January 4, 2025 • 49 mins
In this classic episode of Stuff to Blow Your Mind, Robert and Joe return once more to the world of crabs – specifically the industrious world of hermit crabs. (originally published 1/4/2024)
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Speaker 1 (00:06):
Hey, welcome to Stuff to Blow your Mind. This is
Robert Lamb. Today is Saturday, of course, so I have
a vault episode for you. And oh, this one published
a year ago this very day. This published on one
four twenty four. It is part one in our series
on the Hermit Crab. I hope you enjoy.
Speaker 2 (00:26):
Welcome to Stuff to Blow Your Mind, a production of iHeartRadio.
Speaker 1 (00:36):
Hey, welcome to Stuff to Blow your Mind. My name
is Robert.
Speaker 3 (00:39):
Lamb and my name is Joe McCormick. And we're back
after the holidays. All right, I guess you've already been back, Rob,
I'm back for the first time.
Speaker 1 (00:46):
Now, Yeah, that's right. I left a little early and
then and then I came back to you know, scrambled
together a few episodes. But now it's time to return
proper with a true core episode of Stuff Below Your Mind.
But we're ringing in the new year once more with crabs,
because of course, crab content is suitable for any holiday,
(01:08):
and there is an abundance of it, you know.
Speaker 3 (01:11):
I don't know if it's just the name of Christmas
Island that created this correlation, but I think we tend
to do crab content in the winter have you noticed
that that's not on purpose, at least not on my part.
Speaker 1 (01:23):
No, this is great. I think the Christmas Island crab
thing kicked it off a bit a while back. That's
part of it. For sure. There's something maybe holiday centric
about crabs. It also helps that sometimes my family and
I travel during the winter break and go somewhere where
crabs are abundant. And yeah, I'm excited to talk about
(01:45):
crabs once more because over the holidays, my family and
I were fortunate enough to once more visit Glover's Reef,
a partially submerged atoll located off the southern coast of Belize.
Tremendous fun. We stayed on a small island all week.
There were other human certainly, but we spend as much
time as possible getting into the water to snorkel to
check out the fish and the coral. But the predominant
(02:07):
land organism was, without a doubt, the terrestrial hermit crab.
Speaker 3 (02:12):
So this is a holiday with crabs underfoot.
Speaker 1 (02:14):
Yes, I mean, I don't think anyone ever stepped on one,
but they were everywhere. Most hermit crab species are aquatic,
as we'll probably touch on several times during this episode.
But I'm going to be talking mostly about the terrestrial variants,
like those that I encountered on this island, that still
depend on the ocean for reproduction, but which live most
(02:36):
of their lives on land, and that comes with various
complications and innovations. And also they're very visible. You know,
you don't need a snorkel, you don't need a dive
suit to engage with the world of the hermit crab
because on places like this they are everywhere and they
are widespread. You don't also don't have to go to
(02:56):
Belize to encounter hermit crabs, terrestrial hermit crabs, even they
are out there.
Speaker 3 (03:01):
So roughly, how big were or how big was the
range of the ones you were seeing? Is are we
talking like silver dollar size or hand size? Like what
are we dealing with here?
Speaker 1 (03:12):
Yeah? The size differential is one of the things that
makes hermit crab watching in the wild so fun because
you never know exactly what size you're gonna encounter. Like
some of the very small ones, you know, oh so cute,
it's the size of a dime or something, you know,
it's very small. But other times it'll be like I'm
probably exaggerating to save the size of a catcher's met
but at least the size of a very large fist,
(03:34):
you know, just a just a big chonker of a
hermit crab. And as you're going, as we were going
about on the little pathways on the island, you know,
they would be moving around pretty much all the time.
That they're very busy. They're constantly trooping about, they're scavenging,
they're competing for shells. Though I don't think we ever
directly observed this, but clearly it is happening. And if
(03:57):
you come across one while it's say, crossing the sand path,
they'll suddenly stop, and then if you get a little
bit closer, they'll retreat into their shells, and as they
do that, that'll cause them to roll over onto their back,
and then of course they cap the shell opening with
their larger claw and then give them enough time and
then get back up and they continue on with their business.
Speaker 3 (04:16):
Mm hmm.
Speaker 1 (04:17):
So yeah, there's just something magical about her crabs, at
least to someone like me who doesn't get to observe
them all the time. But even the team on the
island here, they seem to find a certain amount of
joy in the creatures, despite how accustomed they were to
their presence. I heard that one of the cooks brought
some shells for the crabs with her from the mainland,
(04:38):
with the names of each of her children written on them,
and then and then would enjoy like running into various
crabs who would claim these shells and make them their homes.
Speaker 3 (04:48):
Oh, that's funny. So like when people write funny things
on a dollar, you know, it's like, are you expecting
to encounter this again?
Speaker 1 (04:55):
Yeah? Yeah, And yeah. There's just something they're like a
little like io machines, you know. There's just something about
how industrious and relentless they are as they scavenge the terrain.
For instance, at this place that we were staying, this
a place called Off the Wall. The communal dining area
at the place has a sand floor, and Jim and Kindre,
(05:17):
who run the place, told us that first thing in
the morning, when you go in there, the sand is
completely devoid of human footprints because during the night the
crabs have come, the hermit crabs have come, and so
in the morning they are only crab tracks, and not
even the slightest crumb left behind, because they have come
and claimed everything.
Speaker 3 (05:36):
Crab wipe.
Speaker 1 (05:37):
Yeah, so I love it. After experiencing all that, I
was like, well, we've got to find some more things
to talk about with hermit crabs. We've talked about them before,
but now we're going to go in a little more depth.
Speaker 3 (05:48):
Well, it turns out I think hermit crabs are very
interesting and there is a lot we can talk about.
So I guess we will start with the basics. What
are hermit crabs? Are hermit crabs crab? The answer is
sort of. Hermit crabs are decapod crustaceans that means decapod.
They're ten legged invertebrates with a hard exoskeleton that grow
(06:11):
by molting, so they shed their old exoskeleton and emerge soft,
and then a new exoskeleton hardens when they need to
get bigger when they grow bigger. But they are considered
distinct from what are called true crabs. True crabs belong
to the infraorder Brachyuria. Hermit crabs belong to the related
infraorder animura a n O m U r A. They're
(06:34):
close cousins to true crabs, but different. Other animurins or
false crabs include the lithodoidea or the king crabs. And
the Porcelinidae, which are the porcelain crabs. And one thing
animurins generally have in common is that. Okay, so these
decapods all have five pairs of legs ten legs total,
(06:56):
and in the animurans, the last pair of legs farthest
away from the head is fun sized. So these animals
are still decapods, but a lot of them look like
they have only eight legs instead of ten, or maybe
six legs and two claws. Those front legs, the chelli
or the claws are legs, but in crabs they're often
(07:17):
claw shaped, but they look like they have only eight
legs instead of ten because the hindmost pair is tiny
and often hidden or tucked away under another body part.
Speaker 1 (07:28):
Yeah, and we'll get back to this particular detail later
on in our discussion. If not this episode, then perhaps
the second episode.
Speaker 3 (07:35):
So animurans have ten legs, a lot of times it
looks like they only have.
Speaker 1 (07:39):
Eight.
Speaker 3 (07:40):
Hermit crabs belong in the taxonomic superfamily Pagurroidea, and with
a few exceptions, they are mostly notable for exactly what
you're thinking of their dependence on externally scavenged material for
armor and shelter. Usually this armor is a shell that
once belonged to a gastropod, such as a snail, a periwinkle,
(08:04):
or a whelk, though there are some animals in the
family that don't need scavin shelter at all. We can
talk about those in a minute, and there are a
few that rely on things other than mollusk shells. One
example cited in a paper that I'll get to in
a minute is the discorso Pagurus schmitti, which takes up
shelter not in a gastropod shell, but in empty polyheat
(08:27):
worm tubes. The hermit crabs that do rely on external
mollusk shells have bodies that are actually shaped by this need.
So while true crabs have hard exoskeletons covering their entire bodies,
hermit crabs have what you might call non calcified abdomens.
(08:48):
So the front facing part of a hermit crab's body
the head, the thorax, and the front pairs of legs
and claws. These all have hard exoskeletal coating like any
other crab, but the part of the hermit crab the
abdomen in what you might call the tail or the Telson.
This doesn't really resemble a crab body at all in
(09:09):
a lot of species. It looks kind of like a
curly fat worm, and it does not have a hard exoskeleton.
The abdomen is flexible, soft and vulnerable. It is covered
in an external coating, but it's just very thin and soft.
It's very uncrab. This is the part of a hermit
crab that curls up inside the externally sourced shell.
Speaker 1 (09:33):
Yeah, so if you're just encountering hermit crabs out in
the wild, or even seeing them in a an enclosure somewhere,
you're probably not going to see this part of the
organism with its abdomen inside the shell. As we've been discussing,
it actually walks on its second or in third pairs
of legs. The first pairs are modified to form pinchers,
(09:54):
and its fourth and fifth pairs of legs are small
and specialized to grip the inside of the shell. It
also has appendages called europods at the end of its
abdomen to aid and securing that shell. So, you know,
all these things aiding to sort of grip and hold
on to that shell that it has taken on as
its shelter. The larger left europod hooks the central post
(10:17):
of a shell, and they can also use this europod
to hold on to other things when they are out
of the shell, Like I've read about how they can
attach to say like a tree or something, and it
can also use it to maintain balance.
Speaker 3 (10:30):
Yeah, so I think it's interesting that the hermit crab
is an animal. Its body is shaped in for double purpose.
So the front end of it is shaped for facing
the external world. It has the chelly, it has the
claws like many other crabs you would think of, but
the back end of it is shaped entirely for holding
(10:50):
on to this piece of mobile shelter. And the concept
of mobile shelter, while not completely unique, is pretty unique.
What makes the hermit crab interesting To read a quote
from a highly cited paper on hermit crabs that I
was looking at by a biologist named Brian Hazlet. The
paper is called the Behavioral Ecology of Hermit Crabs. Haslet writes, quote,
(11:14):
Many animals utilize exogenous shelters, but almost all eight hundred
species of hermit crabs are mobile while sheltered, the combination
of mobility and protection afforded by this lifestyle must contribute
to the large numbers of these crustaceans found in virtually
all marine environments as well as in tropical terrestrial shores.
(11:38):
So Hazlit is sort of saying the hermit crab plan
is a successful plan, clearly shown by the diversity of
these species found all around the world. That this is
a plan that works because sourcing shelter from outside the
body that you can take with you when you move
works really well. But it also comes with costs, and
(12:02):
we'll talk about those costs as we go on. One
thing I think to understand is that in general, while
a hermit crab can leave its externally acquired shell and
it can survive for some time outside of its external shell,
the acquisition of a shell for external armor is not
optional for a hermit crab. It's not like a nice
(12:24):
to have. It is essential for survival in the wild,
and the hermit crab's evolution has been shaped by the
need for these externally sourced shells.
Speaker 1 (12:35):
Yeah. Yeah, this is not just somewhere it goes to
sleep at night like. It has to have this with it,
and if it does not have the shell, then it
is highly vulnerable to predation. Exposure. It very well likely
will not survive without it.
Speaker 3 (12:48):
Right, So I want to turn to a paper I
was reading for a general overview of hermit crabs and
related species. This was an overview published in the journal
Current Biology called the Hermit Crabs by Mark Brifa and
Sophie L. Moles in two thousand and eight. And they're
going to pat the picture here of the kind of
hermit crab family tree. So there are currently more than
(13:12):
eight hundred known species of hermit crabs. Most of these
species live in the ocean their marine, with a few exceptions.
One is a species called Clibinarius fontic cola, and this
is the only known freshwater hermit crab which lives in Vanuatu,
that's a volcanic archipelago in the Pacific. And there are
(13:36):
other freshwater and amurans, but they are not hermit crabs.
So this is the one freshwater hermit crab out there.
Speaker 1 (13:43):
I should throw in that the hermit crabs that we
were observing in the wild, I believe are the Caribbean
hermit crab, and this is a variety that's common to
the West Atlantic, Belize, Southern Florida, Venezuela, and the West Indies.
Speaker 3 (13:57):
Yes, and the ones you were observing you were saying
were terrestrial or semi terrestrial, right, they spend a lot
of time on land.
Speaker 1 (14:03):
Yeah, these were land boys. We did see one variety
and I didn't identify this one one variety of aquatic
hermit crab out law snorkeling. But yes, the ones that
I'm mostly talking about here are hermit crabs of terrestrial
hermit crabs.
Speaker 3 (14:18):
So there are about a dozen species of land dwelling
or semi land dwelling hermit crab descendants in a family
called Sinobotids. This family includes one famous species that has
shed its need for an externally acquired shell altogether, and
that is the coconut crab or robber crab. We've talked
(14:38):
extensively about these before, but the coconut crab is the
largest land dwelling invertebrate in the world. I can have
a leg span of up to one meter and can
weigh almost five kilograms or about ten pounds. They live
mostly in coastal areas throughout the Indian and Pacific oceans.
I think we talked a good bit about coconut crabs
in our series on the Christmas Island crabs that we
(15:01):
did several years back. This was the the animal where
we were talking about the field notes of Darwin from
the Voyage of the Beagle, where he's like, you know,
they make really good eat and you boil the fat
under their tail and it makes a quart bottle of
limpid oil. And then he also tells a story about
how they like locked one inside of a biscuit tin
(15:21):
with wire and using its claws it was able to
essentially like rip the tin out and escape the box.
Speaker 1 (15:28):
Oh man, there's a whole horror movie for you right there. Yeah,
it would be Charles Darwin and crew on the Beagle
having to fight off the killer coconut crab.
Speaker 3 (15:37):
They come and they just find the empty box. They're like,
it's loose. No one knows where, you know, as long
as we're throwing around.
Speaker 1 (15:46):
Charles Darwin quotes there's another place in the Voyage of
the Beagle where he mentions hermit crabs. This is not
a particularly insightful quote. It's just a mention, but I
still had to drag it out. Quote. In every part
art one meets hermit crabs of more than one species,
carrying on their backs the shells which they have stolen
(16:06):
from the neighboring beach stolen. And yes, there is a
fair amount of shell theft as we'll get into. As
long as you're thrown around quotes unrelated, I want to
throw in this quote from Aristotle from the History of Animals.
Speaker 3 (16:20):
Is he going to tell us where they come from?
Speaker 1 (16:22):
Yes? Yes, you will reveal the at the time, you know.
Non controversial hypothesis on crab origins quote. The hermit crab
grows spontaneously out of soil and slime and finds its
way into untenanted shells. As it grows, it shifts to
a larger shell, as for instance, into the shell of
the neartes, or of the strombus or the like, and
(16:46):
very often into the shell of the small cirrix. After
entering a new shell, it carries it about and begins
again to feed, and by and by, as it grows
it shifts again into another larger one.
Speaker 3 (16:58):
Okay, I give Aristotle half credit on this. I think
he's a bit wrong on the spontaneous generation out of
slime and soil, but he correctly observes the shell shifting
behavior of hermit crabs, which is a major feature of
hermit crabs society that we'll have to talk about later
in the episode.
Speaker 1 (17:19):
Yeah, he's absolutely wrong on spontaneous generation. We don't ever
really have to drive that home. But in a weird way,
like in a very general way, the idea of like
matter becomes crabs, nature becomes crabs. Maybe not that far off,
as we'll discuss later on.
Speaker 3 (17:36):
But apart from the coconut crab, there are various other
species of hermit crab that live basically would live their
adult lives on land, though they still usually live out
part of their life cycle in the water, with females
releasing larvae into the sea, and apart from these exceptions,
hermit crabs are marine species.
Speaker 1 (17:56):
Absolutely. We'll come back to some of the ramifications of
this in a bit now.
Speaker 3 (18:09):
According to Brifa and Moles, there are five families of
hermit crabs, and it breaks down like this. You've got pagurity,
which are the right handed hermit crabs, and you've got diogeneity,
which are the left handed hermit crabs right handed, left handed,
What does that mean? We'll come back to that. Then
you've got cenobitity, which are the land hermit crabs. You've
(18:31):
got parapagurity, which are the deep sea hermit crabs, and
you've got pilochelady, which are symmetrical hermit crabs. Though the
more than eight hundred species of hermit crabs display different
local adaptations and behaviors, for the most part, it seems
like hermit crabs take what you can get foragers, which
(18:53):
is true of many true crabs as well, But hermit crabs,
for the most part, they will eat bits of dead
organic matter, both animal and vegetable. They will eat live
prey when they can catch it. Like true crabs, most
hermit crabs are not very picky about food. Whatever they
can get in their mouth, they're probably gonna eat.
Speaker 1 (19:12):
Yeah. Yeah. Both times that I was in believes there
was a lot of fun to be had, especially with
the kids, of leaving something out for them with permission
of course, like I'm talking about the like like a
cracked coconut, and then seeing the hermit crabs eventually swarm
over the material.
Speaker 3 (19:30):
So while foraging for food is of course essential for survival,
so is foraging for shelter. We will have more to
say about this as we go on, but obviously a
huge part of the hermit crab's survival revolves around acquiring
a good shell to live in, and the majority of
these shells come from As we've said, mollusks like snails,
(19:52):
but hermit crabs don't have to fight the snail for
its shell. They generally move into the shell that is
left behind behind after a snail dies. Also, finding a
shell is not a one time pursuit. Hermit crabs grow
larger throughout their lives, which means they need to trade
up for bigger shells, which can lead to very interesting
(20:14):
mass behaviors. More on that later. One thing the authors
of this overview point out is that the gastropod shell
filled by a hermit crab is not only a hard
surface to protect the soft part of the body, the
soft abdomen, it also forms a kind of shelter against
the external environment. Now what kind of shelter against the
(20:35):
environment would a hermit crab need. One example I recall
from some documentary footage I saw years ago, was the
idea that a hermit crab that's on land is under
the hot sun, and if it's got soft body parts
exposed outside of the shell, it could quickly sort of
bake and dry out without the shelter and moisture provided
by a shell.
Speaker 1 (20:55):
Yeah, absolutely, Yeah. There again, we have to keep in
mind that even they are terrestrial, they are linked inherently
to the ocean, and especially when you're dealing with tropical
heat environments. Yeah, they've they have to use that shell
also to protect themselves and carry around some moisture.
Speaker 3 (21:11):
So I think it makes sense to look at a
hermit crab's external shell in two different ways that both
have some truth to them. On one hand, you could
look at the external shell as an outsourced exoskeleton. It is,
you know, it's like doing the role that would normally
be done by the hard kiteness outer skeleton of a
(21:33):
true crab. But another way to think of it is
that it's like a portable burrow. And this is the
point that Brian Haslitt was making in that quote I
read earlier about the idea of mobile shelter. Lots of
animals find holes to hide in, and rocks or other
objects with recesses to provide a protective home. Hermit crabs
find protective recesses that can actually come along anywhere with them. Now,
(21:57):
I wanted to come back to the concept of ace symmetry,
which we already mentioned Rob, you brought it up earlier,
and it came up in the idea that there are
these different families of hermit crabs, the right handed hermit crabs,
the pagurady and the left handed hermit crabs. The diogeneity.
Speaker 1 (22:15):
Yeah, this is all very important because we think about
the asymmetry of the crab in this case, and this
lines up with the asymmetry of the shells that they
are probably going to be inhabiting.
Speaker 3 (22:28):
Right, So, one thing is that hermit crabs have a
directional curve in the abdomen. The abdomen can kind of
curl in a spiraling direction one way or the other.
But there's also an important difference in the size of
the claws. And from what I could tell, it was
the claw asymmetry that was primarily used to sort these
animals into the different families. One claw is often bigger
(22:52):
than the other in hermit crabs. Now, why would the
animals be asymmetrical in this way. Well, so, the gastropod
shells most often inhabited by hermit crabs also have right
handed or left handed spirals as you're saying, Rob, and
the abdomens are curled so that they fit into the
chiral shell. Meanwhile, one claw is often bigger than the other,
(23:14):
so it can function as what the authors call an operculum,
which in general means a structure that closes an opening
or an aperture, but in the context of gastropods like snails,
it has a specific meaning. A lot of snails are
able not only to retract the soft parts of their
(23:35):
bodies into their shells when threatened, they actually have a
movable hard plate that they can use to close the door,
essentially to block the opening of their shell behind them
after they retract, like a solid trap door. And this
is the snail's operculum. And the interesting thing is it
seems that hermit crabs evolved claw a symmetry at least
(23:59):
in part to fulfill the same function as the operculum
of the snails that formed the shells that the hermit
crabs take over after the snails die. So Brifa and
Moles right that a hermit crab can use its larger
claw to close off the aperture of its shell after
it retreats when threatened. And this connects to what you
(24:20):
were talking about seeing rob where the hermit crabs, you know,
they might flip over on their back and then cover
up the opening of the shell with one claw, maybe
the bigger claw.
Speaker 1 (24:30):
Yeah, exactly, Yeah, I got to see this happen so
many times. It's like, imagine some sort of futuristic crab
that has evolved to use abandoned human portagoons or you know,
portable toilets, like you say, at concert venues as its home,
and then it has eolved its larger pincher to be
(24:50):
the exact shape needed to serve as the door of
that portagon.
Speaker 3 (24:55):
I thought you were going to say it has evolved
a claw that can say either vacant in use. I
guess it would never want it to say vacant, so
it says in use on its claw.
Speaker 1 (25:04):
Yeah. I mean, and maybe it wants people to goe.
That's how you get mimics. That's exactly how to get mimics.
Speaker 3 (25:10):
So anyway, you end up with these asymmetries. You have
right handed and left handed hermit crabs, the Pagurids and
the diogenids, respectively. There are also what are known as
symmetrical hermit crabs called the pilocelids, which actually do unlike
the others. They have hardened exoskeletons on their abdomens, though
they do still hide in burrows like in recesses in
(25:33):
wood or rock that are thought to leave these burrows
to feed. So they're related animals, but they live somewhat
different lifestyles. Now we need to talk more about the
selection of shells among asymmetrical hermit crabs and how that
important biological need shapes hermit crab behavior and even what
(25:54):
you might call hermit crabs society. One thing you might
naturally wonder about with hermit crabs and the selection of shell,
is one shell as good as the next? You know,
is any shell just as good as another? And the
answer is no, not at all, in multiple ways. One
big factor is, of course size. A shell that is
too small or too large will greatly reduce a hermit
(26:17):
crab's fitness, and studies show that when a hermit crab's
shell is too small, for one thing, it just increases mortality.
Too small a shell means the hermit crab is more
likely to die, but it also has less room to grow,
and females with smaller shells produce fewer offspring. So it
is not good for a hermit crab to have too
(26:38):
small of a shell. However, it doesn't just want the
biggest shell possible, because if the shell is too big,
that increases the energy cost of carrying it. So you are,
you know, massively wasting a lot of energy lugging around
a shell that is heavy and too big for you.
It's kind of like, I don't know, being encumbered in
D and D or something. You know, you've got too
(27:00):
much of a load. This is harming your ability to
do everything else.
Speaker 1 (27:04):
Yeah.
Speaker 3 (27:04):
Absolutely, so finding a shell of just the right size
is crucial, and that right size will change throughout the
hermit crab's life as it grows.
Speaker 1 (27:16):
Yeah, so let's get into this a bit more, like
it's such an important aspect of the hermit crab, and
it's you know, it's the first thing we think about,
but it really defines almost everything about their social interaction.
And it's interesting to think about hermit crab society, or
at least you know that think of them as social
organisms because we call them hermit crabs, which is a
(27:37):
bit misleading because in human history and into sort of
common usage, what is a hermit hermit is someone who
withdraws from society and or civilization. So it might lead
you to believe that hermit crabs are also loners in
a certain sense. They are, but you know, that doesn't
mean that they don't have interactions with others of their kind.
In fact, they have a lot of interactions, and they're
(27:59):
very complex. So don't be too literal in thinking that
a hermit crab is an actual hermit, in the same
way that you wouldn't think that a king crab actually
rules over decapods or something.
Speaker 3 (28:10):
Right, and this hue is decrees.
Speaker 1 (28:11):
Yeah. Yeah. As Mark e. Elidra pointed out in an
article for Natural History Magazine back in I believe twenty nineteen,
hermit crabs live actually highly social lives, absolutely full of drama,
just way more drama than you'd expect your local human
hermit to have, I'd wager.
Speaker 3 (28:31):
Yeah, I mean, I guess unless hermits were like constantly
fighting one another to try to trade clothes.
Speaker 1 (28:37):
Yeah, or a pillar. You know, if you have your
your pillar, develloers, it'd be like, no, I want the
I want the taller pillar.
Speaker 3 (28:42):
Yeah, I'm gonna do exactly. I'm going to bang my
pillar on your pillar until you give me your pillar,
unless I decide I want my old pillar back.
Speaker 1 (28:51):
So the various dramas that they encounter and instigate, includes,
but is not limited to, according to Eldra, commotion of
social aggregations, intergenerational inheritance of homes, life or death, competitive struggles.
So the author points out that in contrast to a
(29:12):
lot of other social organisms you might think about, terrestrial
hermit crabs socialize with non relatives, and this is crazy
to think about. The reason, he points out, is that
while they spend most of their lives on land, we're
talking about terrestrial hermit crabs again, not the aquatic ones.
They spend most of their lives on land, but they
are born in the sea. That's where the larva larvae
(29:35):
are released. They become mixed in the ocean, and then
they land on far flung shores via the tides. So
I want to read this quote from Eldra. He says, quote,
By the time an immature crab first arrives on land,
it is therefore far away from any of its relatives,
encountering instead only an assortment of non kin. Moreover, because
(29:57):
the abundance of terrestrial hermit crabs on shore stretches of
beach often measures in the hundreds of thousands or even
the millions. Each crab is but a stranger within a
vast crowd.
Speaker 3 (30:08):
However, you know, if you think of a human analogy,
imagine a bunch of very selfish humans are thrown into
a mix of you know, they're all living together beside
one another, and not amongst their kin, just amongst strangers.
And you know, maybe imagine they're not very they're not
very nice people, they're not very inclined to be helpful
to others. They still might find reasons to hang out
(30:30):
around one another, even if they're mostly selfish. And one
of those reasons might be the need for trade or
an economy of sorts exactly.
Speaker 1 (30:38):
And what are they going to have an economy of
sorts about, Well, it's going to be the shell, of course.
I also like how this idea it kind of matches
up with the you know, the huge stereotype that one
encounters of big city life, particularly in movies from like
the seventies and I guess into the eighties as well,
Like nobody's related to each other in the city. You
go to the city, it's just everybody's for themselves. You're
(31:00):
gonna you're gonna lose your shell in that big city.
I guess it's kind of kind of that way with
the crabs here. But anyway, the shells that they use,
like you've been saying, yeah, these are scavenged from dead mollusks,
but this is also key. Uh, they have been remodeled.
These are remodeled homes. Elidra points out. Uh, the crabs
(31:20):
you when they have when they have a fresh shell
that is going to like this is okay, something has died,
as the snail has dyed, and now I'm going to
make this shell into a home. You can't just put
it on and wear it out. Uh no, No, you
need to use chemical secretions to weaken the shells calcium carbonate,
as well as additional physical sculpting via your appendages. You're
going to change the shell into something that absolutely suits
(31:44):
you and absolutely suits your purposes. Right.
Speaker 3 (31:47):
So this is another way in which one shell is
not necessarily as good as any other. Size matters a lot,
which is a sort of inherent feature of the shell,
but also the the remodeling condition of the shell matters
a lot. There are shells that have been recently renovated,
and that's much more desirable than a shell that is
a real fixer upper.
Speaker 1 (32:09):
Right, right, And this is unique to terrestrial hermit crabs,
and we'll get it more into why in a second.
But yeah, as Lighter points out, it's absolutely necessary for
terrestrial hermes because they can't depend on water buoyancy to
help them carry that shell around. It's just the basic
reality of living out of the water, and some of
(32:30):
these shells can be quite hefty for the crab, and
so by reducing the shell mass, they're lowering the energy
cost of just traveling across land, and they do a
lot of traveling. Additionally, shell remodeling increases the internal space
in the shell, allowing not only more room for the crab,
but more room for increased water reserves to keep the
organism from drying out. Like we mentioned earlier, the importance
(32:51):
of this being a way to help them sustain themselves
when they are living times in very hot environments. He
also points out that while aquatic hermit crabs would conceivably
benefit from shell remodeling as well, because you know, even
though you have buoyancy, lighter shells could still be a benefit, right,
more internal space could still be a benefit. However, aquatic
(33:14):
hermit crabs have to contend with shell expert predators in
the ocean, organisms that are highly evolved to bypass shell protections. Therefore,
it would be a mistake to sacrifice any of your
shell's protection in order to get any of these benefits. Meanwhile,
on land, the terrestrial hermit crabs have far fewer shell
(33:37):
specialists to contend with, and lighter points to various research
that shown that like your average predator that would be
messing with a hermit crab is just not going to
have like the bite power or the not going to
have the tools necessary to crack open even a partially degraded,
a partially remodeled hermit crab chosen shell. Now, Joe I
(33:59):
included a photo. This is from Lydra's paper and an
example of an unmodified versus a modified shell. The central
axis is often removed, but the shell again retains protection
against the bite strength of terrestrial predators.
Speaker 3 (34:14):
Yeah, and one thing you can see in this picture
is that a lot of the effort in the remodeling
seems to be focused on the interior of the shells,
sort of like expanding the interior cavity and making more
room there and smoothing it out.
Speaker 1 (34:27):
Yeah, and certainly, you know, removing some of the additional
protection of the shell. But again it's apparently not going
to matter for terrestrial variants now. Like we said, one
of the huge factors in hermit crab societies is of
(34:49):
course the need for these shells and the fact that
as the crab grows and molts, they'll need to abandon
smaller shells in favor of larger shells. And as Lidra
points out, there's some really interesting about all of this quote.
Over time, remodeled shells have come to dominate the housing
market of terrestrial hermit crabs. Exhaustively sampling these housing markets,
(35:12):
I have found few unremodeled shells, and also few shells
that are still in the process of being remodeled. Most
shells have already been completely remodeled. Remodeled shells present a
superior home, and as with any superior resource, it is
understandable that terrestrial hermit crabs should prefer remodeled shells over
unremodeled shells. However, over evolutionary time, a mere preference has
(35:37):
transformed into an absolute dependence. As remodeled shells accumulated, terrestrial
hermit crabs came to specialize in living in them, to
the point that life in unremodeled shells became nearly impossible.
My field experiments revealed that after an early life stage,
most terrestrial hermit crabs cannot survive in unremodeled shells for
(35:58):
even a single day.
Speaker 3 (36:00):
Wow, Okay, I did not realize that.
Speaker 1 (36:03):
Yeah, yeah, because you know what's the current hermit crab
to do? If you need a shell, Well, you could
remodel your own shell technically, but most crabs simply can't
do this anymore, in large part because they end up
too big to access the inner parts of a fresh shell.
So only the smallest immature hermit crabs actually can get
in there and do this, which paradoxically often means that
(36:23):
they're left with oversized shells. But as such, all terrestrial
hermit crab individuals highly prefer a remodeled shell over a
fresh one. Even if they can fit inside that fresh
shell and conceivably remodel it and make it their own,
remodeling the shell is still a last resort. Ledra stresses
that this is this is the only factor that ensures
(36:46):
the continued creation of remodeled shells. That some hermit crabs
are going to be put in a position where they
have no choice, wow, because I mean they can do
other things to it should not like a hermit crab
is left without any thing and there, and we'll touch
on how this occurs. In a moment. They may use
something like a bottle cap and that might buy them
(37:06):
a little time, but they need a shell. The thing is,
you don't just find many emptied remodeled shells. He points
out that on a given beach, the only empty remodeled
shells you're likely to find are the ones that have
been physically compromised in one way or another, so like
they're they're broken, they don't actually protect the hermit crab anymore,
(37:28):
or they're clogged with a rock something like that, they're
no longer functional. The competition for remodeled shells is intense,
and they're just you're just not going to As a
hermit crab, you are not going to find them out
there unless you're extremely lucky. As such, hermit crabs have
to remain vigilant at all times, always looking out for
a bigger shell, because either you need one or you're
(37:49):
about to need one, so you need to always be looking.
And also you have to be peeking over your shoulder
because there's probably someone eyeing your shell, that is looking
for a slightly bigger shell, and they're trying to decide
if it's worth trying to take it from you.
Speaker 3 (38:04):
Right, So this leads to the fact that hermit crabs
very often get into well, I guess there's some debate
over how exactly to characterize these encounters, whether they are
purely agonistic fights, or whether you might consider them in
some way a kind of trade or negotiation. Maybe we
can talk about that some more in the next episode.
(38:26):
But they get into these encounters that lead to shell swapping.
Speaker 1 (38:31):
Yeah, they're at the very least aggressive negotiations. Yeah, but
so I'll continue to categorize them as battles. But yeah,
give with that caveat in mind. Basically, what seems to
be happening is one crab will attempt to flip the
other on its back and force its opponent out of
their shell. But as Lijra points out, this kind of
(38:53):
thing can last hours and it might just end in
a stalemate. It might just end in everyone just going
home or carrying on with the shell they had two
hours ago. And that alone, I think that's pretty fascinating.
Most animal competitions and struggles are fascinating, but it's the
onlookers that make this even more interesting. Leider writes, quote.
(39:15):
As bystanders gather at the site, and as the moment
of evictioneers order emerges out of the chaos of commotion
in the aggregation, the crabs array themselves literally into a line,
each holding the shell of the crab ahead of it.
This social formation emanates from the pair of antagonists, with
(39:35):
the line of crabs there after being size ordered from
biggest to smallest unquote. Because if a crab is forced
to give up its shell, the winner will leave its shell,
and this will set off what's called a vacancy chain.
All of the onlookers will have a shot at leveling
up their current shell situation to a new one that
(39:57):
is slightly bigger.
Speaker 3 (39:58):
You can find video of this online. By the way,
there are multiple documentaries that have captured versions of this,
and it's amazing to see they literally do just organize
themselves in a size ordered line where they're each grasping
the shell of the slightly bigger one, like feeling around
on it, trying to make sure that it's what they want.
(40:19):
Because the whole process, by the way of in which
Hermit crabs assess a shell for the qualities they want
is interesting on its own. There seem to be some
visual processes going on. They you know, look at a
shell to assess from a distance whether it's something they
would want. But that's never enough. They have to inspect
it physically. They like feel all over it with their
(40:40):
antennae and their chelly, you know, the claws and the legs.
And then usually they will want to sort of like
dip into it with their legs and maybe they're abdomen
to see if they fit right, and they may end
up changing their mind and wanting to go back to
the previous shell, though obviously that could be a tricky
thing if a bencha, Yeah, hermit crabs are lined up
(41:02):
all trying to level up at the same time. It
is an amazing thing to see.
Speaker 1 (41:07):
Yeah, to your point about like sizing up the shell,
trying it on. Like, sometimes you have a situation where
you remember the asymmetry of shells and hermit crabs here,
and sometimes you have a you have like a like
what a left handed crab trying to get into a
right handed shell or vice versa, And and that's going
(41:27):
to be a situation where the crab is going to
quickly realize this does not fit, this is not the
shell I want to live. We may come back with
more details on that regarding the left right handedness and
hermit crabs and shells. Now, Elidra again points out that
all this competition is based again not on kinship, but
on selfishness and competition. And he has this wonderful part
(41:52):
in the paper where he says that it's what's kind
of the antithesis of something like a US social ant,
you know, where all the ants and a call in
the ark, and they work together to ensure the success
of the colony, the success of their genetic line. But
that is not the case with the hermit crab. And
Leidra writes the following quote. If in an alternative world,
(42:13):
interactions in terrestrial hermit crabs were among close kin rather
than strangers, then the crabs social lives might be different,
with individuals potentially being more interested in bequeathing their finest
shell to a close relative than in stealing the coveted
shell of a stranger. Now, there have been plenty of
(42:33):
other researchers and also science journalists and writers and so
forth that have commented on all of this. Elizabeth Preston
wrote all about this topic for The New York Times
in twenty nineteen in an article titled, even hermit crabs
have wealth inequality. This was based on a twenty twenty study.
This is because the New York Times paper came out
(42:55):
a month before the twenty twenty study. This was in
a December publication, so that's why the dates would seem
to be in the wrong order here. But that particular
paper was a comparison of wealth inequality in humans and
non humans by Chase at all. This was a study that,
as I recall, received a fair amount of mainstream attention
at the time because, of course, wealth inequality is always
(43:17):
a topic of interest among human beings, and crabs are
inherently interesting. You can throw hermit crabs into any study
and it's going to be fascinating, even if there's not
really connective tissue there.
Speaker 3 (43:30):
Well, is there connective tissue here?
Speaker 1 (43:32):
To a certain extent, it seems to okay, I mean so,
in the study, Chase and his co authors gathered around
three hundred hermit crabs on Long Island Beach and took
away all their shells, which, okay for science, I will
allow this, but you know, obviously I can't help it
sympathize because this is literally all these crabs care about.
The researchers weighed and measured the various shells, and then
(43:54):
they considered how they were distributed across the sample population
of hermit crab. And this is a quote here from
that article by Preston quote. The distribution curve they found
peaked around medium sized shells, then dropped as the shells
got larger, before tapering off very gradually through the largest
shells of all this matches the shape of wealth distribution
(44:17):
curves in many human societies, so it's interesting. But at
the same time, the New York Times article of citing
anthropologists Monique Molder, points out that we shouldn't get two
carried away comparing hermit crabs to humans in this scenario, because,
first of all, there are plenty of other factors involved
in human inequality. You know, it's one of those it's
(44:37):
often described as a wicked problem. You know, it's complex
enough that you can't just point to necessarily there are
certainly large factors, but there are multiple factors. And Molder here,
who again as an anthropologist, speculated that vacancy chains are
probably also not the only factor in terrestrial hermit crabs
as well. I mean, you know, there are other factors
as well into how they are dealing with each other,
(44:59):
even on the the basis of their shells. Still, you know,
we can't help but compare ourselves to the hermit crabs. Again,
part of it is just that hermit crabs are that interesting,
and we as human beings are that self absorbed. What
we can't help but see ourselves in the crabs. We
can help what anthropomorphize the crabs, and you know, especially
when we see them, you know, in a very complex fashion,
(45:19):
struggle over limited resources like this. That again, I think
if you're just casually aware of hermit crabs, you might
not realize that just any shell, it's not a situation
where any shell will do, and it is a situation
where the shells have been augmented, and therefore it's competition
not just for random garbage left over by dead snails,
(45:43):
it's competition for mostly previously augmented shells, like the products
of a hermit crab civilization, if you will.
Speaker 3 (45:52):
Well, that's funny if you think of it as like
more fighting over fighting over a limited pool of finished
goods rather than creating new goods. It's almost like a
human post apocalyptic scenario exactly. Yeah, it's kind of mad Max.
Speaker 1 (46:08):
It's kind of Fallout right. It reminds me that in
at least some of the Fallout games you do encounter
a giant hermit crab that is using what some sort
of like a bus or something like a school bus
for it's uh, it's abdomen. I can't remember offhand, but
I remember when I would when I would play the
most recent Fallout game, I would occasionally encounter that that
creature and yeah, yeah, I mean it's it's it's interesting.
(46:30):
Where are they getting all these school buses? What are
they changing about? I guess they're taking all the seats out?
Speaker 3 (46:35):
Yeah, is it a right handed bus or a left
handed bus?
Speaker 1 (46:39):
I don't know. Yeah, And are they sizing up from
different buses? Like they start with a like a shorter bus,
then they go to a full sized school bus, and
they're going to like a megabus. Then it's a double
decker bus. Those are only that's only in Fallout London propertly,
But you know, uh, you could go wild with with
the scenario.
Speaker 3 (46:57):
Well, hey, we've got more hermit crab stuff to talk about,
So join us again next time.
Speaker 1 (47:02):
That's right, we have some more content lined up regarding
the hermit crabs. We're going to fish around for a
bit more. Because I'm a hermit crabs. There's a lot
of research out there. That's one of the reasons I
felt pretty secure in going in and discussing them again,
even though we've discussed them in the past, because there's
constantly new hermit crab research coming out and there are
some remaining mysteries and controversies about hermit crabs. So we'll
(47:26):
get into all of that in the next episode. In
the meantime, we'll remind you that Stuff to Blow Your
Mind is a science podcast with core episodes on Tuesdays
and Thursdays. That's the main event. You can also tune
in for a short episode on Wednesday, a listener mail
episode on Mondays, and on Fridays. We set aside most
serious concern to just talk about a weird movie on
(47:46):
Weird House Cinema. If you listen to us on Apple
or an Apple device, what have you going in and
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the drum about this in a while, but hey, if
(48:07):
you haven't rated and reviewed the show before, why didn't
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That also helps us out in the long run.
Speaker 3 (48:16):
Huge thanks as always to our excellent audio producer JJ Posway.
If you would like to get in touch with us
with feedback on this episode or any other, to suggest
a topic for the future, or just to say hello,
you can email us at contact at stuff to Blow
your Mind dot com.
Speaker 2 (48:38):
Stuff to Blow Your Mind is production of iHeartRadio. For
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Apple Podcasts, or wherever you're listening to your favorite shows.
Speaker 1 (49:02):
Have not the pocop
Hey, welcome to Stuff to Blow your Mind. This is
Robert Lamb. Today is Saturday, of course, so I have
a vault episode for you. And oh, this one published
a year ago this very day. This published on one
four twenty four. It is part one in our series
on the Hermit Crab. I hope you enjoy.
Speaker 2 (00:26):
Welcome to Stuff to Blow Your Mind, a production of iHeartRadio.
Speaker 1 (00:36):
Hey, welcome to Stuff to Blow your Mind. My name
is Robert.
Speaker 3 (00:39):
Lamb and my name is Joe McCormick. And we're back
after the holidays. All right, I guess you've already been back, Rob,
I'm back for the first time.
Speaker 1 (00:46):
Now, Yeah, that's right. I left a little early and
then and then I came back to you know, scrambled
together a few episodes. But now it's time to return
proper with a true core episode of Stuff Below Your Mind.
But we're ringing in the new year once more with crabs,
because of course, crab content is suitable for any holiday,
(01:08):
and there is an abundance of it, you know.
Speaker 3 (01:11):
I don't know if it's just the name of Christmas
Island that created this correlation, but I think we tend
to do crab content in the winter have you noticed
that that's not on purpose, at least not on my part.
Speaker 1 (01:23):
No, this is great. I think the Christmas Island crab
thing kicked it off a bit a while back. That's
part of it. For sure. There's something maybe holiday centric
about crabs. It also helps that sometimes my family and
I travel during the winter break and go somewhere where
crabs are abundant. And yeah, I'm excited to talk about
(01:45):
crabs once more because over the holidays, my family and
I were fortunate enough to once more visit Glover's Reef,
a partially submerged atoll located off the southern coast of Belize.
Tremendous fun. We stayed on a small island all week.
There were other human certainly, but we spend as much
time as possible getting into the water to snorkel to
check out the fish and the coral. But the predominant
(02:07):
land organism was, without a doubt, the terrestrial hermit crab.
Speaker 3 (02:12):
So this is a holiday with crabs underfoot.
Speaker 1 (02:14):
Yes, I mean, I don't think anyone ever stepped on one,
but they were everywhere. Most hermit crab species are aquatic,
as we'll probably touch on several times during this episode.
But I'm going to be talking mostly about the terrestrial variants,
like those that I encountered on this island, that still
depend on the ocean for reproduction, but which live most
(02:36):
of their lives on land, and that comes with various
complications and innovations. And also they're very visible. You know,
you don't need a snorkel, you don't need a dive
suit to engage with the world of the hermit crab
because on places like this they are everywhere and they
are widespread. You don't also don't have to go to
(02:56):
Belize to encounter hermit crabs, terrestrial hermit crabs, even they
are out there.
Speaker 3 (03:01):
So roughly, how big were or how big was the
range of the ones you were seeing? Is are we
talking like silver dollar size or hand size? Like what
are we dealing with here?
Speaker 1 (03:12):
Yeah? The size differential is one of the things that
makes hermit crab watching in the wild so fun because
you never know exactly what size you're gonna encounter. Like
some of the very small ones, you know, oh so cute,
it's the size of a dime or something, you know,
it's very small. But other times it'll be like I'm
probably exaggerating to save the size of a catcher's met
but at least the size of a very large fist,
(03:34):
you know, just a just a big chonker of a
hermit crab. And as you're going, as we were going
about on the little pathways on the island, you know,
they would be moving around pretty much all the time.
That they're very busy. They're constantly trooping about, they're scavenging,
they're competing for shells. Though I don't think we ever
directly observed this, but clearly it is happening. And if
(03:57):
you come across one while it's say, crossing the sand path,
they'll suddenly stop, and then if you get a little
bit closer, they'll retreat into their shells, and as they
do that, that'll cause them to roll over onto their back,
and then of course they cap the shell opening with
their larger claw and then give them enough time and
then get back up and they continue on with their business.
Speaker 3 (04:16):
Mm hmm.
Speaker 1 (04:17):
So yeah, there's just something magical about her crabs, at
least to someone like me who doesn't get to observe
them all the time. But even the team on the
island here, they seem to find a certain amount of
joy in the creatures, despite how accustomed they were to
their presence. I heard that one of the cooks brought
some shells for the crabs with her from the mainland,
(04:38):
with the names of each of her children written on them,
and then and then would enjoy like running into various
crabs who would claim these shells and make them their homes.
Speaker 3 (04:48):
Oh, that's funny. So like when people write funny things
on a dollar, you know, it's like, are you expecting
to encounter this again?
Speaker 1 (04:55):
Yeah? Yeah, And yeah. There's just something they're like a
little like io machines, you know. There's just something about
how industrious and relentless they are as they scavenge the terrain.
For instance, at this place that we were staying, this
a place called Off the Wall. The communal dining area
at the place has a sand floor, and Jim and Kindre,
(05:17):
who run the place, told us that first thing in
the morning, when you go in there, the sand is
completely devoid of human footprints because during the night the
crabs have come, the hermit crabs have come, and so
in the morning they are only crab tracks, and not
even the slightest crumb left behind, because they have come
and claimed everything.
Speaker 3 (05:36):
Crab wipe.
Speaker 1 (05:37):
Yeah, so I love it. After experiencing all that, I
was like, well, we've got to find some more things
to talk about with hermit crabs. We've talked about them before,
but now we're going to go in a little more depth.
Speaker 3 (05:48):
Well, it turns out I think hermit crabs are very
interesting and there is a lot we can talk about.
So I guess we will start with the basics. What
are hermit crabs? Are hermit crabs crab? The answer is
sort of. Hermit crabs are decapod crustaceans that means decapod.
They're ten legged invertebrates with a hard exoskeleton that grow
(06:11):
by molting, so they shed their old exoskeleton and emerge soft,
and then a new exoskeleton hardens when they need to
get bigger when they grow bigger. But they are considered
distinct from what are called true crabs. True crabs belong
to the infraorder Brachyuria. Hermit crabs belong to the related
infraorder animura a n O m U r A. They're
(06:34):
close cousins to true crabs, but different. Other animurins or
false crabs include the lithodoidea or the king crabs. And
the Porcelinidae, which are the porcelain crabs. And one thing
animurins generally have in common is that. Okay, so these
decapods all have five pairs of legs ten legs total,
(06:56):
and in the animurans, the last pair of legs farthest
away from the head is fun sized. So these animals
are still decapods, but a lot of them look like
they have only eight legs instead of ten, or maybe
six legs and two claws. Those front legs, the chelli
or the claws are legs, but in crabs they're often
(07:17):
claw shaped, but they look like they have only eight
legs instead of ten because the hindmost pair is tiny
and often hidden or tucked away under another body part.
Speaker 1 (07:28):
Yeah, and we'll get back to this particular detail later
on in our discussion. If not this episode, then perhaps
the second episode.
Speaker 3 (07:35):
So animurans have ten legs, a lot of times it
looks like they only have.
Speaker 1 (07:39):
Eight.
Speaker 3 (07:40):
Hermit crabs belong in the taxonomic superfamily Pagurroidea, and with
a few exceptions, they are mostly notable for exactly what
you're thinking of their dependence on externally scavenged material for
armor and shelter. Usually this armor is a shell that
once belonged to a gastropod, such as a snail, a periwinkle,
(08:04):
or a whelk, though there are some animals in the
family that don't need scavin shelter at all. We can
talk about those in a minute, and there are a
few that rely on things other than mollusk shells. One
example cited in a paper that I'll get to in
a minute is the discorso Pagurus schmitti, which takes up
shelter not in a gastropod shell, but in empty polyheat
(08:27):
worm tubes. The hermit crabs that do rely on external
mollusk shells have bodies that are actually shaped by this need.
So while true crabs have hard exoskeletons covering their entire bodies,
hermit crabs have what you might call non calcified abdomens.
(08:48):
So the front facing part of a hermit crab's body
the head, the thorax, and the front pairs of legs
and claws. These all have hard exoskeletal coating like any
other crab, but the part of the hermit crab the
abdomen in what you might call the tail or the Telson.
This doesn't really resemble a crab body at all in
(09:09):
a lot of species. It looks kind of like a
curly fat worm, and it does not have a hard exoskeleton.
The abdomen is flexible, soft and vulnerable. It is covered
in an external coating, but it's just very thin and soft.
It's very uncrab. This is the part of a hermit
crab that curls up inside the externally sourced shell.
Speaker 1 (09:33):
Yeah, so if you're just encountering hermit crabs out in
the wild, or even seeing them in a an enclosure somewhere,
you're probably not going to see this part of the
organism with its abdomen inside the shell. As we've been discussing,
it actually walks on its second or in third pairs
of legs. The first pairs are modified to form pinchers,
(09:54):
and its fourth and fifth pairs of legs are small
and specialized to grip the inside of the shell. It
also has appendages called europods at the end of its
abdomen to aid and securing that shell. So, you know,
all these things aiding to sort of grip and hold
on to that shell that it has taken on as
its shelter. The larger left europod hooks the central post
(10:17):
of a shell, and they can also use this europod
to hold on to other things when they are out
of the shell, Like I've read about how they can
attach to say like a tree or something, and it
can also use it to maintain balance.
Speaker 3 (10:30):
Yeah, so I think it's interesting that the hermit crab
is an animal. Its body is shaped in for double purpose.
So the front end of it is shaped for facing
the external world. It has the chelly, it has the
claws like many other crabs you would think of, but
the back end of it is shaped entirely for holding
(10:50):
on to this piece of mobile shelter. And the concept
of mobile shelter, while not completely unique, is pretty unique.
What makes the hermit crab interesting To read a quote
from a highly cited paper on hermit crabs that I
was looking at by a biologist named Brian Hazlet. The
paper is called the Behavioral Ecology of Hermit Crabs. Haslet writes, quote,
(11:14):
Many animals utilize exogenous shelters, but almost all eight hundred
species of hermit crabs are mobile while sheltered, the combination
of mobility and protection afforded by this lifestyle must contribute
to the large numbers of these crustaceans found in virtually
all marine environments as well as in tropical terrestrial shores.
(11:38):
So Hazlit is sort of saying the hermit crab plan
is a successful plan, clearly shown by the diversity of
these species found all around the world. That this is
a plan that works because sourcing shelter from outside the
body that you can take with you when you move
works really well. But it also comes with costs, and
(12:02):
we'll talk about those costs as we go on. One
thing I think to understand is that in general, while
a hermit crab can leave its externally acquired shell and
it can survive for some time outside of its external shell,
the acquisition of a shell for external armor is not
optional for a hermit crab. It's not like a nice
(12:24):
to have. It is essential for survival in the wild,
and the hermit crab's evolution has been shaped by the
need for these externally sourced shells.
Speaker 1 (12:35):
Yeah. Yeah, this is not just somewhere it goes to
sleep at night like. It has to have this with it,
and if it does not have the shell, then it
is highly vulnerable to predation. Exposure. It very well likely
will not survive without it.
Speaker 3 (12:48):
Right, So I want to turn to a paper I
was reading for a general overview of hermit crabs and
related species. This was an overview published in the journal
Current Biology called the Hermit Crabs by Mark Brifa and
Sophie L. Moles in two thousand and eight. And they're
going to pat the picture here of the kind of
hermit crab family tree. So there are currently more than
(13:12):
eight hundred known species of hermit crabs. Most of these
species live in the ocean their marine, with a few exceptions.
One is a species called Clibinarius fontic cola, and this
is the only known freshwater hermit crab which lives in Vanuatu,
that's a volcanic archipelago in the Pacific. And there are
(13:36):
other freshwater and amurans, but they are not hermit crabs.
So this is the one freshwater hermit crab out there.
Speaker 1 (13:43):
I should throw in that the hermit crabs that we
were observing in the wild, I believe are the Caribbean
hermit crab, and this is a variety that's common to
the West Atlantic, Belize, Southern Florida, Venezuela, and the West Indies.
Speaker 3 (13:57):
Yes, and the ones you were observing you were saying
were terrestrial or semi terrestrial, right, they spend a lot
of time on land.
Speaker 1 (14:03):
Yeah, these were land boys. We did see one variety
and I didn't identify this one one variety of aquatic
hermit crab out law snorkeling. But yes, the ones that
I'm mostly talking about here are hermit crabs of terrestrial
hermit crabs.
Speaker 3 (14:18):
So there are about a dozen species of land dwelling
or semi land dwelling hermit crab descendants in a family
called Sinobotids. This family includes one famous species that has
shed its need for an externally acquired shell altogether, and
that is the coconut crab or robber crab. We've talked
(14:38):
extensively about these before, but the coconut crab is the
largest land dwelling invertebrate in the world. I can have
a leg span of up to one meter and can
weigh almost five kilograms or about ten pounds. They live
mostly in coastal areas throughout the Indian and Pacific oceans.
I think we talked a good bit about coconut crabs
in our series on the Christmas Island crabs that we
(15:01):
did several years back. This was the the animal where
we were talking about the field notes of Darwin from
the Voyage of the Beagle, where he's like, you know,
they make really good eat and you boil the fat
under their tail and it makes a quart bottle of
limpid oil. And then he also tells a story about
how they like locked one inside of a biscuit tin
(15:21):
with wire and using its claws it was able to
essentially like rip the tin out and escape the box.
Speaker 1 (15:28):
Oh man, there's a whole horror movie for you right there. Yeah,
it would be Charles Darwin and crew on the Beagle
having to fight off the killer coconut crab.
Speaker 3 (15:37):
They come and they just find the empty box. They're like,
it's loose. No one knows where, you know, as long
as we're throwing around.
Speaker 1 (15:46):
Charles Darwin quotes there's another place in the Voyage of
the Beagle where he mentions hermit crabs. This is not
a particularly insightful quote. It's just a mention, but I
still had to drag it out. Quote. In every part
art one meets hermit crabs of more than one species,
carrying on their backs the shells which they have stolen
(16:06):
from the neighboring beach stolen. And yes, there is a
fair amount of shell theft as we'll get into. As
long as you're thrown around quotes unrelated, I want to
throw in this quote from Aristotle from the History of Animals.
Speaker 3 (16:20):
Is he going to tell us where they come from?
Speaker 1 (16:22):
Yes? Yes, you will reveal the at the time, you know.
Non controversial hypothesis on crab origins quote. The hermit crab
grows spontaneously out of soil and slime and finds its
way into untenanted shells. As it grows, it shifts to
a larger shell, as for instance, into the shell of
the neartes, or of the strombus or the like, and
(16:46):
very often into the shell of the small cirrix. After
entering a new shell, it carries it about and begins
again to feed, and by and by, as it grows
it shifts again into another larger one.
Speaker 3 (16:58):
Okay, I give Aristotle half credit on this. I think
he's a bit wrong on the spontaneous generation out of
slime and soil, but he correctly observes the shell shifting
behavior of hermit crabs, which is a major feature of
hermit crabs society that we'll have to talk about later
in the episode.
Speaker 1 (17:19):
Yeah, he's absolutely wrong on spontaneous generation. We don't ever
really have to drive that home. But in a weird way,
like in a very general way, the idea of like
matter becomes crabs, nature becomes crabs. Maybe not that far off,
as we'll discuss later on.
Speaker 3 (17:36):
But apart from the coconut crab, there are various other
species of hermit crab that live basically would live their
adult lives on land, though they still usually live out
part of their life cycle in the water, with females
releasing larvae into the sea, and apart from these exceptions,
hermit crabs are marine species.
Speaker 1 (17:56):
Absolutely. We'll come back to some of the ramifications of
this in a bit now.
Speaker 3 (18:09):
According to Brifa and Moles, there are five families of
hermit crabs, and it breaks down like this. You've got pagurity,
which are the right handed hermit crabs, and you've got diogeneity,
which are the left handed hermit crabs right handed, left handed,
What does that mean? We'll come back to that. Then
you've got cenobitity, which are the land hermit crabs. You've
(18:31):
got parapagurity, which are the deep sea hermit crabs, and
you've got pilochelady, which are symmetrical hermit crabs. Though the
more than eight hundred species of hermit crabs display different
local adaptations and behaviors, for the most part, it seems
like hermit crabs take what you can get foragers, which
(18:53):
is true of many true crabs as well, But hermit crabs,
for the most part, they will eat bits of dead
organic matter, both animal and vegetable. They will eat live
prey when they can catch it. Like true crabs, most
hermit crabs are not very picky about food. Whatever they
can get in their mouth, they're probably gonna eat.
Speaker 1 (19:12):
Yeah. Yeah. Both times that I was in believes there
was a lot of fun to be had, especially with
the kids, of leaving something out for them with permission
of course, like I'm talking about the like like a
cracked coconut, and then seeing the hermit crabs eventually swarm
over the material.
Speaker 3 (19:30):
So while foraging for food is of course essential for survival,
so is foraging for shelter. We will have more to
say about this as we go on, but obviously a
huge part of the hermit crab's survival revolves around acquiring
a good shell to live in, and the majority of
these shells come from As we've said, mollusks like snails,
(19:52):
but hermit crabs don't have to fight the snail for
its shell. They generally move into the shell that is
left behind behind after a snail dies. Also, finding a
shell is not a one time pursuit. Hermit crabs grow
larger throughout their lives, which means they need to trade
up for bigger shells, which can lead to very interesting
(20:14):
mass behaviors. More on that later. One thing the authors
of this overview point out is that the gastropod shell
filled by a hermit crab is not only a hard
surface to protect the soft part of the body, the
soft abdomen, it also forms a kind of shelter against
the external environment. Now what kind of shelter against the
(20:35):
environment would a hermit crab need. One example I recall
from some documentary footage I saw years ago, was the
idea that a hermit crab that's on land is under
the hot sun, and if it's got soft body parts
exposed outside of the shell, it could quickly sort of
bake and dry out without the shelter and moisture provided
by a shell.
Speaker 1 (20:55):
Yeah, absolutely, Yeah. There again, we have to keep in
mind that even they are terrestrial, they are linked inherently
to the ocean, and especially when you're dealing with tropical
heat environments. Yeah, they've they have to use that shell
also to protect themselves and carry around some moisture.
Speaker 3 (21:11):
So I think it makes sense to look at a
hermit crab's external shell in two different ways that both
have some truth to them. On one hand, you could
look at the external shell as an outsourced exoskeleton. It is,
you know, it's like doing the role that would normally
be done by the hard kiteness outer skeleton of a
(21:33):
true crab. But another way to think of it is
that it's like a portable burrow. And this is the
point that Brian Haslitt was making in that quote I
read earlier about the idea of mobile shelter. Lots of
animals find holes to hide in, and rocks or other
objects with recesses to provide a protective home. Hermit crabs
find protective recesses that can actually come along anywhere with them. Now,
(21:57):
I wanted to come back to the concept of ace symmetry,
which we already mentioned Rob, you brought it up earlier,
and it came up in the idea that there are
these different families of hermit crabs, the right handed hermit crabs,
the pagurady and the left handed hermit crabs. The diogeneity.
Speaker 1 (22:15):
Yeah, this is all very important because we think about
the asymmetry of the crab in this case, and this
lines up with the asymmetry of the shells that they
are probably going to be inhabiting.
Speaker 3 (22:28):
Right, So, one thing is that hermit crabs have a
directional curve in the abdomen. The abdomen can kind of
curl in a spiraling direction one way or the other.
But there's also an important difference in the size of
the claws. And from what I could tell, it was
the claw asymmetry that was primarily used to sort these
animals into the different families. One claw is often bigger
(22:52):
than the other in hermit crabs. Now, why would the
animals be asymmetrical in this way. Well, so, the gastropod
shells most often inhabited by hermit crabs also have right
handed or left handed spirals as you're saying, Rob, and
the abdomens are curled so that they fit into the
chiral shell. Meanwhile, one claw is often bigger than the other,
(23:14):
so it can function as what the authors call an operculum,
which in general means a structure that closes an opening
or an aperture, but in the context of gastropods like snails,
it has a specific meaning. A lot of snails are
able not only to retract the soft parts of their
(23:35):
bodies into their shells when threatened, they actually have a
movable hard plate that they can use to close the door,
essentially to block the opening of their shell behind them
after they retract, like a solid trap door. And this
is the snail's operculum. And the interesting thing is it
seems that hermit crabs evolved claw a symmetry at least
(23:59):
in part to fulfill the same function as the operculum
of the snails that formed the shells that the hermit
crabs take over after the snails die. So Brifa and
Moles right that a hermit crab can use its larger
claw to close off the aperture of its shell after
it retreats when threatened. And this connects to what you
(24:20):
were talking about seeing rob where the hermit crabs, you know,
they might flip over on their back and then cover
up the opening of the shell with one claw, maybe
the bigger claw.
Speaker 1 (24:30):
Yeah, exactly, Yeah, I got to see this happen so
many times. It's like, imagine some sort of futuristic crab
that has evolved to use abandoned human portagoons or you know,
portable toilets, like you say, at concert venues as its home,
and then it has eolved its larger pincher to be
(24:50):
the exact shape needed to serve as the door of
that portagon.
Speaker 3 (24:55):
I thought you were going to say it has evolved
a claw that can say either vacant in use. I
guess it would never want it to say vacant, so
it says in use on its claw.
Speaker 1 (25:04):
Yeah. I mean, and maybe it wants people to goe.
That's how you get mimics. That's exactly how to get mimics.
Speaker 3 (25:10):
So anyway, you end up with these asymmetries. You have
right handed and left handed hermit crabs, the Pagurids and
the diogenids, respectively. There are also what are known as
symmetrical hermit crabs called the pilocelids, which actually do unlike
the others. They have hardened exoskeletons on their abdomens, though
they do still hide in burrows like in recesses in
(25:33):
wood or rock that are thought to leave these burrows
to feed. So they're related animals, but they live somewhat
different lifestyles. Now we need to talk more about the
selection of shells among asymmetrical hermit crabs and how that
important biological need shapes hermit crab behavior and even what
(25:54):
you might call hermit crabs society. One thing you might
naturally wonder about with hermit crabs and the selection of shell,
is one shell as good as the next? You know,
is any shell just as good as another? And the
answer is no, not at all, in multiple ways. One
big factor is, of course size. A shell that is
too small or too large will greatly reduce a hermit
(26:17):
crab's fitness, and studies show that when a hermit crab's
shell is too small, for one thing, it just increases mortality.
Too small a shell means the hermit crab is more
likely to die, but it also has less room to grow,
and females with smaller shells produce fewer offspring. So it
is not good for a hermit crab to have too
(26:38):
small of a shell. However, it doesn't just want the
biggest shell possible, because if the shell is too big,
that increases the energy cost of carrying it. So you are,
you know, massively wasting a lot of energy lugging around
a shell that is heavy and too big for you.
It's kind of like, I don't know, being encumbered in
D and D or something. You know, you've got too
(27:00):
much of a load. This is harming your ability to
do everything else.
Speaker 1 (27:04):
Yeah.
Speaker 3 (27:04):
Absolutely, so finding a shell of just the right size
is crucial, and that right size will change throughout the
hermit crab's life as it grows.
Speaker 1 (27:16):
Yeah, so let's get into this a bit more, like
it's such an important aspect of the hermit crab, and
it's you know, it's the first thing we think about,
but it really defines almost everything about their social interaction.
And it's interesting to think about hermit crab society, or
at least you know that think of them as social
organisms because we call them hermit crabs, which is a
(27:37):
bit misleading because in human history and into sort of
common usage, what is a hermit hermit is someone who
withdraws from society and or civilization. So it might lead
you to believe that hermit crabs are also loners in
a certain sense. They are, but you know, that doesn't
mean that they don't have interactions with others of their kind.
In fact, they have a lot of interactions, and they're
(27:59):
very complex. So don't be too literal in thinking that
a hermit crab is an actual hermit, in the same
way that you wouldn't think that a king crab actually
rules over decapods or something.
Speaker 3 (28:10):
Right, and this hue is decrees.
Speaker 1 (28:11):
Yeah. Yeah. As Mark e. Elidra pointed out in an
article for Natural History Magazine back in I believe twenty nineteen,
hermit crabs live actually highly social lives, absolutely full of drama,
just way more drama than you'd expect your local human
hermit to have, I'd wager.
Speaker 3 (28:31):
Yeah, I mean, I guess unless hermits were like constantly
fighting one another to try to trade clothes.
Speaker 1 (28:37):
Yeah, or a pillar. You know, if you have your
your pillar, develloers, it'd be like, no, I want the
I want the taller pillar.
Speaker 3 (28:42):
Yeah, I'm gonna do exactly. I'm going to bang my
pillar on your pillar until you give me your pillar,
unless I decide I want my old pillar back.
Speaker 1 (28:51):
So the various dramas that they encounter and instigate, includes,
but is not limited to, according to Eldra, commotion of
social aggregations, intergenerational inheritance of homes, life or death, competitive struggles.
So the author points out that in contrast to a
(29:12):
lot of other social organisms you might think about, terrestrial
hermit crabs socialize with non relatives, and this is crazy
to think about. The reason, he points out, is that
while they spend most of their lives on land, we're
talking about terrestrial hermit crabs again, not the aquatic ones.
They spend most of their lives on land, but they
are born in the sea. That's where the larva larvae
(29:35):
are released. They become mixed in the ocean, and then
they land on far flung shores via the tides. So
I want to read this quote from Eldra. He says, quote,
By the time an immature crab first arrives on land,
it is therefore far away from any of its relatives,
encountering instead only an assortment of non kin. Moreover, because
(29:57):
the abundance of terrestrial hermit crabs on shore stretches of
beach often measures in the hundreds of thousands or even
the millions. Each crab is but a stranger within a
vast crowd.
Speaker 3 (30:08):
However, you know, if you think of a human analogy,
imagine a bunch of very selfish humans are thrown into
a mix of you know, they're all living together beside
one another, and not amongst their kin, just amongst strangers.
And you know, maybe imagine they're not very they're not
very nice people, they're not very inclined to be helpful
to others. They still might find reasons to hang out
(30:30):
around one another, even if they're mostly selfish. And one
of those reasons might be the need for trade or
an economy of sorts exactly.
Speaker 1 (30:38):
And what are they going to have an economy of
sorts about, Well, it's going to be the shell, of course.
I also like how this idea it kind of matches
up with the you know, the huge stereotype that one
encounters of big city life, particularly in movies from like
the seventies and I guess into the eighties as well,
Like nobody's related to each other in the city. You
go to the city, it's just everybody's for themselves. You're
(31:00):
gonna you're gonna lose your shell in that big city.
I guess it's kind of kind of that way with
the crabs here. But anyway, the shells that they use,
like you've been saying, yeah, these are scavenged from dead mollusks,
but this is also key. Uh, they have been remodeled.
These are remodeled homes. Elidra points out. Uh, the crabs
(31:20):
you when they have when they have a fresh shell
that is going to like this is okay, something has died,
as the snail has dyed, and now I'm going to
make this shell into a home. You can't just put
it on and wear it out. Uh no, No, you
need to use chemical secretions to weaken the shells calcium carbonate,
as well as additional physical sculpting via your appendages. You're
going to change the shell into something that absolutely suits
(31:44):
you and absolutely suits your purposes. Right.
Speaker 3 (31:47):
So this is another way in which one shell is
not necessarily as good as any other. Size matters a lot,
which is a sort of inherent feature of the shell,
but also the the remodeling condition of the shell matters
a lot. There are shells that have been recently renovated,
and that's much more desirable than a shell that is
a real fixer upper.
Speaker 1 (32:09):
Right, right, And this is unique to terrestrial hermit crabs,
and we'll get it more into why in a second.
But yeah, as Lighter points out, it's absolutely necessary for
terrestrial hermes because they can't depend on water buoyancy to
help them carry that shell around. It's just the basic
reality of living out of the water, and some of
(32:30):
these shells can be quite hefty for the crab, and
so by reducing the shell mass, they're lowering the energy
cost of just traveling across land, and they do a
lot of traveling. Additionally, shell remodeling increases the internal space
in the shell, allowing not only more room for the crab,
but more room for increased water reserves to keep the
organism from drying out. Like we mentioned earlier, the importance
(32:51):
of this being a way to help them sustain themselves
when they are living times in very hot environments. He
also points out that while aquatic hermit crabs would conceivably
benefit from shell remodeling as well, because you know, even
though you have buoyancy, lighter shells could still be a benefit, right,
more internal space could still be a benefit. However, aquatic
(33:14):
hermit crabs have to contend with shell expert predators in
the ocean, organisms that are highly evolved to bypass shell protections. Therefore,
it would be a mistake to sacrifice any of your
shell's protection in order to get any of these benefits. Meanwhile,
on land, the terrestrial hermit crabs have far fewer shell
(33:37):
specialists to contend with, and lighter points to various research
that shown that like your average predator that would be
messing with a hermit crab is just not going to
have like the bite power or the not going to
have the tools necessary to crack open even a partially degraded,
a partially remodeled hermit crab chosen shell. Now, Joe I
(33:59):
included a photo. This is from Lydra's paper and an
example of an unmodified versus a modified shell. The central
axis is often removed, but the shell again retains protection
against the bite strength of terrestrial predators.
Speaker 3 (34:14):
Yeah, and one thing you can see in this picture
is that a lot of the effort in the remodeling
seems to be focused on the interior of the shells,
sort of like expanding the interior cavity and making more
room there and smoothing it out.
Speaker 1 (34:27):
Yeah, and certainly, you know, removing some of the additional
protection of the shell. But again it's apparently not going
to matter for terrestrial variants now. Like we said, one
of the huge factors in hermit crab societies is of
(34:49):
course the need for these shells and the fact that
as the crab grows and molts, they'll need to abandon
smaller shells in favor of larger shells. And as Lidra
points out, there's some really interesting about all of this quote.
Over time, remodeled shells have come to dominate the housing
market of terrestrial hermit crabs. Exhaustively sampling these housing markets,
(35:12):
I have found few unremodeled shells, and also few shells
that are still in the process of being remodeled. Most
shells have already been completely remodeled. Remodeled shells present a
superior home, and as with any superior resource, it is
understandable that terrestrial hermit crabs should prefer remodeled shells over
unremodeled shells. However, over evolutionary time, a mere preference has
(35:37):
transformed into an absolute dependence. As remodeled shells accumulated, terrestrial
hermit crabs came to specialize in living in them, to
the point that life in unremodeled shells became nearly impossible.
My field experiments revealed that after an early life stage,
most terrestrial hermit crabs cannot survive in unremodeled shells for
(35:58):
even a single day.
Speaker 3 (36:00):
Wow, Okay, I did not realize that.
Speaker 1 (36:03):
Yeah, yeah, because you know what's the current hermit crab
to do? If you need a shell, Well, you could
remodel your own shell technically, but most crabs simply can't
do this anymore, in large part because they end up
too big to access the inner parts of a fresh shell.
So only the smallest immature hermit crabs actually can get
in there and do this, which paradoxically often means that
(36:23):
they're left with oversized shells. But as such, all terrestrial
hermit crab individuals highly prefer a remodeled shell over a
fresh one. Even if they can fit inside that fresh
shell and conceivably remodel it and make it their own,
remodeling the shell is still a last resort. Ledra stresses
that this is this is the only factor that ensures
(36:46):
the continued creation of remodeled shells. That some hermit crabs
are going to be put in a position where they
have no choice, wow, because I mean they can do
other things to it should not like a hermit crab
is left without any thing and there, and we'll touch
on how this occurs. In a moment. They may use
something like a bottle cap and that might buy them
(37:06):
a little time, but they need a shell. The thing is,
you don't just find many emptied remodeled shells. He points
out that on a given beach, the only empty remodeled
shells you're likely to find are the ones that have
been physically compromised in one way or another, so like
they're they're broken, they don't actually protect the hermit crab anymore,
(37:28):
or they're clogged with a rock something like that, they're
no longer functional. The competition for remodeled shells is intense,
and they're just you're just not going to As a
hermit crab, you are not going to find them out
there unless you're extremely lucky. As such, hermit crabs have
to remain vigilant at all times, always looking out for
a bigger shell, because either you need one or you're
(37:49):
about to need one, so you need to always be looking.
And also you have to be peeking over your shoulder
because there's probably someone eyeing your shell, that is looking
for a slightly bigger shell, and they're trying to decide
if it's worth trying to take it from you.
Speaker 3 (38:04):
Right, So this leads to the fact that hermit crabs
very often get into well, I guess there's some debate
over how exactly to characterize these encounters, whether they are
purely agonistic fights, or whether you might consider them in
some way a kind of trade or negotiation. Maybe we
can talk about that some more in the next episode.
(38:26):
But they get into these encounters that lead to shell swapping.
Speaker 1 (38:31):
Yeah, they're at the very least aggressive negotiations. Yeah, but
so I'll continue to categorize them as battles. But yeah,
give with that caveat in mind. Basically, what seems to
be happening is one crab will attempt to flip the
other on its back and force its opponent out of
their shell. But as Lijra points out, this kind of
(38:53):
thing can last hours and it might just end in
a stalemate. It might just end in everyone just going
home or carrying on with the shell they had two
hours ago. And that alone, I think that's pretty fascinating.
Most animal competitions and struggles are fascinating, but it's the
onlookers that make this even more interesting. Leider writes, quote.
(39:15):
As bystanders gather at the site, and as the moment
of evictioneers order emerges out of the chaos of commotion
in the aggregation, the crabs array themselves literally into a line,
each holding the shell of the crab ahead of it.
This social formation emanates from the pair of antagonists, with
(39:35):
the line of crabs there after being size ordered from
biggest to smallest unquote. Because if a crab is forced
to give up its shell, the winner will leave its shell,
and this will set off what's called a vacancy chain.
All of the onlookers will have a shot at leveling
up their current shell situation to a new one that
(39:57):
is slightly bigger.
Speaker 3 (39:58):
You can find video of this online. By the way,
there are multiple documentaries that have captured versions of this,
and it's amazing to see they literally do just organize
themselves in a size ordered line where they're each grasping
the shell of the slightly bigger one, like feeling around
on it, trying to make sure that it's what they want.
(40:19):
Because the whole process, by the way of in which
Hermit crabs assess a shell for the qualities they want
is interesting on its own. There seem to be some
visual processes going on. They you know, look at a
shell to assess from a distance whether it's something they
would want. But that's never enough. They have to inspect
it physically. They like feel all over it with their
(40:40):
antennae and their chelly, you know, the claws and the legs.
And then usually they will want to sort of like
dip into it with their legs and maybe they're abdomen
to see if they fit right, and they may end
up changing their mind and wanting to go back to
the previous shell, though obviously that could be a tricky
thing if a bencha, Yeah, hermit crabs are lined up
(41:02):
all trying to level up at the same time. It
is an amazing thing to see.
Speaker 1 (41:07):
Yeah, to your point about like sizing up the shell,
trying it on. Like, sometimes you have a situation where
you remember the asymmetry of shells and hermit crabs here,
and sometimes you have a you have like a like
what a left handed crab trying to get into a
right handed shell or vice versa, And and that's going
(41:27):
to be a situation where the crab is going to
quickly realize this does not fit, this is not the
shell I want to live. We may come back with
more details on that regarding the left right handedness and
hermit crabs and shells. Now, Elidra again points out that
all this competition is based again not on kinship, but
on selfishness and competition. And he has this wonderful part
(41:52):
in the paper where he says that it's what's kind
of the antithesis of something like a US social ant,
you know, where all the ants and a call in
the ark, and they work together to ensure the success
of the colony, the success of their genetic line. But
that is not the case with the hermit crab. And
Leidra writes the following quote. If in an alternative world,
(42:13):
interactions in terrestrial hermit crabs were among close kin rather
than strangers, then the crabs social lives might be different,
with individuals potentially being more interested in bequeathing their finest
shell to a close relative than in stealing the coveted
shell of a stranger. Now, there have been plenty of
(42:33):
other researchers and also science journalists and writers and so
forth that have commented on all of this. Elizabeth Preston
wrote all about this topic for The New York Times
in twenty nineteen in an article titled, even hermit crabs
have wealth inequality. This was based on a twenty twenty study.
This is because the New York Times paper came out
(42:55):
a month before the twenty twenty study. This was in
a December publication, so that's why the dates would seem
to be in the wrong order here. But that particular
paper was a comparison of wealth inequality in humans and
non humans by Chase at all. This was a study that,
as I recall, received a fair amount of mainstream attention
at the time because, of course, wealth inequality is always
(43:17):
a topic of interest among human beings, and crabs are
inherently interesting. You can throw hermit crabs into any study
and it's going to be fascinating, even if there's not
really connective tissue there.
Speaker 3 (43:30):
Well, is there connective tissue here?
Speaker 1 (43:32):
To a certain extent, it seems to okay, I mean so,
in the study, Chase and his co authors gathered around
three hundred hermit crabs on Long Island Beach and took
away all their shells, which, okay for science, I will
allow this, but you know, obviously I can't help it
sympathize because this is literally all these crabs care about.
The researchers weighed and measured the various shells, and then
(43:54):
they considered how they were distributed across the sample population
of hermit crab. And this is a quote here from
that article by Preston quote. The distribution curve they found
peaked around medium sized shells, then dropped as the shells
got larger, before tapering off very gradually through the largest
shells of all this matches the shape of wealth distribution
(44:17):
curves in many human societies, so it's interesting. But at
the same time, the New York Times article of citing
anthropologists Monique Molder, points out that we shouldn't get two
carried away comparing hermit crabs to humans in this scenario, because,
first of all, there are plenty of other factors involved
in human inequality. You know, it's one of those it's
(44:37):
often described as a wicked problem. You know, it's complex
enough that you can't just point to necessarily there are
certainly large factors, but there are multiple factors. And Molder here,
who again as an anthropologist, speculated that vacancy chains are
probably also not the only factor in terrestrial hermit crabs
as well. I mean, you know, there are other factors
as well into how they are dealing with each other,
(44:59):
even on the the basis of their shells. Still, you know,
we can't help but compare ourselves to the hermit crabs. Again,
part of it is just that hermit crabs are that interesting,
and we as human beings are that self absorbed. What
we can't help but see ourselves in the crabs. We
can help what anthropomorphize the crabs, and you know, especially
when we see them, you know, in a very complex fashion,
(45:19):
struggle over limited resources like this. That again, I think
if you're just casually aware of hermit crabs, you might
not realize that just any shell, it's not a situation
where any shell will do, and it is a situation
where the shells have been augmented, and therefore it's competition
not just for random garbage left over by dead snails,
(45:43):
it's competition for mostly previously augmented shells, like the products
of a hermit crab civilization, if you will.
Speaker 3 (45:52):
Well, that's funny if you think of it as like
more fighting over fighting over a limited pool of finished
goods rather than creating new goods. It's almost like a
human post apocalyptic scenario exactly. Yeah, it's kind of mad Max.
Speaker 1 (46:08):
It's kind of Fallout right. It reminds me that in
at least some of the Fallout games you do encounter
a giant hermit crab that is using what some sort
of like a bus or something like a school bus
for it's uh, it's abdomen. I can't remember offhand, but
I remember when I would when I would play the
most recent Fallout game, I would occasionally encounter that that
creature and yeah, yeah, I mean it's it's it's interesting.
(46:30):
Where are they getting all these school buses? What are
they changing about? I guess they're taking all the seats out?
Speaker 3 (46:35):
Yeah, is it a right handed bus or a left
handed bus?
Speaker 1 (46:39):
I don't know. Yeah, And are they sizing up from
different buses? Like they start with a like a shorter bus,
then they go to a full sized school bus, and
they're going to like a megabus. Then it's a double
decker bus. Those are only that's only in Fallout London propertly,
But you know, uh, you could go wild with with
the scenario.
Speaker 3 (46:57):
Well, hey, we've got more hermit crab stuff to talk about,
So join us again next time.
Speaker 1 (47:02):
That's right, we have some more content lined up regarding
the hermit crabs. We're going to fish around for a
bit more. Because I'm a hermit crabs. There's a lot
of research out there. That's one of the reasons I
felt pretty secure in going in and discussing them again,
even though we've discussed them in the past, because there's
constantly new hermit crab research coming out and there are
some remaining mysteries and controversies about hermit crabs. So we'll
(47:26):
get into all of that in the next episode. In
the meantime, we'll remind you that Stuff to Blow Your
Mind is a science podcast with core episodes on Tuesdays
and Thursdays. That's the main event. You can also tune
in for a short episode on Wednesday, a listener mail
episode on Mondays, and on Fridays. We set aside most
serious concern to just talk about a weird movie on
(47:46):
Weird House Cinema. If you listen to us on Apple
or an Apple device, what have you going in and
just make sure that you're still subscribed to the show,
that nothing's changed there. Make sure you're still getting downloads
worth it time check. That helps us out. And hey,
as far as just rating and reviewing, we haven't beat
the drum about this in a while, but hey, if
(48:07):
you haven't rated and reviewed the show before, why didn't
you do that to throw us a good five stars somewhere?
That also helps us out in the long run.
Speaker 3 (48:16):
Huge thanks as always to our excellent audio producer JJ Posway.
If you would like to get in touch with us
with feedback on this episode or any other, to suggest
a topic for the future, or just to say hello,
you can email us at contact at stuff to Blow
your Mind dot com.
Speaker 2 (48:38):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from my Heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you're listening to your favorite shows.
Speaker 1 (49:02):
Have not the pocop
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