Category Archives: invertebrates

Episode 041: Comb Jellies and Sea Sponges THE CONTROVERSY

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We’re learning about comb jellies this week, along with the sea sponge, and the MASSIVE CONTROVERSY ABOUT THE TWO THAT IS PITTING SCIENTIST AGAINST SCIENTIST I might be overstating it just a bit

The lovely Arctic comb jelly:

The lovely Venus’s girdle comb jelly:

A fossil comb jelly. Probably lovely when it was alive:

A sea sponge (most are not this Muppet-like):

Show transcript:

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

For this week’s episode, we’re revisiting jellyfish, more properly known as jellies. The first jelly episode is far and away our most popular and I can’t figure out why. I mean, I’m glad people like it. This time, we’re going to learn all about comb jellies, which are not really as exciting as true jellies. There is no ship-sinkingly enormous comb jelly lurking in the oceans of the world. But they are really interesting.

When you think of a jelly, you probably picture a roughly bell-shaped thing with long stinging tentacles. But most comb jellies are more like egg-shaped blobs, and either don’t have tentacles at all or only have relatively small tentacles that don’t sting. Although they look alike superficially, comb jellies and true jellies are so different that scientists don’t think they’re very closely related at all. Comb jellies are officially called ctenophores (TEN-oh-fours), spelled with a c-t at the beginning if you were wondering. I looked up the pronunciation. Yeah, I know, I pronounced Pliny wrong all through episode 12, but come on, it looks like it should be pronounced Pliny and not Plinny. It’s not like anyone ever came up to me and said, “Hey, what about that Plinny, what a guy.” I just read the name.

But I digress, inexplicably.

Instead of pulsing its bell to maneuver in the water, a comb jelly has rows of tiny compact filaments called cilia, fused together in combs that help it swim. The combs are also called swimming plates.

There are two main types of comb jellies, those with tentacles and those without tentacles. The ones without are called Nuda, or Beroids, and while they don’t have tentacles, they do have combs of extra-large cilia, called macrocilia, that sever prey into pieces small enough to swallow. Mostly they eat other comb jellies. Beroids also have big mouths, but a beroid can actually seal its mouth shut while it’s moving so it’s more streamlined.

Comb jellies with tentacles are divided into eight orders roughly based on body shape. The most common order, the cydippida, are egg-shaped with a pair of thin tentacles that they use sort of like fishing lines. The tentacles are long and sticky, trapping tiny organisms or particles of food. Some species have branched tentacles but none have more than two. The tentacles can retract—when you see a picture of a comb jelly with a weird spring-like thing sticking out from its bottom, that’s a retracted tentacle, not anything gross like a poop. The tentacles contain cells called colloblasts. When an organism touches a tentacle, the colloblast cells rupture and basically release glue that keeps the prey from escaping.

A cydippid comb jelly also has eight combs that run from the top of the body to the bottom, which makes it look sort of like a fancy decorated egg. Comb jelly cilia are iridescent, by the way, so they reflect light in rainbow patterns. Basically what I’m saying is, these little guys are actually really pretty.

All comb jellies are predators, but most eat plankton and other tiny food, because most comb jellies are really small—only a few inches long at most. Bigger species may eat krill and small crustaceans. The biggest comb jelly, Cestum veneris, more often called Venus’s girdle, can grow some five feet long, or 1.5 meters, but only some two inches, or 5 cm, wide. It looks like a nearly transparent or purplish ribbon and lives in tropical and subtropical seas. I wouldn’t want to touch it, but it’s not exactly dangerous. In fact, it’s so delicate that a diver attempting to touch one may accidentally destroy it instead. A lot of comb jellies are that delicate, making them hard to study, so we still don’t know a whole lot about them.

Comb jellies only have one body opening, called a mouth for convenience sake although the jelly uses it for anything that requires a body opening. Until recently, researchers thought that included pooping. Yeah, now you see why it’s not exactly a mouth. But it turns out that a comb jelly has pores on the opposite end of its body from its mouth opening that it uses to release at least some particles of indigestible food. This is interesting since it helps scientists understand how the anus evolved.

There aren’t that many species of comb jellies, maybe 100 or so. But new ones are discovered occasionally, especially deep-sea comb jellies. While comb jellies that live near the surface of the ocean are usually transparent, many deep-sea species are red, since it’s a color most deep-sea animals can’t see. Most are also bioluminescent, and when threatened some species will secrete a luminescent goo. The predator may get confused and attack the goo while the comb jelly swims away as fast as its frantically waving cilia can take it.

If you’ve listened to episode 15, about the hammerhead shark and megalodon, you’ll remember that we don’t have a lot of shark fossils because shark skeletons are made of cartilage, not bone. We just have a lot of shark teeth, mostly. Now think about how big and solid sharks are, then think about how smooshy jellies are. Then try to imagine what a jelly fossil might look like. Yeah.

We do have some comb jelly fossils, though. But we don’t have many. Like, five. We have five. The oldest are from the mid-Cambrian, some 500 million years ago, but they were very different from the comb jellies living today. They had lots more combs, for one thing—between 24 and 80 instead of 8. Researchers have found other fossils that may be of comb jellies. There’s a good possibility that they were widespread throughout the oceans back then—but from genetic testing and other molecular analysis, it appears that the comb jellies alive today are all descended from a common ancestor that survived the Cretaceous-Paleogene extinction around 65 million years ago. So it’s possible that in addition to so many dinosaurs dying off, almost all comb jellies went extinct then too.

Just think, if that one species hadn’t survived and evolved into the comb jellies we have today, researchers might not have a clue what animal those comb jelly fossils represented. If you know about the Burgess shale fossils that have baffled and fascinated paleontologists for decades now, because so many of the fossils don’t resemble anything living today, then it’ll make sense to learn that a few of those five comb jelly fossils were actually found in the Burgess shale.

There are some other comb jelly fossils discovered in China and dated to 520 million years ago. But they don’t resemble the comb jellies living today at all because they had skeletons and spines. Pretty much every fossil found from the Cambrian had supportive or armored structures, even ones like comb jellies that don’t have those things today. I’ll probably do a whole episode eventually about the Cambrian period and the Burgess shale discoveries.

Anyway, there’s some controversy going on right now regarding whether comb jellies or sponges were the species that gave rise ultimately to all other animals, so let’s take a quick side trip and learn about sponges.

The sponge is a very simple animal, still around today. They don’t have any specialized structures like nerves or a digestive system or a circulatory system or organs. They’re just a sponge, basically. And if you were wondering, the sponge you use to clean your kitchen is named after the sea sponge, not vice versa, and you can still get actual dried sea sponges to use for cleaning. They’ve been used that way for millennia. It wasn’t until 1866 that scientists even realized sponges were animals and not plants.

Living sponges just hang out in the ocean or freshwater, stuck to a rock or something. Water flows through them and washes food and oxygen in and waste out. That’s it. That’s all a sponge does is let water flow through it. I feel like there’s a life lesson to be learned there, but I’m too busy doing ten things at once to figure it out.

Mostly sponges eat bacteria and other tiny food particles, although some eat small crustaceans and a few have developed a symbiotic relationship with plantlike microorganisms, which live safely in the sponge and produce enough food for both it and the sponge. Every so often a sponge will release eggs or sperm into the water. If the conditions around a sponge deteriorate, some species will create bundles of unspecialized cells called gemmules. When conditions improve, the gemmules will either grow into new sponges or, if the sponge that created them has died, it will recolonize the original sponge’s skeleton.

A sponge’s skeleton is a sponge, by the way. If you’ve got a natural sea sponge in your house, that’s what you’re cleaning your kitchen counters with, the skeleton of a sea sponge. Different sponges use different minerals to create their skeletons and most are pretty hard, but the ones sold as natural sponges are softer and throughout history have been used for everything from padding armor, applying paint, and filtering water. Loofah sponges aren’t actually made from sea sponges, though. They’re actually from the dried insides of the sponge gourd. I did not actually know that until just now.

Oh, and guess what else I just learned? There’s a small population of bottlenose dolphins in Western Australia that use sponges. The dolphins frequently hunt close to the bottom of the bay. To keep from scraping its rostrum, or bill, in the sand, a dolphin will sometimes stick a sponge under its chin. Researchers think that one especially smart dolphin figured this out and has been teaching her children how to do it ever since.

So that’s the sea sponge. Useful for many things, not much of a party animal. Compared to sea sponges, comb jellies are intellectual masterminds. Even though comb jellies don’t have brains.

Instead, comb jellies have a nerve net. The nerves are concentrated around its mouth and on its tentacles. It does also contain an organ that helps the jelly sense its orientation, basically so it knows which way is up. It usually swims with its mouth pointing upward, incidentally. But while the comb jelly’s nervous system is pretty sophisticated for such a simple animal, it’s also very different from other animals’ nervous systems. Like, super different. Its nerves are constructed from different molecules and use different neurotransmitters.

Its nerve cells are so different from other animals’ that some researchers think it actually evolved separately. Specifically, neuroscientist Leonid Moroz thinks so. He thinks that the first ancestor of comb jellies split off from the sea sponges some three quarters of a billion years ago and evolved separately from all other animals.

Since comb jellies use a different set of chemicals as other animals to accomplish the same tasks, a couple of articles I read make a big deal about how evolution must therefore follow a prescribed path—that animals must have certain traits to survive. But assuming comb jellies did split off from sponges that early and did evolve separately from other animals, they were still competing against those other animals. It’s not like they had an ocean to themselves, although that would be awesome if they did, because who knows what they might have evolved into?

The controversy about whether sea sponges or comb jellies were basically the trunk of the tree of animal life started in 2008, when a study in the journal Nature compared DNA sequences across a number of animal species and suggested that the comb jellies were evolutionarily first. A 2013 paper published in Science by another team of researchers made the same conclusion based on the genome of a species of comb jelly called the sea walnut. That is such a cute name. Don’t you just want to cuddle the little sea walnut and make little hats for it?

All this ignited what some articles call a firestorm of controversy. I like to imagine researchers reading the articles and FREAKING OUT. Moroz’s studies of the comb jelly’s nervous system, and the complete genome of a different comb jelly, the sea gooseberry, appeared in Nature in 2014. Moroz now thinks that nervous systems have developed independently at least nine times in various different groups.

The controversy at this point appears to have several factions. Moroz’s group thinks comb jellies split off from sponges, and that everything else split off from comb jellies but developed separately in the neurological sense. Another group thinks comb jellies split off from sponges and everything evolved from comb jellies, and that comb jellies aren’t all that weird neurologically. Another group thinks comb jellies and sponges split off from a common ancestor of both that had a simple nervous system, which comb jellies retained but sponges lost, and that everything else evolved from comb jellies. But then there’s the other side, the ones who think sure, comb jellies split off from sponges, but so did everything else ultimately, and comb jellies are no more the base of all animal life than the man in the moon.

One thing everyone agrees on, though, is that we still don’t know enough about comb jellies. And they are really pretty.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on iTunes or whatever platform you listen on. We also have a Patreon if you’d like to support us that way. Rewards include stickers and twice-monthly bonus episodes.

Thanks for listening!

Episode 028: Crawdads and Cicadas

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Hello from Finland! While I’m far from home, I’m thinking of animals of my native land. So join me to learn about crawdads (aka crayfish aka crawfish aka freshwater lobsters aka everything) and cicadas!

A lovely blue crayfish from Indonesia:

Fite me

The giant Tasmanian crayfish:

A periodical cicada:

A cicada killer about to do horrible things to a cicada. Nature is disgusting.

Show transcript:

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

For this week’s episode, which I’m putting together right before I leave for Finland on a madcap two-week adventure—okay, two weeks staying in the city of Helsinki while attending a conference and eating a lot of pastries—I’m going to look at two invertebrates that live close to home. The first is the crawdad. I’ve always wondered if those muddy holes near creeks and streams that we call crawdad holes around here are actually crawdad holes. Sometimes they’re nowhere near water. So I looked it up.

Yes, they are actually holes dug by crawdads. So that’s one mystery solved. The crawdad has a lot of different names depending on where you live: crayfish, crawfish, mountain lobsters, freshwater lobsters, mudbugs, and many other names. In Australia they may be called yabbies. There are a lot of species throughout the world, most of them in North America. Some also live in South America, Australia, New Zealand, Madagascar, Japan, and Europe. In fact, they live everywhere except Africa and Antarctica.

Crawdads are freshwater crustaceans and eat just about anything. Some species prefer running water, others like still water, but they all need clean water. If you find crawdads in the creek behind your house, you can be happy to know the creek has clean water—but don’t drink it, seriously. That’s a gross story for another time, but trust me, don’t drink untreated water.

Crawdads look like little lobsters and are closely related to them, and people do eat them. Some species are kept as pets in freshwater aquariums, although if you add them to your aquarium definitely make sure you’re not just providing your fish with a crunchy new snack, since a lot of fish eat crustaceans. Also keep in mind that many species of crawdad like to climb and dig so can make a mess of your nicely arranged tank.

One especially sought-after aquarium crawdad is a blue crayfish. Like blue lobsters, crawdads of normally drab colored species are occasionally found that are bright blue. It’s rare but not ridiculously rare. But there aren’t very many species that are always blue. This particular crawdad is beautiful, purplish pink on its body with blue and white claws and legs. But when they started showing up in the pet trade in the early 2000s, scientists didn’t have any idea what species they were. And the pet sellers weren’t telling where they were found.

After some digging, German researcher Christian Lukhaup traced the crawdads to a creek in Indonesia. It’s a new species, announced in 2015. We don’t know how widespread it is. Researchers worry it may be rare and threatened, and unfortunately most of the ones sold as pets have been gathered from the wild.

Many species of crawdads dig burrows. The bottom of the burrow ends in water, whether it’s a creek or the water table or just wet mud. Crawdads breathe through gills, but their gills are in their abdomen under their shell. As long as the gills are wet, the crawdad doesn’t have to actually be in the water to breathe. Crawdads are nocturnal animals and stay in their burrows during the day, then come out at night. The top of the burrow is usually surrounded by mud that the crawdad has pushed out of its hole. Other crawdad species live under rocks.

One of the smallest crawdad species is found in eastern Australia. It’s less than an inch long—usually only 12 to 18 millimeters in length, not counting its antennae—and is called a lake yabby or eastern swamp crayfish. It was only discovered a few years ago. It’s bluish-black and spends a lot of its time in its burrow, which usually reaches down to the water table so the yabby can survive during the dry season, when the shallow lakes and swamps where it lives may dry up completely.

New species of crawdad are found all the time. In 2009 a possible new species was reported in Tennessee. Two biologists, one from the University of Illinois and the other from Eastern Kentucky University, took a research trip to Shoal Creek, near the Tennessee-Alabama border. The very first crawdad they found, after only two hours of searching, turned out to be a new species—and it’s not exactly small. It’s some five inches long, which is roughly the length between the tip of my pinky finger and the base of my palm. I just measured out of curiosity. Most crawdads in the area are about half that length. DNA testing confirmed that it’s a new species and it was formally described in 2010. It’s related to another big crawdad found in Kentucky and Tennessee, which can grow up to 9 inches long. Both species appear to be rare and live under rocks in the deepest parts of a few streams and small rivers.

The biggest species of crawdad living is the Tasmanian giant freshwater lobster. It lives a long time, up to 60 years, if nothing eats it, and can weigh as much as 13 pounds and grow over two and a half feet long.

There are mysteries associated with the crawdad. For instance, most of Asia doesn’t have crawdads at all, but the ones that are found in Asia are more closely related to the crawdads of the southeastern United States than the crawdads of the southeastern United States are related to the crawdads of the northwestern United States. The northwestern U.S. crawdads appear more closely related to those found in Europe. But the big mystery is why there aren’t any crawdads in Africa.

Crawdads evolved from their marine ancestors around 200 million years ago. Around the same time, a big chunk of the earth’s land was smushed together in a big continent called Gondwana. The continents move around all the time—very, very slowly from a human perspective—due to plate tectonics. That’s why some of the animals found in, for instance, South America are closely related to animals found in Africa, because those two continents were once joined together. If you look on a map or globe you can even see that they fit together like puzzle pieces.

So crawdads evolved when Gondwana was just starting to break up into smaller continents. That explains why there are so many crawdads in different parts of the world—crawdads had time to spread out across much of Gondwana before it broke apart. But what would later be called Africa was right in the middle of Gondwana, and we know it had plenty of freshwater that crawdads could have lived in. Why didn’t crawdads populate that area?

It’s possible they did, but that as Africa moved farther toward the equator over millions of years, the crawdads died out. Crawdads prefer temperate climates—not too hot and not too cold. But there are two problems with that hypothesis. First, we haven’t found any crawdad fossils anywhere in Africa. By itself that’s not too unusual, since arthropods don’t fossilize well. They don’t have bones and their shells decompose relatively quickly. Plus, everything eats them so they don’t typically lie around undisturbed in the mud. But the other problem is more, well, problematic. Africa is a huge continent and most of it has never been that close to the equator. Parts of it have always been rainy and temperate, the perfect crawdad environment. And the island of Madagascar, which separated from Africa some 135 million years ago, does have crawdads. Plus, there are crawdads in parts of Australia that are much warmer than most of Africa. Plus, crawdads from the United States have been introduced into parts of Africa and have done so well they’re now an invasive species. What gives?

Africa does have a lot of freshwater crabs, which occupy the same ecological niche that crawdads do. It’s possible crawdads might have been outcompeted by the crabs. But freshwater crabs prefer tropical climates, not temperate. And in the parts of Africa where crawdads have been introduced, they’re actually thriving so well they’re endangering the native freshwater crabs.

So at the moment, we don’t know why Africa doesn’t have any native crawdads. The reason is probably more complicated than any one thing. For instance, if crawdads in one area were already dealing with freshwater crabs horning in on their food sources and territories, and the temperature was steadily increasing over the centuries, any little setback might have caused the crawdads to go extinct.

There are rumors of gigantic crawdads yet to be discovered. The remote Japanese Lake Mashu, formed some 11,000 years ago in the crater of a dormant volcano, is supposedly home to giant crayfish. There are rumors that trout poachers in 1978 and 1985 captured huge crawdads in the lake, although no pictures exist and no one is sure how big huge is supposed to be in this case. There is one report of a crawdad some two feet long found in the lake. A fisherman also reported seeing one that was three feet long, although he didn’t capture or measure it. As far as we know, the only crawdad living in the lake is a North America species introduced into the lake in the 1930s. It typically grows around 6 inches long, but a 1992 study of the lake’s crawdads didn’t find any larger than two and a half inches long.

During World War II, Australian marines patrolling swampland in Borneo found a crawdad that measured more than four feet long and weighed 49 pounds. It was caught in fresh water although it resembled a marine lobster. The marines nicknamed it Bagaton. The corpse was kept but so far it hasn’t been studied, but take this whole story with a grain of salt because I can only find two sources online that mention it at all.

While I was finishing up my crawdad research, I was on Twitter complaining that I didn’t quite have enough information for a full episode and I wasn’t sure what animal to pair it with. One of the hosts of Rumor Flies, an awesome podcast about rumors and myths, suggested cicadas. That made perfect sense to me, since cicadas are THE sound of summer in the southeastern United States.

I happen to love the sound of cicadas. Yes, they’re loud, but I find their chiming restful. Cicadas call during the day when it’s hottest, not at night—the insects you hear at night are usually katydids and tree crickets. This is what cicadas sound like.

[cicada sound—really you are not missing much, it’s just a rhythmic drone that I find soothing]

On the other hand, cicadas are creepy-looking although they’re harmless. When I was very small I was afraid of cicada shells, which are what’s left behind when a cicada hatches from its nymph form into its adult form. The adult cicada has wings and the male has a really, really loud song—so loud that he disengages his own hearing while he sings so he won’t deafen himself. Cicadas don’t have ears like mammals, they have a membraneous structure called tympana that detects sound. Males produce their loud songs with a structure called a tymbal in their abdomen. The abdomen is mostly hollow, which helps amplify the rapid clicking of the tembals. Some cicada songs are louder than 120 decibels, which is the same decibel level as a chainsaw.

There are a lot of cicada species around the world, but most live in the tropics. Seven species are known as periodical cicadas, which live most of their lives underground as nymphs, eating sap from the roots of certain trees, but emerge from underground as adults all at once. They sing, mate, lay eggs, and die in a matter of weeks, and the babies that hatch from their eggs don’t emerge from underground for another 13 or 17 years, depending on the species. Other cicada species have similar life cycles, but they don’t all emerge from underground at the same time—some emerge every summer while others remains as nymphs.

Cicadas are eaten by birds, bats, spiders, and even squirrels. There’s even a wasp called a cicada killer that preys specifically on cicadas—it captures a cicada, takes it back to its underground nest, and lays eggs in it. The eggs hatch and eat the cicada’s insides. BUT THE CICADA IS STILL ALIVE. I try not to think about insects too often. Cicada killers have black and yellow stripes like yellow jackets, but are much larger, up to two inches long. They will sting but only if provoked. They have to be big because cicadas are big insects, also about two inches long in most species.

Cicadas are edible, and are considered delicacies in many cultures. The females are meatier since the males have that hollow abdomen. In case you were wondering what to look for when you go shopping.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on iTunes or whatever platform you listen on. We also have a Patreon if you’d like to support us that way. For only a dollar pledge a month on Patreon you’ll have access to all the patron-only episodes, which I release twice a month. Some recent episodes have covered scientists eating mammoth meat, animals with weird teeth, and the Beast of Busco. Also you get stickers.

Thanks for listening!

Episode 027: Creatures of the Deeps

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This week is our six-month anniversary! To celebrate, we’ll learn about some of the creatures that live at the bottom of the Mariana Trench’s deepest section, Challenger Deep, as well as other animals who live in deep caves on land. We also learn what I will and will not do for a million dollars (hint: I will not implode in a bathysphere).

A xenophyophore IN THE GRIP OF A ROBOT

A snailfish from five miles down in the Mariana trench:

The Hades centipede. It’s not as big as it looks, honest.

The tiny but marvelous olm.

Show transcript:

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

For this week’s episode, we’re going to find out what lives in the deepest, darkest places of the earth—places humans have barely glimpsed. We’re not just talking deep sea, we’re talking the abyssal depths.

Like onions and parfaits, the earth is made up of many layers. The core of the earth is a ball of nickel and iron surrounded by more nickel and iron. The outer core is molten metal, but the inner core, even though it’s even hotter than the outer core—as hot as the surface of the sun—has gone through the other side of liquid and is solid again. Surrounding the core, the earth’s mantle is a thick layer of rocks and minerals some 1900 miles deep, and on top of that is the crust of the earth, which doesn’t actually sound very appealing but that’s where we live and we know it’s really pretty, with trees and oceans and stuff on top of it. The upper part of the mantle is broken up into tectonic plates, which move around very slowly as the molten metals and rocks beneath them swirl around and get pushed up through cracks in the mantle.

Under the oceans, the crust of the earth is only around 3 miles thick. And in a few places, there are crevices that actually break entirely through the crust into the mantle below. The deepest crack in the sea floor is the Mariana Trench in the western Pacific. At its deepest part, a narrow valley called Challenger Deep, the crack extends seven miles into the earth.

The pressure at that depth is immense, over 1,000 times that at sea level. Animals down there can’t have calcium carbonate shells because the pressure dissolves the mineral. It’s almost completely dark except for bioluminescent animals, and the water is very cold, just above freezing.

The trench is crescent shaped and sits roughly between Japan to the north and Papua New Guinea to the south, and the Philippines to the west. It’s caused by the huge Pacific plate, which is pushing its way underneath the smaller Mariana plate, a process called subduction. But near that activity, another small plate, the Caroline plate, is subducting beneath the Pacific plate. Subduction around the edges of the Pacific plate is the source of the earthquakes, tsunamis, and active volcanos known as the Ring of Fire. Some researchers think there’s a more complicated reason for Mariana Trench and other especially deep trenches nearby, though. There seems to be a tear in the Caroline plate, which is deforming the Pacific Plate above it.

Challenger Deep is such a deep part of the ocean that we’ve barely seen any of it. The first expedition that got all the way down was in 1960, when the bathyscape Trieste reached the bottom of Challenger Deep. This wasn’t an unmanned probe, either. There were two guys in that thing, Jacque Piccard and Don Walsh, almost ten years before the moon landing, on a trip that was nearly as dangerous. They could see out through one tiny thick window with a light outside. The trip down took almost five hours, and when they were nearly at the bottom, one of the outer window panes cracked. They stayed on the bottom only about 20 minutes before releasing the weights and rising back to the surface.

The next expedition didn’t take place until 1995 and it was unmanned. The Kaiko could collect samples as well as record what was around it, and it made repeated descents into Challenger Deep until it was lost at sea in 2003. But it not only filmed and collected lots of fascinating deep-sea creatures, it also located a couple of wrecks and some new hydrothermal vents in shallower areas.

Another unmanned expedition, this one using a remotely operated vehicle called the Nereus, was designed specifically to explore Challenger Deep. It made its first descent in 2009, but in 2014 it imploded while diving in the Kermadec Trench off New Zealand. It imploded. It imploded. This thing that was built to withstand immense pressures imploded.

In 2012, rich movie-maker James Cameron reached the bottom of the Mariana Trench in the Deepsea Challenger. He spent nearly three hours on the bottom. Admittedly this was before the Nereus imploded but you could not get me into a bathysphere if you paid me a million dollars okay well maybe a million but I wouldn’t do it for a thousand. Maybe ten thousand. Anyway, the Deepsea Challenger is currently undergoing repairs after being damaged in a fire that broke out while it was being transported in a truck, which is just the most ridiculous thing to happen it’s almost sad. But it’s still better than imploding.

In addition to these expeditions, tethered cameras and microphones have been dropped into the trench over the years too. So what’s down there that deep? What have these expeditions found?

The first expedition didn’t see much, as it happens. As the bathyscape settled into the ooze at the bottom of the trench, sediment swirled up and just hung in the water around them, unmoving. The guys had to have been bitterly disappointed. But they did report seeing a foot-long flatfish and some shrimp, although the flatfish was more likely a sea cucumber.

There’s actually a lot of life down there in the depths, including amphipods a foot long, sea cucumbers, jellyfish, various kinds of worms, and bacterial mats that look like carpets. Mostly, though, there are Xenophyophores. They make big delicate shells on the ocean bottom, called tests, made from glued-together sand grains, minerals like lead and uranium, and anything else they can find, including their own poops. We don’t know a lot about them although they’re common in the deep sea all over the world. While they’re unicellular, they also appear to have multiple nuclei.

For the most part, organisms living at the bottom of the Challenger Deep are small, no more than a few inches long. This makes sense considering the immense water pressure and the nutrient-poor environment. There aren’t any fish living that deep, either. In 2014 a new species of snailfish was spotted swimming about five miles below the surface, a new record; it was white with broad fins and an eel-like tail. Snailfish are shaped sort of like tadpoles and depending on species, can be as small as two inches long or as long as two and a half feet. A shoal of Hadal snailfish were seen at nearly that depth in 2008 in the Japan Trench.

While there are a number of trenches in the Pacific, there aren’t very many deeps like Mariana Trench’s Challenger Deep—at least, not that we know of. The Sirena Deep was only discovered in 1997. It’s not far from Challenger Deep and is not much shallower. There are other deeps and trenches in the Pacific too. But like Challenger Deep, there aren’t any big animals found in the abyssal depths, although the other deeps haven’t been explored as much yet.

In 2016 and early 2017, NOAA, the U.S. Coast Guard, and Oregon State University dropped a titanium-encased ceramic hydrophone into Challenger Deep. To their surprise, it was noisy as heck down there. The hydrophone picked up the sounds of earthquakes, a typhoon passing over, ships, and whalesong—including the call of a whale researchers can’t identify. They think it’s a type of minke whale, but no one knows yet if it’s a known species we just haven’t heard before or a species completely new to science. For now the call is referred to as the biotwang, and this is what it sounds like.

[biotwang whale call]

But what about animals that live in deep places that aren’t underwater? It’s actually harder to explore land fissures than ocean trenches. Cave systems are hard to navigate, frequently extremely dangerous, and we don’t always know how deep the big ones go. The deepest cave in the world is Krubera Cave, also called Voronya Cave, in Georgia—and I mean the country of Georgia, not the American state. Georgia is a small country on the black sea between Turkey and Russia. So far it’s been measured as a mile and a third deep, but it’s certainly not fully explored. Cave divers keep pushing the explored depth farther and farther, although I do hope they’re careful.

We’ve found some interesting animals living far beneath the earth in caves. The deepest living animal ever found is a primitive insect called a springtail, which lives in Krubera cave and which was discovered in 2010. It’s pale, with no wings, six legs, long antennae, and no eyes. There are a whole lot of springtail species, from snow fleas to those tee-tiny gray bouncy bugs that live around the sink in my bathroom no matter how carefully I clean. All springtails like damp places, so it makes sense that Krubera cave has four different species including the deepest living one. They eat fungi and decomposing organic matter of all kinds. Other creatures new to science have been discovered in Krubera cave, including a new cave beetle and a transparent fish.

A new species of centipede was described in 2015 after it was discovered three-fourths of a mile deep in three different caves in Croatia. It’s called the Hades centipede. It has long antennae, leg claws, and a poisonous bite, but it’s only about an inch long so don’t panic. Also it lives its entire life in the depths of Croatian caves so you’re probably safe. There are only two centipedes that live exclusively in caves and the other one is named after Persephone, Hades’ bride. It was discovered in 1999.

A cave salamander called an olm, which in local folklore was once considered a baby dragon, was recently discovered 370 feet below ground in a subterranean lake, also in Croatia. It’s a fully aquatic salamander that only grows a few inches long. Its body is pale with pink gills. It has eyes, but they’re not fully developed and as it grows, they become covered with layers of skin. It can sense light but can’t otherwise see, but it does have well-developed electroreceptor skills, hearing, smell, and can also sense magnetic fields. It eats snails, insects, and small crustaceans and has very few natural predators.

In 1952 researchers created an artificial riverbed in a cave in France that recreates the olm’s natural habitat as closely as possible. The olms are fed and protected but not otherwise interacted with by humans. There are now over 400 olms in the cave, which is a good thing because in the wild, olms are increasingly threatened by pollution, habitat loss, and unscrupulous collectors who sell them on the pet trade black market.

Olms live a long, long time—probably 100 years or longer. Some individuals in the artificial riverbed are 60 years old and show no signs of old age. Researchers aren’t sure why the olm lives so long. We don’t really know a whole lot about the olm in general, really. They and the caves where they live are protected in Croatia.

There are a few places in the world where people have drilled down into the earth, usually by geologists checking for pockets of gas or water before mining operations start. In several South African gold mines, researchers found four new species of tiny bacteria-eating worms, called nematodes, living in water in boreholes a mile or more deep. After carefully checking to make sure the nematodes hadn’t been introduced into the water from mining operations, the researchers theorized the nematodes already lived in the rocks but that the boreholes created a perfect environment for them. Nematodes are well-known extremophiles, living everywhere from hot springs to the bellies of whales. They can withstand drought, freezing, and other extreme conditions by reverting to what’s called the dauer stage, where they basically put themselves in suspended animation until conditions improve.

The boreholes also turned up some other interesting creatures, including flatworms, segmented worms, and a type of crustacean. They’re all impossibly tiny, nearly microscopic.

If you go any deeper, though, the only living creatures you’ll find are bacteria and other microbes. In a way, though, that’s reassuring. The last thing we want to find when we’re poking around in the world’s deepest cracks is something huge that wants to eat us.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on iTunes or whatever platform you listen on. We also have a Patreon if you’d like to support us that way. Rewards include stickers and twice-monthly bonus episodes.

Thanks for listening!

Episode 016: Jellyfish

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If you look at this episode and think, “Oh, ho hum, think I’ll skip this one because snore, jellyfish,” you are so wrong! Jellies are fascinating, creepy, and often beautiful. Come learn all about our squishy friends in the sea!

A Portuguese man o’war. Creepy as heck:

A lion’s mane jelly. You do not want this guy on your ship. Incidentally, a lot of the photos you find of divers with enormous lion’s mane jellies are fakes that make the jellies look gigantic.

The cosmic jelly, a deep-sea creature:

The creepy Stygiomedusa gigantea, guardian of the underworld:

A newly discovered golden jelly.

Further reading:

Jelly Biologist (I’ve been enjoying browsing this site)

Show transcript:

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

This week’s episode is about jellyfish—also called jellies, which is more accurate since they’re not fish at all.

Originally, I was going to focus on the Portuguese man o’war, another in the ongoing feature of “animals that scared me as a kid” and technically not even a jelly. But there’s so much to learn about jellies that we’re going to cover a whole lot more than that.

Jellies are interesting animals, to say the least. Their bodies have radial symmetry, meaning they’re the same in all directions. While the body shape varies, most jellies have a bell-like shape. The bell is generally rather thin, made up of an external covering, an internal covering, and an elastic gel-like material in between. Inside, the jelly has a digestive cavity with four to eight oral arms surrounding the mouth and long tentacles hanging beneath. The jelly also has a simple nerve net that can detect light and react to other stimuli, and which takes the place of a brain.

Jellies don’t have brains. They don’t have hearts, specialized sensory organs, or much of anything else. But they’ve been around for some 650 million years, possibly much longer, so clearly it all works.

The jelly’s life cycle is pretty weird. Most start out as polyps that stick to rocks or shells and use their little tentacles to catch microscopic organisms. A polyp can bud, producing new polyps that are clones of the original. Eventually, a polyp will constrict its body and develop into a stack of larvae. Each larva develops into a tiny jelly, which separates from the stack and swims away.

Once it’s grown, a jelly reproduces by releasing sperm, if it’s male, which the water carries to the female to fertilize her eggs. Some female jellies have brood pouches on the oral arms, some just carry the fertilized eggs inside the body while they develop. The embryos develop into swimming larvae called planula, which leave the female and attack themselves to something firm, where they transform into polyps.

This seems needlessly complicated, but again, it works for the jelly.

Polyps can live for years, while adult jellies, which I’m delighted to report are called medusas, usually only live a few months. The immortal jellyfish throws another step into this process. It can transform back into a polyp from any stage of its life if it needs to. As a polyp, the immortal jellyfish is tiny, only about a millimeter long. As a full-grown medusa it’s not all that much bigger, less than four millimeters in diameter. Because it can transform back into a polyp as many times as it needs to, apparently without any kind of degradation or injury, the immortal jellyfish is effectively, well, immortal.

Before you get too excited, though, keep in mind that there’s not a whole lot of research into the immortal jellyfish yet. It’s not even known if they will transform back into polyps in the wild, since it’s only ever been observed in captivity.

Almost all jellies have stinging cells, usually concentrated on the tentacles or oral arms, which they use to stun and kill prey. The stinging cells contain venom-filled nematocysts, which are coiled structures that uncoil and sting when touched. Humans are not jelly prey, but jelly stings can still be uncomfortable—and sometimes fatal—to humans.

You’ve probably heard of the infamous box jellyfish, the most dangerous species of which is common around Australia. Unlike most jellies, box jellyfish have true eyes and a relatively well-developed nervous system. They’re active, hard for humans to detect while swimming since they’re nearly transparent, and in the case of Chironex fleckeri, their venom can kill a human in as little as two minutes. Most fatalities occur in children, but most stings don’t result in death.

Another vicious and occasionally fatal stinger is the Portuguese man o’war, although it isn’t actually a jelly. It’s not even a single animal, it’s a colony. One member is the float, another the feeding polyps, and so forth. The man o’war takes its name from a type of ship, which the float somewhat resembles. The float is bluish or purplish, generally under a foot long [30 cm], and filled with gas. Underneath the float are feeding polyps from which hang purple tentacles, typically around 30 feet long [9 m] but sometimes up to 200 feet long [61 m]. If something attacks the man o’war, it can vent some of the gas in its bladder and submerge temporarily.

When I was a kid, my family occasionally went to the beach in North Carolina. Man o’wars are tropical animals but they do occasionally drift farther north. I was fully aware of this as a kid and did not want to get in the water farther than my waist. My grandfather and one of my aunts reassured me that they’d both been stung by a man o’war once, and it wasn’t any more painful than a wasp sting.

That did not make me feel any better. In fact, it made me even more scared because then I KNEW there were man o’wars out there. I wasn’t afraid of being stung, I was afraid of touching those creepy tentacles.

As it happens, my grandfather and Aunt Barbara probably had not encountered a Portuguese man o’war but a smaller animal called a by-the-wind sailor, which is now my favorite name of anything. It has a blue bladder float like the man o’war, but its sting is much milder, A man o’war sting is incredibly painful, more of a shock, that can lead to intense muscle and joint pain, open wounds on the skin at the sting site, headache, chills and fever, nausea, and can cause victims to faint and drown. Occasionally the venom travels to the lymph nodes and causes even more serious symptoms, including swelling of the larynx, an inability to breathe, and cardiac distress. Even a dead man o’war can sting if you touch its tentacles. Why would you touch its tentacles.

I’m not the only one who feels this way about man o’wars, clearly, because one of its other names if the floating terror. That sounds like the title of a pulp science fiction novel.

The bluebottle is a smaller related species found in the Indian and Pacific Oceans. The man o’war is found in those oceans and the Atlantic. A few weeks ago, in early May 2017, hundreds of man o’wars washed ashore in Georgia and South Carolina. Man o’wars are pretty common around Florida, especially in winter, and occasionally they wash ashore in the thousands.

The man o’war eats fish and other organisms that get caught in the stinging tentacles, but there are some fish that live among the tentacles, even feeding on them, like the man o’war fish and the clownfish. Not a lot of things eat Portuguese man o’wars, but the loggerhead turtle and ocean sunfish do. I like them both. The blanket octopus is immune to the man o’war’s venom and may carry broken-off tentacles to deter predators.

If you’re stung by a man o’war, treat the sting the same way you’d treat other jelly stings. Rinse with vinegar to remove any remaining bits of tentacle or nematocysts, then apply heat for 45 minutes, either with a hot pack or by immersing in hot water. Don’t rinse with urine or vodka; it can make the stings worse—and definitely don’t rinse with fresh water. If you don’t have vinegar, rinse with sea water, but keep in mind that you may be pouring nematocysts back onto the patient with the water. This treatment is from a very recent study conducted by researchers at the University of Hawaii at Manoa, released only a few weeks ago as this episode goes live, so if you’ve heard differing advice for jelly stings, it may be out of date.

Jellies are related to some surprising things: coral, sea anemones, a rare parasitic worm, the freshwater hydra—a ten mm long tubular animal with stinging tentacles at one end that it can stretch four or five times the length of the body to catch its tiny prey. Like jellies, the hydra can regenerate parts of its body if they’re injured or bitten off. And the hydra doesn’t appear to age, making it biologically immortal, although in a different way than the immortal jellyfish.

So what’s the largest jelly known, not counting ridiculously long tentacles like the man o’war’s? That would be the lion’s mane jellyfish. Its bell can have a diameter of over seven feet [2 m] and it has pretty darn long tentacles, too—sometimes over 120 feet long [36.5 m]. It likes cold water and the biggest individuals live where it’s coldest. While small individuals are brown or tan in color, the big ones are usually red or purple. The sting of a lion’s mane jellyfish isn’t usually that bad, but it has a lot of tentacles, so it can inflict thousands of stings upon contact.

In 1973, the Australian ship Kuranda collided with a huge jelly in the South Pacific while traveling through a storm on her way to the Fiji Islands. The jelly was so enormous that the deck was covered in jellyfish goo and tentacles up to two feet deep [61 cm]. One crew member died after getting stung. The weight of the jelly was so great, an estimated 20 tons [18 metric tons] that it started to push the ship nose-down and the captain, Langley Smith, sent out an SOS. The salvage tug Hercules arrived and sprayed the Kuranda’s deck with a high-pressure hose, dislodging the jelly. Samples were sent to Sydney and tentatively identified as a lion’s mane jelly.

But remember, lion’s mane jellies don’t live in the warm waters near Fiji and Australia. There are other reports of lion’s mane jellies seen in the area, though, so it’s possible there’s a gargantuan warm-water variety that hasn’t been discovered yet.

Most jellies live near the surface of the ocean, but there are some deep-sea species known, with more being discovered every year. A gorgeous jelly, dubbed the cosmic jellyfish by the press, was spotted 9,800 feet [2987 m] below the surface near American Samoa this February. It has an umbrella-like bell with short tentacles that point both downward and upward. You may have seen it in the news described as looking like a flying saucer, which it does. A similar jelly was discovered in the Mariana Trench in 2016, almost two and a half miles underwater [4 km]. These are lovely jellies with translucent bells and glowing red and yellow innards, but there are less lovely ones down there.

The big red jellyfish discovered in 2002 is an ugly cuss. It lives in waters up to 4900 feet deep [1493 m] and is over a foot in diameter [30 cm]. It’s dull red in color and doesn’t have tentacles, just thick oral arms.

Stygiomedusa gigantea, also known as the guardian of the underworld by at least one website, and now by me, isn’t so much ugly as horrifying. Its bell is some three feet across [1 m], and while it doesn’t have tentacles or even stinging cells, it does have four 30-foot-long [9 m] oral arms that resemble dark brown or reddish strips of cloth that drift in the ocean currents.

Some deep-sea jellies don’t have tentacles or oral arms. Deepstaria enigmatica, a rare jelly described in 1967, basically just looks like a big mesh bag. Its close relative, Deepstaria reticulum, is very similar, but it’s reddish instead of whitish. The Deepstaria hangs motionless in the deep with its three-foot-wide [1 m] bell open, waiting for something to swim into it. When it does, the bell contracts like a bag, the fish or other organism is stung by nematocysts lining the bell, and the jelly pushes its stunned prey into its mouth with tiny cilia inside the bell.

Isopods, which are small crustaceans, frequently hitch rides inside Deepstaria bells. It’s not known if they’re parasites or confer some benefits to the jellies, but they don’t seem to be affected by the stings.

There are plenty of mysteries associated with enormous jellies, although the two most famous ones I dug into started to seem less and less likely once I got closer to the primary sources. According to Eric Frank Russell in his 1957 book Great World Mysteries, in 1953 a diver testing a new type of deep-sea diving suit in the South Pacific saw an enormous jelly-like monster kill a shark. The diver had been testing how deep he could dive in the suit and noticed a fifteen-foot [4.6 m] shark following him down. I’m going to quote the relevant section instead of paraphrasing, because it’s pretty amazing.

“The shark was still hanging around some 30 feet [9 m] from me and about 20 feet [6 m] higher, when I reached a ledge below which was a great black chasm of enormous depth. It being dangerous to venture farther, I stood looking into the chasm while the shark waited for my next move. Suddenly the water became distinctly colder. While the temperature continued to drop with surprising rapidity, I saw a black mass rising from the darkness of the chasm. It floated upwards very slowly. As at last light reached it I could see that it was of a dull brown color and tremendous size, a flat ragged-edged thing about one acre in extent. It pulsated sluggishly and I knew that it was alive despite its lack of visible limbs or eyes. Still pulsating, this frightful vision floated past my level, by which time the coldness had become most intense. The shark now hung completely motionless, paralyzed either by cold or fear. While I watched fascinated, the enormous brown thing reached the shark, contacted it with its upper surface. The shark gave a convulsive shiver and was drawn unresisting into the substance of the monster. I stood perfectly still, not daring to move while the brown thing sank back into the chasm as slowly as it had emerged. Darkness swallowed it and the water started to regain some warmth.”

I am skeptical, I admit. Eric Frank Russell was primarily a science fiction writer and this sounds like something from a novel, probably one called The Floating Terror. If he described the monster as 20 feet across or even 30 or 40 [6, 9, 12 m], I’d be going, “Hmm, but hey, the deep sea is full of amazing things.” But an acre? That’s 208 feet 9 inches across. 43,450 square feet. A lot of meters [4,046 square meters]. It’s three times the size of my yard, which takes me like an hour to mow. It’s just too big to believe, not without corroborating details—like a first-hand account of the actual diver. We don’t even know his name. And what about the diver’s buddy? Divers don’t go down alone, although maybe they did back in 1953. The whole story is just too thin, too fantastical to be believed.

The other promising mystery I looked into is a supposed legend from Chile, a sea monster that resembles a cow hide stretched flat but with eyes all around the edges and four big eyes in the middle. It rises to the ocean’s surface and swallows animals it encounters.

At first glance this sounds ridiculous, until you realize that many jellies have semi- or fully transparent bells and their internal organs, such as they are, may resemble eye-like blobs in the center of their bodies. Some jellies do have light-sensitive eye spots near their edges too. But the research I did to follow up this story, which I took from Karl Shuker’s blog, but which is originally from Jorge Luis Borges’ 1969 book called The Book of Imaginary Beings, indicated that the actual legend is much different and much less jelly-like.

El Cuero is a cowhide monster called Threquelhuecuvu among the Mapuche of Patagonia. It lives in rivers, lakes, and the ocean. It’s nearly circular, has claws around its edges, and one pair of red eyes. It also has tentacles on its head and a mouth in its middle, which it uses to suck bodily fluids from its prey. It’s supposed to come out of the water and come on land, and when an animal steps on it, it wraps its body around the animal and suffocates it. Then it drags its prey into the water to eat it. The only way to kill it is to throw cacti into the water. When the monster grabs the cacti, it’s pierced through with spines and dies.

It’s generally supposed that the monster is based on freshwater stingrays, although they’re not known to live in Patagonia. But in 1976, after a bus full of tourists ended up on the bottom of Lake Moreno, divers who retrieved the drowned victims reported enormous rays in the depths.

There is a freshwater stingray species in South America which has thorn-like denticles on its body and a closely related species, also with denticles, sometimes travels upriver from the ocean off the Chilean Patagonian coast. That might be the source of the cowhide monster.

So those two mysteries are almost certainly bust. But don’t feel discouraged. Not only was that 20-ton ship-sinking 1973 lion’s mane jelly a real, documented thing that happened [note from episode 248: sorry, it turns out it wasn’t real], there are lots of jelly species being discovered all the time.

Not all are deep-sea species. In 2013, a fisherman in northeast Italy hauled up a net full of golden jellies he’d never seen before. He contacted the local university, and a researcher came out and determined that the lovely golden jellies were completely unknown to science. In 2015, a 9-year-old boy caught a new species of box jelly that’s only around an inch long [3 cm].

There are freshwater jellies too, but not a lot is known about them. To add to the confusing and complex life cycle of marine jellies, many freshwater jellies also have a dormant stage where they basically turn into tiny jelly seeds, tough and capable of surviving even if dried out.

And back in the Cambrian era, some 500 million years ago, some jellies actually had skeletons. Fossil impressions show plates, spines, and spokes from comb jellies, which today are completely soft-bodied. Comb jellies are different from the kind of jellies I’ve mostly talked about in this episode, and not even closely related to them. I’d dig into them next, but we’re already pushing 20 minutes and there’s a limit to how much jellyfish information I can expect my listeners to tolerate in one sitting. We’ll save the comb jellies for another episode.

You can find Strange Animals Podcast online at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon if you’d like to support us that way.

Thanks for listening!

Episode 010: Electric Animals

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This week’s episode is about electric animals! There are so many of them that I could only touch on the highlights.

We start with the electric eel. It’s not actually an eel but it is most definitely electric. This one has just read some disturbing fanfic:

The oriental hornet is a living solar panel:

The platypus’s bill is packed with electricity sensors. I couldn’t make this stuff up if I tried:

Amphisbaenids are not electric AS FAR AS WE KNOW. Bzzt.

Thanks for listening! We now have a Patreon if you’d like to subscribe! Rewards include patron-only episodes and stickers!

Show transcript:

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

This week we’re looking at electric animals! You’ve probably heard of the electric eel, but you may not know there are a lot of fish, insects, and even a few mammals that can sense or generate electric impulses. This is a re-record of the original episode with some updated information.

All animals generate electric fields in their nerves and the contracting of muscles. Animals that can sense these fields are called electroreceptive. An electroreceptive animal can find hidden prey without using its other senses.

To take that a step further, many electroreceptive animals can also generate weak electrical fields, usually less than a single volt—small electrical pulses or a sort of wave, depending on the species, that can give them information about their environment. Like a dolphin using echolocation, a fish using electro-location can sense where potential prey is, where predators, plants, and rocks are, and can even communicate with other fish of its same species. Of course, those same electric pulses can also attract electroreceptive predators. It’s hard being a fish.

But in some cases, the animal can generate an electric shock so strong it can stun or kill other animals. The most famous is the electric eel, so let’s start with that one.

The electric eel isn’t actually an eel. It’s a type of knife-fish related to carp and catfish. Some other species of knife-fish generate electric fields, but the electric eel is the only one that uses it as a weapon.

The electric eel is a weird fish even without the electric part. It can grow over eight feet long, or 2.5 m, lives in freshwater in South America, and gets most of its oxygen by breathing air at the surface of the water instead of through its gills. It has to surface for air about every ten minutes or it will drown. That’s a weird habit for a fish, but it makes sense when you consider that many electric eels live in shallow streams or floodplains with a tendency to dry up between rains. Oh, and electric eels frequently swim backwards.

A male electric eel makes a foam nest for females with his spit, and the female lays her eggs in it—as many as 17,000 eggs, although 1,200 is more common. The male defends the nest and hatchlings until the rainy season starts and the young electric eels can swim off on their own.

The electric eel has rows of some 6,000 specialized cells, called electrocytes, that act like batteries to store energy. When all the electrocytes discharge at the same time, the resulting shock can be as much as 860 volts, although it’s only delivered at about one amp. I have no idea what that means because I don’t understand electricity.

Since the electrocytes are all found in the animal’s tail, and electric eels are mostly tail, the fish will sometimes curl up and hold its prey against its tail to increase the shock it receives. This honestly sounds like something a villain from a superhero movie would do. The electric eel will also sometimes leap out of the water to shock an animal it perceives as a threat.

You do not want to be in the water when an electric eel discharges. It probably won’t kill you unless you have a heart problem, but it could stun you long enough that you drown. And if more than one electric eel discharges at the same time, the danger increases. There’s a River Monsters episode about electric eels that shows a whole bunch of them in water so shallow that they’re barely covered. Walking through that pond would probably be deadly. I also really love that show.

How does the electric eel not shock itself? Well, it probably does. All of its vital organs are in the front fifth of its body, and well insulated by thick skin and a layer of fat. But its discharges are extremely fast. Think taser, not sticking a fork in a wall socket, which by the way is something you should not do. The charge naturally travels away from its tail and into the nearest object, usually its prey.

There are three known species of electric eel, all of which live in the Amazon basin in South America. Two of the three species were only identified in 2019 after DNA studies of 107 specimens. One of the new species, Electrophorus voltai, can discharge up to 860 volts of electricity, higher than the well-known E. electricus. Researchers think E. voltai has evolved to generate higher jolts because it lives in the highlands of the Brazilian Shield, where the water is clear and doesn’t conduct electricity as well as the mineral-rich water in other electric eel habitats.

One last thing about the electric eel. It can shock people who touch it up to eight hours after it dies.

Most electric animals are fish since water conducts electricity well. Some other notable electric fish are the stargazer, a venomous bottom-dwelling ocean fish that generates shocks from modified eye muscles; the paddlefish; the electric catfish; and of course sharks.

Sharks are the kings of electroreceptive animals. Some sharks can sense voltage fluctuations of ten millionths of a volt. Sharks only sense electricity; they can’t generate it. But some of their cousins, the electric rays, can generate an electric shock equivalent to dropping a toaster in a bathtub, which by the way is another thing you shouldn’t do although why would you even have a toaster in the bathroom?

Scientists are only just discovering electric use in insects. It’s probably more widely spread than we suspect, and it’s used in ways that are very different from fish. The oriental hornet, for instance, converts sunlight into energy like a tiny flying solar panel. Researchers think the hornet uses that extra energy for digging its underground nests.

Flying insects generate a positive charge from the movement of air molecules, which is basically what static electricity is. It also happens to moving vehicles, and which is why you should touch the metal of your car to discharge any static electricity before pumping gasoline so you don’t spark a fire. This episode is full of safety tips. In the case of bees, this static charge helps pollen adhere to their bodies. You know, like tiny yellow socks stuck to a shirt you’ve just taken out of the dryer. When a bee lands on a flower, its charge also temporarily changes the electrical status of the flower. Other bees can sense this change and don’t visit the flower since its nectar has already been taken.

Spiderwebs are statoelectrically charged too, which actually draws insects into the web, along with pollen and other tiny air particles. This helps clean the air really effectively, in fact, so if you have allergies you should thank spiders for helping keep the pollen levels down. The webs only become electrically charged because the spider combs and pulls at the thread during the spinning process.

Only three living mammals are known to be electroreceptive. The South American Guiana dolphin has a row of electroreceptors along its beak, visible dots called vibrissal crypts. They’re basically pores where whiskers would have grown, except that marine mammals no longer grow whiskers. The vibrissal crypts are surrounded by nerve endings and contain some specialized cells and proteins. Researchers think the dolphins use electroreception to find fish and other prey animals in murky water when the animals are so close that echolocation isn’t very effective. A lot of toothed whales, including other dolphins, show these dots, and it’s possible that the Guiana dolphin isn’t the only species that is electroreceptive.

The platypus and its cousin the echidna are the other two electric-sensing mammals. These two are both such odd animals that they’re getting their own episode one day—and that episode is # 45! They are weird way beyond being the mammals that lay eggs deal. So I’ll just mention that their bills are packed with electroreceptors. The platypus in particular uses electroreception as its primary means of finding prey in the mud at the bottom of ponds.

There are undoubtedly more animals out there that make use of electrical fields in one way or another. One possible addition to the list, if it exists at all, is called the Mongolian death worm.

Nomadic tribes in the Gobi Desert describe a sausage-like worm over a foot long, or 30 cm, and the thickness of a man’s arm. Its smooth skin is dark red and it has no visible features, not even a mouth, which makes it hard to tell which end is the head and which is the tail. It squirms or rolls to move. It spends most of its life hidden in the sand, but in June and July it emerges, usually after rain, and can kill people and animals at a distance.

In his book The Search for the Last Undiscovered Animals, zoologist Karl Shuker discusses the death worm at length, including the possibility that it might be able to give electric shocks under the right conditions. Among the reports he recounts are some that sound very interesting in this regard, including that of a visiting geologist poking an iron rod into the sand, who dropped dead with no warning. A death worm emerged from the place where the geologist had been prodding the sand. I’m going to add “don’t poke an iron rod into the sand of the Gobi Desert” to my list of warnings.

The Gobi is a cold desert and has bitter winters, but it’s still a desert, which means it’s arid, which means the death worm probably isn’t a type of earthworm or amphibian—nothing that needs a lot of moisture to stay alive. On the other hand, two types of earthworms have recently been discovered in the Gobi, and there are a few amphibians, especially frogs, that have evolved to live in areas that don’t receive much rain. In episode 156, about some animals of Mongolia, we talk about the Mongolian death worm again if you want to know a little more. Some parts of the Gobi get more moisture than others and may be where the death worm lives.

Shuker suggests it might be a kind of amphisbaenid. Amphisbaenids are legless lizards that look more like worms than snakes. They move more like worms than snakes too, and spend a lot of their lives burrowing in search of worms or insects. No known species of amphisbaenid can generate electric shocks, but then again, only one of the over 2,000 known species of catfish generates electricity.

It’s not completely out of the realm of possibility that electrogenesis might develop in a reptile, assuming that’s what the death worm is. Sand isn’t a good conductor of electricity, but wet sand is. The death worm might ordinarily use weak electrical pulses to stun its small prey, but if it emerges after rain because its tunnels are temporarily flooded, it might feel vulnerable above ground and be more likely to discharge electrically as a warning when approached.

Of course, as always, until we have a body—until we know for sure that the Mongolian death worm is a real animal and not a folktale, we can’t do more than speculate. But it is interesting to think about.

As far as I can find, no living reptiles or birds show any electrical abilities akin to those in fish and other aquatic animals. But electroreceptors in fish were only discovered in the 1950s. There’s a lot we still don’t know. Always another mystery to solve!

You can find Strange Animals Podcast online at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us and get twice-monthly bonus episodes.

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