Monthly Archives: July 2021

Episode 234: Sun Bears, Water Bears

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Thanks to Enzo and Lux for their suggestions! Let’s learn about the sun bear and the water bear this week!

Sun bear just chillin:

Sun bears got long tongues:

The water bear, AKA tardigrade, is not actually a bear. For one thing, it has twice the number of legs as bears have:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

It’s summer in the northern hemisphere, which means hot weather and sunshine and, if you’re lucky, a trip to the lake or ocean. To celebrate summertime, let’s talk about two animals suggested by Enzo and his sister Lux. They wanted to hear about the sun bear and the water bear. Get it? Sun and water?

Enzo’s suggestion is the sun bear, which we talked about a little bit way back in episode 76, but which is a fascinating animal that deserves a lot more attention.

The sun bear lives in southeast Asia in tropical forests and is most closely related to the black bear. It has silky black fur, although some are gray or reddish, and a roughly U-shaped patch of fur on its chest that varies in color from gold to almost white to reddish-orange. Its muzzle is short and is lighter in color than the rest of its face, usually gray. It has small ears too. It’s the world’s smallest bear, only around three feet long from head to tail, or 150 cm, and four feet tall when standing on its hind legs, or 1.2 meters. Researchers think its chest spot acts as a threat display. When a sun bear stands on its hind legs, the chest spot is really obvious, which may warn potential predators away. Even so, tigers and leopards will attack and eat sun bears.

The sun bear spends a lot of time in trees, more than any other bear. It has long claws that it uses for climbing and to tear open logs to get at insect larvae. It eats a lot of termites and especially loves honey, which it licks from the hive with its long tongue–up to 10 inches long, or 25 cm. It also eats a lot of plant material, especially fruit and acorns. It will catch and eat birds and small animals, or sometimes larger animals like deer, but it mostly eats insects and fruit.

The female sun bear makes her den in a hollow tree to give birth. She has one or two cubs at a time, and like other bear cubs they’re born extremely small and with their eyes and ears sealed shut. This is the case with animals like dogs and cats too, but newborn bears are tiny compared to how big the mother bear is. The eyes and ears continue developing after the cub is born, but it’s a few months before it can see and hear properly. A cub remains with its mother for almost three years.

Other than mothers and babies, the sun bear is solitary. Adults don’t typically interact except to mate, although adult sun bears kept in captivity will play together. A 2019 study of sun bears came to a surprising conclusion that they communicate with each other by mimicking facial expressions. This is something humans do all the time, of course, and apes do too. Dogs also mimic facial expressions. Humans, apes, and dogs are all intensely social animals, so researchers have always assumed that the mimicking of facial expressions is important because of that sociability. I mean, that just makes sense. If you see a friend approaching and they have a big smile on their face, naturally you’re going to smile too. But here are these solitary bears with facial communication just as well-developed as in apes. Researchers think it may be a trait that’s so important to mammals as a whole that it develops even in species that don’t spend a lot of time interacting.

The sun bear is threatened by habitat loss and hunting, but it does well in captivity and is popular in zoos. Conservation efforts are in place to protect the sun bear in the wild as well as continue a healthy captive breeding program around the world.

Lux wanted to hear about the water bear, which is also called the tardigrade or the moss piglet. I can’t believe we haven’t covered the tardigrade before—we even have one in our new logo! Patrons may remember parts of this section from a Patreon bonus episode from 2017, but I’ve updated it a lot.

The water bear isn’t a bear at all but a tiny eight-legged animal that barely ever grows larger than 1.5 millimeters. Some species are microscopic. Pictures of the water bear are taken with an electron microscope because otherwise they just look like a teensy little dot.

There are about 1,300 known species of water bear and they all look pretty similar. It looks for all the world like a plump eight-legged stuffed animal made out of couch upholstery. It uses six of its fat little legs for walking and the hind two to cling to the moss and other plant material where it lives. Each leg has four to eight long hooked claws. It has a tubular mouth that looks a little like a pig’s snout or a bear’s snout.

An extremophile is an organism adapted to live in a particular environment that’s considered extreme, like undersea volcanic vents or inside rocks deep below the ocean floor. Tardigrades aren’t technically extremophiles, but they are incredibly tough. Researchers have found tardigrades in environments such as the gloppy ooze at the bottom of the ocean to the icy peaks of the Himalayas. It can survive massive amounts of radiation, dehydration for up to five years, pressures even more intense than at the bottom of the Mariana Trench, temperatures as low as -450 Fahrenheit, or -270 Celsius, heat up to 300 degrees Fahrenheit, or 150 Celsius, and even outer space. It’s survived on Earth for at least half a billion years. Mostly, though, it just lives in moss.

One thing to remember is that different species of tardigrade are good at withstanding different extreme environments. Not every tardigrade is able to do everything we just talked about. They’re tough, but they’re not invulnerable. Many species can withstand incredible heat, but only for half an hour or less. Long-term temperature increases, even if only a little warmer than it’s used to, can cause the tardigrade to die.

Most species of tardigrade eat plant material or bacteria, but a few eat smaller species of tardigrade. It has no lungs since it just absorbs air directly into its body by gas exchange. It has a teeny brain, teeny eyes, and teeny sensory bristles on its body. Its legs have no joints. Its tubular mouth contains tube-like structures called stylets that are secreted from glands on either side of the mouth. Every time the tardigrade molts its cuticle, or body covering, it loses the stylets too and has to regrow them. In some species, the only time the tardigrade poops is when it molts. The poop is left behind in the molted cuticle.

The tardigrade’s success is largely due to its ability to suspend its metabolism, during which time the water in its body is replaced with a type of protein that protects its cells from damage. It retracts its legs and rearranges its internal organs so it can curl up into a teeny barrel shape, at which point it’s called a tun. It needs a moist environment, and if its environment dries out too much, the water bear will automatically go into this suspended state, called cryptobiosis.

The tardigrade’s DNA gets fractured during dehydration but it’s incredibly successful at repairing its DNA upon rehydration, which explains a big part of its success. In 2016, Japanese researchers sequenced the genome of the species of tardigrade that best resists radiation. In the process, they discovered a new protein in the tardigrade’s genome, which they named DSUP, short for damage suppressor. Even more interesting, when cultured human cells were given the ability to create DSUP, after exposure to X-rays, they showed half the DNA damage that non-DSUP cells showed.

Tests in 2007 and 2011 that exposed tardigrades to outer space led to some speculation that tardigrades might actually be from outer space, and that they, or organisms that gave rise to them, might have hitched a ride on a comet or some other heavenly body and ended up on earth. But this isn’t actually the case, since genetic studies show that tardigrades fit neatly into what we know of animal development and evolution.

The tardigrade is probably most closely related to arthropods, like insects and spiders. Their closest relatives were probably lobopodians, extinct wormlike organisms with stubby legs. The famous Hallucigenia creature is a lobopodian, which we talked about in episode 69 about the Cambrian explosion. There’s still a lot we don’t know about the tardigrade’s ancestry, since we have so few fossilized water bears, but many researchers think their oldest ancestors were probably much bigger than the microscopic or nearly microscopic living animals. In other words, maybe once there were water bears you could pick up and hug. Well, they probably weren’t that big, but I like to imagine it. I think that if you hugged a water bear too hard, it would make this noise: [little prrrt sound]

You can find Strange Animals Podcast at That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or Podchaser, or just tell a friend. We also have a Patreon at if you’d like to support us that way, and don’t forget to join our mailing list. There’s a link in the show notes.

Thanks for listening!

Episode 233: The Astonishing Aye-Aye

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Thanks to Elaine, Molly, and Oliver for suggesting the aye-aye! I guess it’s an idea whose time has finally come.

Further reading:

Gimme six! Researchers discover aye-aye’s extra finger

Ah yes, I have many many many fingers:

S p i d e r h a n d s:

A baby aye-aye (blep):

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

I can safely say that this week’s episode is brought to you by popular demand. It was suggested by not one, not two, but three different listeners, two of them very recently. Elaine wanted to know about the aye-aye, and then Molly wanted to know about the aye-aye, and then Oliver wanted to know about the aye-aye. I think it’s high time we all learned about the aye-aye, because it’s a weird and amazing animal.

The aye-aye is a primate, specifically a type of lemur, but it doesn’t look like other lemurs. It kind of looks like a weird possum at first glance. Its shaggy fur is brown or yellowish but the hairs are tipped with white, which gives it a frosty appearance. Its face is white or pale gray. Its eyes are large, very round, and orange or yellow, and it has really big ears sort of like a bat’s ears. It grows up to three feet long, or 90 cm, including its really long tail.

To picture what an aye-aye looks like, imagine a little monkey with brownish fur tipped with white, with a tail longer than its body that’s thickly furred like a squirrel’s tail. Its head looks like a squirrel or possum, but with big orangey staring eyes and big bat ears that are sort of stuck out to the sides of its head instead of on top. Its hind feet look like monkey feet with an opposing digit to help it grab onto branches, because it lives in trees. But its hands look like SPIDERS. The fingers of its hands are extremely long and thin like spider legs. That’s what it looks like.

The aye aye’s fingers are long for an interesting reason, and if you don’t already know, I bet you would never be able to guess. Go on, guess. Just shout it out. I won’t hear it but everyone around you will hear you shout, “THE AYE-AYE’S FINGERS LOOK LIKE SPIDER LEGS BECAUSE IT WANTS TO SCARE PREDATORS INTO THINKING IT’S TWO SPIDERS WITH A MONKEY FRIEND.” You would be wrong, sorry, but that’s a good guess.

No, the aye aye uses its fingers to find grubs and other insects hidden in rotting wood or under bark, just like a woodpecker. Here’s how that works, and you’re not going to believe it, but it’s true. The aye aye is a primate, which means it has five fingers just like monkeys and apes and humans, but again, they’re extremely long and thin. The middle finger is even thinner than the others. It looks like a jointed twig. If it really was a spider, other spiders would ask what happened to that leg because it’s so much thinner than the other legs.

The aye aye uses the thin finger to tap-tap-tap on tree branches and trunks at night, and it listens with its huge ears to the echoes of its tapping. That’s echolocation, just like bats and a few other animals use to navigate, but the aye aye uses it to listen for hollow places in the tree where insects are hiding. It can also hear the tiny movements of insects. Its ears are just that sensitive.

When the aye aye locates an insect, it chews a hole into the wood and then uses its long fingers to fish the insects out. It has claws at the end of its fingers that help it catch the insects, although the claws are actually just claw-like fingernails. Primates don’t have claws, we have nails, and that includes the aye-aye. It doesn’t just eat insects, though. It eats fruit, seeds, various kinds of fungus, honey, flowers, and flower nectar. It actually eats more plant material than insects. It may also eat frogs, since some frogs in Madagascar lay their eggs in small holes in trees that are filled with rainwater, but it’s also possible that the aye-aye doesn’t care about frogs or frog eggs or tadpoles. Frogs definitely use the little holes the aye-aye chews as perfect little nurseries for their eggs.

The aye-aye is native to the forests of Madagascar and mostly lives along the east coast. It spends the day sleeping in trees, in a nest it makes out of twigs and dead leaves. Since it may travel more than a mile at night while it forages, it doesn’t always sleep in the same nest. It can make a new one in less than an hour, and then it crawls inside and wraps its long tail around it and falls asleep, cozy and warm.

The aye-aye hardly ever comes down to the ground. It’s mostly solitary except during mating season, although sometimes a few aye ayes will forage together. When aye-ayes do forage together, it’s usually a male and female, or one female and more than one male, or just two or more males. Female aye-ayes are more aggressive than males and they don’t want anything to do with other females.

The aye aye has so many non-primate characteristics that I hardly know where to start. For one thing, it’s nocturnal. Very few primates are nocturnal. It echolocates to find its food, which is completely weird. Also, its incisors grow continuously like a rodent’s. Incisors are those squarish front teeth. Since it uses its incisors to chew holes in wood, they need to keep growing or they’d get worn down to nothing eventually. The aye-aye’s incisors are very similar to a squirrel’s, and in fact is skull and jaw are also very similar to those of a squirrel. You know what that means. Yes, convergent evolution! It’s everywhere! Its skull and teeth look so much like a big squirrel’s that when scientists first examined the aye-aye back in the 18th and early 19th centuries, they classified it as a rodent. It wasn’t until 1931 that it was recognized as a primate, and even today some researchers think it’s not as closely related to primates as is currently thought. Genetic studies do indicate that it’s most closely related to lemurs, though. The aye-aye also has fewer teeth than lemurs and other primates, only 18 in all.

If you shine a light at an aye-aye at night, its eyes will reflect some of the light just like a cat. This is due to a specialized layer in the eye called the tapetum lucidum, which reflects light toward the retina so the animal can see better in the dark. Very few primates have a tapetum lucidum because most primates are diurnal, or active during the day, instead of nocturnal like the aye-aye.

Most nocturnal animals don’t see colors very well or at all. Naturally, they don’t need to since colors are hard or impossible to see in low light. But when researchers studied aye-aye genetics to learn more about how color vision developed in primates, including humans, they were in for a big surprise. The aye aye is completely nocturnal, but it still has the gene to see colors related to green and blue. Researchers have no idea why this is the case, although naturally they have some theories.

One theory is that the aye-aye uses its color vision to find flowers, especially blue flowers. Another theory is that it can see ultraviolet, which allows it to see urine marks left by other aye-ayes, since urine glows in ultraviolet light. The most ultraviolet light is available at dusk, which is when an aye-aye first ventures out to see what’s going on in its territory.

But let’s go back to the aye-aye’s fingers again. I just can’t get over its fingers. Not only is the skeletal middle finger just plain weird-looking, it’s weird compared to all other animal fingers. That one middle finger has what’s called a ball and socket joint, which is just not a joint found in fingers. You may not be familiar with the term, but you know what a ball-and-socket joint is because you have some in your own body. Your leg bones fit into your hip bone with ball-and-socket joints and your upper arm bones fit into your shoulders the same way. This allows you to move your arms and legs all around, whereas your fingers mostly just bend down, and a little bit up and sideways. But the aye-aye’s thin middle finger is incredibly flexible because of its ball-and-socket joint. All its other fingers have ordinary finger joints.

But wait, there’s more about the aye-aye’s fingers. In 2019, results of a study of the aye-aye’s unusual hands were published, and I just want to point out that the lead author of that paper is quoted as saying, “When you watch [an aye-aye] move, it looks like a strange lemur walking on spiders.” I’m not the only one who thinks their hands look like spiders!

Anyway, the study intended to learn more about the tendons in an aye-aye’s hands. But the researchers found a little structure on the wrist that no one had ever noticed before. It’s a small pseudo-thumb, or false thumb, which acts as an extra digit and helps the aye-aye climb through trees.

The pseudo-thumb isn’t just a little nubbin that helps it balance. No, it’s basically a real digit. It has bone and cartilage inside, muscles that allow it to move just like a regular thumb, and it even has a little thumbprint. It’s also strong. Researchers think that the aye-aye’s other fingers are so specialized that they’re not much help in climbing, so it developed an extra thumb.

Strange and specialized as the aye-aye is, it’s not the only animal we know of that had long, thin fingers that it used to tap on trees to find insects. 55 million years ago an animal called Labidolemur kayi lived in Europe and North America and shared many characteristics with the aye-aye. It was a little smaller than the aye-aye but had the same rodent-like teeth and two long thin fingers. Labidolemur kayi shared an ancestor with both rodents and primates, although it wasn’t a direct ancestor of the aye-aye. The aye-aye developed its rodent-like teeth and long thin fingers independently. Say it with me again: convergent evolution!

The aye aye is not only the only member of its own genus, it’s the only member of its own family. There used to be another species called the giant aye-aye that was at least twice the size of the living aye-aye, but it went extinct an estimated 1,000 years ago. Yes, just one thousand years ago, that’s all. We don’t know much about the giant aye-aye because all we have are some subfossil remains.

The aye-aye is endangered due to habitat loss and persecution by locals, who think it’s bad luck due to its weird appearance. It was actually thought to be extinct in 1933, but in 1957 researchers stumbled across one and probably breathed a sigh of relief that we hadn’t lost the aye-aye after all. In 1966 nine aye-ayes were taken to a small forested island off the eastern coast of Madagascar. The island is a nature reserve, and the aye ayes settled right in and are doing well there. At least now, if deforestation continues on the mainland of Madagascar, the aye-aye will be safe from extinction. Since then aye-ayes have also been introduced to another island and several nature reserves and national parks. It’s also kept in some zoos, and the first aye-aye was born in captivity in 1992.

The female aye-aye has one baby every few years, and she takes care of it by herself. Baby aye-ayes have green eyes and floppy ears.

You can find Strange Animals Podcast at That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or Podchaser, or just tell a friend. We also have a Patreon at if you’d like to support us for as little as one dollar a month and get monthly bonus episodes. There are links in the show notes to join our mailing list and to our merch store.

Thanks for listening!

Episode 232: Almost Domesticated

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Thanks to “dog freak Ruby,” we’re going to learn about some animals that aren’t exactly domesticated but aren’t really wild either.

Further reading:

Memories of Ángela Loij

Mongolian horse and its person:

Mongolian horses:

OH MY GOSH HEART HEART HEART (photo from this website):


An artist’s rendition of the Fuejian dog (left) and a picture of the cuelpo (right):

The cuelpo, happy fox-like canid:

A very fancy rat:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

Before we get started, and before I forget again to tell you about this, I’m planning a bonus Q&A episode for August. If you have any questions about the podcast, podcasting in general, me, or anything else, feel free to email me at, or otherwise contact me through social media!

A few episodes ago I mentioned in passing that the Australian dingo is a type of feral dog. It’s a more complicated situation than it sounds, so while I didn’t want to confuse the issue at the time, I kept thinking about it. Then I remembered that a listener emailed me a while back wanting to know more about how dogs were domesticated. We covered the topic pretty thoroughly back in episode 106, but I realized that there’s an aspect of domestication we didn’t cover in that episode. So thanks to “dog freak Ruby,” here’s an episode about a few animals that are only semi-domesticated.

Domestication, after all, isn’t a switch you can flip. It’s a process, and depending on the animal species and the circumstances, it can take a really long time. It’s not the same thing as taming an animal, either. An individual animal might become tame with the right treatment, but that doesn’t mean any individual of that species would react the same way. Domesticated animals show genetic changes that their wild counterparts don’t, changes that make them more likely to treat humans as friends instead of potential predators.

Generally, a fully domesticated animal requires some level of care from a human to survive, even if it’s just feral cats living near humans so they can find and kill rodents and avoid most predators. Feral domesticated cats don’t live the same way as their wild ancestors do. But sometimes it’s not as cut and dried as it sounds. While mustangs and other feral horse populations are considered domesticated animals, they live like wild animals and don’t need humans to survive. They mostly just need humans to leave them alone so they can thrive on their own. But if you capture a mustang that’s lived its whole life in the wild, with the right treatment it will eventually become tame, because its ancestors were bred for thousands of years to trust and depend on humans.

That brings us to our first semi-domesticated animal, the Mongolian horse. Yes, I’m still really into Mongolia and the Hu, and I’m excited to say I have tickets to see the Hu twice in concert this fall, if everything goes well. I’ve been listening to a program called the Voice of Mongolia in English, which is primarily a shortwave radio program but it’s also released as a podcast, and it talks about various aspects of Mongolian culture. Recently they had an episode about horses, so some of my information comes directly from that show.

Mongolia is a country in central Asia that’s mostly open steppes, which is a type of grassland. The soil isn’t right for most crops, but it’s great for horses. The people of Mongolia are traditionally nomadic, moving around from place to place to find grazing for their horses and other livestock, and about half of the current population still lives this way.

The Mongolian horse is a small, tough breed that probably hasn’t changed much in the last thousand years, possibly longer. It’s one of the oldest breeds of horse in the world and the ancestor of many other horse breeds. For a long time people assumed it was the domesticated descendant of the wild Przewalski’s horse, but genetic testing has determined that domestic horses developed from a different wild horse species that’s extinct now. Genetic testing also showed that the Mongolian horse has the highest genetic diversity of any horse breed tested. It’s incredibly strong for its size, can gallop for miles without tiring, has strong hooves that never need trimming or shoeing, and seldom needs or receives veterinary care.

The main reason for all these traits is that Mongolian horses live like wild horses in most ways. They live loose, grazing as they like, and if they get too far away from their humans, the owners will go out to find them. But they’re still domesticated. Mare’s milk is an important part of the Mongolian diet, so the mares are used to being milked, and people use their horses to ride, carry packs, and pull carts. The stallions are frequently raced. At the same time, though, they’re not really pets. Mongols don’t give their horses names, but instead refer to them with a detailed description. The Voice of Mongolia in English says the Mongolian language has over 300 words to describe horses, while Wikipedia says it’s over 500. Either way, the terminology is so precise that everyone knows exactly which horse someone’s talking about, which if you think about it is more useful than a name.

The Australian dingo is in a similar situation. It’s considered a feral dog breed, but it doesn’t need people to survive. Most feral dogs throughout the world barely scrape by, eating garbage and rats and often dying of starvation or disease. Dingos live like wild animals and do just fine. But at the same time, they’re happy to hang out with people from time to time, acting as hunting companions who are neither dependent on humans nor frightened of them.

The dingo is a strong, tough, lean dog that stands around 22 inches tall at the shoulder, or 56 cm. It has flexible joints like the Norwegian lundehund we talked about in episode 230, which allows it to climb cliffs and fences and otherwise navigate difficult terrain. It’s usually a yellowy or ginger color, sometimes with small white markings, although some dingoes are black and tan. It can survive on very little water. It often hunts in packs and will hunt animals larger than it is, like the red kangaroo.

The dingo was probably brought to Australia by humans, although we’re not sure when. Dingo fossils have been found dating to 3,500 years ago in western Australia, so it was at least that long ago. Genetic studies show that the modern dingo and the dingo of 3,500 years ago are pretty much identical. It also shows that it’s definitely a domestic dog, related to other dog breeds that were once common in Asia around 7,000 years ago, but which are rare now. It’s most closely related to the New Guinea singing dog, which makes sense since New Guinea is so close to Australia. Until somewhere between 6,500 and 8,000 years ago, New Guinea and Australia were connected when sea levels were low. Genetically the two dog breeds have been separated for about 8,300 years, which suggests that the dingo has been in Australia for at least that long.

Traditionally, Aboriginal Australians would take a dingo puppy from its den to keep as a pet, a hunting dog, or sometimes a herding animal. Sometimes the dingo would stick around when it was grown, but sometimes it would return to the wild. There’s a lot of controversy about breeding dingoes as pets, since it would be easy to breed the wild traits and behaviors out. Since the dingo has been killed as a livestock pest since white settlers arrived in Australia, in many places its numbers are in decline and there are worries that the wild dingo could go extinct. There are already problems with the dingo cross-breeding with other dog breeds. It’s a complicated topic, because while the dingo is a dog, it’s not precisely domesticated at this point but also not precisely a wild animal.

There used to be a domesticated canid in South America called the Fuegian dog, which was probably used as a hunting dog, especially to hunt otters. On cold nights, the dogs would wrap themselves around their people like living blankets so everyone stayed nice and warm.

The Fuegian dog wasn’t a dog, though. It was the domesticated form of the culpeo, also called the Andean fox. It’s actually not a fox although it looks a lot like one. It’s related to wolves and jackals, and it lives on the western slopes of the Andes Mountains all the way down to the southern tip of Patagonia. It eats small animals like rodents and introduced European rabbits. While the culpeo is sandy or tawny in color with gray on its back and a black tip to its tail, the Fuegian dog was sometimes brown and white or all white. Reportedly the Fuegian dog was not very tame in general and was an aggressive animal compared to actual dogs. It would hunt on its own and basically acted like a wild animal that just happened to hang out with humans a lot, like the dingo does today.

The culpeo is doing just fine, but the Fuegian dog is extinct. The Fuegian dog was tamed by a Patagonian people called the Selk’nam [shelknam], or ‘Ona, who were nomadic hunter-gatherers. They lived in such a remote part of South America that Europeans didn’t encounter them until the late 19th century when settlers showed up to raise sheep and rubber trees. We’ve talked about what happened to them in a previous episode, although I can’t remember which one. The Selk’nam didn’t understand the concept of livestock, so they figured those sheep were literally fair game. The sheep were living on their own hunting grounds, after all. The Selk’nam killed some of the sheep, and in retaliation, the European settlers murdered all the Selk’nam. I was going to tell you the name of the man who started the genocide, but I don’t think anyone should remember his name. It wasn’t just “oh, you killed my sheep, I’m going to shoot you because I’m mad,” either. There was a bounty on Selk’nam people, and that’s all I’m going to say because it’s just too awful and disturbing.

By 1930, only about 100 Selk’nam remained alive, and the very last member of the people, Ángela Loij, died in 1974. There’s a link in the show notes to a page with lots of information about her as a person.

In 1919 when Christian missionaries visited what was left of the Selk’nam, they discovered that all the dogs had been killed off by the people themselves because the dogs were too fierce and killed livestock. It sounds like a last, desperate attempt by the Selk’nam to stop the murder of their people by keeping their dogs from killing any sheep. But by then it was too late, and the genocide wasn’t really about the sheep in the end. It was racism and hatred. Remember that all people are equal, no matter what they look like or how they live. Don’t ever let anyone tell you otherwise.

Okay. Let’s finish with the story of another semi-domesticated animal, one that doesn’t involve people being terrible to each other. The kind of rat you can buy as a pet is considered semi-domesticated, and it hasn’t actually been domesticated for very long. The person mainly responsible for the pet rat is a man called Jack Black. Not the actor Jack Black; this was a different guy who lived in the mid-19th century.

Jack Black was a ratcatcher in London, England who said he was the Queen’s official rat-catcher even though he wasn’t. He was definitely an extravagant character who always wore what he called his uniform, which included a big leather sash over one shoulder decorated with rats made of iron, a crown, and the initials V.R. for Victoria Regina, or Queen Victoria. He told people the queen herself gave him the sash, but actually his wife made it for him. Black also carried a big domed cage with him to hold the rats he caught.

He mainly caught rats to sell to people who were training their dogs to kill rats, which was also a popular thing to watch. I mean, that doesn’t sound like any fun to me but this was before video games were invented. Occasionally, though, Black would catch a rat that had interesting markings or that was an unusual color. These rats he would keep, tame, and breed to produce more rats with different colors and patterns. He sold the tame, pretty young rats to people as pets. He especially liked white rats, which made popular pets then and are still popular today.

Pet rats, usually called fancy rats, are a subspecies of the brown rat, or Norway rat, which we talked about in episode 143. We also talked about Jack Black briefly in that episode, but at the time I didn’t realize he wasn’t really a royal rat catcher. By 1900 fancy rats were popular pets and remain so today, and are becoming more and more domesticated. If they’re not fully domesticated they’re well on their way, all thanks to a guy who thought rats were neat.

You can find Strange Animals Podcast at That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or Podchaser, or just tell a friend. We also have a Patreon at if you’d like to support us for as little as one dollar a month and get monthly bonus episodes. There are links in the show notes to join our mailing list and to our merch store.

Thanks for listening!

Episode 231: Fish of the Twilight Zone

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Let’s learn about some strange fish of the mesopelagic, or the twilight zone deep in the ocean! Thanks to Page, Joel, Anonymous Animal Lover, Brigham, and Fireburster for suggestions this week!

Further reading:

In Defense of the Blobfish

Further viewing:

Pacific viperfish (video embedded)

The Pacific viperfish, head-on (or rather teeth-on), still from video linked above:

Sloane’s viperfish, rocking those teeth:

The blobfish as it’s usually seen on the internet:

The blobfish as it looks when it’s cozy in its deep-sea environment:

The barreleye, which I have helpfully labeled for you:

Look at the bristlemouth’s sharp thin teeth! Good thing it’s only a few inches long:

An indignant bristlemouth (someone should take MS Paint away from me):

The bristlemouth is the most abundant vertebrate in the WORLD (photo by Paul Caiger):

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

Where on earth does the time go? Suddenly we’re halfway through 2021 and I’m still vaguely thinking we’re only a few months in. I’m getting seriously behind on listener suggestions, so let’s have an episode about some weird fish that’s all listener suggestions. Thanks to Page, Joel, an animal lover who wants to remain anonymous, Brigham (whose name I hope I’m pronouncing correctly), and someone who calls themself Fireburster. Fireburster and Anonymous Animal Lover also both left us really nice reviews, so thank you! I picked all these suggestions at random, just grabbing fish suggestions that sounded interesting, but the great thing is they all turned out to live in a specific part of the deep sea.

Brigham and Fireburster both suggested the same fish, so let’s start with that one: the dragon fish. Neither of them specified which kind of dragon fish they’re talking about, though. It’s a popular name for weird fish of various kinds. We’ve even talked about a few before, the Pacific blackdragon of episode 193, which was coincidentally suggested by Page, and the barbeled dragonfish in that same episode. That’s the episode about William Beebe’s mystery fish, which happens to be my current favorite.

We only talked about the barbeled dragonfish briefly before, so let’s learn more about them now.

The barbeled dragonfish gets its name from the filament that hangs down from its chin, called a barbel. If you’ve ever wondered what the proper name for a catfish’s whiskers is, they’re also barbels. The dragonfish’s barbel has a photophore at the end that produces blue-green bioluminescent light, and the fish flashes the light to attract prey. Its head is large and its jaws are full of sharp teeth, so when an animal comes close, CHOMP! The barbeled dragonfish grabs it.

The dragonfish isn’t very big, with the blackdragon that we talked about in episode 193 being the largest at only 16 inches long, or 40 cm. Most species are about half that. So what happens when an animal the same size as or even bigger than the dragonfish happens along?

The dragonfish eats it, that’s what happens. It has large jaws that it can unhinge to swallow prey that’s bigger than it is, and its stomach can expand considerably to hold whatever it swallows. Mostly it just eats tiny animals like krill and amphipods, though.

We don’t know a whole lot about dragonfish. Various species live throughout most of the world’s oceans, especially in tropical and subtropical areas, and they don’t live in the deepest parts of the ocean. Instead, they’re found in what’s called the twilight zone, or more properly the mesopelagic. Only 1% of all light shining down from the surface makes it down this far, which is why so many animals produce their own bioluminescent light. The dragonfish also has photophores along its sides that it can flash to help attract prey or attract mates. On nights when the moon isn’t too bright, the dragonfish will migrate closer to the surface to find more food, but it makes sure to go back to the twilight zone before the sun rises.

[twilight zone music]

One genus of dragonfish is called the viperfish, and they’re a little different from other dragonfish. Instead of a barbel on the chin, viperfish have a light at the end of a long spine that’s a modified dorsal fin. This is similar to the anglerfish we’ve talked about many times before, even though dragonfish and anglerfish aren’t related. Convergent evolution, at it again!

The viperfish has teeth so long they don’t fit in its mouth. Instead, they stick out, which gives it its other name of fangfish. Sloane’s viperfish has the largest teeth of all the viperfish species, so long that they form a cage across its mouth to stop prey from escaping before the fish can swallow it. Unlike most dragonfish, Sloane’s viperfish sometimes swims toward its prey very quickly, slamming into it and wounding it with its fangs. It even has a sort of built-in shock absorber in its spine right behind its head. The Pacific viperfish can also be aggressive when hunting.

This is probably a good place to learn a little more about the twilight zone, AKA the mesopelagic. It’s measured not by depth but by how much light is available from the surface, in this case only 1% of light. There’s also not as much oxygen in the water here as at the surface. Many, if not most, animals that live in the mesopelagic migrate closer to the surface at night to find food, then retreat to the darkness below to avoid being seen as the sun rises and fills the upper layers of water with more light.

Lots and lots of animals live in the mesopelagic, from giant squid to oarfish, although most of the animals here are small. Below this layer of water is the bathypelagic, and below that is the real depths, the abyssopelagic where conditions are extreme and life gets really weird and scarce. The uppermost layer of the ocean is called epipelagic, if you were wondering. No plants live in the mesopelagic or below, because there’s not enough light. Obviously, the ocean isn’t always deep enough to have a bathypelagic layer or below, and quite often the mesopelagic ends at the sea floor.

It’s hard to study mesopelagic animals because many of them can’t survive at the surface. They’re built to withstand the increased water pressure at depths up to 3,300 feet, or 1000 meters, below the surface, and when they’re dragged up in nets they often die within minutes. Many marine animals have an organ called a swim bladder that’s filled with gases, which helps the animal stay neutrally buoyant in the water so it doesn’t float upward or sink downward when it’s not moving. The animal can adjust the amount of gas in its bladder as it swims upward, but when it’s pulled upward quickly in a net it can’t expel enough gas fast enough and the swim bladder can burst or expand so much that it squishes the rest of its insides, killing the animal before it even reaches the surface. Animals that don’t migrate vertically often don’t have a swim bladder since they don’t need it, and they’re just adapted for water pressure that’s as much as 120 times greater than pressure at the surface. This pressure difference is why blobfish look so blobby, so let’s talk about the blobfish next, Anonymous’s suggestion.

The blobfish lives on the sea floor in deep water near Australia and New Zealand. It grows about a foot long at most, or 30 cm, and is grayish with little spikes all over it. It has a gelatinous body with weak muscles and a weak skeleton, but it doesn’t need either since the intense pressure of the water presses in around the fish all the time and keeps it just the way it should be. It looks like a fish. Its gelatinous flesh is slightly less dense than the water around it, which means it can float just above the sea floor without much effort, just drifting along, giving its tail and broad fins a little flap every so often. It eats whatever detritus floats down from far above, although it’s also mostly on the lookout for small crustaceans that live on the sea floor.

The problem comes when a fishing net catches a blobfish and brings it to the surface. Suddenly there’s no nice firm water around the fish. Instead of being slightly less dense than the water around it, the blobfish is suddenly way more dense than the water, and it expands as a result. Then someone looks at this horrible dead pinkish blob that was once a happy live fish and thinks, “Gross! I’ll take a picture of that for the internet,” and that’s why the blobfish gets its name. Poor blobfish!

Fortunately, scientists have developed a compression chamber for the animals they study. When a deep-sea animal is put in the compression chamber and brought to the surface, the compression chamber keeps the water pressure where the animal needs it. The animal doesn’t die horribly, and that allows researchers to observe a live animal instead of a dead blobby one.

Next, let’s learn about Page’s suggestion, the barreleye fish. It lives in the North Pacific in deep water, and it has upward-pointing eyes that are very sensitive to light. It’s a small fish, only about six inches long, or 15 cm, and is mostly dark in color, as you would expect from a deep-sea fish. It’s chonky in shape with large fins that help it stay motionless in the water while it looks for tiny fish and jellyfish silhouetted against the water’s surface far above. Then the barreleye will move quickly to grab its prey.

It seems like there’s something I’m forgetting to tell you. Hmm. There’s something unusual about the barreleye fish, I just know it.

Oh yeah. The domed top of its head is transparent and its eyeballs are inside the dome. You can see the internal eyeballs and its brain through its transparent head, which is otherwise filled with liquid. It is really weird-looking. Its eyes are tubular, which gives it its name, and they can rotate around to focus on things or look straight ahead when it wants to. The eyes also have bright green lenses, which helps filter out the faint sunlight from above so the fish can better see the bioluminescent glow of other deep-sea animals.

It wasn’t until 2004 that researchers realized the barreleye’s eyes were covered by the transparent dome, because it’s fragile and would end up destroyed when a fish was dragged up by nets. The first photographs and video of the barreleye in its natural environment, taken by deep-sea remote vehicles, must have freaked the researchers out completely.

If you’re wondering why the barreleye has its eyeballs hidden inside a transparent dome, researchers have wondered that too. The best guess is that the dome protects the large, sensitive eyes from jellyfish stings, since barreleyes love to eat jellyfish.

Finally, Joel suggested the bristlemouth fish. The bristlemouth is a small, slender fish that generally grows no longer than a person’s finger, although one species grows up to 14 inches long, or 36 cm. Males are smaller than females. It lives throughout the world’s oceans and is black or dark brown to hide it in the twilight zone where it lives. Like the barbeled dragonfish, which by the way really likes to eat it, it migrates closer to the surface at night to find food, then goes deeper again in the daytime to hide in the darkness.

The bristlemouth gets its name from its teeth, as you may have guessed. It has a large mouth lined with lots of short, thin teeth. It mostly eats small crustaceans, especially copepods, but will also grab tiny fish and other animals. Its lower jaw is longer than its upper jaw and can open wide to grab animals larger than it is. Unlike the other fish we’ve talked about today, its eyes are small and it doesn’t use them to find prey. Instead, it uses its lateral line system, which allows it to detect tiny movements in the water. The male bristlemouth also has a good sense of smell to help it find a female. All bristlemouths start out life as male, but some males metamorphose into females as they age.

The bristlemouth also has rows of light-emitting photophores on its underside to help hide it from predators. Its photophores glow to match the amount of light shining down from far above, which means its silhouette is much harder to see by fish or other animals below it.

There’s still a lot we don’t know about the bristlemouth, but we do know one thing. It’s the most abundant fish in the ocean. Literally there are more bristlemouths in the world than any other vertebrate, estimated at hundreds of trillions of them, possibly as many as a quadrillion, which is a million billion. That’s a lot of fish. There are so many that Navy sonar bounces off them and looks like a false bottom of the ocean. The United States Navy calls it the Deep Scattering Layer and wasn’t sure what was causing it, but the mystery was solved in 2010 when a research vessel with fine-mesh nets kept bringing up unbelievable numbers of the tiny fish. Specifically, the abundant ones are bristlemouth fish in the genus Cyclothone, which mostly lives in tropical areas.

The first person to see a bristlemouth in its natural habitat was William Beebe in the 1930s, during a bathysphere descent into the twilight zone, which brings us right back to where we started this episode.

You can find Strange Animals Podcast at That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or Podchaser, or just tell a friend. We also have a Patreon at if you’d like to support us that way, and don’t forget to join our mailing list. There’s a link in the show notes.

Thanks for listening!