Kind: captions
Language: en
fiddler crab claws are proportionally
bigger than any other known animal
weapon on earth there's about a hundred
and three different species of fiddler
crabs they live all over the world in
the tropics and they eat algae off the
surface of the mud
Brooke Swanson studies the costs and
benefits of this surprisingly large claw
so females have two little claws and
they can actually eat twice as fast as
the males the male's only have these
giant claws and can't use their weapon
claw to eat the huge claw comes at a
great cost males must eat extra food to
fuel their muscles but they are only
able to gather it half as fast as the
females all right so he's betting me
three times already
can you show me what these guys can do
we can use this force meter to measure
how strong their claws are this just
measures how hard they squeeze exactly
put their claw right there this squeeze
that's about 20 Newtons so the crab is
producing about 20 Newtons with its
claws five pounds of force so like
having a bag of sugar on a pin pushing
on you so it's not just five pounds
that's five pounds concentrated on a
very sharp exactly that's why it hurts
so much
so is this strong enough to pierce
another crab shell a machine in the lab
can measure that using the shell of a
dead crab that could take about 5
Newton's of force 5 Newtons so way less
than the squeezing force the big claws
pinching strength is 4 times more than
what is needed to pierce another crab
shell so this is technically a lethal
weapon
exactly crab claws are powerful enough
to kill a rival but there's a paradox so
they're plenty strong enough to kill
each other but when we keep them in the
lab we hardly ever see them fighting and
I've never seen one kill another one in
the lab
and when you study these in the field
it's very rare to see them fighting
there as well
male fiddler crabs sometimes duel with
their weapons on the beach but they
spend much more time using their giant
claws in another way so here we have two
male fiddler crabs and their body size
is about about the same but if you look
at their claws huge the claws twice as
big as the other wow that is so obvious
what they spend most of their time doing
is not fighting with these claws but
waving them in the air so they walk
around on the sand and they wave the
claw and they're signalling to the other
crabs how big and how strong they are so
what makes the claw good signal is that
it's hyper variable there's a lot of
variation between crabs and so if you're
looking at crabs by their claws you can
easily tell the difference
you can easily tell that this crab is
bigger and stronger and a better fighter
and that's what makes the claw a good
signal this is awesome you'd think that
the species with the really big weapons
would use them to fight all the time and
yet what we see is the reverse that the
species with the biggest weapons are
actually the most peaceful