How Do Coconut Crabs Work?

The coconut crab is the world's largest land-dwelling arthropod -- they grow longer than your average dog and can open coconuts with their claws. Learn more in this episode of BrainStuff, based on this article: https://animals.howstuffworks.com/marine-life/coconut-crabs.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff, a production of I Heart Radio.
Hey brain Stuff, Lauren Boga bom Here. If you or
a friend had a hermit crab when you were a kid,
or if you have one now, you're familiar with how
they'll make a home in a snail shell in the
wild or a terrarium. They'll squeeze into an empty shell

(00:23):
that's just the right size for them to carry around
as mobile protection. They're soft bellies, sheltered and their legs
free for crawling. Most of the ones we keep as
pets in the US are just an inch or too long,
up to about five centimeters. Okay, now picture that little buddy,
but twenty to thirty times larger and having grown just

(00:43):
enough offenses that they no longer need to carry a
defensive shell. And that's what you're looking at when you
consider the coconut crab, a close cousin to the pet
hermit crabs that we keep. The coconut crab is native
to the islands in the Pacific and Indian Oceans, and
they're the world's biggest land dwelling arthropods. They can weigh

(01:03):
up to nine pounds that's about four kilos with a
leg span of around three ft or one meter. This
is only about the third of the leg span of
the Japanese spider crab, which is the biggest arthur pod period,
but as it's an ocean dweller, it has less of
a chance to startle us with its sheer size. Most
coconut crabs are longer than most dogs, and coconut crabs

(01:26):
have been known to eat kittens, rats, chickens, and each other.
They've even been proposed as a possible culprit in the
disappearance of the body of Amelia Earhart, as we've discussed
before on the show. For the article this episode is
based on How Stuff Works, spoke with Shinichio Oka, chief
research scientist at the Okinawa Choshima Research Center in Japan.

(01:48):
He said, the coconut crabs have no seashell as protection
from enemies, so they have powerful claws and a large
body to protect themselves. In addition, they're mighty claws. Let
the monopoly is the terrestrial hard foods, including coconuts, which
other animals are unable to get into. So exactly how

(02:08):
strong are the claws of a coconut crab? OCAs said,
we could find that coconut crabs can generate the pinching
force of ninety times of their body weight. The calculated
pinching force of the largest coconut crab is almost equal
to the bite force of the adult lions. So these
overgrown coconuts smashing kitten eating crustaceans are nightmare versions of

(02:32):
the petite and mildly pinchet hermit crabs that we know.
But they actually do spend some of their life cycle
in the same manner as their dainty your cousins. Coconut
crabs spend most of their lives on land, but they
start out in the sea. A female coconut crab deposits larva,
which she's been carrying around in her abdomen since they
were just fertilized eggs, into the ocean, and the babies

(02:55):
float around in the currents for a month or so
eating other plankton, before gay enough body weight that they
dropped the sea floor and find nice cozy snail shells
to move into. Just like your childhood hermit crab friend,
the young coconut crabs move in and out of shells
as they bulk up and get used to living on land,
and sometimes a juvenile coconut crab will use a coconut

(03:17):
husk or empty seashell is armor until its own shell
gets harder. After about a year, the teens of the
species eventually find that there are no shells left on
the beach large enough to accommodate their bulk, and so
they move out altogether. From here on out, they live
the rest of their lives out of the water. Adult
coconut crabs can't swim and will drown if totally submerged.

(03:42):
Adult coconut crabs bodies have kelcium based exo skeletons, which
hard enough more than hermit crabs do once they mature,
so they're free to grow as monstrous size as they
can manage. Every few months, coconut crabs molt their too
tight exo skeletons and then grow a larger one they
the old one after they've shed it. Coconut crabs will

(04:03):
eat almost anything, all kinds of fruit, plant matter, dead
animals they find lying around, food you've left lying around
other crab species, or even their own friends. Actually, coconut
crabs don't really have friends. They're pretty solitary. They have
an excellent sense of smell, which makes them great at
finding rotting carcasses and anything else potentially edible. Coconut crabs

(04:25):
are also sometimes called robber crabs because they've been known
to steal items like silverware that has even the faint
odor of food about it. But their most important source
of nutrients is coconuts. Because coconuts seem to be what
allows them to achieve the gigantism they're known for. Coconut
crabs will climb trees to get at coconuts and use

(04:47):
their pinchers to open them. Study found that the coconut
crabs that have access to coconuts are likely to have
around double the mass of those living in coconut free environments.
So a coconut crab is lucky enough to have coconuts around,
and if it's strong enough to pan opener its way
into a coconut, it's able to grow a lot bigger

(05:08):
and then access even more coconuts the size ceiling gets
a whole lot higher. But coconut crabs are not invulnerable,
their numbers seem to be declining, probably because the islands
that they live on aren't what they used to be.
Introduced species like dogs, pigs, and humans eat the adults,
and invasive rats gobble up the smaller, more vulnerable babies.

(05:33):
They're extremely slow growing and can live to be about
fifty years old. Coconut crabs have been listed as data
deficient by the International Union for Conservation of Nature, meaning
nobody really knows enough about these animals to understand their
conservation needs. Although it's likely that they're not doing well,
their status was last assessed in so more research is

(05:54):
needed to understand where coconut crabs stand m Today's episode
is based on the article called the coconut Crab, a
crustacean on steroids on house toff works dot com, written
by Jesselyn Shields. Brain Stuff is production of I Heart
Radio in partnership with how Stuffwork dot Com, and it's
produced by Tyler Clang. Four more podcasts my heart Radio

(06:17):
visit the i heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.