Totally Slothsome: All about sloths
28 min
•Jan 20, 20264 months agoSummary
This episode of Brains On! explores the fascinating biology and behavior of sloths, revealing that their slowness is an energy-efficient adaptation rather than laziness. Through interviews with zoologist Lucy Cook and ecologist Jonathan Polly, the episode uncovers surprising facts about sloth anatomy, swimming abilities, and their weekly pooping ritual that supports a symbiotic relationship with moths and algae.
Insights
- Sloth slowness is a sophisticated survival strategy driven by low-nutrient diet, not laziness or lack of capability
- Sloths demonstrate remarkable adaptations for energy conservation including multi-chambered stomachs, specialized vertebrae, and dense fur insulation
- Seemingly inefficient behaviors like weekly ground trips for defecation serve critical ecological functions supporting moth reproduction and predator camouflage
- Sloths can swim three times faster than they crawl, challenging assumptions about their physical capabilities
- Symbiotic relationships between sloths, moths, and algae demonstrate complex interdependencies in rainforest ecosystems
Trends
Growing public interest in animal biology and biomimicry for sustainable living practicesEducational content positioning animals as models for energy efficiency and environmental sustainabilityExpansion of science education podcasts into multiple languages to reach diverse audiencesLive event tours as revenue diversification strategy for podcast brands targeting family audiencesIncreased focus on correcting misconceptions about animal behavior through scientific expertise
Topics
Sloth Biology and AnatomyEnergy Efficiency in AnimalsSymbiotic Relationships in EcosystemsAnimal Adaptations and EvolutionRainforest EcologySustainable Living PrinciplesPredator-Prey RelationshipsMoth Life CyclesAnimal MetabolismCamouflage and Survival StrategiesComparative Animal BehaviorZoological Research MethodsBiodiversity ConservationAnimal LocomotionEcosystem Interdependence
Companies
Bombus
Sponsor providing sports socks and slip-on shoes; promoted with code 'family26' for 20% discount
People
Lucy Cook
Zoologist and founder of Sloth Appreciation Society; expert interviewed about sloth biology and behavior
Jonathan Polly
Ecologist at University of Wisconsin-Madison; studied sloth weekly defecation behavior and moth relationships
Zach Peary
Research partner of Jonathan Polly; collaborated on sloth research and behavioral studies
Christina Arru
Co-host and voice of Brains On en Español; hosts separate podcast 'Catanly the Stars'
Molly Bloom
Primary host of Brains On! Science podcast for kids
Quotes
"Sloths are really icons of sustainable living. They've survived tens of millions of years on this planet because they're really good at saving energy."
Lucy Cook
"When sloths swim, they're actually three times faster than they are when they're crawling along the ground."
Lucy Cook
"It must be important. There must be a better thing. If they're literally dying to do it but also really work and hard to do it too."
Jonathan Polly
"They're not thinking, oh, I gotta go poop so I can keep my algae alive. Not at all. It's one of those indirect benefits."
Jonathan Polly
Full Transcript
Friends, we are so super duper excited to tell you that we just added a bunch more cities to our 2026 live show tour. Get ready for singing, dancing, magic tricks, game shows, mystery sounds, and scientists falling from the sky. In a totally safe way, we promise. Plus, there's a chance for you to attend special meet and greet parties in every city. So come on! This spring we're coming to Milwaukee, St. Paul, Atlanta, Fort Lauderdale, Chattanooga, Durham, San Francisco, Portland, Buffalo, Toronto, and an Arbor. We're basically gonna be everywhere. Look behind you. Are we there? No? Well, we probably will be soon. Head over to brainson.org slash events for tickets. And make sure you grab passes to our meet and greet party. You get to ask us questions, take pictures with us, and I'll even do some close-up magic. That's brainson.org slash events. Can't wait to see you. Brains on Universe. You're listening to brains on where we're serious about being curious. Come on, Harvey, you can do it. Just say totally flossum. I'm sorry, Sandin. I cannot complete this task. I do not recognize the command. Slossum. I created my own word by combining sloths with awesome. See? Slossum. Are you looking for a recipe for some sauce? Ugh, no. Why is this so hard? Sandin, what are you doing? Oh, hey, Christiana Hey, Molly. I'm just trying to expand Harvey's vocabulary. You? We're just heading over to the studio. Slossum. He's doing it again. Oh, yeah. He's always trying to get us to adopt his word inventions. Sandin, this is just like when you tried to make terrific happen. Or a tic-tastic. But but but but slossum is different. Is it? It's kind of a mouthful. Yeah. Can you even say it three times fast? Slossum. Slossum. Slossum. Slossum. Slossum. Slossum. of the Brains on Universe. I'm Molly Bloom and my co-host today is Christina Arru from Miami. Hi Christina! Hi Molly! So not only is Christina a Brains on fan, she's also one of the voices of Brains on an Espanol. If you haven't checked it out yet, there are currently six episodes of Spanish Brains on. You can find it by searching for Brains on an Espanol at our website or wherever you get your podcasts. So Christina, I'm curious what was your favorite fact you learned working on Brains on an Espanol. Learning why are shoes smell. And the reason is because our glances get bigger and they can trap more odors. Exactly. You've learned so much. So Christina, you're also have another podcast that you host as well, right? Yes, it is called Catanly the Stars, Young and Famous with Christina Arru and I'm Christina Arru. That makes sense. So what do you do on your podcast? I interview young Latinx stars. Very cool. So like who are some of the stars you've talked to recently? Natalia Clement and Jardina. Well, you're an accomplished podcaster but you also happen to be a super fan of sloths. So Christina, what is your favorite thing about sloths? That they move slow. Why do you like that about them? Because it's just so cute. They move slow even though they can move fast and they're the slow to mammal on earth. I am also a very big sloth fan. I wrote a report on three-toed sloths back in third grade and have been in love ever since and it turns out our listeners are obsessed too. You all send us so many sloth questions. So we're going to start by answering this one. Why are sloths so slow? Thanks to Camilla and Arthur for that question. If there is one thing, sloths are famous for. It's being slow. They move slowly, they digest slowly, they even blink slowly. If a sloth were a brains-on co-hoved, the beginning of the show would sound like this. Or serious about being curious. Okay, yeah, we should probably stop there because that could take a while. But yeah, sloths are slow. But it's not because they're lazy. It's because they're really, really efficient. That means they use every bit of energy they have very wisely because it's really hard for sloths to get energy. Yeah, they live in trees and eat flowers and leaves. But those things don't have a lot of nutrients. So they have to make the most of what little they get. For example, sloths have multi-chambered stomachs like a cow that let them slowly digest that food and squeeze out every bit of nutrition from this limited diet. They also move as little as possible to save energy. And when they do move, they move slowly. They also have three extra vertebrae in their neck so they can swivel their heads almost all the way around. Another neat energy saving trick. Why move to see something when you can just turn your head? Sloths have so many fascinating adult patients that let them live in this very specific tree-dwelling lifestyle. Here to tell us more about how amazingly cool sloths are is theologist Lucy Cook. Chief Defender of the Sloth Appreciation Society. Welcome, Lucy. Hello! Hello! Hello! Hello! What inspired you to start the Sloth Appreciation Society? Well, that's a very good question. I started the Sloth Appreciation Society. It was about 10 years ago, now. I felt that sloths were getting a bad rap and that people didn't really understand how amazing they are. And I still remember very clearly the first time I saw a sloth and it kind of blew my mind, you know, and I just was mesmerized by how slow they are. As a zoologist, I just wanted to understand them. But also, on top of that, they have these amazing faces that look a bit like their humans. You know, with these wonderful smiles. So, you know, there's a lot to love. We're going to ask you a few questions sent into us from our listeners. This one is from Ivy in Austin, Texas. How are sloths able to swim? So sloths live on leaves and when they are digesting their leaves, they generate quite a lot of gas. As if there wasn't enough reasons to love sloths, they're the only mammal that we know of that doesn't fart. And so, what happens with all this gas is that it forms an imbuilt buoyancy device that basically makes them bob along in water. Wow! Could you just describe what it looks like when they do swim? When sloths do swim, it's incredibly cute, because they do a sort of a doggie paddle. A sloppy paddle, I should say, really. The legs don't do much, but the arms do a sort of a sort of sloppy doggie paddle out the front, whilst their big inflated fart-filled belly, bobs, keeps them, keeps the body up. So cute. Yeah. And did they swim as slow as they do everything else? No! No, that's the amazing thing. What? They can actually, I think it's something like, when they swim, they're actually three times faster than they are when they're crawling along the ground. So yeah, they swim a lot faster than they crawl, which is amazing. Our next question is from Lillian in California. Are sloths babies just as slow as their parents? Or do they have more energy like human kids? I would say, I don't know the answer to that. So, I mean, how wonderful to be asked a question that's so imaginative that I've not been asked it before and I don't know the answer. So thank you very much for that. I've watched sloths, mothers, and babies together, and the babies are also very slow like their mothers. And you know, the thing is about being fast, is it burns a lot of energy, and when you're a little baby, you want to use all your energy for growing and getting bigger. So my guess would be that they are as slow, if not slower than their parents, so that all of their energy goes into growing into into adults and isn't wasted on on on whizzing around unnecessarily. Look from California, well, in with this question, why do sloths have line claws? Well, so sloths have claws because it helps them dangle from trees. You know, sloths are just amazing energy savers. They really kind of wrote the book on sustainable living. And you know, one of the ways that they save a lot of energy is by hanging from trees. And the way that they dangle is using those claws which are actually very long and curved. And so they sort of grip on like a like a like a clothesline peg and just dangle there. Levi from Knoxville, Tennessee, wrote in with this question, is sloths leaps up by down? Why don't their hands let go and they're sleeping? They just clamp those claws tight. And so I suspect that that's the control of that muscle that clamps that claw and that limb onto the tree. That's not controlled by their consciousness. That's something that's an unconscious control so that it can't be overridden by being asleep. Marina from Milwaukee was wondering, how do sloths snuck at headaches when the blood rushes to their head? Exactly how, how do they do that? It's amazing, right? My understanding is is that they have the valves in their blood vessels such that they pump blood against the force of with more efficiency against the force of gravity. And then the other thing that's really cool is because they're upside down, they have these really huge stomachs that they eat a lot of food and and that because they're upside down could crush their lungs and make breathing really difficult. So they also have scientists have discovered that they have sticky bits on their ribs that prevent the stomach from collapsing on their lungs and make breathing easier. So they have all of these extraordinary adaptations to leading an inverted life. I have a question, how heavy are sloths? So this is surprising, right? So a lot of their size is taken up by their fur. They have a very deep and dense fur coat and that's one of their energy saving tactics that they, even though they live in the tropics where it's really, really warm, they wear this really thick coat like they're an Arctic creature and that keeps all their body warm thin. So they seem a lot bigger and in fact when you see sloths that have got wet, they look like drowned rats. I mean they really you can see then they have these sort of skinny limbs and you know they have this big old belly which is full of digesting leaves but their limbs are long and skinny. So they're actually really light and a three toed sloth is about the size of a large house cat but it doesn't weigh anything like as much as as a house cat. That is amazing. Sloths are so cool and so you know as the founder of the Soth Appreciation Society do you feel like there's like any lessons that like humans could learn from the sloth way of life? You know we're all very aware these days about the need to be much more clever and careful about our energy use and how to recycle energy and how to respect the planet and and I just think sloths are really icons of sustainable living. They've survived tens of millions of years on this planet because they they're really good at saving energy and so I think they've got a whole lot to teach us about that and they're the original tree huggers so they should encourage us all to go out there and and hug a tree. Thanks for answering our question Lucy. I've really enjoyed this interview. Really really good question so I'm really impressed thank you everybody. Thank you Lucy. Today's episode is sponsored by Bombus. It's the time of the year we think about hmm what am I going to do differently this year? Maybe I'm going to read more. Maybe I'm going to work out more. Maybe I'm going to learn a new skill but really at the top of my list is number one to get comfy and that's where Bombus comes in. They're bringing a serious comfort to all my everyday go-to's. The all new Bombus sports socks are engineered with sport specific comfort for running golf hiking skiing, snowboarding and all sport. This year I'm going to walk my dog more longer walks, better walks and these socks are going to help me stay comfy while I do it. And for all my other resolutions like going to the bookstore and picking out more books to read I'm going to wear my new squishy Saturday Swade slip-on shoes which are super comfortable for being on the go. Head over to bombus.com slash family 26 and use code family 26 for 20% off your first purchase. That's B-O-M-B-A-S dot com slash family 26 code family 26 at checkout. Sloths have lots of incredible adaptations or biological tricks that allow them to live the most efficient lives. But there's one sloth behavior that confused scientists because it wasn't efficient at all. You see sloths live their whole lives up in a big tall tree. Now about every week a three-tone sloth will descend. It'll climb down from that big tall tree and it'll poop at the base of it. That's Jonathan Polly. He's an ecologist at the University of Wisconsin-Madison and he studies sloths. And then it will crawl right back up. Well this is really ritualized by ritualized I mean it's really every week it's really something that they do kind of on a weekly basis. This poop behavior was surprising because it seemed to be the opposite of what sloths usually do which is try to use as little energy as possible. Climbing down a tree and then back up again takes a lot of energy. Why would they do this just a poop? Why not just poop way up in the tree and let it fall down. Plus being on the ground is dangerous for sloths. They're much more likely to be eaten by predators like a jaguar or dog or coyote. Lucky for us and all curious people everywhere Jonathan Polly is something of a sloth sloth. He and his research partner, Zach Peary, started studying sloths about 10 years ago. And one of the things they wanted to understand was why sloths make this weekly trick to go to the ground just a poop. It must be important. There must be a better thing. If they're literally dying to do it but also really work and hard to do it too. In just a minute Jonathan is going to walk us through a sort of scientific detective story. It is a detective story. It was a lot of fun. But first it's time for your ears to play detective. It's the... Here it is. Hey, super short. So we will hear it again. I feel like it's so short we should hear it three times. Here it is. All right. Christina, what is your guess? My guess is it's something banging against something metal. Wonderful. Wonderful thought we're going to hear it again so have another chance to guess. Just a little bit. We are working on an episode all about generations and what we call them. You may have heard people mention baby boovers, millennials or Gen Z. Every kid sixth grade or younger is part of generation alpha but that name doesn't mean much. If you could give your generation a new name, what would it be? Record yourself telling us about what you would name your generation and why. Then have your grownup head to brainson.org slash contact and send us your answer. We'll play some of them on our upcoming episode. Thanks. You are listening to brainson. I'm Molly and here is the mystery sound again. I have a new idea on what it is. Let's hear it one more time and then I'm going to love to hear your new idea. Okay one more time. All right. What is your new thought? It's a bird. Did talking about birds sort of jog that in your memory? Yeah. I love that. And it sounds like a bird's flapping its wings really hard. Excellent guess. You ready for the answer? Yes. All right. Here it is. Hello my name is Pedro Myers and that was the mystery sound of my chicken flapping. Hey! I knew it was a bird. I knew it was a bird. You got it. 100%. I knew it was a bird. Nice work. Really great. It was a bird. It was a chicken flapping its wings really hard. Just like you said. Yes. Excellent. I just didn't know what type of bird it was. Yeah I think it would be very difficult to identify what kind of bird just by the sound. It seems probably impossible. So I think you got it as right on as you possibly could. Well done. All right. We've solved that mystery, but now it's time to solve the case of the perilous poop journey. You recall our detective scientist Dr. Jonathan Polly was on the case. He and his research partner were trying to figure out why sloths would bother making their way to the ground to poop. The first clue? Moths. Sloths have a kind of flightless moth living in their fur. A sloth moth if you will. Like the best roommates, the moth don't play loud music or leave their dishes in the sink. They don't harm the sloth at all. They just keep it company. And it turns out the moth wouldn't exist without sloth poop. When the sloth comes down for its weekly poop, female moth will jump down onto the poop and later eggs. Now those eggs developing a larvae and those larvae then eat the poop. They actually create a really cool chamber within each sloth dung. And it'll eat that. It'll eat the sloth dung for its own energy and its own nutrition. And eventually it will eat enough and grow enough that it will pupate and it will turn into a moth. And for one beautiful fleeting moment, this moth, it has the ability to fly. And so what does that flying moth do? Well, it drifts up into the tree. At the top of that tree is often a sloth. And they land in the fur of the sloth. And when they land in the fur of the sloth, they actually lose the ability to fly. Their wings get so beaten up that they're not really able to fly effectively. So then they're stranded. And so the cycle continues. Okay, the moth need to sloth to survive and make more moth babies. But it doesn't seem like the sloth and getting anything out of it. That brings us to the second clue. algae. And so what we realized is that the more moths that a sloth has on its fur, the more algae that a sloth has on its fur, sloths carry really thick mass of green algae that make them blended very well with the trees. The idea being that if you're really green and you carry this algae, these things like harpy eagles which use vision to hunt both see you as well. So maybe you'll be able to avoid being killed. So as these moths live their whole lives in the sloths fur, they eventually die and start decomposing, feeding the algae on the sloths back and making it more protected from predators. Now this is not something that they're thinking of. They're not thinking, oh, I gotta go poop so I can keep my algae alive. Not at all. It's one of those indirect benefits that those sloths that do this behavior and maintain their moths have the algae and live longer. And that's how Jonathan solved the case of the perilous poop journey. And it all started with a question. It's good to ask questions. That's what we should be doing every day. And thanks to Jonathan's questions and detective work, we also know sloths are the slowest mammals in the world. But there are some other slow animals that deserve to be recognized as well. Sounds like the perfect time for. So you think you can slow-mo. Welcome back to so you think you can slow-mo. Your top time consuming talent show. I'm your host, Sid Slothworthy. Let's meet today's contestants. Can you go all up? Get a mate. We're off the banana slug. Super slimed to be here, bro. And Tina the Tortoise. Hiya. Each of you will have a chance to showcase your slowest skills today. So are you ready for the slow-mo show off? Are you know it? Yes. Kenny Koala. What will you be doing for us today? Crikey. I reckon my best talent is napping. First I slowly, scaly eucalyptus tree, find an ace spot and get comfortable. Then I'll start to dose off. I usually sleep for at least 18 hours a day. And if I get hungry, I'll just nab a bit of eucalyptus to snack on. But Kenny, isn't eucalyptus poisonous? Well mate, to most everyone else, yes. The koala can flush out the toxins, meaning I can eat pounds of leaves without ever getting sick. The leaves don't give me much energy though, so I have to nab. Wow, Lee, that's a lady impressive. Thanks, Kenny. A Kenny? And he's falling asleep. Well onto the next contestant. Here to perform the world's slowest and slimy asomba, it's Brock the banana slug. Usher me to the right, usher me to the left. Just look at him slide across that stage. It's taking him ages. I move at a whopping six and a half inches per minute. And that's if I'm in a rush. I'm absolutely mesmerized by your moves. What's your secret, Brock? It's all in the slime, dude. Not only does it help me glide, but it protects me from predators trying to cop these moves. And from eating me. This slime is most poisonous, bro. A defensive dancer. We love to see it. Thank you, Brock. Okay, last but not least, all the way from the Golapagos Islands, we have Tina the Tortoise. Tina, what talent do you have for us? I brought a snack because I'm the most gradual, grazer I know. Well, let me get this straight. Your talent is eating. Well, kind of. I have a super slow metabolism, which means it takes a long time for my body to transform food into energy. I can go up to a whole year without eating or drinking a single thing. Let's get it, Lefarget. That is one slow stomach. And now we wait. This could take a while. Looks like that's all the time we have for today. We'll check back in with Tina in a couple of weeks. Thanks for watching. So you think you can slow-mo. Sloths are lazy. They just live extremely energy-efficient lives. They have all sorts of amazing adaptations that allow them to live happily and slowly up in the trees. Three-toed sloths make a dangerous pooping journey once a week, but they do it in support of their moth friends and algae camouflage. Just like sloths, other animals use their slow nature as a way to survive. Wow, these facts are totally slothsome. Anybody? Come on. Oh, Sandin. That's it for this episode of Frans on. Frans on is produced by Minica Wilhelm, Sandin Totton, Mark Sanchez, and Molly Bloom. We had production help from Ruby Guthrie and Christina Lopez and engineering help from Veronica Rodriguez and Alejandro Juan. Special thanks to Kathy Arru, Lope Do Santos, Rosie Tupont, Paul Guthrie, and Jack Silvernagle. Now it's time for the brains honor a role. These are the incredible kids who keep the show going with their questions ideas, mystery sounds, drawings, and high fives. Avni from Los Gatos, California, Oliver from Irunga, Australia, Gordon from Hong Kong, Ophelia and Guenavir from Panama City Beach, Florida, Henry from Walden, New York, Lyra from Atlanta, River from Pennsylvania, Nora, and Ethan from Overland Park, Kansas. Nico from South Bend, Indiana, Zena from Portola Valley, California, Everly and Sutton from Ohio, California, Daniel from London, England, Robert from Midland, Georgia, Uriah, Ari, and Bodie from Chango, Illinois, Emerson from Jonesboro, Tennessee, Madeline and Juliana from Maple Valley, Washington, Malaya and Nia from Albany, California, Ishaan from Sacramento, Archie from Melbourne, Australia, Amalie from Oxford, England, Oli and Emmy from Clovis, California, Milan from Cambridge, Ontario, Gibran from Dubai, blaze from Pennsylvania, Benton from Alexandria, Virginia, Oscar from Cincinnati, Penelope from Newark, Delaware, Adina and Arise from Austin, Texas, Paisley from Australia, Arthur and Andre from Atlanta, Joe from Portland, Oregon, Grayson from Brooklyn, New York, Emerson from British Columbia, Vera and Audrey from St. Paul, Minnesota, Jeffrey from Los Angeles, Rachel and James from Edmonton, Alberta, Jack from Whitby, Ontario, Marlow from Bristol, UK, Marley from Toronto, PJ from Evanston, Illinois, Zach from Blue Haven, Australia, Harvey from Sheffield, England, Keon from Calgary, Alberta, Margaret and Galen from Littleton, Colorado, Luca from Greensboro, Pennsylvania, Tessa from Massachusetts, Henry from Phoenix, Sanjana from Concord, North Carolina, Lucy, Jack Guthrie and Rose from Arlington, Texas, Matthew from David, Connecticut, Harper from Detroit, Frankie from Georgia, Marshall from Redmond, Washington, Carmen from Utah, Edie from Victoria, Australia, Sean from Wayne, New Jersey, Francis and Hansi from Asheville, North Carolina, Sky from Niska, New and New York, Evelyn from Houston, Texas, Amira from Santa Cruz, California, and Estrella, Geo and CC from Saga, Massachusetts. We'll be back soon with more answers to your questions. Thanks for listening.