Tag Archives: eels

Episode 471: Mystery Larvae

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Further reading:

I Can Has Mutant Larvae?

200-Year-Old ‘Monster Larva’ Mystery Solved

‘Snakeworm’ mystery yields species new to science

Hearkening back to the hazelworm

Show transcript:

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

A few weeks ago when I was researching big eels, I remembered the mystery eel larva we talked about back in episode 49, and that led me down a fun rabbit hole about other mystery larvae.

Let’s start with that eel larva. Eel larvae can be extremely hard to tell apart, so as a catchall term every eel larva is called a leptocephalus. They’re flattened side to side, which is properly referred to as laterally compressed, and transparent, shaped roughly like a slender leaf, with a tiny head at the front. Depending on the species, an eel may remain in its larval form for more than a year, much longer than most other fish, and when it does metamorphose into its next life stage, it usually grows much longer than its larval form. For instance, the larvae of conger eels are only about 4 inches long, or 10 cm, while an adult conger can grow up to 10 feet long, or 3 meters.

On January 31, 1930, a Danish research ship caught an eel larva 900 feet deep, or about 275 meters, off the coast of South Africa. But the larva was over 6 feet long, or 1.85 meters!

Scientists boggled at the thought that this larva might grow into an eel more than 50 feet long, or 15 meters, raising the possibility that this unknown eel might be the basis of many sea serpent sightings.

The larva was preserved and has been studied extensively. In 1958, a similar eel larva was caught off of New Zealand. It and the 1930 specimen were determined to belong to the same species, which was named Leptocephalus giganteus.

In 1966, two more of the larvae were discovered in the stomach of a western Atlantic lancet fish. They were much smaller than the others, though—only four inches and eleven inches long, or 10 cm and 28 cm respectively. Other than size, they were pretty much identical to Leptocephalus giganteus.

The ichthyologist who examined them determined that the larvae were probably not true eels at all, but larvae of a fish called the spiny eel. Deep-sea spiny eels look superficially like eels but aren’t closely related, and while they do have a larval form that resembles that of a true eel, they’re much different in one important way. Spiny eel larvae grow larger than the adults, then shrink a little when they develop into their mature form. The six-foot eel larva was actually a spiny eel larva that was close to metamorphosing into its adult form.

Not everyone agrees that Leptocephalus giganteus is a spiny eel. Some think it belongs to the genus Coloconger, also called worm eels, which are true eels but which have large larvae that only grow to the same size as adults. But worm eels don’t grow much bigger than about two feet long, or 61 cm. If the mystery larvae does belong to the genus Coloconger, it’s probably a new species. Until scientists identify an adult Leptocephalus giganteus, we can’t know for sure.

Another mystery larva is Planctosphaera pelagica, which sits all alone in its own class because the only thing it resembles are acorn worms, but scientists are pretty sure it isn’t the larva of an acorn worm. It’s not much to look at, since the larva is just a little barrel-shaped blob that grows about 25 mm across. This sounds small compared to the eel larva we just discussed, but it’s actually quite large compared to similar larvae. Acorn worm larvae are usually only about a millimeter long.

Planctosphaera has been classified as a hemichordate, which are related to echinoderms but which show bilateral symmetry instead of radial symmetry. Hemichordates are also closely related to chordates, which include all vertebrates. They’re marine animals that resemble worms but aren’t worms, so it’s likely that Planctosphaera is also wormlike as an adult.

Planctosphaera isn’t encountered very often by scientists. It has limited swimming abilities and mostly floats around near the surface of the open ocean, eating tiny food particles. One suggestion is that it might actually be the larva of a known species, but one where an occasional larva just never metamorphoses into an adult. It just grows and grows until something eats it. So far, attempts to sequence DNA from a Planctosphaera hasn’t succeeded and attempts to raise one to maturity in captivity hasn’t worked either.

Some people have estimated that an adult Planctosphaera might be a type of acorn worm that can grow nine feet long, or 2.75 meters, which isn’t out of the realm of possibility. The largest species of acorn worm known is Balanoglossus gigas, which can grow almost six feet long, or 1.8 meters, and not only is it bioluminescent, its body contains a lot of iodine, so it smells like medicine. It lives in mucus-lined burrows on the sea floor.

Another mystery larva is Facetotecta, which have been found in shallow areas in many oceans around the world. Unlike the other larvae we’ve talked about, they’re genuinely tiny, measured in micrometers, and eleven species have been described. They all have a cephalic shield, meaning a little dome over the head, and scientists have been able to observe several phases of their development but not the adult form. The juvenile form was observed and it looked kind of like a tiny slug with nonfunctioning eyes and weak muscles.

Scientists speculate that facetotecta may actually be the larva of an endoparasite that infests some marine animals. That would explain why no adult form has been identified. Genetic testing has confirmed that Facetotecta is related to a group of parasitic crustaceans.

DNA has solved some mysteries of what larvae belong to which adults. For instance, Cerataspis monstrosa, a larval crustacean that was first described in 1828. It’s over a cm long, pinkish-purple in color with stalked eyes, little swimming leg-like appendages, and neon blue horn-like structures on its head and back which act as armor. The armor doesn’t help too much against big animals like dolphins and tuna, which love to eat it, and in fact that’s where it was initially discovered, in the digestive tract of a dolphin. But scientists had no idea what the monstrous larva eventually grew up to be.

In 2012 the mystery was solved when a team of scientists compared the monster larva’s DNA to that of lots of various types of shrimp, since the larva had long been suspected to be a type of shrimp. It turns out that it’s the larval form of a rare deep-sea aristeid shrimp that can grow up to 9 inches long, or 23 cm.

Let’s finish with another solved mystery, this one from larvae found on land. In 2007, someone sent photos and a bag of little dead worms to Derek Sikes at the University of Alaska Museum. Usually when someone sends you a bag of dead worms, they’re giving you an obscure but distressing message, but Sikes was curator of the insect collection and he was happy to get a bag of mystery worms.

The worms had been collected from an entire column of the creatures that had been crawling over each other so that the group looked like a garden hose on the ground. Sikes thought they were probably fly larvae but he had never heard of larvae traveling in a column. If you’ve listened to the hazelworm episode from August 2018, you might have an idea. The hazelworm was supposed to be a snake or even a dragon that was only seen in times of unrest. It turns out that it the larvae of some species of fungus gnat travel together in long, narrow columns that really do look like a moving snake. But that’s in Europe, not Alaska.

Sikes examined the larvae, but since they were dead he couldn’t guess what type of insect they would grow up to be. Luckily, a few months later he got a call from a forester who had spotted a column of the same worms crossing a road. Sikes got there in time to witness the phenomenon himself.

The larvae were only a few millimeters long each, but there were so many of them that the column stretched right across the road into the forest. He collected some of them carefully and took them back to the museum, where he tended them in hopes that they would pupate successfully.

This they did, and the insects that emerged were a little larger than fruit flies and were black in color. Sikes identified them as fungus gnats, but when he consulted fungus gnat experts in Germany and Japan, they were excited to report that they didn’t recognize the Alaskan gnats. It was a new species, which Sikes described in late 2023. His summer students helped name the species, Sciara serpens, which are better known now as snakeworm gnats. He and his co-authors think the larvae form columns when they cross surfaces like roads and rocks, to help minimize contacting the dry ground. Fungus gnats live in moist areas with lots of organic matter, like forest leaf litter and the edges of ponds.

So the next time you see a huge long snake crossing the road, don’t panic. It might just be a whole lot of tiny, tiny larvae looking for a new home.

Thanks for your support, and thanks for listening!

BONUS: here’s the Hazelworm episode too!

The hazelworm today is a type of reptile, although called the slow worm, blind worm, or deaf adder. It lives in Eurasia, and while it looks like a snake, it’s actually a legless lizard. It can even drop and regrow its tail like a lizard if threatened. It spends most of its time underground in burrows or underneath leaf litter or under logs. It grows almost 2 feet long, or 50 cm, and is brown. Females sometimes have blue racing stripes while males may have blue spots. It eats slugs, worms, and other small animals, so is good for the garden.

But that kind of hazelworm isn’t what we’re talking about here. Back in the middle ages in central Europe, especially in parts of the Alps, there were stories of a big dragonlike serpent that lived in areas where hazel bushes were common. Like its slow-worm namesake, it lived most of its life underground, especially twined around the roots of the hazel. Instead of scales, it had a hairy skin and was frequently white in color. It was supposed to be the same type of snake that had tempted Adam and Eve in the Garden of Eden.

It had a lot of names besides hazelworm, including white worm for its color, paradise worm for its supposed history in the Garden of Eden, and even war worm. That one was because it was only supposed to show itself just before a war broke out.

People really believed it existed, although stories about it sound more like folklore. For instance, anyone who ate hazelworm flesh was supposed to become immortal. It was also supposed to suck milk from dairy cows and spread poison.

Some accounts said it was enormous, as big around as a man’s thigh and some 18 feet long, or 5.5 meters. Sometimes it was even supposed to have feet, or have various bright colors. Sometimes drawings showed wings.

There does seem to be some confusion about stories of the hazelworm and of the tatzelwurm, especially in older accounts. But unlike the tatzelwurm, the mystery of the hazelworm has been solved for a long time—long enough that knowledge of the animal has dropped out of folklore.

Back in the 1770s, a physician named August C. Kuehn pointed out that hazelworm sightings matched up with a real animal…but not a snake. Not even any kind of reptile. Not a fish or a bird or a mammal. Nope, he pointed at the fungus gnat.

The fungus gnat is about 8 mm long and eats decaying plant matter and fungus. You know, sort of exactly not like an 18-foot hairy white snake.

But the larvae of some species of fungus gnat are called army worms. The larvae have white, gray, or brown bodies and black heads, and travel in long, wide columns that do look like a moving snake, especially if seen in poor light or in the distance. I’ve watched videos online of these processions and they are horrifying! They’re also rare, so it’s certainly possible that even people who have lived in one rural area their whole life had never seen an armyworm procession. Naturally, they’d assume they were seeing a monstrous hairy snake of some kind, because that’s what it looks like.

Sightings of smaller hazelworms may be due to the caterpillar of the pine processionary moth, which also travels in a line nose to tail, which looks remarkably like a long, thin, hairy snake. Don’t touch those caterpillars, by the way. They look fuzzy and cute but their hairs can cause painful reactions when touched.

The adult moths lay their eggs in pine trees and when the eggs hatch the larvae eat pine needles and can cause considerable damage to the trees. They overwinter in silk tents, then leave the trees in spring and travel in a snaky conga line to eat pine needles. Eventually they burrow underground to pupate. They emerge from their cocoons as adult moths, mate, lay eggs, and die, all within one day.

Episode 469: Axolotl and Friends

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Thanks to Aila, Stella, George, Richard from NC, Emilia, Emerson, and Audie for their suggestions this week!

Further reading:

Creature Feature: Snipe Eel

How removing a dam could save North Carolina’s ‘lasagna lizard’

Why Has This North Carolina Town Embraced a Strange Salamander?

Scentists search for DNA of an endangered salamander in Mexico City’s canals

An X-ray of the slender snipe eel:

The head and body of a slender snipe eel. The rest is tail [picture by opencage さん http://ww.opencage.info/pics/ – http://ww.opencage.info/pics/large_17632.asp, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=26595467]:

The hellbender:

A wild axolotl with its natural coloration:

A captive bred axolotl exhibiting leucism:

Show transcript:

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

This week we’re going to talk about some amphibians and fish. Thanks to Aila, Stella, George, Richard from NC, Emilia, Emerson, and Audie for their suggestions!

We’ll start with Audie’s suggestion, the sandbar shark. It’s an endangered shark that lives in shallow coastal water in the Atlantic and Indo-Pacific Oceans. A big female can grow over 8 feet long, or 2.5 meters, while males are smaller on average. It can be brown or gray in color, and its dorsal fin is especially big for a shark its size.

The sandbar shark eats fish, crustaceans like crabs, cephalopods like octopuses, and other small animals. It spends a lot of time near the bottom of the seabed, looking for food, and it will also swim into the mouths of rivers. Since it resembles a bull shark, which can live just fine in rivers for quite a while and which can be dangerous to swimmers, people are sometimes afraid of the sandbar shark, but it hardly ever bites people. It just wants to be left alone to find little fish to eat.

Emilia and Emerson both asked to learn more about eels. Eels are fish, but not every animal that’s called an eel is actually an eel. Some are just eel-shaped, meaning they’re long and slender. Electric eels aren’t actually eels, for instance, but are more closely related to catfish.

The longest eel ever reliably measured was a slender giant moray. That was in 1927 in Queensland, Australia. The eel measured just shy of 13 feet long, or 3.94 meters. We talked about some giant eels in episode 401, but this week let’s talk about a much smaller eel, one that Emerson suggested.

That’s the snipe eel, the name for a family of eels consisting of nine species known so far. They live in every ocean in the world, and some species are deep-sea animals but most live a little nearer the surface. The largest species can grow an estimated 5 feet long, or 1.5 meters, but because all species of snipe eel are so incredibly thin, even the longest individual weighs less than a football, either American or regular, take your pick.

The snipe eel gets its name from its mouth, which is long and slightly resembles the beak of a bird called the snipe. The snipe is a wading bird that pokes its long, flexible bill into mud to find small animals like insect larvae, worms, and snails. But unlike the bird’s bill, the snipe eel’s jaws have a bend at the tip. The upper jaw bends upward, the lower jaw bends downward so that the tip of the jaws are separated. It doesn’t look like that would be very helpful for catching food, but scientists think it helps because the fish’s mouth is basically always open. Since it mainly eats tiny crustaceans floating in the water, it doesn’t even need to open its mouth to catch food. It has tiny teeth along the jaws that point backwards, so when a crustacean gets caught on the teeth, it can’t escape.

The slender snipe eel is especially unusual because it can have as many as 750 vertebrae in its backbone. That’s more than any other animal known. Most of its length is basically just an incredibly long, thin tail, with its organs bunched up right behind its head. Even its anus is basically on its throat.

We don’t know a whole lot about the snipe eel, since it lives deep enough that it’s hardly ever seen by humans. Most of the specimens discovered have been found in the stomachs of larger fish.

Now, let’s leave the world of fish behind and look at some amphibians. First, George wanted to learn about the hellbender, and points out that it’s also called the snot otter or lasagna lizard. I don’t understand the lasagna part but it’s funny.

The hellbender is a giant salamander that lives in parts of the eastern United States, especially in the Appalachian Mountains and the Ozarks. It can grow nearly 30 inches long, or 74 cm, and is the fifth heaviest amphibian alive today in the whole world. It spends almost all its life in shallow, fast-moving streams hiding among rocks. As water rushes over and around rocks, it absorbs more oxygen, which is good for the hellbender because as an adult it breathes through its skin. To increase its surface area and help it absorb that much more oxygen, its skin is loose and has folds along the sides.

The hellbender is flattened in shape and is brown with black speckles on its back. It mostly eats crayfish, but it will also eat frogs and other small animals. Its skin contains light-sensitive cells, which means that it can actually sense how much light is shining on its body even if its head is hidden under a rock, so it can hide better.

Aila and Stella suggested we talk about the axolotl, and a few years ago Richard from NC sent me a lot of really good information about this friendly-looking amphibian. I’d been planning to do a deep dive about the axolotl, which we haven’t talked about since episode 275, but sometimes having a lot of information leads to overload and I never did get around to sorting through everything Richard sent me.

Richard also suggested we talk about a rare mudpuppy, so let’s learn about it before we get to the axolotl. It’s called the Neuse river waterdog, although Richard refers to it as the North Carolina axolotl because it resembles the axolotl in some ways, although the two species aren’t very closely related.

The mudpuppy, also called the waterdog, looks a lot like a juvenile hellbender but isn’t as big, with the largest measured adult growing just over 17 inches long, or almost 44 cm. It lives in lakes, ponds, and streams and retains its gills throughout its life.

The mudpuppy is gray, black, or reddish-brown. It has a lot of tiny teeth where you’d expect to find teeth, and more teeth on the roof of its mouth where you would not typically expect to find teeth. It needs all these teeth because it eats slippery food like small fish, worms, and frogs, along with insects and other small animals.

The Neuse River waterdog lives in two watersheds in North Carolina, and nowhere else in the world. It will build a little nest under a rock by using its nose like a shovel, pushing at the sand, gravel, and mud until it has a safe place to rest. If another waterdog approaches its nest, the owner will attack and bite it to drive it away.

The mudpuppy exhibits neoteny, a trait it shares with the axolotl. In most salamanders, the egg hatches into a larval salamander that lives in water, which means it has external gills so it can breathe underwater. It grows and ultimately metamorphoses into a juvenile salamander that spends most of its time on land, so it loses its external gills in the metamorphosis. Eventually it takes on its adult coloration and pattern. But neither the mudpuppy nor the axolotl metamorphose. Even when it matures, the adult still looks kind of like a big larva, complete with external gills, and it lives underwater its whole life.

The axolotl originally lived in wetlands and lakes in the Mexico Central Valley. This is where Mexico City is and it’s been a hub of civilization for thousands of years. A million people lived there in 1521 when the Spanish invaded and destroyed the Aztec Empire with introduced diseases and war. The axolotl was an important food of the Aztecs and the civilizations that preceded them, and if you’ve only ever seen pictures of axolotls you may wonder why. Salamanders are usually small, but a full-grown axolotl can grow up to 18 inches long, or 45 cm, although most are about half that length.

Most wild axolotls are brown, greenish-brown, or gray, often with lighter speckles. They can even change color somewhat to blend in with their surroundings better. Captive-bred axolotls are usually white or pink, or sometimes other colors or patterns. That’s because they’re bred for the pet trade and for medical research, because not only are they cute and relatively easy to keep in captivity, they have some amazing abilities. Their ability to regenerate lost and injured body parts is remarkable even for amphibians. Researchers study axolotls to learn more about how regeneration works, how genetics of coloration work, and much more. They’re so common in laboratory studies that you’d think there’s no way they could be endangered—but they are.

A lot of the wetlands where the axolotl used to live have been destroyed as Mexico City grows. One of the lakes where it lived has been completely filled in. Its remaining habitat is polluted and contains a lot of introduced species, like carp, that eat young axolotls as well as the same foods that axolotls eat. Conservationists have been working hard to improve the water quality in some areas by filtering out pollutants, and putting up special barriers that keep introduced fish species out.

Even if the axolotl’s habitat was pristine, though, it wouldn’t be easy to repopulate the area right away. Axolotls bred for the pet trade and research aren’t genetically suited for life in the wild anymore, since they’re all descended from a small number of individuals caught in 1864, so they’re all pretty inbred by now.

Mexican scientists and conservationists are working with universities and zoos around the world to develop a breeding program for wild-caught axolotls. So far, the offspring of wild-caught axolotls that are raised in as natural a captive environment as possible have done well when introduced into the wild. The hard part is finding wild axolotls, because they’re so rare and so hard to spot.

Scientists have started testing water for traces of axolotl DNA to help them determine if there are any to find in a particular area. If so, they send volunteers into the water with nets and a lot of patience to find them.

The axolotl reproduces quickly and does well in captivity. Hopefully its habitat can be cleaned up soon, which isn’t just good for the axolotl, it’s good for the people of Mexico City too.

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, corrections, or suggestions, email us at strangeanimalspodcast@gmail.com.

Thanks for listening!

Episode 451: the Stellar Jay and the Gulper Eel

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Thanks to Joelle, Jacob, and Anna for their suggestions this week!

Further reading/watching:

Gulper Eel Balloons Its Massive Jaws

Watch rare footage of a shapeshifting eel with ‘remarkably full tummy’ swimming in the deep sea

The beautiful stellar jay:

The maybe not quite as beautiful but really awesome gulper eel (with its mouth full of water, image taken from first video linked above):

The same eel as above but with its mouth open so you can see just how big it is!

Show transcript:

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

This week we’re going to learn about a bird suggested by Joelle, Jacob, and Anna, and a weird fish also suggested by Jacob.

Let’s start with the bird, the stellar jay, also called Steller’s jay! In the last few years there has been a push among bird enthusiasts to change the common names of birds named after people to names that are more general. While Steller’s jay hasn’t officially been renamed to the stellar jay, a lot of people are calling it that already so that’s what we’ll call it here. The word stellar means outstanding, and that’s definitely a good description of this bird.

The stellar jay is a beautiful bird that lives in western North America down into parts of Central America. It’s closely related to the blue jay found in eastern North America, and if you saw it from the middle down you might think it was a blue jay, except that it doesn’t have white markings on its tail and wings. It has a blue tail and wing feathers with dark bars, but from about the shoulders up it looks very different from the blue jay. It’s silvery-gray, brownish, or black on its head, neck, and back. Some populations have a white eyebrow marking that makes the bird look like it’s frowning. It has a crest like the blue jay, but its crest is bigger, spikier like it hasn’t brushed its hair yet, and the bird itself is bigger overall than its eastern cousin.

The stellar jay lives in forests, especially coniferous forests, where it eats pretty much anything it can find. It’s an omnivore that likes insects and other invertebrates, eggs and baby birds of other species, and even small animals like lizards and mice, but it also eats lots of nuts, berries, seeds, and other plant material. It will visit bird feeders, and especially likes sunflower seeds and raw peanuts.

The stellar jay is a corvid, distantly related to crows and magpies, and it shares the corvid trait of being intelligent, sometimes aggressive, and loud. It will imitate hawks in order to scare other birds away from food, and it will often chase smaller birds away from feeders. During nesting season, the birds get a lot quieter, and the male will sneak his way to and from the nest to feed his mate while she’s sitting on the eggs. The stellar jay prefers to build its nest in a conifer, either in a hollow in the trunk or on branches close to the trunk.

This is what the stellar jay sounds like:

[bird calls]

Jacob also suggested we learn about the gulper eel, which is sort of the opposite of the stellar jay. It’s a deep-sea fish with a lot of names, including pelican eel and my favorite, the umbrella-mouth. It’s black or sometimes dark brown and can grow up to about three feet long, or 90 cm. Much of its length consists of a long, whip-like tail.

The gulper eel’s mouth is ENORMOUS, ridiculously enormous, especially considering how slender the rest of the fish is. Its lower jaw is hinged and is extremely long, with a stretchy pouch of skin that forms its mouth and I guess you can call them cheeks. It is a very weird fish. Most of the time it keeps its jaw folded down against its sides, so that the jaws are barely visible and it looks more or less like a regular eelh. But when it wants to, the gulper eel can unfold its jaw and gulp in water to inflate its pouch, which makes it look like a black balloon with a tail. It sometimes does this if it feels threatened so that it looks bigger, but the huge jaws are actually for swallowing animals whole.

Not only can its mouth stretch to engulf animals bigger than the gulper eel is, its stomach can stretch just as much. It has tiny teeth, though, so it’s not likely that it would try to eat animals stronger than it is, because if it swallowed a big fish, that fish might thrash around inside the gulper eel and kill it. More often, the gulper eel’s stretchy mouth and stomach allow it to eat large groups of very small animals, mostly shrimp and other small crustaceans. It also helps it swallow squid and other soft-bodied animals that are larger than it is but not dangerous.

The gulper eel has a well-developed lateral line system, more properly called the octavolateralis system. All fish and some amphibians have this system, and in many species you can see it. It’s a line or a series of dots along the fish’s sides, and it’s actually a series of modified cells that are super sensitive to water motion. The lateral line system is what allows schools of fish to stay in formation while moving around as a group, and it also helps a fish know when a predator is approaching or when potential prey is nearby. It can even help the fish sense obstacles in the water that aren’t moving, like rocks. In the gulper eel, instead of the sensory cells being in a tiny canal under the skin, they’re on the surface to increase the amount of information the fish can gather from tiny water movements.

At the end of the tail, the gulper eel has a tiny organ called a caudal appendage, which is translucent. It has tiny tentacles and glows with a pinkish light, although it occasionally flashes red. Some researchers report that the lateral line also sometimes produces bioluminescence. The bioluminescence may lure small animals to the gulper eel the same way the anglerfish’s lure does. It’s possible that the gulper eel sometimes hangs in the deep water with its long tail curved up over its head, waiting for prey to approach, but for the most part it’s an active hunter of small crustaceans and other animals.

You may remember from other episodes that most deep-sea animals can’t see the color red. Some predatory fish, including a species of dragon fish, use that to their advantage by emitting red light that they can see but their prey can’t. It’s possible that the gulper eel’s tail emits red light to help it find groups of the tiny crustaceans it mostly eats. It has very small eyes and we don’t even know if it can see the color red or not. We also don’t know if its bioluminescent tail also gives off other light wavelengths that would act as a lure to small animals, or if it uses its caudal appendage to communicate with other gulper eels.

The gulper eel lives in many of the world’s oceans, especially in tropical areas, in depths up to 9,800 feet, or 3,000 meters. Sometimes it lives in shallower water too. Because it lives so deep most of the time, we don’t know a whole lot about it. Luckily, in the last few years scientists have learned a lot more about it from deep-sea rover observations.

You can find Strange Animals Podcast 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 for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 401: El Gran Maja and Other Giant Eels

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Thanks to Murilo for suggesting El Gran Maja for our first monster month episode of 2024!

Further reading:

The Loch Ness Monster: If It’s Real, Could It Be an Eel?

Further watching:

Borisao Blois’s YouTube channel [I have not watched very many of his videos so can’t speak to how appropriate they all are for younger viewers]

El Gran Maja, YouTube star:

The European eel [photo by GerardM – http://www.digischool.nl/bi/onderwaterbiologie/, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=284678]:

A supposed 21-foot eel, a product of trick photography:

The slender giant moray eel [photo by BEDO (Thailand) – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=40262310]:

Show transcript:

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

It’s monster month, where we talk about weird, mysterious, and sometimes spooky creatures! This year I’ve decided to be less spooky and more weird, so let’s kick off the month with an episode all about gigantic eels. Thanks to Murilo for suggesting our first giant eel, El Gran Maja.

El Gran Maja is an eel that is supposed to live off the coast of northern Puerto Rico, and it’s supposed to grow 675 meters long. That’s 2,215 feet, or almost half a mile. That is an excessive amount of eel.

Obviously, an eel that big couldn’t actually exist. By the time its front end noticed danger, its back end could already be eaten by a whole family of sharks. But maybe it was based on a real eel that grows really long. Let’s take a look at some eels we know exist, and then we’ll return to El Gran Maja and learn some very interesting things about it.

Eels are fish, but not every animal that’s called an eel is actually an eel. Some are just eel-shaped, meaning they’re long and slender. Electric eels aren’t actually eels, for instance, but are more closely related to catfish. Most eels live in the ocean at the beginning and end of their lives, and freshwater in between.

For example, the European eel has a life cycle that’s pretty common among eels. It hatches in the ocean into a larval stage that looks sort of like a transparent leaf. Over the next six months to three years, the larvae swim and float through the ocean currents, closer and closer to Europe, feeding on plankton and other tiny food. Toward the end of this journey, they grow into their next phase, where they resemble eels instead of leaf-shaped tadpoles, but are still mostly transparent. They’re called glass eels at this point. The glass eels make their way into rivers and slowly migrate upstream. Once a glass eel is in a good environment it metamorphoses again into an elver, which is basically a small eel. As it grows it gains more pigment until it’s called a yellow eel. Over the next decade or two it grows and matures, until it reaches its adult length—typically around 3 feet, or about a meter. When it’s fully mature, its belly turns white and its sides silver, which is why it’s called a silver eel at this stage. Silver eels migrate more than 4,000 miles, or 6500 km, back to the Sargasso Sea to spawn, lay eggs, and die.

One place where European eels live is Loch Ness in Scotland, and in the 1970s the idea that sightings of the Loch Ness Monster might actually be sightings of unusually large eels became popular. A 2018 environmental DNA study brought the idea back up, since the study discovered that there are a whole, whole lot of eels in Loch Ness. The estimate is a population of more than 8,000 eels in the loch, which is good since the European eel is actually critically endangered. But most of the eels found in Loch Ness are smaller than average, and the longest European eel ever measured was only about 4 feet long, or 1.2 meters.

An eel can’t stick its head out of the water like Nessie is supposed to do, but it does sometimes swim on its side close to the water’s surface, which could result in sightings of a string of many humps undulating through the water.

But the Loch Ness monster aside, the European eel isn’t very big compared to many species of eel. The European conger eel is the heaviest eel known, although not the longest. It lives off the coast of Europe down to northern Africa, and also in the Mediterranean Sea. An exceptionally large female might be as much as 10 feet long, or 3 meters, but it’s also chonkier than other eels. The largest conger ever measured reportedly weighed 350 lbs, or almost 159 kg, and was caught in a net off the coast of Iceland, although that report isn’t very reliable.

In 2015, a lot of newspaper reports talked about a huge eel caught off the coast of Devon, England. They printed pictures of a massively huge eel hung up in front of the fishermen who caught it. The articles said the eel was as much as 21 feet long, or 6.4 meters, and weighed 160 lbs, or just over 72 kg.

But if you think about it, there’s something fishy (sorry) about the story. If you picture a big man, say a football player who’s fit and strong, he might be about six feet tall, or 1.8 meters, and weigh a bit more than 200 lbs, or maybe 95 kg. But the eel weighed a lot less than that hypothetical man, and eels are strongly muscled even though they’re slender in shape. A 21 foot eel should weigh much more than a football player.

Most likely, reporters looked at the photo and compared it to the fishermen, and came up with the 21 foot length themselves. But it’s a trick photo, even if the trick wasn’t planned, because the eel was hung up very close to the camera while the fishermen were much farther back, which makes the eel look huge in comparison. Not only that, but when you hang a dead eel up by its head, it stretches so that it looks longer than it really was when it was alive. Other pictures of the eel make it look much shorter.

As it turns out, the fishermen who caught the eel didn’t even measure it. They thought it might have been up to 10 feet long, but it might have been closer to 7, or 2 meters. That’s still a big eel, and the weight may be close to a reliable record of heaviest eel, but it’s nowhere near the longest eel ever measured.

That record goes to the slender giant moray eel, which lives in muddy coastal water of the Pacific Ocean. It’s brown and isn’t especially exciting to look at unless you’re an eel enthusiast or an actual eel yourself, but the longest eel ever reliably measured was a slender giant moray. That was in 1927 in Queensland, Australia. The eel measured just shy of 13 feet long, or 3.94 meters.

In other words, the longest eel ever measured is approximately 2,202 feet, or 671 meters, shorter than El Gran Maja. But to learn more about El Gran Maja we have to talk about something called the bloop.

The bloop is a sound recorded in 1997 off the tip of South America by the National Oceanic and Atmospheric Administration, AKA NOAA. The sound itself came from the middle of the South Pacific Ocean, and was so loud that it was recorded by sensors 3,000 miles away, or 5,000 km. But it was also an ultra-low-frequency sound, so that humans and most other animals wouldn’t be able to hear it at all.

This is what the bloop sounds like, sped up 16 times so that people can hear it:

[bloop sound]

It turns out that the bloop was made by a big iceberg breaking into pieces, and similar sounds have been recorded since by NOAA and other researchers. But when the bloop was first made public, its source was still a mystery, and pretty much everyone on the internet lost their minds with excitement thinking it was a deep-sea creature far bigger than a blue whale. People speculated about the size of the bloop monster and estimated it had to be about 705 feet long, or 215 meters, for it to make such a loud call.

A film-maker and artist named Borisao Blois was interested in the bloop monster and wanted to animate it, but decided it needed a rival to fight—and he wanted the rival to be even bigger. He invented El Gran Maja and animated a fight between the two. Because Blois wanted his monster to be exciting to look at during his films, he gave it a huge wide mouth filled with sharp, comb-like teeth, and six all-white eyes. The first video was released in 2001 and has more than 89 million views. Many more videos followed, along with creations made by other artists who were inspired by the original.

The videos Blois has made about El Gran Maja are popular, and some people even think it might be a real monster. Considering that an eel that big would need to eat an astounding amount of food every day to survive, and it’s big enough to swallow entire ships whole, it’s probably a good thing that it’s just a made-up monster.

You can find Strange Animals Podcast 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 for as little as one dollar a month and get monthly bonus episodes.

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Episode 049: The Brantevik Eel and Friends

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This week’s episode is about some interesting eels, including the Brantevik eel.

A European eel:

A leptocephalus, aka an eel larva:

A moray eel. It has those jaws you can see and another set of jaws in its throat:

Episode transcript:

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

This week, we’re going to learn about the Brantevik eel and some other eels, including an eel mystery.

The Brantevik eel is an individual European eel, not a separate species. Its friends knew it as Åle, which I’ve probably misprounounced, so I’m nicknaming it Ollie. So what’s so interesting about Ollie the eel?

First, let’s learn a little bit about the European eel in general to give some background. It’s endangered these days due to overfishing, pollution, and other factors, but it used to be incredibly common. It lives throughout Europe, from the Mediterranean to Iceland, and has been a popular food for centuries.

The European eel hatches in the ocean into a larval stage that looks sort of like a transparent flat tadpole, shaped roughly like a leaf. Over the next six months to three years, the larvae swim through the ocean currents, closer and closer to Europe, feeding on microscopic jellyfish and plankton. Toward the end of this journey, they grow into their next phase, where they resemble eels instead of tadpoles, but are mostly transparent. They’re called glass eels at this point. The glass eels make their way into rivers and other estuaries and slowly migrate upstream. Once a glass eel is in a good environment it metamorphoses again into an elver, which is basically a small eel. As it grows it gains more pigment until it’s called a yellow eel. Over the next decade or two it grows and matures, until it reaches its adult length—anywhere from two to five feet, or 60 cm to 1.5 meters. When it’s fully mature, its belly turns white and its sides silver, which is why it’s called a silver eel at this stage. Silver eels migrate more than 4,000 miles, or 6500 km, back to the Sargasso Sea to spawn, lay eggs, and die.

One interesting thing about the European eel is that during a lot of its life, it has no gender. Its gender is determined only when it grows into a yellow eel, and then it’s mostly determined by environmental factors, not genetics.

Until the late 19th century, everyone thought these different stages—larva, glass eel, elver, yellow eel, and silver eel—were all separate animals. No one knew how or even if eels reproduced. The ancient Greeks thought eels were a type of worm that appeared spontaneously from rotting vegetation. Some people thought eels mated with snakes or some types of fish. By the 1950s the eel’s life cycle was more or less understood, but many researchers thought the European eels never made it to the Sargasso Sea to spawn. It was just too far, so they thought the eels that arrived in Europe were all larvae of the American eel, which is almost identical in appearance to the European eel. The Sargasso Sea is off the coast of the Bahamas, so the American eel doesn’t have nearly as far to travel. These days we know from DNA studies that the American and European eels are different species. The European eel is just a world-class swimmer.

European eels are nocturnal and may live in fresh water, brackish water, or sometimes they remain in the ocean and live in salt water, generally in harbors and shallows. They eat anything they can catch, from fish to crustaceans, from insect larvae to dead things, and on wet nights they’ll sometimes emerge from the water and slide around on land eating worms and slugs. Many populations don’t eat at all during the winter.

Now, back to the Brantevik eel. Brantevik is a tiny fishing village in Sweden. In 1859, an eight-year-old boy named Samuel Nilsson caught an eel and released it into his family’s well to eat insect larvae and other pests. This was a common practice at the time when water wasn’t treated, so the fewer creepy-crawlies in the water, the better.

And there the eel stayed. Ollie got famous over the years, at least in Sweden. Its 100th well anniversary was celebrated in 1959, and children’s books and even movies featured it. But in summer of 2014, Ollie died. Its well is now on the property of Tomas Kjellman, whose family bought the cottage and its well in 1962. Everyone knew about the resident eel, which the family treated as something of a pet. In fact, they discovered it was dead when they opened the well’s cover to show the eel to some visiting friends.

Ollie’s remains were removed from the well and shoved in the family’s freezer, and later sent to be analyzed at the Swedish University of Agricultural Science’s Institute of Freshwater Research. That analysis confirmed that Ollie was over 150 years old.

In the wild, European eels don’t usually live longer than twenty years, and ten years is more likely. But in captivity, where eels don’t spawn, they can live a long time. A female European eel named Putte lived over 85 years in an aquarium at Halsinborgs Museum in Sweden.

What most people don’t know is that Ollie wasn’t alone. Another eel still lives in the well and is doing just fine, but it’s younger, only about 110 years old.

The larvae of European eels are small, only about three inches at the most, or 7.5 cm. Even conger eel larvae are small, only 4 inches long, or 10 cm, and conger eels can grow 10 feet long, or 3 meters. But on January 31, 1930, a Danish research ship caught an eel larva 900 feet deep off the coast of South Africa—and that larva was six feet 1.5 inches long, or 1.85 meters.

Scientists boggled at the thought that this six-foot eel larva might grow into an eel more than 50 feet long, or 15 meters, raising the very real possibility that this unknown eel might be the basis of many sea serpent sightings.

The larva was preserved and has been studied extensively. In 1958, a similar eel larva was caught off New Zealand. It and the 1930 specimen were determined to belong to the same species, which was named Leptocephalus giganteus. Leptocephalus, incidentally, is a catchall genus for all eel larvae, which can be extremely hard to tell apart.

In 1966 two more of the larvae were discovered in the stomach of a western Atlantic lancet fish. They were much smaller than the others, though—only four inches and eleven inches long, or 10 cm and 28 cm. Dr. David G. Smith, an ichthyologist at Miami University, determined that the eel larvae were actually not true eels at all, but larvae of a spiny eel. Deep-sea spiny eels are fish that look like eels but they’re not closely related. And while spiny eels do have a larval form that resembles that of a true eel, they’re much different in one important way. Spiny eel larvae grow larger than the adults, then shrink when they develop into their mature form.

So the six-foot eel larvae, if it had lived, would have eventually developed into a spiny eel no more than six feet long itself at the most, and probably shorter.

More recent research has called Dr. Smith’s findings into question, and many scientists today consider L. giganteus to be the larvae of a short-tailed eel, which is a true eel—but not a type that grows much larger than its larvae. So either way, the adult form would probably not be much longer than a conger eel.

But…we still don’t have an adult. So there’s still a possibility that a very big deep-living marine eel is swimming around in the world’s oceans right now.

The longest known eel is the slender giant moray, which can reach 13 feet in length, or 4 meters. Morays are interesting eels for sure. They live in the ocean, especially around coral reefs, and have two sets of jaws, their regular jaws with lots of hooked teeth, and a second set in the throat that are called pharyngeal jaws, which also have teeth. The moray uses the second set of jaws to help grab and swallow prey that might otherwise wriggle out of its mouth. The moray has a strong bite and doesn’t see very well, although its sense of smell is excellent. This occasionally causes problems for divers who think it would be fun to feed an eel and end up with a finger bitten off. Don’t feed the eels, okay? Not only that, but a moray can’t release its bite even if it’s dead, so if one bites a diver, someone has to pry the eel’s jaws open before the bite can be treated. And as if all that wasn’t warning enough to not feed wild animals, and frankly just stay out of the water entirely, research suggests that some morays are venomous. Oh, and the giant moray sometimes hunts with a fish called the roving coralgrouper, which grows to some four feet long, or 120 cm, which is a rare example of interspecies cooperative hunting.

Some people believe that at least some sightings of the Loch Ness monster can be attributed to eels—European eels, in this case. An eel can’t stick its head out of the water like Nessie is supposed to do, but it does sometimes swim on its side close to the water’s surface, which could result in sightings of a string of many humps undulating through the water. But while eels do live in and around Loch Ness, it’s unlikely that any European eel would grow much larger than around five feet, or 1.5 meters. Still, you never know. Loch Ness is the right habitat for an eel to grow to its maximum size, and while we have learned a lot about eels in general, and the European eel in particular, since Ollie was released into a well in Brantevik, we certainly don’t know everything about them.

One last note about eel larvae. Occasionally on facebook and other social media, well-meaning people will share warnings about a nearly invisible wormlike parasite that can be found in drinking water, with pictures of, you guessed it, eel larvae. Eel larvae are not parasites, are not found in fresh water at all, and even if you did accidentally swallow one, you’d just digest it and get a little protein out of the bargain. So you don’t need to worry about those clickbait warnings, the eels do.

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 Apple Podcasts or whatever platform you listen on. We also have a Patreon if you’d like to support us that way.

Thanks for listening!