kind of device, which consisted of a bisected broom handle and a force-measuring plate. The sloths were encouraged to dangle from it, and it was found that they exerted a force equivalent to 100 percent of their body weight, with some even getting up to 150 percent. This is twice as much force as a human or a chimp.

Sloths don’t have the musculature of primates, but their feet are extremely well-muscled, and this probably relates to their lifestyle – sloths are not agile animals, so if they lose their grip they can’t just skip merrily to the next branch like a monkey can, and so their ability to hang on becomes their main defence. There are many stories of hunters having to cut down trees to get to a sloth, and of the corpses of sloths that have been attacked by jaguars being found still clasped to a branch.

Sloth in Costa Rica

The scientists investigating the sloth think that even these grip estimates are probably much lower than the sloth is actually capable of – as one of them says, you can’t say to a sloth ‘grip that stick as hard as you can’. But there is another related mystery. While primates are predominantly right-handed/footed, sloths have a very strong left-handed bias, with the left side being consistently stronger than the right-hand side. Does anyone have any theories? I am scratching my head.

You can read the whole article here (you might need to register but you don’t need to pay anything).

And here is Finlay, one of the sloths who had his grip measured at the Sanctuary. Just look at that little face! And also look at those claws. If I was a jaguar I’d think twice about trying to eat an animal with such splendid weapons.

3 thoughts on “A Surprisingly Strong Animal

  1. Alittlebitoutoffocus

    Re your right/left hand grip dilemma… I would say that if you are predominantly right handed, you would ‘learn’ to hang around on your left hand more often (to do more dexterous things with your right). Hence it would have a stronger (at least hanging) grip. QED? 🤔


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