Episode 179 – Brown-Throated Sloth: The Slowest Mammal

“…and today we’re talking about the sloooowest mammal in the world. But more on that later.”

The Amazon jungle is home to a wide variety of animals both fast and slow, with one of the slowest being the brown-throated sloth. But with so many fierce predators on the jungle floor, it helps to spend all your time hanging out in the trees. The only problem is, there aren’t a lot of good things to eat way high up in the trees. So to stay healthy, and stay slow, the sloth has some unorthodox ways of getting his vitamins here in Life, Death, and Taxonomy.


Sloths have long arms compared to their shorter legs. They also have round heads and faces with thick necks.

Their tails are short, and may be around three inches long. 

They have moderately long fur, kind of like an orangatang, but it appears coarse. It’s brown, grey, and beige all over. Their faces are lighter with dark brown eye masks, kind of like a raccoon. 

Measure Up

Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words Measure Up into ldtaxonomy at gmail dot com. We do have a Measure Up intro this week from our friend Joy.


  • 42 to 80 cm (17 to 31 in)
  • How many sloths go into the longest ever verifiable home run?
  • Hint: The longest ever home run was hit by Joey Meyer of the Denver Zephyrs. There have been other mythical hits in baseball history, including an astronomical hit by Mickey Mantle, but those are unconfirmed. But some baseball loremasters may still consider Mantle the GOAT. 
  • 225 sloths. The hit was 582 feet (177 m).


  • 2.25 to 6.3 kg (5.0 to 13.9 lb)
  • How many sloths go into the weight it would take to crush a Lego brick?
  • Hint: This has apparently been a big debate on Reddit, and it’s a relevant stat in the question, “how tall can a lego tower get?”
  • 68 sloths. 950 pounds (432kg).

Fast Facts about the Three-Toed Sloth

Three toed sloths are from South and Central America and can be found in all types of forests.

Sloths are extremely slow. They’re ground speed is around one mpm (miles per month), and we’ll learn more about slowness later.

They are almost completely arboreal. Since their bodies are built for branches, they can move slightly faster when they’re in the trees. On the ground, they’re completely vulnerable to predation, and they only ever come down to go to the bathroom. 

They don’t poo very often, but when they do, they climb down to the ground, do a little doo doo dance to create a hole or divot in the ground, and then make their deposits. Sloths relieve themselves in one fell poop. Then they make their way up the tree. 

Sloths are personal energy conservation conscious, if you could say they’re conscious of anything. They conserve as much energy as possible and live efficient lives. Because of that, we have no idea why they chose to spend so much energy pooping, when other arboreal mammals poop from up in the trees. Half of all sloth deaths happen during this poo poo process.

Enough about that because sloths have another interesting fact. Sloths live solitary lifestyles but they always have friends with them: sloth moths. There are a few species of moths that have adapted to exclusively live in the coarse fur of sloths. These moths only leave the sloth when… you guessed it, the sloth poos.

And we’re back to this. Sloth moths lay their eggs in sloth troughs. Three toed sloths have a ton of moths on them and their two toed kin have less. One was recorded with 120 months living in the slow moving apartment. 

Major Fact: A rolling stone gathers no moss, but a sleeping sloth does

We recently did one of the fastest mammals on Earth, the pronghorn – now it’s time to cover the exact opposite, the winner for the world’s slowest mammal. The slow loris is a sharp contender, but the three-toed sloth takes the cake.

They can top out at a blistering 0.15 miles per hour, about two and a half football fields an hour. And that’s if they’re absolutely legging it through the trees. On the ground, they move about 8 ft per minute.

If Usain Bolt had a 100-meter race with a three-toed sloth, he would finish in 9.5 seconds while the sloth would take 50 minutes to cross the finish line. He could run it, cool down, shower, watch two episodes of Friends, and then gently encourage the sloth for the last few feet of the race. Believe it or not, though, they can actually swim with a decent breaststroke at about 24 feet per minute.

The sloth is so slow, and spends so much time completely motionless, that algae and fungi often grow on its fur, turning the sloth a greenish color. The algae actually works to provide much-needed nutrition to the sloth and the fungi destroys parasites that cause diseases like malaria.

Moths also live in its fur, and their poop fertilizes the algae and fungi. The algae grows naturally, but the fungi are picked up when the sloth descends to the forest floor to relieve itself… once every week!

Feces and urine often make up a full third of its body weight. Their organs are actually attached to their ribs so that they can carry all this extra baggage while hanging without squeezing the lungs.

But why do they move so slowly? The reason is because of their diet. The leaves they eat are really low in nutrition and also have toxins as a natural form of defense.Like a cow or the LDT alumn – the hoatzin bird – the sloth has a multi-chambered stomach to digest the very-hard-to-digest leaves. In fact, it takes a full week to digest a meal, which explains the weekly pooping schedule. It’s actually the slowest digestion period of any mammal.

Ending: So hang out, chill with some moths, and make sure you poop at least once a week like the three-toed sloth here in Life, Death, and Taxonomy.