December 14, 2019 • 48 mins
Welcome to Christmas Island, a place where it’s still only Christmas once a year… but where red crabs swarm across the land and enormous coconut crabs feast on carrion in the forests. So deck the halls with boughs of SCUTTLING HORROR as Robert and Joe celebrate the holiday season in style. (Originally published Dec. 25, 2018)
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Episode Transcript
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Speaker 1 (00:05):
Hey, you welcome to Stuff to blow your mind. My
name is Robert Lamb and I'm Joe McCormick, and it's Saturday.
Time to go into the Old Vault for an episode
from December of This published December, and this was part
one of our two part episode about the Christmas Island
Crabs or Christmas Island Wildlife more generally. Yeah, I remember
(00:26):
the original title for this was Christmas Island Crabs Part
one colon Crabs rule everything around me um and and
then the next one, Part two also originally had a
Wu Tang themed title as well. But yeah, this was
just a really nothing to do with Christmas itself for
the most part. I think we maybe we sang some
Christmas songs. I think you made one up. I don't
(00:47):
remember which part it was in, But for the most part,
this is all about crabs and only marginally about Christmas.
It's like life, life is also all about crabs and
marginally about Christmas. Okay, yeah, I think I think that's
that's solid. All right, let's let's dive right in. It
was the Island of Christmas, and all across the land,
(01:09):
the red crabs were flowing across Root Street and sand
like a red tide of scuttling, claw snapping doom. They
streamed through my front door and into my rooms. Meanwhile,
in the forests the giants they're crawled coconut crabs, hulking
monsters with claws. They hunted for carrion crab bird and
ratted and gobbled it up, rancid, sinew and fat. Welcome
(01:39):
to Stuff to Blow your Mind from how Stuff Works
dot Com. Hey, welcome to Stuff to Blow your Mind.
My name is Robert Lamb, and I'm Joe McCormick, and
getting in that holiday spirit, we're gonna be talking about
crab Horror. Yes, this is this pair of episode. I've
(02:00):
been looking forward to all year. This has been my
my goal. I forget when, but earlier in the year
I was reading about Christmas Island and the various creatures
that that call it home, and I realized, we have
to do this episode for Christmas. Even though this really
has nothing to do with Christmas, no, virtually nothing with Christmas,
though I do enjoy um like forcing decapods upon Christmas
(02:26):
and uh and and and at least in my mind,
allowing them to take over the holiday Decapods with bows
of all is it bows should have said clause of
the glory. Either way, I appreciate the holiday zeal. Now,
so we're going to be going to Crab Horror Island,
and there are many wonderful movies and maybe we'll save
(02:46):
it for next time to talk about our favorite Crab
Island movies. But the giant crab is one of my
favorite kind of movie monsters, and they've always got to
have their own island of terror, right right, and and
so in discussing Christmas Island and these two episodes, we're
going to talk about crabs or you know, decapods anyway
that are either enormous, uh, singularly and enormous or collectively enormous.
(03:10):
I think the first episode we're going to focus on
the collectively enormous, and the second episode will focus on
the decapods who are individually enormous. Now, this first episode
is going to focus on the Christmas Island Red Crab. Robert,
will you take me on a mystical adventure to crab
Horror Island. Yes, we're talking about Christmas Island so named.
(03:31):
It's in the Indian Ocean about three hundred and fifty
kilometers or two hundred and twenty miles south of Java
and Sumatra and around Uh let's see one thou fifty
kilometers are nine hundred and sixty miles northwest of the
closest point on the Australian Mainland. Technically part of Australia
though right it is an Australian external territory. It has
(03:52):
an area of a hundred square kilometers or fifty two
square miles, so not huge, No, not a big place
at all. It's a very old, though very old volcanic
seamount island. It was first visited by Europeans in sixty three.
Captain William Minors of the Royal Mary and English East
India Company vessel. He just named the island when he
(04:14):
sailed past it on Christmas Day of that year. That's
that's the only Christmas high end there he didn't find,
you know, and naturally occurring Christmas tree there. Uh, there's
no wasn't where the elf workshop was exactly. There's there's
nothing else about it except it was Christmas Day when
he found it. It could have easily it could have
easily turned out to be Christmas Eve Island, or Boxing
(04:36):
Day Island or Halloween Island. That would perhaps be a
little more appropriate, yea. So that one of the cool
things about this place is that when when they were
able to take a closer look at it, they realized
that it was uninhabited at least by humans. So it's
obvious that what makes this island unique is not anything
about the indigenous culture or anything, since it was apparently
(05:00):
uninhabited originally, but it was not uninhabited by wildlife. As
we've made clear, the wildlife there was of a terrific
scuttling variety, oh correct. And one of the really cool
things about the scuttling life on Christmas Island it is
that so much of it is on Christmas Island. We're
talking about land crabs, crabs that need only returned to
the water to mate, but mostly live on land. And
(05:21):
you'll find these elsewhere. To be sure, this is not
the only place land crabs can be found, uh, And
we're we're talking about both true crabs as well as
hermit crabs here. Hermit crabs are decapods, but not true crabs.
But forgive us as we as we talk about them
in these episodes, I will probably end up calling them
both crabs in the unofficial sense. The Christmas Island is
(05:44):
home to more land crabs than anywhere else on Earth.
We're talking more than twenty terrestrial and semi terrestrial crabs species,
plus a hundred and sixties species or thereabouts in the
reefs and shallows around the island. Yeah, so Robert tell
me a little bit about crabs. Well, just to refresh everybody,
crabs are crustaceans. But we should be clear that again,
(06:04):
there are true crabs of the decapoda soap order bracci ura,
which means small tail um, which references their smaller abdomen.
And then there are the ano mora or mixed tail crabs,
which included hermits and as we'll discuss later in the
second episode, robber crabs. But still again we're often going
to refer to them both as crabs in the unofficial sense.
(06:28):
And these were these are ancient creatures. These were the
first animals to develop true legs, none of those false legs. Yeah,
I mean, we we've talked about crabs in the show before.
I think back to our episode about Carl Sagan and
the Samurai crabs. So so hopefully everyone is is on
board for two more episodes of crab based content. But
(06:48):
so it's not just the varieties of crab and crab
like creatures that live on Christmas Island that make it
Crab Island Earth, Uh, it is is the number are
of a particular species of crab there, the Christmas Island
red crab, where there are supposedly tens of millions of
(07:09):
these crabs on the island. And this is not a
big island. Remember it's a hundred thirty five square kilometers, right,
a small island. And yet yeah, I've seen the figures
of like fifty million of these creatures living, living in
the forest, living, you know, pretty much all over the island.
And that's a reduced number. I remember we watched a
documentary about the island from the nineteen eighties that suggested
(07:29):
the time it was believed that there were over a
hundred million of the crabs. They're right. That was a
nine eight eight David Attenborough narrated special titled Kingdom of
the Crabs. Great title, and that's a great one to
watch if you get a chance, because it really shows
off what makes this island visually astounding. But it's the
sheer numbers of the crabs, and the Christmas Island red
(07:51):
crab is pretty much found only on Christmas Island. Yeah,
I think maybe on another nearby island or island group,
but they're not found like all over the place. So
I do want to come back to the human history
for a little bit before we explore the Red uh
Crab in depth. So the most you know, essential thing
about human history of Christmas Island is that for the
(08:12):
longest there seems to have been none. It is a
geographically isolated place now from everything I've read so far,
and it's always possible on missing something, but there's no
evidence that humans ever visited the place before the seventeenth century.
See this, despite Java being again only two miles away.
It's a short enough distance for modern humans anyway that
(08:34):
boats of asylum seekers frequently make it their point of
destination in reaching Australia, because again it's an Australian external territory,
So if you reach Christmas Island, you are, you know,
in a legal sense, in Australia. However, it's also worth
pointing out that the seas can be deadly surrounding Christmas
Island and their stories out there boats of asylum seekers
(08:55):
breaking on the Rocky coast with lethal results. I think
I've read about this in cases the early visitors to
the island also that you know, it was kind of
dangerous to land there. And for example, there was one
case where I read that a crew was driven to
land there because there was scurvy on the ship, and
it was only because the disease had gotten so bad
that they risked trying to land. Yeah, that's sort of
(09:17):
the typical story book reasons for landing on an uninhabited
island with a strange crab population. Yeah, but out of
the scurvy pan into the crabs. Yeah, and you know it,
but but it is. It is weird to think about
places like this, places where where humans just didn't take
up residents. And of course you have to, of course
realize that moving to an isolated island is a difficult proposition,
(09:41):
like you've really got to have a reason to go
there and a reason to stay there, and a way
to um to to safely arrived there as well. But still,
you know, it's enough to make one wonder. For instance,
Homo erectus, or a Java man, lived on the island
of Java relatively close by one point seven years ago.
Humans practiced agriculture. They're on Java as early as b C.
(10:07):
Java was known to traders and other powers. The Kingdom
of Mataram ruled there until they lost power to the
Dutch East India Company in seventeen forty nine and became
a vassal state of the Company UM, a statement that
I think really drives home the power of the East
India Company UM, the idea that you would have a
(10:27):
vassal state to a corporation. Yeah, but that's a Jova.
My point is that I just find it so enthralling
that this island remained either free of human contact for
so long or only encountered minimal influence. You know. It's
I guess it's possible that it's at some point somebody
wound up there by purpose or accident and they didn't stay,
didn't stay long enough to leave a footprint, you know.
(10:50):
Galapagos Islands or another example of this, though there there
have been at least disputed claims of Inca artifacts found
on the Galapagos Islands, perhaps due to Inca sailors being
blown off course. The Statials in the Indian Ocean are
another example of islands that were uninhabited through most of
recorded history, though they may have been visited by early
seafares as well, depending on who you talked to. But
(11:12):
with Christmas Island I found no such thing, and not
even a crackpot theory. So it really does seem as
if humans, not even the Vikings, went there the by
no Vikings or anything. So it really does seem that
nobody visited it until the seventeenth century, with the earliest
sighting I think having occurred in sixteen fifteen. Now after that,
of course, it actually did become an economically significant island
(11:35):
because of mineral deposits discovered there. That's right. It was
explored by British naturalist John Murray, and this was eighteen
seventy two. He discovered that there were phosphate deposits on
the island, which would play a key role in the
island's future. Exportation of phosphate begin in eighteen by the
Christmas Island Phosphate Company, and this activity led to the
(11:58):
loss of twenty of the island's rainforest area. Yeah, Now,
phosphate was important in the late eighteen hundreds because it
had been discovered by that time that phosphate, when treated
with sulfuric acid, could be used as an ingredient in
plant food, and of course synthetic fertilizers became very important
in the development of commercial agriculture at scale, and so
now there was a reason and economic reason for people
(12:21):
to not only go to Christmas Island but to work there,
and so settlement began in the eighteen eighties. Uh later on,
during the Second World War, there was a Japanese occupation
of the island from ninety five, and in the post
war period it was administered by Singapore, which was then
a British colony, and then Australia purchased the island for
(12:43):
two point nine million pounds on January one, nineteen fifty
eight day that's known as Territory Day on Christmas Island.
Today it has around I've read two thousand full time
human residents and the ethnic makeup is mostly Chinese and
melee Um originally brought in for labor. Now a big
(13:03):
portion of the land of the island today is basically
a national park. It's like a big wildlife preservation area. Yeah,
two thirds of its landmasters are national park now and
a big part of the wildlife significance here is the
Christmas Island red crabs. So I guess we should dive
headfirst into a puddle of crabs after we come back
from a break. Thank thank alright, we're back, So it
(13:28):
is time to dive into a pit of crabs. The
Christmas Island red crab or get Karkoitia natalis. And these
are crabs that live, as we mentioned earlier, primarily not
in the ocean, not even on the shoreline, but in
inland forests. So if you picture Christmas Island, it's sort
of a terraced rainforest. It's a you know, a volcanic island.
(13:50):
It's got some steep slopes that go up onto rainforest
covered terraces, and the crabs go all the way up
into the forests and make their burrows inland. Yeah, we're
talking against something like fifty million of these little land
dwellers uh in the forest chewing up leaf litter, and
here on Christmas Island they are the chief decay agents
(14:11):
for that leaf litter. I've seen estimates of something like
four thousand crabs per acre to keep the leaf litter down. Yes,
and they primarily feed on plant matter, Like you say,
so that is going to be leaf litter. It's also
things like fallen fruits and seeds, flowers, et cetera. But
they're also crabs after all, so you might not be
(14:31):
surprised to learn that they are opportunistic omnivores. My favorite
pairs of words. So if you get a little bit
of meat from say another dead red crab or something
like that presenting itself, this is a legitimate score, and
they will say, gentlemen, get that in my mouth parts.
It's time to masticate. But the crabs are important for
the maintenance of the ecosystem in multiple ways. So they
(14:53):
clear the forest floor of like leaf litter, but also
saplings and flowers other plants that would create dense underbrush,
and so they keep the forest floors clean and this
actually helps contribute to forest biodiversity. They also prevent the
soil from being packed too densely because of the burrows
they dig. They're like natural soil tillers. They turn the soil,
(15:16):
and this also helps contribute to forest biodiversity. But so
we might have a pretty good sense of what the
life of an ocean dwelling crab is like. What is
the life of a land crab Like crabs, as you
can imagine, in between chewing up things in their environment
and eating it, they have to stay moist and this means,
for one thing, staying out of the direct sun. So
the red crabs on Christmas Island like to stay in
(15:39):
the shady forests and they live in these dugout burrows
that they can hide from the sun in and they
have guilt chambers that have adapted for terrestrial life. They
have to keep them moist, and they also I love this,
they have to manually wet their eyes stalks. Yes, I
love this. It's pretty cool to watch if you can
find video of this. So their ice talks emerge from
little cups in their carapace, and they don't have eyelids
(16:02):
of course, by the way, it just try to imagine
life without eyelids kind of a terror. So they wet
and wash their eyes by filling their eye cups up
with drops of water and then dipping their eyestalks down
into the cups to rinse them off. Yeah, I think
this is This is one of the great things about
watching any crab close up, but especially with the Christmas
(16:25):
craps is those tiny, little sort of methodical movements that
you see take place with their mouth parts and their
their eyes stalks totally. Now, despite their life in the woods,
they still have to return to the sea to spawn,
and this results in a vast, scuttling migration that is
truly unlike anything else on earth. This is why you
will you will see. You know, there's so many different
(16:48):
documentaries about Christmas Islands. One there's so much great footage
because they they go on these enormous migrations and we're
talking a several kilometer journey each year. Yeah, this is
crab Apocalypse. This is where the real show is on
Christmas Island. So around the beginning of the rainy season,
which is sometime October through December, the red crabs begin
(17:11):
this migration for their breeding cycle. And the migration begins
with the males, usually the biggest males, who will crawl
out over land from their forest burrows to the shore
where they're going to eventually get there and dig new
burrows for mating. And as the males make this journey,
the females eventually joined them in the journey and they
(17:32):
march towards the sea. Now, once the crabs reached the shore,
but before they dig their burrows to mate, uh, they
typically wash themselves off in seawater, though strangely enough, they
have to be careful not to get fully sucked out
into the sea, because these are land dwelling crabs. This
is how they've evolved, and they can neither breathe underwater,
nor can they swim very well. These are crabs who
(17:54):
are not very good at being crabs. Yeah, so the
truly aquatic crabs in the neighborhood are just probably watching
this in halfing at them. Yeah, but there's so many
of them. How could you laugh at them? Because they
could really gang up on you if they got a
hold of your right But so they would rinse themselves
off in the sea water. And then the males dig
the burrows. Now, sometimes when they dig the burrows, usually
(18:17):
they'll go up a little bit from the beach and
one of the forested areas just right by the beach,
and they'll dig these burrows. And sometimes the males have
to defend their burrows from other males, who of course think, hey,
why dig one when you can just claim somebody else's.
So there are sometimes these fights and dominance displays, a
lot of claw waving to keep the burrows secure. And
(18:38):
then of course the females come in and they will
find a male with a burrow and initiate the mating.
And by the way, if you've never watched crabs mating before,
it's one of the funnier looking types of animal sex.
I think it's just crabs look funny no matter what
they're doing. But also if you can just watch their
(18:58):
eyes while they're mating, it's really something special. It's you know,
it's like two google eyed robots trying to be sexy
at each other and then throwing some claws and swiveling
mouth parts. It's just awesome. Now you mentioned the waving
of the clause, I want to I was reading a
little bit about crab clause in Douglas j Emlin's book
Animal Weapons. Uh And he goes. He spends a little
bit of time talking about, you know, how these are
(19:19):
high energy adaptations to pack with powerful muscles. They need
to be able to break through the exo skeletons of
of rival males in many cases. Uh And he mostly
looks at fidler crabs in this book. But but but
it's interesting stuff. The economics of not only having growing,
evolving gigantic class but waving them around, because that's that's
(19:40):
part of having the cleaving clause or a claw, is
to wave that sucker around, yeah, or like flexing your muscles,
like showing off the guns. Yeah, you have to show
off the guns. That's that's part of having them, right. Yeah.
So the female will generally find a male and a
male with the burrow and they will mate. And then
after are mating, what the males do is they just
(20:01):
pack up and headback inland. Their work is done, and
they leave the females by themselves in these seaside burrows.
And there's another interesting thing about this. Okay, so the
red crabs are sort of moon worshiping druids. The breeding
migration has to be timed exactly according to the cycle
of the moon because the cycle of the moon affects
(20:23):
the tides. So the adult crabs arrive at the shore
and then they mate, and after mating, the females produce
eggs within about three days, and then they remain in
their burrows for another twelve or thirteen days. And after
this they emerge from the hole in the ground and
they release their eggs into the sea water. And it
has to be timed exactly at the turn of high tide,
(20:45):
as the moon goes from its last quarter to a
new moon. And this is because it's when the tide
conditions are just right to be releasing the young. But
if the migration is delayed by weather so that breeding
can't be timed exactly right with the phase of the moon,
the crabs will just wait. They'll just wait until the
next month to breed because it it's not it's not
(21:05):
going the moon isn't right. So when the time is right,
the females release their eggs acts, which looks kind of
like a weird foamy sponge that they carry on the
underside of their bodies. They release these eggs acts into
the water. Yet again, I can't help but notice that
my wonder at these animals is combined with hilarity on
seeing this, because in some cases the female crabs have
(21:27):
to release their eggs into like rough surf while clinging
to rocks above the water, and they're trying to be
careful not to fall in. And when you see footage
of this, the way they're just frantically shaking their bodies
to knock the eggs acts off, dumping thousands of eggs
off a cliff, I can't help but laugh. It's funny.
And then also sometimes they'll they'll go into the surf
(21:47):
on a beach and you'll see them like raising their
claws and shaking their bodies, like get off, just dumping
all these eggs off into the water. I don't know,
it's it's funny to me. Well, by in comparisons, they're
maybe not great moms, but by but by Christmas Island
red Crab standards moms of the year. Yeah, exactly, and
(22:09):
that this does make me think about the ways that
we anthropomorphize good parenting. I want to come back to
that in just a minute. So the eggs are released
into the surf and they hatch pretty much immediately, and
then you've got these hatchling crab larvae that live in
the water for about a month, transforming through large larval stages,
and then they returned the shore in this seething foam
(22:30):
of what looks like pink ants. This is also just
astonishing to see, like the original migration from the forest
to the shore with the beaches and rocks covered in
this surging, pink shag carpet of tiny millimeter sized baby crabs.
And then they mold and immediately after molting they are
committed to an air breathing life on land and they
(22:53):
travel inland to do as their ancestors did before them,
and this growth from about a five millimeter baby crab
staged adulthood usually takes about four years, during which time
they mostly tend to hide out undercover until they get
big enough to fend for themselves. But yeah, back to
this idea about the way we look at non human
animals and tend to to judge their parenting. I mean,
(23:15):
that's inherently what I was doing when I think it's
funny just watching the mother crabs chuck their eggs off
a cliff. But it's like it's hilarious watching a crab
vigorously shake its body to knock all the eggs off
and stuff. But it's because we've so deeply internalized the
brood protection tendencies of mammals. Mammals tend to keep their
(23:36):
offspring close and take care of them for for like
extended periods of time while they mature, and that would
make no sense for crabs to do. First of all,
of course, it is just mechanically the case, because the
eggs need to hatch in the water. That's what chemically
and mechanically they do. But also mathematically, the parents have
a totally different relationship with their offspring. Mammals tend to produce,
(23:59):
you know, relatively small numbers of offspring and invest a
lot of energy into caring for and protecting them. But
I was trying to do a little bit of rough
math about the red crab. So let's assume there are
fifty million adult red crabs on the island, and then
you've got mated pairs, and each mated pair of adult
crabs produces tens of thousands of eggs. I've seen a
(24:19):
common figure of a hundred thousand eggs per female crab sited.
So if fifty million crabs made it and produced twenty
five million eggs sponges, and each of those had a
hundred thousand eggs in it, and all those eggs survived
to adulthood, that would be two trillion, five hundred billion crabs.
Now Christmas Island is about a hundred and thirty five
(24:41):
square kilometers. If my math is right, this means that
just after one year there would be a Christmas Island
would have eighteen point five billion crabs per square kilometer.
So you're saying, as a red crab mom, you have
to be willing to let some of those crabs go
because you have you have the numbers on your side, right,
I mean, it's just a totally different way of of
(25:03):
having a relationship between generations, right. They're going for for numbers.
You know, it's quantity rather than quality. And it's just
impossible for all those young to sustainably survive. Even if
a decent fraction of them survived, it would be ridiculous.
Only a tiny fraction of them can possibly make it
to adulthood in any ecologically sustainable way. And so most
(25:24):
they get dumped out into the water to hatch, never
make it back to shore alive. They get washed out
to sea, never to return. Apparently, whale sharks migrate to
the Christmas Island area to eat red crab larvae when
they hatch, and among those that do make it back
to the beach in that in that you know foamy
pink shag carpet I mentioned, they're obviously going to be
(25:45):
pretty easy prey at that stage too. You can even
sometimes see I've seen footage of this of adult red
crabs just kind of shoveling clawfulls of young red crabs
into their mouths because hey, what are the chances that
these are mine? It's pretty slim. Again, it's a numbers game. Well,
plus it's they're just against so many of them. It's like,
if you make way too much a pancake batter, uh,
(26:06):
you may treat yourself to a few spoonfuls of unclick
pancake batter. I mean, why not, it's there. You can
only make so many pancakes. You can make similar argument.
You'd be like, look, if I made all of this
into pancakes, our house would be packed with pancakes six
ft high exactly. But anyway, given this kind of life cycle,
in these kind of odds, the way to be a
(26:27):
good parent is to do exactly what the female crabs do.
They shake them off into the water where they've got
a chance, and then they call it a day. There's
nothing more you can do at that point. And if
somehow you were still around when they hatched and malted,
who knows, you might just gobble them up. So, despite
how funny it looks, I rebuke my instincts. I do
not think that the red crabs are bad parents. I
(26:48):
think they're awesome crab parents. All Right, we're gonna take
a quick break and when we come back, we're going
to get into the human element. What happens when we
have the human element to the red crab element? Alright,
we're bad. Now. We discussed earlier how crazy these migrations are.
You know, when the island can sometimes in areas, become
just thick with crabs that are moving from forest to
(27:09):
shore or returning from shore to forest. And this doesn't
even take into consideration the fact that sometimes there are
multiple waves of migration during the same year. So you've
got crabs going both ways. Like one set of crabs
they moved down to the shore, and then there's another,
uh you know, trigger of the rainy season, another set
of crabs they start moving to the shore. Then then
(27:31):
the other ones are going home. So you can have
crabs going this way, crabs going that way. There on
the golf course, there on the streets, there in the
grocery store. I mean, it can become quite thick with
crabs on Christmas Island. And yet there are people here,
that's right, And those people have vehicles. Yeah that they
also have pets. Uh. We'll get into some of those
(27:52):
complications in a bit, but just the roads. You're talking
about something like a million crabs a year crushed by
road traffic on Christmas High but that's still only gonna
shake out to something like one percent of the population.
And the dead, by the way, are apparently swiftly cannibalize again. Crabs.
Crabs are gonna do what crabs are gonna do. No.
I mentioned earlier that there's this great old British TV
(28:14):
documentary called Kingdom of the Crabs and narrated by David
Attenborough from nineteen I think, yeah, that was the same
year that we got John Carpenters They Live, Killer Clowns
from Outer Space, The Blob the remake, the really cool
eighties remake, as well as of course Mac and Me. Well,
this is right up there with those. But it's got
so many great moments, and one of the best moments
(28:35):
from it is when you're watching hundreds of crabs scuttling
across a pair of railroad tracks, and then a train
emerges in the background and it's barreling towards the crab crossing,
and then the crabs show no sign of getting out
of the way, and then the train conductor starts blowing
his horn at the crabs as if that's going to
(28:56):
deter them. I guess it's like when people like they
stop in the road because the turtle is crossing and
they honked their horn at it. I never actually haunk
my Hornet's say, squirrels chip bunks, but I will almost
wreck my vehicle to avoid them. But I I guess
that's human nature. Like you don't want to squish crabs unnecessarily.
I mean maybe some people do. There are probably a
(29:18):
few people on the island who kind of get off
on it. Well, I've read that it can. It can
also hurt your tires. Yeah, you have people with flat
tires due to the crabs. Probably hurts trains less, probably, um.
But the humans have had to put in place many
steps to help the crabs cope with roads and tracks
and the other ways that we have unfortunately disrupted their
(29:41):
migration zones. I mean, it's not the crabs fault, right,
They didn't ask us to put a road there, but
railroad tracks there to do all that kind of stuff.
So these adaptations are are pretty interesting. They include barriers
of course around the edges of roads and put walls
around the roads to keep the crabs from walking onto
the roads. And these lead to of crab funnels that
(30:02):
route the crabs to specially designed safe crossings, so you
might have an underpass with a great on top of it,
or even there's even a five meter high crab bridge
climbable by crab to help them over one stretch of road.
Oh yeah, and you included a picture of these in
our notes. It's pretty incredible because it looks like one
of the recognizers those enemy ships in the Tron movies. Yeah,
(30:26):
it looks like like that, the big clamp that comes
down on top of you, right, except instead of being
made out of brightly colored light, it's covered in brightly
colored red crabs right now. Interestingly enough, early accounts of
Christmas Island make no real mention of the crab hoards,
so you could you can look at that one of
two ways, right, Well, either it didn't occur in at
(30:48):
least with the same at the same level, or they
just forgot to mention it, which seems unlikely, so maybe
they didn't witness it. Well, it's true too, but there
is this suspected link between the current levels and the
recent levels of of of the red crab population with
the extinction of two species of rat that were on
(31:11):
the island when Europeans first arrived. And uh, and it's
possible that these two species of rat may have kept
the populations more in check. What are these rats alright?
One is called mcclear's rat or memor rattis McCleary and
the other is the bulldog rat or Rattus nativitatis. And
(31:33):
those are just two of only five native mammal species
on Christmas Island to have been officially listed as extinct
since humans showed up. That being both of these rats,
and the reason that they went extinct, it's it's probably
because exotic rodents were brought in by early human colonizers
or brought in. I would say they just came along
(31:54):
with let rats do. Okay, So the ideas that humans
brought different kinds of rodents, those rodents out competed the
native rodents, but those rodents weren't as much of a
competition with the red crabs. Well it's more than just
outcompete as apparently like straight up killed them off with illness.
It was looking at a two thousand eight study published
(32:15):
in PLS one, and they pointed out that there seems
to be a direct cause here, and it seems to
be disease. They collected DNA samples from the islands now
extinct native rats via late nineteenth in early twentieth century
museum specimens, and they attributed the extinction event here to
ship jumping black rats infected with the protozoan Tripanasoma Louizy,
(32:39):
an organism that is related to an organism that causes
sleeping sickness in humans. And indeed, Native Island rats were
seen to stagger around following the arrival of the S
S Hindustan in eight and this protozoan is light is
likely spread by fleas, so we have you know, it's
(32:59):
a similar situation that we've seen with certainly with with
human populations and UH and other organisms, where an exotic
variant brought in a parasite that the UH, the native
inhabitants were just simply unable to deal with. Now, in
terms of other native Christmas Island mammals, others have had
a tough time as well. The Christmas Island shrew is
(33:20):
critically endangered. There's also a particular batu, the Christmas Island Pipistrelli. Yes,
thank you for help on that one. Now, it's it's
a ute name. It is a cute name, a cute
name for a bat. It's critically endangered, if not outright extinct,
(33:41):
and apparently the reasoning behind that is is not completely understood.
There's also the Christmas Island flying fox, which is another
type of bat. It is also in decline for unknown reasons.
And then you have the exotic mammals. We've already mentioned
black rats, but you also have a house mice, you
have feral cats and wild dog. Now do we know
what the explicit relationship between that change in the mammal
(34:04):
populations and the surge and crabs is. The belief is
that those populated the original populations of rodents were helping
to keep the population of crabs in check, and apparently
the the the exotic mammals have not been able to
keep their numbers in check the same in the same rate.
I see, So they're not adapted to to crab Island, right, Yeah,
(34:27):
it's it's one of those situations where again you just
see humans show up in the unbalanced things. Yes, Now,
in the case of the red crabs, it would almost
seem like the unbalancing made more spectacle. Right. Like, the
reason we're talking about Christmas Island is because we have
this enormous surge that arguably might not be the same
level uh if we had also not managed to kill
(34:49):
off two whole species of rodents on the island. True,
and there's going to be even more stuff along those
lines coming up. So there are actually multiple ongoing through
rats to the life cycle of these amazing animals. If
if you care about the beauty of the crab army
scuttling through the forests, you should care about these issues.
One is climate related. So there is a paper from
(35:14):
in Global Change Biology called Linking L neno Local rainfall
and migration timing in a tropical migratory species by Alison K.
Shaw and Catherine A. Kelly, and the authors here find
that species who's mating and migratory behaviors are determined by weather,
like the Christmas Island red crab. Remember it's the it's
(35:34):
certain things about the beginning of the rainy season that
tell them time to go to the beach and mate. Uh.
They will probably be adversely affected by the way climate
change is upsetting normal weather patterns that were used to
So the authors write, quote, we find that the timing
of the annual crab breeding migration is closely related to
(35:55):
the amount of rain that falls during a migration window
period prior to potential egg release states, which is in
turn related to the Southern Oscillation index and atmospheric l
ne NEO Southern oscillation index. As reproduction in this species
is conditional on successful migration, they don't reproduce if they
(36:15):
don't migrate, major changes in migration patterns could have detrimental
consequences for the survival of the species. So, in other words,
climate change messes around with the amount of timing of
the rainfall on Christmas Island, and then the crabs get
the short end of the stick and could find themselves
unable to use their normal migration and breeding instincts in
(36:36):
order to produce the next generation. And this could also
have follow on effects with the animals that depend on
these migratory animals for food, like the Christmas Island red
crab is sort of a keystone species on the island
in many ways. One of the things we already mentioned
is that those whale sharks come to eat the Christmas
Island red crab larvae in the water. But another thing
(36:57):
is as we mentioned, they maintain the state of the
forest by clearing leaf litter and clearing out other plants
in the undergrowth of the forest and you know, and
by turning the soil right, Yeah, they're their aerators. Now,
there is another culprit that is putting the Christmas Island
red crabs at risk, and that is yellow crazy ants
(37:18):
crazy ants. Again, it's different crazy ants somewhat. So we
did an episode about crazy ants before, but that was
focused on a completely different animal. We were mainly talking
about the raspberry crazy ant of the genus Nylandria. The
yellow ant is a totally different genus. It's an apolo
Lepus gracillips and these are ants with a slender body,
(37:39):
long legs, and like the crazy ants in genus Nylandria,
they're also easily recognized by these movement patterns that give
them their name. Their motion is sometimes described as frantic
or erratic or crazy, and like raspberry crazy ants, these
ants can also form what are known as super colonies,
which means they build separate but friendly nests which do
(38:01):
not attack one another and form a kind of web
of allied ant armies that can easily overwhelm the habitats
that they spread to, and so they're considered a very
problematic invasive species. Like other crazy ants. Also, they spray
formic acid as a defensive and offensive biological weapon, and
formic acid is a powerful chemical. Uh, it's apparently a
(38:23):
potent poison against land crabs. So you can imagine a
bunch of ants come up against one of these Christmas
Island red crabs and the ants spray formic acid in
its eyes, in the segment joints of the crabs, so
you know, like getting in the leg joints, and this
can leave the crabs unable to move or to survive.
And then after the crabs die, of course, the ants
(38:43):
get a feast of crab meat. And this has had
a huge impact on crab populations. It's been estimated that
in the last fifteen years the ants have reduced the
crab populations on the island by as much as tykes.
So local land crabs have been put severely at risk
by the yellow crazy ants. Interestingly, the yellow crazy ants
existed on the island for many decades. I think they
(39:05):
were introduced sometime in the first half of the twentieth century.
I've seen estimates in the nineteen teens or twenties around then. Uh,
And they were on the island a long time before
they became so destructive to the land crabs beginning around
the nineteen nineties. So what changed around the nineteen nineties.
I was reading a report that was put together by
(39:27):
Parks Australia together with Latrobe University, and it appears that
it was only in the nineteen nineties or so that
these massive super colonies of yellow crazy ants began forming.
So what caused that change? What happened then? Uh? The
author's point to the emergence of a mutualism, actually a
symbiotic relationship, and this is a mutualism between the yellow
(39:49):
crazy ants and another group of insects called scale insects.
So it's like the like the two enemies, they they
forged a truce and and then we're united against the
forces of the crab. Yes, so another non native species,
the scale insects. What they do is they cling to
plant stems and they suck the sap from the plants
(40:11):
for energy, and they produce a sugary waste product from
their anal pores in the process. And the ants love
this sugary poop. They go straight to the anal pores
and they eat it up. So they have formed this
mutualistic protective relationship with the tree sucking candy poopers. The
scale insects suck from the trees, they produce sugary poop.
(40:32):
The yellow the yellow crazy ants eat the sugary poop
and they protect the scale insects. And it appears that
this emerging symbiosis between the yellow crazy ants and the
scale insects is related to the ant's ability to form
these ecologically devastating super colonies. But here's so, then you
take the question one step back, Well, what caused this
(40:53):
mutualism to begin in the first place. Uh, the authors
of this report don't know. They speculate that change ng
rainfall patterns on Christmas Island. We're putting stress on trees
and this made the sap more concentrated, which means it's
even more sugary goodness for the scale insects. And this
increases the population of the scale insects, which produces more
(41:16):
delicious sugary poop for their yellow ant friends, which means
more ants to protect the scale insects, which means even
more scale insects. And then you get this dangerous feedback loop.
It's this is all Christmas Island is in so many ways.
This Uh, this wonderful look at the horrible cascading effects
of colonialism, of human intervention in general, I mean at
(41:38):
the macroscopic climate level and at the local invasive level. Yeah,
like at every level. We have messed with this island,
and we messed it with it in one way, and
now we're messing with it in a different way, and
and now in fact we're gonna keep messing with it
in order to try to fix part of what we did.
Because the question is can anything be done to save
(41:59):
these amazing red crabs? I mean, these are It is
a wonderful thing to see these animals doing what they do.
And so I was reading an interesting article about this
on the Conversation in UH posted in by two Latrobe
University professors Susan Lawler and Peter Green, and apparently Parks
Australia has been trying to do all kinds of things
(42:19):
to help the crabs survive the crazy ants or to
knock the crazy ant super colonies back, like they tried
poison bading the ants by hand. But apparently this is
just not an efficient solution. In seen, they launched a
new project and this was Killer Wasps. I like it
tell me more so, the Killer Wasps they're only about
two millimeters long, and they're naturally found in India and
(42:40):
Southeast Asia. They're called tach Cardia vegas Summerville and the
author selected this tiny wasp because it attacks this specific
species of scale insect that has formed the mutualistic relationship
with the crazy ants uh so. And the wasp is
a parasite oid that lays its eggs in the body
(43:02):
of the female of this one species of scale insect,
which hatch into more wasps that lay more eggs in
these species of scale insects, and hopefully this will severely
control the population of this one particular species of scale insect,
which is also invasive on the island. Uh And the
author's note that they've had to be very cautious because
(43:23):
they cite examples that, you know, in the past, we've
tried to introduce animals to places in the hope that
they would control the pest problem, but then they became
a problem in their own right. They said, the example
of the cane toad in Australia, which was brought into
control cane beetles, but then it became its own kind
of problem. And I'm reminded, of course, of the old
(43:44):
nursery rhyme. There was an old lady who swallowed a
fly right, and she's forced to keep swallowing progressively larger
and parasitic wasps and larger and more destructive organisms to
try and uh savor until if she dies at the
end of the song. Well, the authors, so we hope
that that happened. The authors claimed they performed rigorous research beforehand.
(44:04):
Uh they tested really hard to make sure this wasp
would not harm other local species. And they said, you know,
according to their tests, everything seemed to check out. So
they introduced the wasps in sixteen, and I checked with
a more recent news article on the wasp control project
from it looks like the effort is having early markers
for success. The wasps have become established, their range is spreading.
(44:27):
But we'll have to wait a few more years before
we see the full effect on the crab populations. But
I hope it works, and I hope it doesn't have
any unexpected effects. Less to become Island of the wasps,
Kingdom of the wasps. You don't want to have to
think about Crab Island needing to be protected. You want
to think that Crab Island is an armored claw wielding
(44:47):
force to be reckoned with, and that it you know,
it can withstand anything on its own. But I don't know. Yeah,
natural populations or even unnatural populations are vulnerable. Yeah, I
mean look at Skull Island right King Kong's homeland. Oh,
I don't know anything about population dynamics there. Or a
monster Island where all the giant Japanese monsters with kaiju.
(45:10):
That's clearly these are places that need to be protected.
We don't need to go in there and try and
to feed them with our robots. Is there is there
a crab kaju? Yes, there are. There are crab kaiju
up the wazoo. Yes, nice. Yes, they have their own
movies sometimes. Yeah, Godzillafa. Want to forget its name? I can.
I can never remember the names of the adversary that
(45:34):
maybe it. But yeah, he found a giant crab in
one episode. It was I finally remember it from my childhood.
But we'll get into we'll get into monster crabs a
bit more in the next episode of Stuff to Blow
your Mind, because we will talk about another resident of
Christmas Island that is an enormous deco pod. In fact,
that the largest land crab that you will find on
(45:54):
Earth now naturally, would love to hear from everybody out there.
We have listeners all over the world. I wonder if
we have just a single listener that lives on Christmas Island,
if we do email us yes, Likewise, we have a
lot of Australian and listeners UH and just listeners who
have traveled around the world in general. If you have
ever been to Christmas Island and witnessed any of the
(46:18):
species we discussed here, or just I mean even if
you've just been there and you saw nothing at all,
We want to hear from you. Whatever you have to
share about Christmas Island would be gratefully appreciated. And in
the meantime, you can check out all the episodes of
Stuff to Blow Your Mind. It's stuff to Blow your
Mind dot com. That's where you'll find all the episodes.
Links out to our various social media accounts, including UH
(46:38):
the discussion the module, which is our group on Facebook.
Look up stuff to Blow your Mind Discussion module and
you can easily join that and interact with other listeners
as as as well as Joe and myself. The website
Stuff to Blow your Mind dot com also has a
link to our store where you can buy some cool
merchandise stickers, shirts, etcetera. Um, it's probably probably a bit
(47:00):
late now for for Christmas gifts, at least for this Christmas,
but hey, you can go ahead and start start banking
ahead for next year. It's a great way to support
the show. And if you want to support the show
without spending a dime, well you can simply rate and
review us wherever you have the power to do so.
Huge thanks as always to our excellent audio producers Alex
Williams and Torry Harrison. If you would like to get
(47:21):
in touch with us directly to let us know feedback
on this episode or any other, to suggest topic for
the future, or just to say hi, let us know
where you listen from that kind of thing, you can
email us at blow the Mind at how stuff works
dot com for moral this and thousands of other topics.
(47:45):
Does it how stuff works dot com, theddutory bar, proper
(48:05):
par
Hey, you welcome to Stuff to blow your mind. My
name is Robert Lamb and I'm Joe McCormick, and it's Saturday.
Time to go into the Old Vault for an episode
from December of This published December, and this was part
one of our two part episode about the Christmas Island
Crabs or Christmas Island Wildlife more generally. Yeah, I remember
(00:26):
the original title for this was Christmas Island Crabs Part
one colon Crabs rule everything around me um and and
then the next one, Part two also originally had a
Wu Tang themed title as well. But yeah, this was
just a really nothing to do with Christmas itself for
the most part. I think we maybe we sang some
Christmas songs. I think you made one up. I don't
(00:47):
remember which part it was in, But for the most part,
this is all about crabs and only marginally about Christmas.
It's like life, life is also all about crabs and
marginally about Christmas. Okay, yeah, I think I think that's
that's solid. All right, let's let's dive right in. It
was the Island of Christmas, and all across the land,
(01:09):
the red crabs were flowing across Root Street and sand
like a red tide of scuttling, claw snapping doom. They
streamed through my front door and into my rooms. Meanwhile,
in the forests the giants they're crawled coconut crabs, hulking
monsters with claws. They hunted for carrion crab bird and
ratted and gobbled it up, rancid, sinew and fat. Welcome
(01:39):
to Stuff to Blow your Mind from how Stuff Works
dot Com. Hey, welcome to Stuff to Blow your Mind.
My name is Robert Lamb, and I'm Joe McCormick, and
getting in that holiday spirit, we're gonna be talking about
crab Horror. Yes, this is this pair of episode. I've
(02:00):
been looking forward to all year. This has been my
my goal. I forget when, but earlier in the year
I was reading about Christmas Island and the various creatures
that that call it home, and I realized, we have
to do this episode for Christmas. Even though this really
has nothing to do with Christmas, no, virtually nothing with Christmas,
though I do enjoy um like forcing decapods upon Christmas
(02:26):
and uh and and and at least in my mind,
allowing them to take over the holiday Decapods with bows
of all is it bows should have said clause of
the glory. Either way, I appreciate the holiday zeal. Now,
so we're going to be going to Crab Horror Island,
and there are many wonderful movies and maybe we'll save
(02:46):
it for next time to talk about our favorite Crab
Island movies. But the giant crab is one of my
favorite kind of movie monsters, and they've always got to
have their own island of terror, right right, and and
so in discussing Christmas Island and these two episodes, we're
going to talk about crabs or you know, decapods anyway
that are either enormous, uh, singularly and enormous or collectively enormous.
(03:10):
I think the first episode we're going to focus on
the collectively enormous, and the second episode will focus on
the decapods who are individually enormous. Now, this first episode
is going to focus on the Christmas Island Red Crab. Robert,
will you take me on a mystical adventure to crab
Horror Island. Yes, we're talking about Christmas Island so named.
(03:31):
It's in the Indian Ocean about three hundred and fifty
kilometers or two hundred and twenty miles south of Java
and Sumatra and around Uh let's see one thou fifty
kilometers are nine hundred and sixty miles northwest of the
closest point on the Australian Mainland. Technically part of Australia
though right it is an Australian external territory. It has
(03:52):
an area of a hundred square kilometers or fifty two
square miles, so not huge, No, not a big place
at all. It's a very old, though very old volcanic
seamount island. It was first visited by Europeans in sixty three.
Captain William Minors of the Royal Mary and English East
India Company vessel. He just named the island when he
(04:14):
sailed past it on Christmas Day of that year. That's
that's the only Christmas high end there he didn't find,
you know, and naturally occurring Christmas tree there. Uh, there's
no wasn't where the elf workshop was exactly. There's there's
nothing else about it except it was Christmas Day when
he found it. It could have easily it could have
easily turned out to be Christmas Eve Island, or Boxing
(04:36):
Day Island or Halloween Island. That would perhaps be a
little more appropriate, yea. So that one of the cool
things about this place is that when when they were
able to take a closer look at it, they realized
that it was uninhabited at least by humans. So it's
obvious that what makes this island unique is not anything
about the indigenous culture or anything, since it was apparently
(05:00):
uninhabited originally, but it was not uninhabited by wildlife. As
we've made clear, the wildlife there was of a terrific
scuttling variety, oh correct. And one of the really cool
things about the scuttling life on Christmas Island it is
that so much of it is on Christmas Island. We're
talking about land crabs, crabs that need only returned to
the water to mate, but mostly live on land. And
(05:21):
you'll find these elsewhere. To be sure, this is not
the only place land crabs can be found, uh, And
we're we're talking about both true crabs as well as
hermit crabs here. Hermit crabs are decapods, but not true crabs.
But forgive us as we as we talk about them
in these episodes, I will probably end up calling them
both crabs in the unofficial sense. The Christmas Island is
(05:44):
home to more land crabs than anywhere else on Earth.
We're talking more than twenty terrestrial and semi terrestrial crabs species,
plus a hundred and sixties species or thereabouts in the
reefs and shallows around the island. Yeah, so Robert tell
me a little bit about crabs. Well, just to refresh everybody,
crabs are crustaceans. But we should be clear that again,
(06:04):
there are true crabs of the decapoda soap order bracci ura,
which means small tail um, which references their smaller abdomen.
And then there are the ano mora or mixed tail crabs,
which included hermits and as we'll discuss later in the
second episode, robber crabs. But still again we're often going
to refer to them both as crabs in the unofficial sense.
(06:28):
And these were these are ancient creatures. These were the
first animals to develop true legs, none of those false legs. Yeah,
I mean, we we've talked about crabs in the show before.
I think back to our episode about Carl Sagan and
the Samurai crabs. So so hopefully everyone is is on
board for two more episodes of crab based content. But
(06:48):
so it's not just the varieties of crab and crab
like creatures that live on Christmas Island that make it
Crab Island Earth, Uh, it is is the number are
of a particular species of crab there, the Christmas Island
red crab, where there are supposedly tens of millions of
(07:09):
these crabs on the island. And this is not a
big island. Remember it's a hundred thirty five square kilometers, right,
a small island. And yet yeah, I've seen the figures
of like fifty million of these creatures living, living in
the forest, living, you know, pretty much all over the island.
And that's a reduced number. I remember we watched a
documentary about the island from the nineteen eighties that suggested
(07:29):
the time it was believed that there were over a
hundred million of the crabs. They're right. That was a
nine eight eight David Attenborough narrated special titled Kingdom of
the Crabs. Great title, and that's a great one to
watch if you get a chance, because it really shows
off what makes this island visually astounding. But it's the
sheer numbers of the crabs, and the Christmas Island red
(07:51):
crab is pretty much found only on Christmas Island. Yeah,
I think maybe on another nearby island or island group,
but they're not found like all over the place. So
I do want to come back to the human history
for a little bit before we explore the Red uh
Crab in depth. So the most you know, essential thing
about human history of Christmas Island is that for the
(08:12):
longest there seems to have been none. It is a
geographically isolated place now from everything I've read so far,
and it's always possible on missing something, but there's no
evidence that humans ever visited the place before the seventeenth century.
See this, despite Java being again only two miles away.
It's a short enough distance for modern humans anyway that
(08:34):
boats of asylum seekers frequently make it their point of
destination in reaching Australia, because again it's an Australian external territory,
So if you reach Christmas Island, you are, you know,
in a legal sense, in Australia. However, it's also worth
pointing out that the seas can be deadly surrounding Christmas
Island and their stories out there boats of asylum seekers
(08:55):
breaking on the Rocky coast with lethal results. I think
I've read about this in cases the early visitors to
the island also that you know, it was kind of
dangerous to land there. And for example, there was one
case where I read that a crew was driven to
land there because there was scurvy on the ship, and
it was only because the disease had gotten so bad
that they risked trying to land. Yeah, that's sort of
(09:17):
the typical story book reasons for landing on an uninhabited
island with a strange crab population. Yeah, but out of
the scurvy pan into the crabs. Yeah, and you know it,
but but it is. It is weird to think about
places like this, places where where humans just didn't take
up residents. And of course you have to, of course
realize that moving to an isolated island is a difficult proposition,
(09:41):
like you've really got to have a reason to go
there and a reason to stay there, and a way
to um to to safely arrived there as well. But still,
you know, it's enough to make one wonder. For instance,
Homo erectus, or a Java man, lived on the island
of Java relatively close by one point seven years ago.
Humans practiced agriculture. They're on Java as early as b C.
(10:07):
Java was known to traders and other powers. The Kingdom
of Mataram ruled there until they lost power to the
Dutch East India Company in seventeen forty nine and became
a vassal state of the Company UM, a statement that
I think really drives home the power of the East
India Company UM, the idea that you would have a
(10:27):
vassal state to a corporation. Yeah, but that's a Jova.
My point is that I just find it so enthralling
that this island remained either free of human contact for
so long or only encountered minimal influence. You know. It's
I guess it's possible that it's at some point somebody
wound up there by purpose or accident and they didn't stay,
didn't stay long enough to leave a footprint, you know.
(10:50):
Galapagos Islands or another example of this, though there there
have been at least disputed claims of Inca artifacts found
on the Galapagos Islands, perhaps due to Inca sailors being
blown off course. The Statials in the Indian Ocean are
another example of islands that were uninhabited through most of
recorded history, though they may have been visited by early
seafares as well, depending on who you talked to. But
(11:12):
with Christmas Island I found no such thing, and not
even a crackpot theory. So it really does seem as
if humans, not even the Vikings, went there the by
no Vikings or anything. So it really does seem that
nobody visited it until the seventeenth century, with the earliest
sighting I think having occurred in sixteen fifteen. Now after that,
of course, it actually did become an economically significant island
(11:35):
because of mineral deposits discovered there. That's right. It was
explored by British naturalist John Murray, and this was eighteen
seventy two. He discovered that there were phosphate deposits on
the island, which would play a key role in the
island's future. Exportation of phosphate begin in eighteen by the
Christmas Island Phosphate Company, and this activity led to the
(11:58):
loss of twenty of the island's rainforest area. Yeah, Now,
phosphate was important in the late eighteen hundreds because it
had been discovered by that time that phosphate, when treated
with sulfuric acid, could be used as an ingredient in
plant food, and of course synthetic fertilizers became very important
in the development of commercial agriculture at scale, and so
now there was a reason and economic reason for people
(12:21):
to not only go to Christmas Island but to work there,
and so settlement began in the eighteen eighties. Uh later on,
during the Second World War, there was a Japanese occupation
of the island from ninety five, and in the post
war period it was administered by Singapore, which was then
a British colony, and then Australia purchased the island for
(12:43):
two point nine million pounds on January one, nineteen fifty
eight day that's known as Territory Day on Christmas Island.
Today it has around I've read two thousand full time
human residents and the ethnic makeup is mostly Chinese and
melee Um originally brought in for labor. Now a big
(13:03):
portion of the land of the island today is basically
a national park. It's like a big wildlife preservation area. Yeah,
two thirds of its landmasters are national park now and
a big part of the wildlife significance here is the
Christmas Island red crabs. So I guess we should dive
headfirst into a puddle of crabs after we come back
from a break. Thank thank alright, we're back, So it
(13:28):
is time to dive into a pit of crabs. The
Christmas Island red crab or get Karkoitia natalis. And these
are crabs that live, as we mentioned earlier, primarily not
in the ocean, not even on the shoreline, but in
inland forests. So if you picture Christmas Island, it's sort
of a terraced rainforest. It's a you know, a volcanic island.
(13:50):
It's got some steep slopes that go up onto rainforest
covered terraces, and the crabs go all the way up
into the forests and make their burrows inland. Yeah, we're
talking against something like fifty million of these little land
dwellers uh in the forest chewing up leaf litter, and
here on Christmas Island they are the chief decay agents
(14:11):
for that leaf litter. I've seen estimates of something like
four thousand crabs per acre to keep the leaf litter down. Yes,
and they primarily feed on plant matter, Like you say,
so that is going to be leaf litter. It's also
things like fallen fruits and seeds, flowers, et cetera. But
they're also crabs after all, so you might not be
(14:31):
surprised to learn that they are opportunistic omnivores. My favorite
pairs of words. So if you get a little bit
of meat from say another dead red crab or something
like that presenting itself, this is a legitimate score, and
they will say, gentlemen, get that in my mouth parts.
It's time to masticate. But the crabs are important for
the maintenance of the ecosystem in multiple ways. So they
(14:53):
clear the forest floor of like leaf litter, but also
saplings and flowers other plants that would create dense underbrush,
and so they keep the forest floors clean and this
actually helps contribute to forest biodiversity. They also prevent the
soil from being packed too densely because of the burrows
they dig. They're like natural soil tillers. They turn the soil,
(15:16):
and this also helps contribute to forest biodiversity. But so
we might have a pretty good sense of what the
life of an ocean dwelling crab is like. What is
the life of a land crab Like crabs, as you
can imagine, in between chewing up things in their environment
and eating it, they have to stay moist and this means,
for one thing, staying out of the direct sun. So
the red crabs on Christmas Island like to stay in
(15:39):
the shady forests and they live in these dugout burrows
that they can hide from the sun in and they
have guilt chambers that have adapted for terrestrial life. They
have to keep them moist, and they also I love this,
they have to manually wet their eyes stalks. Yes, I
love this. It's pretty cool to watch if you can
find video of this. So their ice talks emerge from
little cups in their carapace, and they don't have eyelids
(16:02):
of course, by the way, it just try to imagine
life without eyelids kind of a terror. So they wet
and wash their eyes by filling their eye cups up
with drops of water and then dipping their eyestalks down
into the cups to rinse them off. Yeah, I think
this is This is one of the great things about
watching any crab close up, but especially with the Christmas
(16:25):
craps is those tiny, little sort of methodical movements that
you see take place with their mouth parts and their
their eyes stalks totally. Now, despite their life in the woods,
they still have to return to the sea to spawn,
and this results in a vast, scuttling migration that is
truly unlike anything else on earth. This is why you
will you will see. You know, there's so many different
(16:48):
documentaries about Christmas Islands. One there's so much great footage
because they they go on these enormous migrations and we're
talking a several kilometer journey each year. Yeah, this is
crab Apocalypse. This is where the real show is on
Christmas Island. So around the beginning of the rainy season,
which is sometime October through December, the red crabs begin
(17:11):
this migration for their breeding cycle. And the migration begins
with the males, usually the biggest males, who will crawl
out over land from their forest burrows to the shore
where they're going to eventually get there and dig new
burrows for mating. And as the males make this journey,
the females eventually joined them in the journey and they
(17:32):
march towards the sea. Now, once the crabs reached the shore,
but before they dig their burrows to mate, uh, they
typically wash themselves off in seawater, though strangely enough, they
have to be careful not to get fully sucked out
into the sea, because these are land dwelling crabs. This
is how they've evolved, and they can neither breathe underwater,
nor can they swim very well. These are crabs who
(17:54):
are not very good at being crabs. Yeah, so the
truly aquatic crabs in the neighborhood are just probably watching
this in halfing at them. Yeah, but there's so many
of them. How could you laugh at them? Because they
could really gang up on you if they got a
hold of your right But so they would rinse themselves
off in the sea water. And then the males dig
the burrows. Now, sometimes when they dig the burrows, usually
(18:17):
they'll go up a little bit from the beach and
one of the forested areas just right by the beach,
and they'll dig these burrows. And sometimes the males have
to defend their burrows from other males, who of course think, hey,
why dig one when you can just claim somebody else's.
So there are sometimes these fights and dominance displays, a
lot of claw waving to keep the burrows secure. And
(18:38):
then of course the females come in and they will
find a male with a burrow and initiate the mating.
And by the way, if you've never watched crabs mating before,
it's one of the funnier looking types of animal sex.
I think it's just crabs look funny no matter what
they're doing. But also if you can just watch their
(18:58):
eyes while they're mating, it's really something special. It's you know,
it's like two google eyed robots trying to be sexy
at each other and then throwing some claws and swiveling
mouth parts. It's just awesome. Now you mentioned the waving
of the clause, I want to I was reading a
little bit about crab clause in Douglas j Emlin's book
Animal Weapons. Uh And he goes. He spends a little
bit of time talking about, you know, how these are
(19:19):
high energy adaptations to pack with powerful muscles. They need
to be able to break through the exo skeletons of
of rival males in many cases. Uh And he mostly
looks at fidler crabs in this book. But but but
it's interesting stuff. The economics of not only having growing,
evolving gigantic class but waving them around, because that's that's
(19:40):
part of having the cleaving clause or a claw, is
to wave that sucker around, yeah, or like flexing your muscles,
like showing off the guns. Yeah, you have to show
off the guns. That's that's part of having them, right. Yeah.
So the female will generally find a male and a
male with the burrow and they will mate. And then
after are mating, what the males do is they just
(20:01):
pack up and headback inland. Their work is done, and
they leave the females by themselves in these seaside burrows.
And there's another interesting thing about this. Okay, so the
red crabs are sort of moon worshiping druids. The breeding
migration has to be timed exactly according to the cycle
of the moon because the cycle of the moon affects
(20:23):
the tides. So the adult crabs arrive at the shore
and then they mate, and after mating, the females produce
eggs within about three days, and then they remain in
their burrows for another twelve or thirteen days. And after
this they emerge from the hole in the ground and
they release their eggs into the sea water. And it
has to be timed exactly at the turn of high tide,
(20:45):
as the moon goes from its last quarter to a
new moon. And this is because it's when the tide
conditions are just right to be releasing the young. But
if the migration is delayed by weather so that breeding
can't be timed exactly right with the phase of the moon,
the crabs will just wait. They'll just wait until the
next month to breed because it it's not it's not
(21:05):
going the moon isn't right. So when the time is right,
the females release their eggs acts, which looks kind of
like a weird foamy sponge that they carry on the
underside of their bodies. They release these eggs acts into
the water. Yet again, I can't help but notice that
my wonder at these animals is combined with hilarity on
seeing this, because in some cases the female crabs have
(21:27):
to release their eggs into like rough surf while clinging
to rocks above the water, and they're trying to be
careful not to fall in. And when you see footage
of this, the way they're just frantically shaking their bodies
to knock the eggs acts off, dumping thousands of eggs
off a cliff, I can't help but laugh. It's funny.
And then also sometimes they'll they'll go into the surf
(21:47):
on a beach and you'll see them like raising their
claws and shaking their bodies, like get off, just dumping
all these eggs off into the water. I don't know,
it's it's funny to me. Well, by in comparisons, they're
maybe not great moms, but by but by Christmas Island
red Crab standards moms of the year. Yeah, exactly, and
(22:09):
that this does make me think about the ways that
we anthropomorphize good parenting. I want to come back to
that in just a minute. So the eggs are released
into the surf and they hatch pretty much immediately, and
then you've got these hatchling crab larvae that live in
the water for about a month, transforming through large larval stages,
and then they returned the shore in this seething foam
(22:30):
of what looks like pink ants. This is also just
astonishing to see, like the original migration from the forest
to the shore with the beaches and rocks covered in
this surging, pink shag carpet of tiny millimeter sized baby crabs.
And then they mold and immediately after molting they are
committed to an air breathing life on land and they
(22:53):
travel inland to do as their ancestors did before them,
and this growth from about a five millimeter baby crab
staged adulthood usually takes about four years, during which time
they mostly tend to hide out undercover until they get
big enough to fend for themselves. But yeah, back to
this idea about the way we look at non human
animals and tend to to judge their parenting. I mean,
(23:15):
that's inherently what I was doing when I think it's
funny just watching the mother crabs chuck their eggs off
a cliff. But it's like it's hilarious watching a crab
vigorously shake its body to knock all the eggs off
and stuff. But it's because we've so deeply internalized the
brood protection tendencies of mammals. Mammals tend to keep their
(23:36):
offspring close and take care of them for for like
extended periods of time while they mature, and that would
make no sense for crabs to do. First of all,
of course, it is just mechanically the case, because the
eggs need to hatch in the water. That's what chemically
and mechanically they do. But also mathematically, the parents have
a totally different relationship with their offspring. Mammals tend to produce,
(23:59):
you know, relatively small numbers of offspring and invest a
lot of energy into caring for and protecting them. But
I was trying to do a little bit of rough
math about the red crab. So let's assume there are
fifty million adult red crabs on the island, and then
you've got mated pairs, and each mated pair of adult
crabs produces tens of thousands of eggs. I've seen a
(24:19):
common figure of a hundred thousand eggs per female crab sited.
So if fifty million crabs made it and produced twenty
five million eggs sponges, and each of those had a
hundred thousand eggs in it, and all those eggs survived
to adulthood, that would be two trillion, five hundred billion crabs.
Now Christmas Island is about a hundred and thirty five
(24:41):
square kilometers. If my math is right, this means that
just after one year there would be a Christmas Island
would have eighteen point five billion crabs per square kilometer.
So you're saying, as a red crab mom, you have
to be willing to let some of those crabs go
because you have you have the numbers on your side, right,
I mean, it's just a totally different way of of
(25:03):
having a relationship between generations, right. They're going for for numbers.
You know, it's quantity rather than quality. And it's just
impossible for all those young to sustainably survive. Even if
a decent fraction of them survived, it would be ridiculous.
Only a tiny fraction of them can possibly make it
to adulthood in any ecologically sustainable way. And so most
(25:24):
they get dumped out into the water to hatch, never
make it back to shore alive. They get washed out
to sea, never to return. Apparently, whale sharks migrate to
the Christmas Island area to eat red crab larvae when
they hatch, and among those that do make it back
to the beach in that in that you know foamy
pink shag carpet I mentioned, they're obviously going to be
(25:45):
pretty easy prey at that stage too. You can even
sometimes see I've seen footage of this of adult red
crabs just kind of shoveling clawfulls of young red crabs
into their mouths because hey, what are the chances that
these are mine? It's pretty slim. Again, it's a numbers game. Well,
plus it's they're just against so many of them. It's like,
if you make way too much a pancake batter, uh,
(26:06):
you may treat yourself to a few spoonfuls of unclick
pancake batter. I mean, why not, it's there. You can
only make so many pancakes. You can make similar argument.
You'd be like, look, if I made all of this
into pancakes, our house would be packed with pancakes six
ft high exactly. But anyway, given this kind of life cycle,
in these kind of odds, the way to be a
(26:27):
good parent is to do exactly what the female crabs do.
They shake them off into the water where they've got
a chance, and then they call it a day. There's
nothing more you can do at that point. And if
somehow you were still around when they hatched and malted,
who knows, you might just gobble them up. So, despite
how funny it looks, I rebuke my instincts. I do
not think that the red crabs are bad parents. I
(26:48):
think they're awesome crab parents. All Right, we're gonna take
a quick break and when we come back, we're going
to get into the human element. What happens when we
have the human element to the red crab element? Alright,
we're bad. Now. We discussed earlier how crazy these migrations are.
You know, when the island can sometimes in areas, become
just thick with crabs that are moving from forest to
(27:09):
shore or returning from shore to forest. And this doesn't
even take into consideration the fact that sometimes there are
multiple waves of migration during the same year. So you've
got crabs going both ways. Like one set of crabs
they moved down to the shore, and then there's another,
uh you know, trigger of the rainy season, another set
of crabs they start moving to the shore. Then then
(27:31):
the other ones are going home. So you can have
crabs going this way, crabs going that way. There on
the golf course, there on the streets, there in the
grocery store. I mean, it can become quite thick with
crabs on Christmas Island. And yet there are people here,
that's right, And those people have vehicles. Yeah that they
also have pets. Uh. We'll get into some of those
(27:52):
complications in a bit, but just the roads. You're talking
about something like a million crabs a year crushed by
road traffic on Christmas High but that's still only gonna
shake out to something like one percent of the population.
And the dead, by the way, are apparently swiftly cannibalize again. Crabs.
Crabs are gonna do what crabs are gonna do. No.
I mentioned earlier that there's this great old British TV
(28:14):
documentary called Kingdom of the Crabs and narrated by David
Attenborough from nineteen I think, yeah, that was the same
year that we got John Carpenters They Live, Killer Clowns
from Outer Space, The Blob the remake, the really cool
eighties remake, as well as of course Mac and Me. Well,
this is right up there with those. But it's got
so many great moments, and one of the best moments
(28:35):
from it is when you're watching hundreds of crabs scuttling
across a pair of railroad tracks, and then a train
emerges in the background and it's barreling towards the crab crossing,
and then the crabs show no sign of getting out
of the way, and then the train conductor starts blowing
his horn at the crabs as if that's going to
(28:56):
deter them. I guess it's like when people like they
stop in the road because the turtle is crossing and
they honked their horn at it. I never actually haunk
my Hornet's say, squirrels chip bunks, but I will almost
wreck my vehicle to avoid them. But I I guess
that's human nature. Like you don't want to squish crabs unnecessarily.
I mean maybe some people do. There are probably a
(29:18):
few people on the island who kind of get off
on it. Well, I've read that it can. It can
also hurt your tires. Yeah, you have people with flat
tires due to the crabs. Probably hurts trains less, probably, um.
But the humans have had to put in place many
steps to help the crabs cope with roads and tracks
and the other ways that we have unfortunately disrupted their
(29:41):
migration zones. I mean, it's not the crabs fault, right,
They didn't ask us to put a road there, but
railroad tracks there to do all that kind of stuff.
So these adaptations are are pretty interesting. They include barriers
of course around the edges of roads and put walls
around the roads to keep the crabs from walking onto
the roads. And these lead to of crab funnels that
(30:02):
route the crabs to specially designed safe crossings, so you
might have an underpass with a great on top of it,
or even there's even a five meter high crab bridge
climbable by crab to help them over one stretch of road.
Oh yeah, and you included a picture of these in
our notes. It's pretty incredible because it looks like one
of the recognizers those enemy ships in the Tron movies. Yeah,
(30:26):
it looks like like that, the big clamp that comes
down on top of you, right, except instead of being
made out of brightly colored light, it's covered in brightly
colored red crabs right now. Interestingly enough, early accounts of
Christmas Island make no real mention of the crab hoards,
so you could you can look at that one of
two ways, right, Well, either it didn't occur in at
(30:48):
least with the same at the same level, or they
just forgot to mention it, which seems unlikely, so maybe
they didn't witness it. Well, it's true too, but there
is this suspected link between the current levels and the
recent levels of of of the red crab population with
the extinction of two species of rat that were on
(31:11):
the island when Europeans first arrived. And uh, and it's
possible that these two species of rat may have kept
the populations more in check. What are these rats alright?
One is called mcclear's rat or memor rattis McCleary and
the other is the bulldog rat or Rattus nativitatis. And
(31:33):
those are just two of only five native mammal species
on Christmas Island to have been officially listed as extinct
since humans showed up. That being both of these rats,
and the reason that they went extinct, it's it's probably
because exotic rodents were brought in by early human colonizers
or brought in. I would say they just came along
(31:54):
with let rats do. Okay, So the ideas that humans
brought different kinds of rodents, those rodents out competed the
native rodents, but those rodents weren't as much of a
competition with the red crabs. Well it's more than just
outcompete as apparently like straight up killed them off with illness.
It was looking at a two thousand eight study published
(32:15):
in PLS one, and they pointed out that there seems
to be a direct cause here, and it seems to
be disease. They collected DNA samples from the islands now
extinct native rats via late nineteenth in early twentieth century
museum specimens, and they attributed the extinction event here to
ship jumping black rats infected with the protozoan Tripanasoma Louizy,
(32:39):
an organism that is related to an organism that causes
sleeping sickness in humans. And indeed, Native Island rats were
seen to stagger around following the arrival of the S
S Hindustan in eight and this protozoan is light is
likely spread by fleas, so we have you know, it's
(32:59):
a similar situation that we've seen with certainly with with
human populations and UH and other organisms, where an exotic
variant brought in a parasite that the UH, the native
inhabitants were just simply unable to deal with. Now, in
terms of other native Christmas Island mammals, others have had
a tough time as well. The Christmas Island shrew is
(33:20):
critically endangered. There's also a particular batu, the Christmas Island Pipistrelli. Yes,
thank you for help on that one. Now, it's it's
a ute name. It is a cute name, a cute
name for a bat. It's critically endangered, if not outright extinct,
(33:41):
and apparently the reasoning behind that is is not completely understood.
There's also the Christmas Island flying fox, which is another
type of bat. It is also in decline for unknown reasons.
And then you have the exotic mammals. We've already mentioned
black rats, but you also have a house mice, you
have feral cats and wild dog. Now do we know
what the explicit relationship between that change in the mammal
(34:04):
populations and the surge and crabs is. The belief is
that those populated the original populations of rodents were helping
to keep the population of crabs in check, and apparently
the the the exotic mammals have not been able to
keep their numbers in check the same in the same rate.
I see, So they're not adapted to to crab Island, right, Yeah,
(34:27):
it's it's one of those situations where again you just
see humans show up in the unbalanced things. Yes, Now,
in the case of the red crabs, it would almost
seem like the unbalancing made more spectacle. Right. Like, the
reason we're talking about Christmas Island is because we have
this enormous surge that arguably might not be the same
level uh if we had also not managed to kill
(34:49):
off two whole species of rodents on the island. True,
and there's going to be even more stuff along those
lines coming up. So there are actually multiple ongoing through
rats to the life cycle of these amazing animals. If
if you care about the beauty of the crab army
scuttling through the forests, you should care about these issues.
One is climate related. So there is a paper from
(35:14):
in Global Change Biology called Linking L neno Local rainfall
and migration timing in a tropical migratory species by Alison K.
Shaw and Catherine A. Kelly, and the authors here find
that species who's mating and migratory behaviors are determined by weather,
like the Christmas Island red crab. Remember it's the it's
(35:34):
certain things about the beginning of the rainy season that
tell them time to go to the beach and mate. Uh.
They will probably be adversely affected by the way climate
change is upsetting normal weather patterns that were used to
So the authors write, quote, we find that the timing
of the annual crab breeding migration is closely related to
(35:55):
the amount of rain that falls during a migration window
period prior to potential egg release states, which is in
turn related to the Southern Oscillation index and atmospheric l
ne NEO Southern oscillation index. As reproduction in this species
is conditional on successful migration, they don't reproduce if they
(36:15):
don't migrate, major changes in migration patterns could have detrimental
consequences for the survival of the species. So, in other words,
climate change messes around with the amount of timing of
the rainfall on Christmas Island, and then the crabs get
the short end of the stick and could find themselves
unable to use their normal migration and breeding instincts in
(36:36):
order to produce the next generation. And this could also
have follow on effects with the animals that depend on
these migratory animals for food, like the Christmas Island red
crab is sort of a keystone species on the island
in many ways. One of the things we already mentioned
is that those whale sharks come to eat the Christmas
Island red crab larvae in the water. But another thing
(36:57):
is as we mentioned, they maintain the state of the
forest by clearing leaf litter and clearing out other plants
in the undergrowth of the forest and you know, and
by turning the soil right, Yeah, they're their aerators. Now,
there is another culprit that is putting the Christmas Island
red crabs at risk, and that is yellow crazy ants
(37:18):
crazy ants. Again, it's different crazy ants somewhat. So we
did an episode about crazy ants before, but that was
focused on a completely different animal. We were mainly talking
about the raspberry crazy ant of the genus Nylandria. The
yellow ant is a totally different genus. It's an apolo
Lepus gracillips and these are ants with a slender body,
(37:39):
long legs, and like the crazy ants in genus Nylandria,
they're also easily recognized by these movement patterns that give
them their name. Their motion is sometimes described as frantic
or erratic or crazy, and like raspberry crazy ants, these
ants can also form what are known as super colonies,
which means they build separate but friendly nests which do
(38:01):
not attack one another and form a kind of web
of allied ant armies that can easily overwhelm the habitats
that they spread to, and so they're considered a very
problematic invasive species. Like other crazy ants. Also, they spray
formic acid as a defensive and offensive biological weapon, and
formic acid is a powerful chemical. Uh, it's apparently a
(38:23):
potent poison against land crabs. So you can imagine a
bunch of ants come up against one of these Christmas
Island red crabs and the ants spray formic acid in
its eyes, in the segment joints of the crabs, so
you know, like getting in the leg joints, and this
can leave the crabs unable to move or to survive.
And then after the crabs die, of course, the ants
(38:43):
get a feast of crab meat. And this has had
a huge impact on crab populations. It's been estimated that
in the last fifteen years the ants have reduced the
crab populations on the island by as much as tykes.
So local land crabs have been put severely at risk
by the yellow crazy ants. Interestingly, the yellow crazy ants
existed on the island for many decades. I think they
(39:05):
were introduced sometime in the first half of the twentieth century.
I've seen estimates in the nineteen teens or twenties around then. Uh,
And they were on the island a long time before
they became so destructive to the land crabs beginning around
the nineteen nineties. So what changed around the nineteen nineties.
I was reading a report that was put together by
(39:27):
Parks Australia together with Latrobe University, and it appears that
it was only in the nineteen nineties or so that
these massive super colonies of yellow crazy ants began forming.
So what caused that change? What happened then? Uh? The
author's point to the emergence of a mutualism, actually a
symbiotic relationship, and this is a mutualism between the yellow
(39:49):
crazy ants and another group of insects called scale insects.
So it's like the like the two enemies, they they
forged a truce and and then we're united against the
forces of the crab. Yes, so another non native species,
the scale insects. What they do is they cling to
plant stems and they suck the sap from the plants
(40:11):
for energy, and they produce a sugary waste product from
their anal pores in the process. And the ants love
this sugary poop. They go straight to the anal pores
and they eat it up. So they have formed this
mutualistic protective relationship with the tree sucking candy poopers. The
scale insects suck from the trees, they produce sugary poop.
(40:32):
The yellow the yellow crazy ants eat the sugary poop
and they protect the scale insects. And it appears that
this emerging symbiosis between the yellow crazy ants and the
scale insects is related to the ant's ability to form
these ecologically devastating super colonies. But here's so, then you
take the question one step back, Well, what caused this
(40:53):
mutualism to begin in the first place. Uh, the authors
of this report don't know. They speculate that change ng
rainfall patterns on Christmas Island. We're putting stress on trees
and this made the sap more concentrated, which means it's
even more sugary goodness for the scale insects. And this
increases the population of the scale insects, which produces more
(41:16):
delicious sugary poop for their yellow ant friends, which means
more ants to protect the scale insects, which means even
more scale insects. And then you get this dangerous feedback loop.
It's this is all Christmas Island is in so many ways.
This Uh, this wonderful look at the horrible cascading effects
of colonialism, of human intervention in general, I mean at
(41:38):
the macroscopic climate level and at the local invasive level. Yeah,
like at every level. We have messed with this island,
and we messed it with it in one way, and
now we're messing with it in a different way, and
and now in fact we're gonna keep messing with it
in order to try to fix part of what we did.
Because the question is can anything be done to save
(41:59):
these amazing red crabs? I mean, these are It is
a wonderful thing to see these animals doing what they do.
And so I was reading an interesting article about this
on the Conversation in UH posted in by two Latrobe
University professors Susan Lawler and Peter Green, and apparently Parks
Australia has been trying to do all kinds of things
(42:19):
to help the crabs survive the crazy ants or to
knock the crazy ant super colonies back, like they tried
poison bading the ants by hand. But apparently this is
just not an efficient solution. In seen, they launched a
new project and this was Killer Wasps. I like it
tell me more so, the Killer Wasps they're only about
two millimeters long, and they're naturally found in India and
(42:40):
Southeast Asia. They're called tach Cardia vegas Summerville and the
author selected this tiny wasp because it attacks this specific
species of scale insect that has formed the mutualistic relationship
with the crazy ants uh so. And the wasp is
a parasite oid that lays its eggs in the body
(43:02):
of the female of this one species of scale insect,
which hatch into more wasps that lay more eggs in
these species of scale insects, and hopefully this will severely
control the population of this one particular species of scale insect,
which is also invasive on the island. Uh And the
author's note that they've had to be very cautious because
(43:23):
they cite examples that, you know, in the past, we've
tried to introduce animals to places in the hope that
they would control the pest problem, but then they became
a problem in their own right. They said, the example
of the cane toad in Australia, which was brought into
control cane beetles, but then it became its own kind
of problem. And I'm reminded, of course, of the old
(43:44):
nursery rhyme. There was an old lady who swallowed a
fly right, and she's forced to keep swallowing progressively larger
and parasitic wasps and larger and more destructive organisms to
try and uh savor until if she dies at the
end of the song. Well, the authors, so we hope
that that happened. The authors claimed they performed rigorous research beforehand.
(44:04):
Uh they tested really hard to make sure this wasp
would not harm other local species. And they said, you know,
according to their tests, everything seemed to check out. So
they introduced the wasps in sixteen, and I checked with
a more recent news article on the wasp control project
from it looks like the effort is having early markers
for success. The wasps have become established, their range is spreading.
(44:27):
But we'll have to wait a few more years before
we see the full effect on the crab populations. But
I hope it works, and I hope it doesn't have
any unexpected effects. Less to become Island of the wasps,
Kingdom of the wasps. You don't want to have to
think about Crab Island needing to be protected. You want
to think that Crab Island is an armored claw wielding
(44:47):
force to be reckoned with, and that it you know,
it can withstand anything on its own. But I don't know. Yeah,
natural populations or even unnatural populations are vulnerable. Yeah, I
mean look at Skull Island right King Kong's homeland. Oh,
I don't know anything about population dynamics there. Or a
monster Island where all the giant Japanese monsters with kaiju.
(45:10):
That's clearly these are places that need to be protected.
We don't need to go in there and try and
to feed them with our robots. Is there is there
a crab kaju? Yes, there are. There are crab kaiju
up the wazoo. Yes, nice. Yes, they have their own
movies sometimes. Yeah, Godzillafa. Want to forget its name? I can.
I can never remember the names of the adversary that
(45:34):
maybe it. But yeah, he found a giant crab in
one episode. It was I finally remember it from my childhood.
But we'll get into we'll get into monster crabs a
bit more in the next episode of Stuff to Blow
your Mind, because we will talk about another resident of
Christmas Island that is an enormous deco pod. In fact,
that the largest land crab that you will find on
(45:54):
Earth now naturally, would love to hear from everybody out there.
We have listeners all over the world. I wonder if
we have just a single listener that lives on Christmas Island,
if we do email us yes, Likewise, we have a
lot of Australian and listeners UH and just listeners who
have traveled around the world in general. If you have
ever been to Christmas Island and witnessed any of the
(46:18):
species we discussed here, or just I mean even if
you've just been there and you saw nothing at all,
We want to hear from you. Whatever you have to
share about Christmas Island would be gratefully appreciated. And in
the meantime, you can check out all the episodes of
Stuff to Blow Your Mind. It's stuff to Blow your
Mind dot com. That's where you'll find all the episodes.
Links out to our various social media accounts, including UH
(46:38):
the discussion the module, which is our group on Facebook.
Look up stuff to Blow your Mind Discussion module and
you can easily join that and interact with other listeners
as as as well as Joe and myself. The website
Stuff to Blow your Mind dot com also has a
link to our store where you can buy some cool
merchandise stickers, shirts, etcetera. Um, it's probably probably a bit
(47:00):
late now for for Christmas gifts, at least for this Christmas,
but hey, you can go ahead and start start banking
ahead for next year. It's a great way to support
the show. And if you want to support the show
without spending a dime, well you can simply rate and
review us wherever you have the power to do so.
Huge thanks as always to our excellent audio producers Alex
Williams and Torry Harrison. If you would like to get
(47:21):
in touch with us directly to let us know feedback
on this episode or any other, to suggest topic for
the future, or just to say hi, let us know
where you listen from that kind of thing, you can
email us at blow the Mind at how stuff works
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