From the Vault: The Glorious Hermit Crab, Part 2
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I'm Jason Alexander. And I'm Peter Tilden. And together, our mission on the Really Know Really podcast is to get the true answers to life's baffling questions like why the bathroom door doesn't go all the way to the floor, what's in the museum of failure, and does your dog truly love you? We have the answer. Go to reallyknowreally.com and register to win $500, a guest spot on our podcast, or a limited edition signed Jason bobblehead. The Really Know Really podcast. Follow us on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.

Hey, welcome to Stuff to Blow Your Mind. My name is Robert Lamb. Today is Saturday, so of course we have a vault episode for you. This is going to be The Glorious Hermit Crab Part 2, which originally published 1-9-2024. Let's dive right in. Welcome to Stuff to Blow Your Mind, a production of iHeartRadio. Welcome to Stuff to Blow Your Mind.

Hey, welcome to Stuff to Blow Your Mind. My name is Robert Lamb. And I'm Joe McCormick, and we are back with part two in our series on hermit crabs. Now, Rob, on a recent vacation, you got to oversee the fields of hermit crabs as they crawl about doing their busy, busy business. And so you got very into the idea of talking about these animals, and it turns out there is...

way more interesting stuff to say about hermit crabs than you might think. There's a lot of interesting research on them that kind of has implications beyond the hermit crab just as an animal in itself and can even inform us maybe about human economics and sociology and strange corners of knowledge like that. Yeah, so definitely go back and listen to the previous episode if you did not already, because we'll touch on the basics of what hermit crabs are and what they are not.

For example, they are not considered true crabs. But I mean, in our hearts, they're true crabs. But technically speaking, not true crabs. There's no moral implication there. It's just a different taxonomic division. So.

The so-called true crabs are decapod crustaceans, 10-footed crusty animals in the infraorder Brachyura. These hermit crabs belong to a cousin infraorder called Anomura, A-N-O-M-U-R-A, Anomura, which are not technically true crabs, but they are also decapod crustaceans. They also have 10 legs, 5 pairs of legs, generally 5 antennae, though in the Anomurans, often

even though they have five pairs of legs, often like the last pair of legs will be diminished or hidden in some way. So they can often look like they have eight legs, even though they do really have 10. Maybe the last pair is kind of tucked in somewhere. And that's certainly the case in hermit crabs because, of course, the really characteristic thing about most of the 800 plus species of hermit crabs is

is that they are specially evolved anatomically and behaviorally to depend on shelter, most often a type of mobile shelter, such as the abandoned shell of another animal, most often a gastropod of some kind. And in the last episode, we talked a lot about hermit crabs dependence on and fierce competition for these shells that they use as their mobile shelters.

That's right. They have this unique relationship with their environment. Not only scavenging, certainly generally with hermit crabs, you have the scavenging of old shells, particularly snail, mollusk shells, that sort of thing. And then as we discussed with terrestrial hermit crabs, which is a minority of hermit crab species, they

you will see not only the acquisition of these discarded shells, but then the alteration of these shells to make something that is more in line and more with what the crab wants and also makes it more

more economic, like from an energy standpoint for the crab. So there are all these fabulous ins and outs without even getting to the point of like comparing the competition for hermit crab shells to say the human housing market.

Now, I thought it would be a good place to start today to talk about some alternatives to snail shells in the hermit crab shelter world. So as we talked about last time, hermit crabs do most often look for gastropod shells as their mobile shelters. These shells originally belonged to snails, periwinkles, whelks, animals of that sort.

And these original animals died and left the shells behind for crabs to take up and in some cases remodel to their specifications. There is, though I don't know if I've ever heard this before, I was reading online that there is apparently sort of a myth or an urban legend that hermit crabs have to kill the snails to take their shells from them. And that does not appear to be true. Hermit crabs...

appear to scavenge shells from snails that died for other reasons that died either, you know, were killed by, in some cases, other snails, predatory other snails, or just died for whatever reason. A shell is empty now. And in some cases, a hermit crab can take it up and add it into the the hermit crab shell economy. Yeah, the type competition is not for shells currently occupied by snails.

The competition among terrestrial hermit crabs is for the shells occupied by other hermit crabs. So while across this whole family of animals, snail shells are the most popular for mobile shelter, there are some examples of hermit crabs that use other types of objects and in some cases even living organisms for shelter.

So on the less exciting end, some species make their homes in plant structures, maybe hollow pieces of bamboo or coconut shells, other plant matter like that. But there are also these interesting relationships between hermit crabs and, for example, sea anemones. Rob, I know you have something on that you're going to get into in a bit. But first, I wanted to talk about

coral and sponges. So there is a paper that was published in PLOS One in 2017 by Momoko Igawa and Makoto Kato called A New Species of Hermit Crab, Diogenes heteropsamicola,

replaces a mutualistic sepunculin in a walking coral symbiosis. Again, this was the year 2017. And shout out, I came across this finding because of an article in The Conversation I found by Sarah Minot, which is a summary of this finding. So Rob, I included some images of this hermit crab with its natural, with its coral companion here. This is Diogenes heteropsamicola and

And I would say it's one of the weirder looking ones we found. It does look like a hermit crab in the front, but with a huge kind of foot shaped mass of pink bar soap hanging off its back. So the hermit crab itself is very is bright red and white sort of candy cane color scheme with very tall eye stalks and these long feather like antennae. So this is a marine species of hermit crab.

And then I've got another picture for you to see here, Rob. This is with the crab's abdomen exposed. So this is outside of its shelter. The abdomen, while the front is very red and white and has a crabby appearance, the abdomen looks kind of like a grub. It's like a translucent white worm. Mm-hmm.

So this paper in PLOS One documents the discovery of a hermit crab species that takes up mobile shelter in what are known as solitary corals or sometimes walking corals. The species of hermit crab was found in southern Japan by scientists affiliated with Kyoto University. Again, the new species name is Diogenes heteropsamicolae.

And it's a very tiny crab. It's just a few millimeters in length. So you might wonder why select a chunk of living coral as shelter instead of the shells favored by the vast majority of hermit crabs.

Well, apparently, one major advantage for the crab is the very fact that the coral is living and thus structurally dynamic. So most hermit crabs have to engage in this obsessive ongoing survey of the housing market, trading up for bigger shells as they grow, which, as we know, can involve aggressive competition.

This is because the size of each gastropod shell is basically fixed. I mean, in some species, they might do some interior remodeling, but the overall dimensions of the shell are not going to change much. This species, when it lives inside a wad of living coral, does not have this problem. It has found a forever home because the cavity occupied in the living coral can actually grow along with the crab and

Another thing mentioned in this article is that coral provides active defenses, whereas a dead gastropod shell is a type of armor. It provides a solid barrier against predators. The corals can actually sting. That's right. So you have this added level of like chemical weapon and like living self-repair armor. It's just a fabulous upgrade. Exactly. And apparently it is not only the hermit crab that benefits from the symbiotic relationship.

The coral benefits as well, and that would make this an example of the symbiosis we call mutualism. If only the crab benefited and the coral was not affected either way, it would be what is called commensalism. But this is mutualism because they both get a benefit.

So what is the benefit for the coral? It appears to be that the hermit crab gives the coral the benefit of mobility. So the coral in question is of the genus Heteropsamia.

And this is not the kind of coral that forms into large structured reefs. This is a solitary coral, or again, sometimes called a walking coral. Rob, I attached some pictures of this coral for you to look at in its normal form, just sitting there on the ocean floor. It looks kind of like a blob with some, you can see the polyp cups and the tentacles on top. These

These corals can be found in small masses, usually about 2 to 3 centimeters in diameter, sitting on flat, sandy seafloors. And their polyp cups and feeding tentacles are positioned facing up into the water.

One danger for an organism like this is that it has to be positioned correctly in order to survive. But the coral mass is not ambulatory. It can't walk around. So imagine being sort of a small rock with a mouth and I guess kind of finger teeth.

Alone on the seafloor, it is at risk of either being buried by sediment or being knocked over and left upside down, both of which could be a death sentence for the coral. So, Heteropsamia has evolved a relationship with another organism, not the hermit crab. This is an organism known as a sepunculid worm.

This is a small worm that lives in a cavity on the underside of the coral, and it carries the coral around with it when it crawls along the bottom. It seems that in some cases, specifically in areas around the Amami Islands, which are islands that are far, they're part of Japan, but way south of the main Japanese islands. In these cases, the hermit crabs have taken over the role that was once played by the worms in this relationship.

So how would this this swap occur between, you know, going from the coral partnering with the worm to the coral partnering with the hermit crab? Because, as you know, a lot of times these these tight symbiotic relationships are very sort of finely tuned by evolution like they it would not usually be easy to just swap one animal in for another.

Well, the author of this feature I was reading interviewed the lead author of the paper, Momoko Igawa, and she explained that the normal process of establishing a relationship is.

Between a coral and a sepunculid worm goes like this. So when the coral is young, it begins by attaching itself to a tiny shell and begins to grow around the shell as it matures and builds its solid base. So the coral like lands on a small shell that's

that is already inhabited by a worm. So there's already a relationship between the worm and the inanimate shell. The worm is using the shell for shelter. And then somehow, you know, from the worm's point of view, the shell just suddenly it keeps getting bigger and like it grows all around it. And this is the coral taking up residence on the shell and growing around it, forming a sort of perfect little cavity for the worm to hide in.

And according to a Gawa, it seems likely that a similar process would

led to hermit crabs inhabiting the corals. And in the end, the benefits that they would trade off are similar. So the mobility of the crab protects the coral from being buried in sand or stuck upside down, and the coral helps protect the crab from predators. Yeah, this is fascinating. Again, it just kind of takes the basic concept of the hermit crab that I think most people are familiar with to some degree and just takes it into like weird areas. Yeah.

And indeed, I have another example here to discuss. And this is where we get into deep sea hermit crabs. And I think, you know, if you've ever heard us talk about deep sea biology before, you know, that things can get weird down there.

And so I want to talk about some of these hermit crabs from the family Pirapepguridae. By the way, as long as we're talking about names here, you know, did we stop me if we already talked about this, but did we talk about.

the family of hermit crabs, Diogenidae, being named after Diogenes. Oh, yeah, Diogenes the Cynic. Yeah, who, of course, lived in a tub, according to the story. Right. So, yeah, Diogenes the Cynic, he was an ancient Greek philosopher who

supposedly would live in, I think, the marketplace of Athens just in a big ceramic jar. And as a cynic philosopher, his big thing was that one should not act against their nature according to the expectations of others. So he was

He was very, you know, against society's rules and stuff. Yeah. So in a way, kind of a perfect model for us to look to in naming the hermit crabs. So anyway, we're talking about

deep sea hermit crabs here, and in particular, one that wears not a deceased mollusk, but the living body of a sea anemone. As Mary Kay Wickston described for NOAA back in 2015, young crabs of this particular type start out inhabiting a pilfered shell, you know, a typical, you know, snail shell or what have you.

But then the sea anemone of the family Hormathadiae settles on the shell, overgrows it,

And then ultimately dissolves that shell to become the living housing of the crab. And much with the example we were talking about earlier with the coral, grows and expands with the hermit crab. So now this is indeed another example of a forever home, of a bio armor that will grow with the crab.

Brilliant. Now, the anemone gains mobility this way. You know, the hermit crab is like, hey, you stick with me, baby, I'll show you the world. And so the crab also, as with the coral example, gains chemical protection from predators, specifically protection against octopods.

And this species, the species in this particular write up is not specified or was perhaps not known at the time. I think one of the exciting things about hermit crabs, particularly marine hermit crabs, is we keep discovering new species and we keep making new discoveries about how they live their strange lives in the ocean, especially the deep ocean.

Now, according to a 2020 study by Gus Mal et al. published in Molecular Phylogenetics, there are some cases where these deepwater hermit crabs simply carry around protective sea anemones on their intact shells. And in these cases, especially, the crab actually selects and places the organisms on its own shell. You know, it goes out shopping, decides which ones it wants and places them there. However, the author stresses that

Quote, sea anemones can also mount shells unaided, triggered by mollusk-derived substances in periostrasum of the shell. So the exact mutualistic relationship differs depending on the species of the hermit crab. But it's pretty amazing here, the idea that like in some cases, the hermit crab is shopping. In other cases, it is sought out.

Oh, I want more detail on exactly what the shopping is like. Does the crab like crawl along and sort of feel around the anemone, like pick it up and put it on there? Like what is the selection process like? Yeah, I mean, they're very, very choosy, as we see even just with their selection of snail shells and whatnot among terrestrial hermit crabs. Oh, that's true. Yeah, the selection of the gastropod shell involves an awful lot of feeling usually. You know, it's not just like looking at it. They go and they...

They feel all over it. They turn it around. They climb inside it and try it out and sometimes decide they don't want it. I mean, that's the whole thing. Like sometimes they do try it out and say, no, that's not right. And they go back to the old one. And then sometimes is the case with the shells and might be the case with sea anemones as well, is that they are also dangerous.

Making choices that their survival depends upon. So sometimes they will go with a shell, but they don't like all that much or they is not their first choice or even their second choice, but they need to survive until they can get something better. And so, yeah, perhaps that's the case here as well.

But again, researchers are still making fantastic discoveries regarding deepwater Hermes. For example, a 2022 team from the University of Tokyo discovered a new species of anemone. This is Stilobotus calcifer, named after the fire demon calcifer from the novel and Studio Ghibli film Howl's Moving Castle. Hmm.

This is the one that's in the Disney dub is voiced by Billy Crystal. Okay. Yeah. Wait, this is the it's like for cooking the food, right? They like, yes, they're cooking bacon and eggs and stuff in the pan over this boy. Yeah.

Yeah, yeah, yeah. Very fun character. Great movie. Yeah, it inspired the name for the anemone. And it lives on the shells of a particular hermit crab species. And I included an image of this for you here, Joe. Now, there may be some lighting in the image I provided, but it still looks beautiful. Oh.

It does look very fiery. It looks like a creature that is composed of or living within flame. Oh, yeah, it's beautiful. And I can see why you might call it that given the animation style of that in-house moving castle, like the way the...

The flame just kind of bobs and undulates almost like the way you might see the, I don't know, flesh of a jellyfish moving underwater or something. And I can imagine that if you see this anemone in motion, it probably looks something like that. Yeah, yeah, it's pretty great. If you want to find some of these images for yourself, there is a 2022 Mong Bay article by Liz Kimbrough.

that you can look up. And that's one of the sources I was looking at for this section of the episode. ♪

I'm Jason Alexander and I'm Peter Tilden and together on the Really No Really podcast our mission is to get the true answers to life's baffling questions like why they refuse to make the bathroom door go all the way to the floor. We got the answer. Will space junk block your cell signal? The astronaut who almost drowned during a spacewalk gives us the answer. We talk with the scientist who figured out if your dog truly loves you and the one bringing back the woolly mammoth. Plus...

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Now, on the subject of deep sea hermit crabs, we should also talk about hydrothermal vent environments. We've talked about hydrothermal vents plenty of times on the show before. These are deep sea seabed fissures that release geothermically heated water that can result in very biologically active oases in the deep ocean that provide home to many different unique species of organism.

Now, one of the more famous vent dwellers is the Kiwa-Taileri or Hoff Crab, which is actually a squat lobster. And this is not a hermit crab, but it is kin to hermit crabs. It's not a quote unquote true crab. But in 2004, researchers discovered the first known hermit crab to reside at a hydrothermal vent location.

This one was dubbed Paragiopagurus ventolatus, and it was discovered in the waters of Taiwan. And this was, I was reading about this in a paper by Rafael Lemaitre. Then in a 2011 paper by Komei et al., these hermit crabs were found elsewhere on the Nikko Sea Mount. This is a submarine volcano in like southern Japanese waters.

Now, I was mentioning some of this to my wife as I was researching it. And when I brought up the idea of hydrothermal vent crabs, her question was, well, where do they get their shells? Do they have shells? And I hadn't really thought about this. But yeah, it does seem that while this species prefers gastropod shells, they would prefer to have standard like snail shells. They are indeed scarce shells.

in these habitats, these hydrothermal vents. So they'll end up having to use something else. It's not their first choice, but they will use the empty tubes of the siboglinid worm. This is like a tube worm, and they will use these discarded empty tubes for their shell if they cannot get

an actual gastropod shell. Ah, yeah. So I had read some unspecified references to hermit crabs using worm tubes as mobile shelter. And I wonder if it might be talking about this or maybe related animals that use other worm tubes as well. Yeah, yeah. It's pretty fascinating. I do want to point out this is not an obligate

hydrothermal vent dweller, though. You do have various organisms that have to have that hydrothermal vent environment, and it is something that very much defines them. These creatures apparently can live beyond the hydrothermal vents but have been observed to reside there.

So sea anemones, coral, tubeworm, discarded tubeworm tubes, so many different things can become housing for a hermit crab. Thinking outside the snail shell. Yes. And of course, all these things we're talking about are things that

You would expect they're like an adapted relationship in some way, things you would expect to see with some regularity in nature. You can find weird, isolated examples of hermit crabs using all kinds of stuff as a temporary shelter if they are in a jam. Yeah.

That's right. We mentioned like the intense competition for shells and the cascading events that will occur when a conflict between hermit crabs over a shell resolves and then somebody's left out. Usually it's whichever crab lost in the combat now has no shell. And in those cases, again, its survival is on the line. So it may use something like even like a discarded pop top I saw referenced in one article.

Doesn't mean it's happy about it, but it will use it for the time being. Now, there's another wrinkle to this whole, you know, not true crabs story because there's another cousin of

to true crabs, known as, of course, the king crab. I think a lot of you have heard of the king crab. Sometimes it winds up on the menu, right? There are over 100 species of king crabs. And while we don't know for certain, it is widely hypothesized that king crabs derived from hermit crab ancestors.

Now, this brings us once more to the topic of carcinization. This is convergent evolution in which non-crab crustaceans evolve crab-like bodies. And in this case, we're specifically dealing with what's referred to as the hermit-to-king hypothesis, which we should stress is not universally accepted, but it does seem to be the current scientific consensus. Though, again, not everyone agrees, though.

But thankfully, this is not one of those scientific consensus issues that has been politicized, though I guess it would be maybe amusing if it were. As Knorr and Glinner point out in The Origin of King Crabs, this is 2017, published in Zoological Journal of the Linnaean Society, the hypothesis itself dates back to the 19th century and has been controversial that long as well.

It's not a new controversy. They cite an 1895 paper by French entomologist Eugene Louis Bouvier.

who lived 1856 through 1944. This guy studied mollusks and crustaceans early in his career, and they summarize that the basic idea is that, quote, king crabs are secondarily calcified hermit crabs that left the protective gastropod housing and transformed to a crab-like form. That is such a strange, wonderful path, if that is in fact the case of what happened with king crabs.

that you would get what was originally some type of crustacean ancestor that

that evolved to have this obligate relationship with external shelter. So its backside is this soft, windy, wormy little thing that is protected by a shell. And it makes this, I don't know, what would seem to be a very dramatic and irreversible kind of evolutionary right turn or left turn, whatever you want to call it. It goes down this weird road of depending on these external shells.

And then part of that family goes back in the other direction, changes course again, abandons the shells and becomes fully hardened on the outside.

Yeah, I mean, it's one of the crazy things about evolution, these various changes that occur over time, like, you know, the different species evolving different forms of wings, you know, different morphological approaches to the same basic concept. And then creatures like flightless birds that just

Like, I don't really need to do that anymore. I have it's not necessary. And really, it was it was a huge pain in the butt to do it to begin with. Oh, actually, you know what I think would be a great parallel example is marine mammals. You know, so the all terrestrial life comes from what was originally in the sea. And these animals came evolved from animals that once lived exclusively in the sea.

All marine mammals evolved from terrestrial mammals. So they were once, you know, four footed quadrupedal mammals wandering around on land and they evolved to to go back to full time water life.

Yeah. So there's like this line from like, oh, thank goodness I'm out of here for just a little bit out of that, the fierce competition of the water. And then, you know, millions upon millions of years later, something that will become an orca goes back in again and says, you know, I think I got it this time. I think I'm ready. I'm going back in. And then, of course, plenty of things that don't become orcas that are not success stories as well, I suppose. Yeah.

So, again, the hermit-to-king hypothesis goes back to the 19th century, and initially the evidence was largely morphological. King crabs, lithotids, they don't really look like hermit crabs, certainly not to the average crab looker. The body shape is drastically different, but a few key details would seem to remain. Okay, so you're looking for body features that king crabs have in common with hermit crabs. Like what would they be?

All right. So first...

and claw asymmetries. So the pleon is the abdomen of the crab. And as we've already pointed out, the hermit crab has a highly asymmetrical abdomen that evolved to slide into asymmetrical spiral shells. And as we mentioned already, their right pincher is usually larger so as to cover the opening of the shell when they retreat into it. You know, it becomes the door for the shell. Yeah. Though, of course, there are multiple, there are the right-handed pinchers

hermit crabs and the left-handed hermit crabs. So some are reversed. The diogenates actually are the reversed ones, the left-handed ones.

That's right. Mouth parts are another one. Apparently, between hermits and kings, there are only minor differences. Also, the ceta on the grooming legs. One cetal type, for example, is only present in paragurid hermit crabs and king crabs. This is according to a 2015 study published in Acta Zoologica. Okay.

Also, there are some details in internal organ organization. Also, there are various correspondences in the vascular system between kings and hermits.

And then adding to this hypothesis is the observation, of course, that carcinization may be a thing in general with crab-like forms seemingly having evolved multiple times in shallow water habitats. So it's just a plan that works. And if you already have the basic blueprints in place and you can evolve in the crab-shaped direction, a lot of animals will eventually evolve down that path. Yeah.

And more recently, we have phylogenetic evidence that has been presented to back up the hermit-to-king hypothesis. But, you know,

I think outside of dedicated crab experts, we also have to throw in that the mere title of the hypothesis is instantly attractive. You know, it's like pauper to prince, hermit to king. So it's for at least, you know, the average consumer of all this information. It's hard to shake that that the social implications of this. I don't know. It's you know, it makes it a little more fun and engaging to, again, non-scientists.

And maybe to scientists as well. I mean, it's the kind of thing you probably can't help but reference, at least in the opening matter for a study or a paper. But it's also just a great thing to think about if you're ever going out for a nice king crab dinner. I mean, this could well be the descendant of a hermit crab. ♪

I'm Jason Alexander and I'm Peter Tilden and together on the really no really podcast our mission is to get the true answers to life's baffling questions like why they refuse to make the bathroom door go all the way to the floor we got the answer will space junk block your cell signal the astronaut who almost drowned during a spacewalk gives us the answer we talk with the scientist who figured out if your dog truly loves you and the one bringing back the woolly mammoth plus is

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So finally for today's episode, I wanted to talk a bit more about the shell economy in hermit crabs that do trade in gastropod shells. So of course, last time we talked about the importance of exogenous shells for hermit crab survival and about this, this weird ordered mass behavior that can emerge from hermit crab shell exchanges. So I was reading an interesting article in a scientific American called

by a researcher named Ivan Chase, who's a professor emeritus at Stony Brook University, called Hermit Crabs Trade Up by Exchanging Shells in Queue.

So in this article, Chase talks about how hermit crab research has informed thinking about the sociology and economics of a concept that we brought up specifically when talking about hermit crabs last time, but actually is a broader, general, just dynamic term. And that term is a vacancy chain. So Chase's formal definition of a vacancy chain goes like this, quote,

an organized method of exchanging resources in which every individual benefits by claiming a more desirable possession abandoned by another individual. And this can be illustrated directly by watching hermit crab behavior. So Chase opens the article by telling a story of just some observations he personally made in a tide pool on Long Island in 1986, where he, this was an area where there were hermit crabs,

And he brought in an empty snail shell and just dropped it in the tide pool. And he talks about how he waited a few minutes. And then finally, a little hermit crab comes along. It checks out the shell, feels it out with its claws, you know, measures it. It does it does the full walkthrough and it decides, yes, I want this new shell. So it trades shells, abandons its old shell and walks away with the new one.

But it doesn't stop there because another crab eventually comes along, checks out the abandoned shell, decides it likes that one better than its current shell, walks away with that. And then a few minutes later, it happens again. Another one comes along. This one has a shell that's in really bad shape. It's like a shell that is not the right size. It has a hole in it. And it likes the abandoned shell better than its very dilapidated current shell, walks away with the secondary abandoned shell.

Now, he never mentions if any hermit crab came along to claim the shell abandoned by this third animal. But I guess at each point it becomes less and less likely because less desirable shells are being traded away from hermit crabs.

And so maybe, you know, there's not a crab in the general area that would prefer a shell that is like very small and already has a big hole in it. But multiple animals here have gotten a shell that was better than the one they started with. And so multiple animals are walking away from this series of trades happy. And so based on this observation, Chase Lansdowne,

looked into, Chase and other colleagues in this area looked into questions like, what is the average number of trades that occur after a vacancy first appears? Or what starting conditions lead to more trades in the subsequent series? And so forth. And so

So Chase did research on a species of hermit crab called Pagurus longicarpus, aka the long-wristed hermit crab, which is native to the east coast of North America. And there are a few general findings. Uh,

First of all, crabs usually traded up for larger shells. And this should not be surprising since part of the reasoning behind shell trading is that it allows individual crabs to grow. Crabs grow, of course, you know, like other crustaceans, they have to grow through molting. But when they get bigger, the shell that they have currently doesn't get any bigger. So they have to find a bigger shell to inhabit.

And of course, there could be other reasons for seeking a shell, such as maybe getting a shell in a better condition. But one of the main ones is you need a bigger one as you grow. Next general observation is that the average there was a pretty consistent average number of trades in vacancy chains, and it was about 2.5. It was between two and three.

And this could vary depending on conditions. For example, vacancy chains that started with a larger empty shell were longer than those that started with smaller empty shells. So a big empty shell leads to more trades overall. And so the really interesting thing about a vacancy chain is how even in an environment where multiple individuals are competing aggressively for scarce resources, you know, the number of shells is limited, there's a scarce resource, there's a

A vacancy chain can mean that everybody in the chain wins. It's not a single winner take all competition, but one in which many participants all get an upgrade. So you could almost view the survival value of the empty shell that is placed into the environment at the start of the chain as

The value of that shell being kind of distributed or averaged across multiple beneficiaries because it doesn't only help the first taker who directly occupies that shell, but indirectly helps all of the subsequent crabs in the chain because they all get a better shell than they started with.

Oh, and one thing Chase says in this article, Rob, is that researchers performed similar experiments on Caribbean land hermit crabs. And I think those were the that was the species you saw on your trip.

Yep. Yep. That was the one. Again, we did not get to directly observe competition for shells or the changing out of shells, though obviously this was taking place just when we were looking the other way or, you know, in parts of the island we weren't on or, you know, underneath the leaves of the various plants and so forth. But at one point, my son and another child on the island who had a lot of fun like watching the crabs and

running around. They did find a hermit crab that was unhoused, a naked hermit crab, if you will. So I suspect this was the result of some sort of competition. Man, I feel bad for that crab.

They did as well. They were like, we got to help this guy get a new shell. So I think they were like trying to find some from him. But, you know, in retrospect, it's like, come on, you guys, maybe they were really into it. So maybe they spent an hour looking for shells. But hermit crabs do this nonstop. They are always looking for shells. So you can imagine the frustration where the hermit crab is like, really? Really?

you guys just started doing this. I've done this my whole life. Trust me, just let me find it. There's very little you can do in this situation. I'm not going to live in this half a coconut that you just provided. Oh, it's nice that they offered. It's nice that they tried. I like that they were gentle with the crabs and looking out for their well-being. But to come back to the idea of vacancy chains as a concept, another thing Chase mentions that's interesting is that

Researchers have observed two different kinds of vacancy chains in hermit crabs, synchronous and asynchronous. And these are about the relationship of the trade series to time.

Asynchronous chains are the kind that I described a minute ago where like, you know, he dropped one empty shell in a tide pool. One crab came along and found it, made a trade, you know, several minutes later, another one comes along, makes a trade. That is that is something that occurs with like each step in the process, having some kind of delay in between. Synchronous trades are, on the other hand, are the kind more like we talked about in the previous episode of

where the animals actually organize themselves in a line by size while they're still in their original shells and anticipating a trade and then all suddenly trade at the same time. These synchronous trades happen really fast. And actually, Chase describes particular scenarios that can cause these trades to arise. I wanted to read briefly from the article with one such scenario he describes here.

So Chase writes, quote, one of the strangest examples involves a predatory snail that attacks other kinds of snails, including some whose shells hermit crabs particularly like.

As the predatory snail grasps the prey snail, drills a hole in its shell with a rasp-like tongue, and injects digestive enzymes, nearby hermit crabs gather around, following the scent of chemicals released by the injured snail. When the predatory snail finally pulls its prey from its protective casing, a process that can take as long as an hour, the nearest crab dives into the now-empty shell,

In turn, another crab immediately snatches the first crab's old shell, and so on. Instead of following the careful inspection rituals that we observed on Long Island, crabs at the scene of a mollusk murder make split-second decisions, choosing new homes based on vision alone.

So I thought that's kind of interesting that these different conditions can arise where in some cases animals making trades through the vacancy chain have plenty of time to examine what the new shelter looking at and make an informed decision about whether they want to make the trade.

Other times there's like this immediacy, like all these crabs are gathered around and so crabs are making rapid exchanges. And I have to wonder if in cases like that, they're more likely to make an error in exchange for a shell that is actually not as good as they think it is at first or maybe is not even as good as the shell they abandoned. Yeah, it was kind of a musical chairs aspect of the whole scenario, isn't there?

So the more hurry there is in the market, the less information you can get and the less you're able to make sure you're making a good decision. Yeah. I mean, I guess you see versions of that in the human housing market as well, right? Oh, yeah. When competition's really intense, you have people doing things like buying houses sight unseen, you know, just getting in there, making big cash offers and so forth. Yeah.

Yeah, even though, as we discussed, there are experts who weigh in and say, well, you really can't go one-to-one on this. There's a great deal of nuance to human housing market, as well as the hermit crab competition for shells, but we can't help but compare the two. And it does seem like there are some interesting things that line up. Oh, yeah, yeah. So you wouldn't want to do what

people sometimes do and just like observe a behavior in animals and then say, ah, well, there is just that's what humans do as well. Like you would need evidence that that is actually what humans do as well. But vacancy chains have been studied in animals other than hermit crabs, and they have absolutely been studied in human domains as

Such as in human residential real estate. So, for example, Chase talks about some research in the United States in the 1960s that found that each new housing unit constructed triggered a vacancy chain that allowed not just one family to move into the newly constructed unit, but allowed multiple families to move into what they considered better housing, better apartments.

And Chase refers to one study that found average chain lengths of 2.4 and another that found averages of 3.5. So a lot like with the shells, the construction of a desirable new place to live is

may benefit not only the people who directly move in there, but also the people who choose to move into the living space vacated by the first residents and so on and so on for an average of maybe somewhere between two and four resident moves. In fact, the Harvard sociology professor Harrison White, who apparently coined the term vacancy chain, said,

found that vacancy chains were also created with certain types of job openings, such as the retirement of a pastor at a church that opens a spot for a new pastor to move in, and then a pastor moves into that position vacated by the person who made the first move, and so on.

And this was studied across multiple professions and fields, including everything from sports coaches to drug dealers. And research in the subfield has generally found that when a vacancy opens, sports

Somewhere between 2.5 and 3.5 people are able to move into better paying or more desirable positions through the operation of a vacancy chain. And Chase speculates that this phenomenon probably applies to certain types of consumer goods as well, in addition to housing and job openings. One example, though there's not great research on this to back this up, but one example might be like cars, right?

This would probably only apply to consumer goods where there's like a robust market for used options. But again, this has not been formally studied.

This does remind me of various headlines, though, that came up during the pandemic, I believe, about the value of certain used cars and how there was intense competition for them. However, I don't really retain car news all that well. So maybe listeners out there remember these stories as well. Something about the value for and intense competition for used cars of particular models that might have some way line up. It might line up with what we're talking about here.

Yeah. Well, so maybe we can come back to that in a minute when I because I was thinking about, like, what are the qualities of resources that do lead to these vacancy chains versus resources that don't? And Chase actually gets into that toward the end of his article.

So he poses an interesting question, like, why is it that vacancy chains tend to benefit on average about three parties in markets as different as hermit crab shells, human apartments and football coaching positions? It's kind of weird that we would see this range of roughly two point five to three point five beneficiaries across such wildly different domains.

And Chase writes, quote, my guess is that some as yet undiscovered correspondence between the demography of humans and hermit crabs explains the effect, their birth and death rates, perhaps, or the rates at which new resource units are produced and used. But these are hunches. So we don't really know the answer. But one thing we do know is that vacancy chains do only seem to occur

occur with certain types of resources, resources with particular properties. So there are not vacancy chains created by like boxes of breakfast cereal at the grocery store or, you know, like cans of artichokes. A vacancy chain resource tends to be something that is both scarce and highly coveted. So they're very important to the consumer and they're hard to get.

They tend to be resources that can be possessed by only one competitive unit at a time, though this unit could be a group such as like a family that occupies a house. But the group has to function as like a single unit competing for the resource. And the resource cannot be claimed unless it is empty or vacated by the previous owner.

And these principles are generally true of the human resources studied, such as housing and jobs, but they're also true of hermit crab shells. But this makes vacancy chains kind of interesting because they are a circumstance that arises in a market where

that seems to be based on the type of resource being competed for rather than any characteristics of the competitors. And in the end, Chase raises the question of whether experiments in hermit crabs could maybe help us create better economic and sociological models that would be predictive in certain human economies.

Interesting question. But then again, there's always the danger with that. You don't want to think, aha, I've discovered a principle in hermit crabs. Therefore, I can just apply it to humans. You would need good independent evidence that it actually does apply to humans. Yeah, you couldn't just like, all right, I want to game my position in the company. So I'm going to buy a bunch of hermit crabs. I'm going to label their shells with the names of all of my coworkers, my bosses, my competitors. And then I'm just going to do what the hermit crabs do. Nice.

Not a good idea. Right. So, yes, you do not want to fall into the trap of I have observed hermit crabs, therefore I understand humans. But I do think it's very interesting that you have these similar principles that appear to be in operation in these hermit crab economies and human economies. Yeah, absolutely.

You know, this does not bear a lot of discussion, but as one final tangent for this episode, I want to point out that in 2015, apparently some UFOlogist looked at some NASA Mars Curiosity rover footage and in the lo-fi visual information that was collected, they spotted a hermit crab on the surface of Mars. Hmm.

Yeah. Also, I think a scorpion and maybe a humanoid being. Alf? Was Alf there? Possibly. I think we have to assume it was Alf. Alf, hermit crab and a scorpion.

Now, obviously, you can go back to our episodes that we did in the last several months talking about this very situation, what happens when you have low detail, low quality information, and you really want to see results.

humans or humanoids, aliens and so forth. Well, this is exactly what happens. You spot your your Martian hermit crabs. Hold on. I'm trying to find the image. Oh, OK. Here it is. I'm seeing something on the Daily Express. There's. Yeah. Oh, you know what? I give it to him like that looks more like I'm not saying it is a hermit crab. It's not. But that looks more like a hermit crab than most of the things people see on Mars actually look like the thing they're saying they are.

So you're saying there's hope. I'm saying it really, it's got, it's a nice, nicely selected anomalous image. It has shadows falling on a rock in just a certain way so that it does look like legs. Kudos to them for digging up this one. I want to believe. All right, we're going to go ahead and close out this episode. But, you know, we're going to come back with a third Hermit Crab episode. We've got some feelers coming.

out there we've got some ideas we think we have enough to dish out a part three so again because again there's so much hermit crab research out there there's so many different species of hermit crabs and they're all amazing so tune in for more crab action on thursday because yes stuff to blow your mind publishes core episodes on tuesdays and thursdays monday is lister mail when

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I'm Jason Alexander. And I'm Peter Tilden. And together, our mission on the Really Know Really podcast is to get the true answers to life's baffling questions like why the bathroom door doesn't go all the way to the floor, what's in the museum of failure, and does your dog truly love you? We have the answer. Go to reallyknowreally.com and register to win $500, a guest spot on our podcast, or a limited edition signed Jason bobblehead. The Really Know Really podcast. Follow us on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.