Monthly Archives: August 2026

Episode 497 Megarachne

Posted on by

Podcast: Play in new window | Download (Duration: 7:32 — 7.6MB)

Subscribe: RSS | More

Megarachne as we know it now:

Show transcript:

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

Megarachne is only known from two specimens, neither of which is complete, which adds to the confusion. It lived around 300 million years ago in what is now South America. It was described in 1980 from the first specimen discovered and was named Megarachne, which means big spider. The scientist who described it thought it was a type of primitive spider related to modern tarantulas, but much bigger. He estimated its legspan was 20 inches, or 50 cm, with a body length of just over 13 inches, or 34 cm. That made it the largest spider ever known by a lot.

Other palaeontologists, especially arachnologists who specialize in spiders and their relations, weren’t convinced Megarachne was a spider. But it wasn’t until 2005 when a more complete specimen was discovered that anyone could say for sure what it was. The second specimen made it clear that it wasn’t a spider at all but a sea scorpion, or eurypterid, and not an especially large one compared to some. It probably grew to 21 inches long, or 54 cm.

But by then, Megarachne had gotten really popular as a giant spider. It was in the BBC documentary Walking with Monsters, although the producers changed its name to Mesothelae right before it aired, which was just after the new findings about Megarachne came out. Mesothelae is a suborder of big spiders from parts of Asia that retain many traits of ancestral spiders. It was a valiant attempt by the BBC to make the documentary less incorrect, but of course the spider they were talking about still wasn’t a spider and no spider known has ever grown that large.

But while Megarachne isn’t a giant spider, and isn’t even a very big eurypterid, it is important since not very many eurypterids are known from South America. It also appears to be closely related to Mycterops and Woodwardopterus, similar-looking euripterids from North America and Europe. But some researchers think it’s not as cut and dried as it sounds. Instead of three similar creatures living in different areas, they think there’s something else going on.

Eurypterids were arthropods, the phylum that includes insects, arachnids, and crustaceans, among others. Arthropods have an exoskeleton that they molt periodically as they grow, and many arthropods have complicated life stages compared to other animals. When a shark hatches, it looks like a miniature adult and just grows larger as it gets older, but when an arthropod hatches, it usually doesn’t look anything like its adult form. Some arthropods go through many stages of life before reaching the adult body plan. Crustaceans have numerous larval stages, for instance, that often look very different from the adult. Some researchers think that Megarachne, Mycterops, and Woodwardopterus were all the same animal, and that the differences are due to it being in three different stages of development when it died and was preserved.

We don’t have any way to know if this was correct, of course, not until we hopefully find more fossil remains. Other eurypterids did appear to go through some physical changes during maturation, as far as researchers can tell with the remains we have, but Megarachne, Mycterops, and Woodwardopterus belonged to a different family from other eurypterids and are much rarer. They might have been quite different developmentally.

We can also look at the living relations to see how likely it is that eurypterids had different larval stages where they looked different from the adult form. Eurypterids were probably most closely related to horseshoe crabs, although not everyone agrees. Horseshoe crabs have been around for 445 million years and are really neat animals that we’re lucky to still have in the world. The horseshoe crab hatches into a larva that looks a lot like a trilobite. It does indeed go through physical changes as it grows and molts over the course of three years, so it’s reasonable to assume that eurypterids did too.

On the other hand, some researchers think eurypterids were more closely related to modern scorpions. Scorpions actually give birth to live babies instead of laying eggs, and the female carries the babies on her back for several days up to several weeks, depending on the species. Once the babies have their first molt they look a lot more like miniature adults and pretty soon are able to leave their mother and hunt on their own. So again, it’s possible that eurypterids had a system more like this instead of like the horseshoe crab’s.

While we’re talking about scorpions, did you know that scorpions glow blue-green in ultraviolet light? The scorpion’s exoskeleton contains fluorescent chemicals, but we’re not sure why. Scorpions do have incredibly light sensitive eyes, and can navigate at night using only starlight. Their eyes can’t form sharp images like ours can, though. And scorpions have a lot of eyes. Spiders have four pairs of eyes, but some scorpions have more than that. All species have a pair on top of the cephalothorax, which corresponds to the head, and more on the sides of the cephalothorax. Some species have up to five pairs of eyes in addition to the ones on top of the head. Twelve eyes seems like overkill but it works for the scorpion. Eurypterids had both compound eyes and simple eyes.

That’s all we know about Megarachne right now, at least until we find more fossilized specimens. Let’s hope we do, and while we’re at it, let’s hope we find some more fossilized giant spiders because that would be cool.

Thanks for your support, and thanks for listening!

Episode 496 Two Mystery Invertebrates

Posted on by

Podcast: Play in new window | Download (Duration: 7:45 — 8.5MB)

Subscribe: RSS | More

Further reading:

How did a tiny bee get to French Polynesia? Eight new species help solve a scientific mystery

Secrets in the canopy: Scientists discover 8 striking new bee species in the Pacific

Canopy specialist Hylaeus bees highlight sampling biases and resolve Michener’s mystery

Scientists discover endoparasitic marine tapeworm trapped in Cretaceous amber

Show transcript:

Welcome to the Patreon bonus episode of Strange Animals Podcast for August 2024!

It’s the start of Invertebrate August, so we have two invertebrate mysteries to discuss today, one mostly solved and one not.

Let’s start with the solved mystery, about a tiny bee. In 1934, three tiny bee specimens were collected in French Polynesia, specifically on a particular type of flower in the Tuamotu Archipelago. The bees really were tiny, only 4 mm long. They weren’t described until 1965, when they were placed in the genus Hylaeus. This is a really big genus with over 500 species that live throughout the world, but the species most closely related to the newly described Tuamotu’s masked bee lives in Australia, New Guinea, and New Zealand.

In case you’re kind of hazy on geography, like me, Australia, New Guinea, and New Zealand are part of what’s called Oceania, a giant chunk of the Pacific Ocean where there’s not a whole lot of land. I mean, except for Australia, which is big. The Tuamotu Archipelago is also part of Oceania, and part of French Polynesia, but it’s really remote. It consists of a spread-out collection of 78 low islands, many of them too tiny to support humans, none of them with a source of fresh water except for rain. They’re tropical and quite beautiful, with many unique animals and plants living on and around them. They’re also almost 2,500 miles, or 4,000 km away from the places where the tiny bee’s closest relatives live.

Even in 1965, scientists had questions about the tiny bee. How did 4mm bees get to such remote islands, and were they even still around? The bees hadn’t been seen in the wild since 1934. Since the Tuamotu Archipelago has suffered from European explorers and missionaries bringing invasive species to some islands, colonization by France, and nuclear weapons testing, scientists worried the bee had gone extinct and that they would never solve the mystery of how it got there in the first place.

Bees are attracted to flowers, and the three 1934 specimens were discovered on flowers, so naturally scientists had been looking for the bees on flowers. But it turns out that in the Polynesian islands, bees mostly hang out in the treetops. Once scientists figured this out, they began discovering new species of bee—eight of them in fact, collected between 2014 and 2019 from various islands in Fiji, Micronesia, and French Polynesia.

All eight species are closely related to Tuamotu’s masked bee, so scientists now have a pretty good idea of how it traveled thousands of miles to get to its French Polynesian home. Its ancestors island-hopped. There are more than 1,700 islands in the Pacific Ocean, many of them barely known to humans.

Researchers think there are probably a lot more species of bee to be discovered in the treetops of Pacific islands, now that they know where to look. With luck, they’ll be able to find Tuamotu’s masked bee too, quietly living out its bee life above the scientists’ heads.

Next, let’s discuss our unsolved mystery. Amber, which is fossilized tree resin, is the gift that just keeps on giving to the scientific world, and our mystery involves a flatworm found in amber.

The amber comes from Myanmar and dates to about 99 million years ago. In addition to bits of inorganic matter like tiny pebbles and sand grains, most organisms found in amber from this site are insects and roundworms, animals you’d expect to find on and around trees. The team examining this particular piece of amber found lots of interesting things, but then they discovered this one.

The flatworm is about 10mm long and it’s beautifully preserved, which means the scientists were able to compare it to modern flatworms to see what it might be most closely related to. It’s most similar to a parasitic flatworm found in shark intestines. You know, an animal not typically found in trees. (I stole that joke from paleontologist Kenneth De Baets, by the way. Credit where credit’s due.) It isn’t a complete worm but a partial one, basically a tentacle with little hooks to keep it in place in the host animal’s digestive system.

The modern worm is classified as a type of tapeworm, and tapeworms are distressingly common parasites. If you’ve ever adopted a rescue cat or dog, you’ve probably had to have it treated for a tapeworm infestation. Luckily, tapeworms are also very specific about which species they parasitize, so you can’t get tapeworms from a pet. (It’s still icky.) Fish get tapeworms too, after eating marine invertebrates carrying various kinds of tapeworm larvae.

The question is, how did a parasitic worm found in fish end up in amber? Occasionally there is rare amber found that fell into water and trapped water organisms, but this particular amber wasn’t associated with water. Other items found in the same piece of amber included sand grains, tiny hairlike structures found on some ferns, and the nymph of a scale insect. The team suggests that the tree where the amber came from grew near a beach and that a dead shark washed ashore. While scavengers were picking through the carcass, a piece of worm somehow got separated from the body and ended up in a tree. Possibly a scavenger grabbed a big yummy mouthful of rotting shark guts and either climbed or flew up into a tree to eat it, and part of the worm fell out and landed in a blob of amber.

Because tapeworms are endoparasites, meaning they live inside their hosts, and because they’re soft-bodied and fragile, it’s very rare that one is preserved. Pretty much the only other preserved tapeworm specimen we have isn’t a tapeworm itself but some eggs found in fossilized shark dung, dated to 270 million year ago. Scientists aren’t even completely sure the eggs are from a flatworm since they’re not that well preserved. So it’s fantastic that this particular specimen was so well preserved, and that it made its way into the hands of scientists!

Thanks for your support, and thanks for listening!