How squids outsmart their predators Carly Anne York
In the ocean’s depths,
two titans wage battle:
the sperm whale and the colossal squid.
Sperm whales use echolocation
to hunt these squid for food,
but even against this gigantic animal,
squid can put up an impressive fight.
Scientists know this because on the bodies
of washed-up whales,
they frequently find huge,
round suction scars,
emblazoned there by large,
grasping tentacles.
Ranging in size from
this giant’s impressive 14 meters
to the 2.5 centimeters
of the southern pygmy squid,
these creatures fall into the group
of animals known as cephalopods.
There are about 500 squid
species worldwide,
and they live in all the world’s oceans,
making them a reliable food source
for whales,
dolphins,
sharks,
seabirds,
fish,
and even other squid.
Indeed, squid themselves
are fearsome ocean predators.
But their most extraordinary adaptations
are those that have evolved
to help them thwart their predators.
Squid, which can be found mainly
in estuarine, deep-sea,
and open-water habitats,
often swim together in shoals.
Being out in the open without anywhere
to hide makes them vulnerable,
so as a first line of defense,
they rely on large, well-developed eyes.
In the colossal squid,
these are the size of dinner plates,
the largest known eyes
in the animal kingdom.
When it’s dark or the water is murky,
however,
squid rely on a secondary sensory system,
made from thousands of tiny hair cells
that are only about twelve microns long
and run along their heads and arms.
Each of these hair cells is attached
to axons in the nervous system.
Swimming animals create a wake,
so when the hairs on
the squid’s body detect this motion,
they send a signal to the brain,
which helps it determine
the direction of the water’s flow.
This way, a squid can sense an oncoming
predator in even the dimmest waters.
Aware of the threat, a squid
can then mask itself from a predator.
Squid skin contains thousands
of tiny organs called chromatophores,
each made of black, brown, red
or yellow pigments and ringed in muscle.
Reflecting cells beneath
the chromatophores
mirror the squid’s surroundings,
enabling it to blend in.
So, when the muscles contract,
the color of the pigment is exposed,
whereas when the muscles relax
the colors are hidden.
Each of these chromatophores
is under the individual control
of the squid’s nervous system,
so while some expand,
others remain contracted.
That enables countershading,
where the underside of the squid
is lighter than the top,
to eliminate a silhouette
that a predator might spy from below.
Some predators, however,
like the whales and dolphins,
get around this ruse by using sound waves
to detect a squid’s camouflaged form.
Not to be outfoxed, the squid still
has two more tricks up its sleeve.
The first involves ink,
produced inside its mantle.
Squid ink is made mostly of mucus
and melanin,
which produces its dark coloring.
When squid eject the ink,
they either use it to make
a large smokescreen
that completely blocks the predator’s view
or a blob that roughly mimics the size
and shape of the squid.
This creates a phantom form,
called a pseudomorph,
that tricks the predator
into thinking it’s the real squid.
As a final touch,
squid rely on jet propulsion
to rapidly shoot away from their hunters,
reaching speeds of up to 25 miles per hour
and moving meters away in mere seconds.
This makes them
Earth’s fastest invertebrates.
Some squid species have also developed
unique adaptive behaviors.
The deep-sea vampire squid,
when startled,
uses its webbed arms to make
a cape it hides behind.
The tiny bobtail, on the other hand,
tosses sand over its body
as it burrows away from prying eyes.
The Pacific flying squid
uses jet propulsion for another purpose:
to launch itself right out of the water.
Squids’ inventive adaptations
have allowed them
to proliferate
for over 500 million years.
Even now,
we’re still uncovering new species.
And as we do,
we’re bound to discover even more
about how these stealthy cephalopods
have mastered survival
in the deep and unforgiving sea.