[♩INTRO]
For a Medieval knight, armor was a vital body covering
to block the tip of a sword.
But armor is more than the unwieldy metal suit displayed in castle museums.
Broadly, it’s any protective layer.
So, we still use armor now.
Like, a motorcycle jacket keeps pavement from your skin,
and a face shield makes a barrier to pathogens.
And other organisms use armor, too
except, sometimes, their armor doesn’t look like anything we’d expect.
Sometimes, it’s fancy scales, and sometimes, it’s a bunch of viruses.
First up, though: ants!
All insects have a hard body covering called the cuticle.
It’s mostly made of a big old molecule called chitin,
and since ants don’t have bones, it’s the only rigid structure
to anchor their muscles and hold their guts together.
The cuticle also serves as armor, not unlike knight’s armor.
Those layers of chitin are held together by flexible membranes
with elastic proteins, especially in places like knee joints that need to move.
And overall, those hardened layers serve as a great first defense
against a predator looking for a snack.
But some insects take their armor one step further
including leaf-cutter ants, according to a preliminary 2020 paper.
If you know anything about leaf-cutter ants,
it’s probably that they can hoist nearly 50 times their body weight in leaf cuttings,
to take home to their colony fungus gardens.
But the soldier ants in particular also have some pretty impressive armor.
These are the big-headed ants tasked with things like protecting their colony.
And the authors of the study found that these soldiers have a magnesium-calcite
coating on their cuticles to make them harder and tougher.
In the soldiers, the mineralized coating accumulates as they mature,
and it overall makes their cuticles more than twice as hard.
But, here’s the thing: There’s a tradeoff between the strength of armor
and the difficulty of maneuvering around in it.
So, why do these ant soldiers need super tough armor even
though it may slow them down?
Because their job is to fight other ants!
And ant wars, often over food resources, are brutal.
Battles between leaf-cutter and army ants can last for days,
with rows of soldiers locking limbs.
And if an ant overpowers its foe, it will hold them down and bite them to pieces.
So, an extra-hard cuticle could be lifesaving.
Next up: the Atlantic alligatorfish.
These things don’t really look like alligators, but one thing is for sure:
Their armor is so good it’s… maybe a little excessive.
In a study published in July 2020,
researchers looked at different species of alligatorfish.
They used data from CT scanners to measure the amount of material
in the fishes’ body coverings — basically, their hard, armored plates.
Then, they compared that to the size of their internal skeletons.
The ratios between the two really varied among species,
but the Atlantic alligatorfish was especially well armored:
Its body covering was ten times larger than its skeleton by volume.
It’s not clear why these alligatorfish are so armored up,
but it could have something to do with predators
maybe animals like crabs, or possibly ratfish, which have dangerous tooth plates.
Some species of alligatorfish have even been found with damage marks
on their armor, which suggests they’ve been in a few scuffles.
For now, though, the factors selecting for such extensive armor will likely remain
a mystery until someone spends more time hanging out in the ocean!
Next: Sometimes an organism needs armor for a specialized purpose
like the whale shark.
Like other sharks, they have dermal denticles — a.k.a. skin scales.
A dermal denticle is triangular and made of dentin,
a hard tissue derived from the same cells as teeth.
The denticles overlap, with all the points facing towards a shark’s tail.
So, stroke a shark from its head backward, and it feels smooth.
But, expect a bad time in the other direction.
These denticles are etched with parallel ridges that might help
streamline swimming, helping water flow more smoothly along the shark’s body.
It’s still up for debate.
But either way, what’s odd about whale sharks
is that they also have denticles on their eyes.
A 2020 study found that each iris is ringed by several thousand denticles,
which have ridged lobes like a leaf
making them different from the streamlined skin denticles.
And the authors speculate that this might be to prevent mechanical damage.
If you look at a whale shark, that kind of makes sense:
Unlike other sharks, they don’t have eyelids.
And their eyes also protrude out, potentially exposing them to hazards.
Still, we didn’t used to think these animals relied much on their vision
but this study suggests otherwise.
After all, it wouldn’t be worth the cost of eye armor if seeing wasn’t important.
In evolutionary terms,
structures that are costly but aren’t useful don’t normally stick around.
So, apparently, they’ve got something to see after all.
And actually, this would also explain something else the researchers noticed:
When you approach a whale shark,
they retract and roll their eyeballs back into their sockets.
Which is a sign they’ve got something to defend.
Speaking of specialized armor, check out mantis shrimp
famous for packing a punch.
In a feeding style called smashing, they use club-like appendages to punch prey
with extraordinary force, enough to crack the shells of mollusks and crabs.
Male mantis shrimps also punch each other on the tail
as they compete for territory.
But this is where their sweet armor comes in.
Species of mantis shrimp that punch have armored up their last body segment.
It’s called the telson, and it forms part of the tail.
And the result here is a long piece of abdominal armor.
And these mantis shrimps don’t fight to the death.
Instead, they do a ritualized fight, punching each other’s telsons.
The ritualized fights probably exist for the mantis shrimps
to learn about each other
basically, to size each other up and see if it’s worth fighting or standing down.
So they’re not trying to kill each other.
But the telsons do still have to absorb quite the impact.
And 2010 research on the Caribbean rock mantis shrimp
showed exactly how they do it.
Instead of setting up a mantis shrimp fight club, they did…
something even weirder.
They glued dead mantis shrimps to plexiglass
and dropped steel balls on their telsons.
They found that the telson is like a punching bag,
absorbing and dissipating impacts.
Specifically, the telson’s center, a bull’s eye to a mantis shrimp opponent,
is reinforced with minerals.
And other research has shown that they’re arranged in a layered,
spiral-like structures that absorbs energy.
Meanwhile, the area surrounding the telson cushions
the blow like a boxer’s punching bag.
Curved ridges running lengthwise stiffen it along the central axis,
but also allow the telson to flex inward when smacked.
Oh, and in case you’re wondering:
The shrimps do molt, losing their super hard shells as they grow out of them.
And just like a soft-shell crab,
a newly-molted mantis shrimp is soft until its shell hardens after a few weeks.
So, if one of these guys encounters another male…
they’ll just flee, since both their clubs and their telson shields are useless.
The animals we’ve talked about so far have basically had one kind of armor:
one adaptation that helps them out in various situations.
But that’s not true for everyone.
Some organisms have adaptable armor — like a genus called Daphnia.
Sometimes called water fleas, these are tiny crustaceans common in freshwater.
And they’re eaten by a ton of small organisms,
including tadpoles, insects, salamanders, and minnows.
Daphnia is therefore in need of some serious defenses.
The problem is that their wide range of habitats makes for
a wide range of predators.
And every predator is different.
So, Daphnia employs what’s called induced body armor,
which appears as-needed.
Depending on which predators are around,
juvenile Daphnia develop different features as they grow.
For instance, Daphnia grow neck spines when they grow up
in a habitat with larval midges.
In contrast, Daphnia that grow up around tadpole shrimps
get tail spines and more angular heads.
And there are more options than that, too
including hard helmets, spiny head lobes, and jagged crests.
What’s happening here is that chemicals emitted by the predators
are actually cueing the water flea’s development.
Like, when researchers exposed Daphnia to a chemical naturally emitted
by those midges, that triggered their bodies
to start developing those neck spines.
Researchers think these customized responses interfere with how each predator
captures and processes prey.
And honestly, it’s a really clever strategy for a group
of creatures that live in so many different environments.
Finally, armor, in all its variations, can even be life-like.
Just ask some bacteria.
It’s odd to think of bacteria as needing to protect themselves.
But, like any organism, a bacterium faces threats from its environment.
One of the main ones is from viruses called bacteriophages,
which attack, infect, and kill bacteria.
Bacteriophages are called phages for short.
And after hijacking their hosts’ machinery to copy their own DNA,
they often free themselves by killing the bacteria
specifically, by releasing enzymes
that destroy the bacterial cell membranes or wall.
But, some phages have formed a sort of truce with bacteria.
They’re called filamentous bacteriophages,
and they’re long, spaghetti-like viruses.
These phages do a lot of their business as normal,
replicating their genetic material inside the bacterium.
But when they’re done, they bind to special receptors on the bacteria,
and are transported out of the cell using special cell machinery.
So, the phage gets to replicate and ride around in the bacterium,
but the bacterium survives.
And somehow, that’s not even the best part.
The phage also secretes liquid crystalline droplets
that form a coating around the bacterium.
And this biofilm directly helps the bacteria by keeping it from drying out,
and making it stickier so it can attach to surfaces more easily.
But the biofilm also protects the bacterium
from the damaging effects of antibiotics!
That’s great for them, but kind of a problem for us,
since that natural hazmat suit gives bacteria resistance to our medications.
And an estimated 80% of our infections
have to do with bacteria encased in biofilms.
The medical community continues to agonize over
how to get at biofilmed bacteria — such as those that make plaque on our teeth.
New approaches range from photosensitizing chemicals that make
toxic molecules to anti-adhesion coatings that resist the sticky biofilms.
It’s ultimately a work in progress, but still: watch out, phages!
So, overall, the armor worn by knights was great and everything,
but it didn’t outshine the startling array of armor in nature.
Natural armor evolves again and again to defend organisms
against abrasion, competition, predation, and pathogens.
And it does so in some pretty clever ways.
If you liked this episode and are a fan of sharing cool things about the world…
Well, you might also be interested in SciShow Kids!
It’s our science channel for early elementary learners,
and we’re releasing new episodes over there every Monday.
If you have a kid or teacher in your life, we think they’ll really enjoy it.
We’ve even got an episode on mantis shrimp!
You can find it over at youtube.com/scishowkids.
[♩OUTRO]