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Isn't it awful when you're watching a video
and you really want to know what someone's saying,
and you can't hear them?
I think about this a lot
because good video is good audio.
You have to put the microphone right in the right spot.
I have a microphone right here.
You have to treat your room--
in my case, I've got sound blankets, sound foam.
Audio is a physical thing.
It needs to be physically absorbed or reflected.
Humans, even with all of our technology,
are still struggling to absorb sound.
So when I saw this new research that says
we might be able to block all sound
with just a layer of wallpaper--
How?
All it took was a little bit of engineering,
a little bit of biomimicry,
and a sonic arms race between bats and moths.
[intro music]
Hey, howdy, human beings who are,
you know, loud usually, like myself. Trace here.
Predators and prey are locked
in this deadly game of cat and mouse.
Actually, that's not a great example
'cause cats and mice are just examples
and predators and prey-- it's not so much a metaphor
as just, like, the thing I'm talking about.
But, anyway, you get what I mean--cat and mouse.
The natural interaction of prey animals
with predator animals means that over many generations,
each side is going to influence the other
to adapt and thus evolve.
Rodents, for example, are very sensitive to noise.
So owls have specially shaped serrated feathers
for near-silent flight.
We humans then take these evolutionary inventions
and we use them to our advantage.
This is called
And recently, there was this very cool biomimicry discovery,
but to understand it fully,
you need to go back and understand bats and moths'
sonic arms race.
And to do that, we have to go back 65 million years
to the evolution in bats of
Don't worry-- this'll all make sense.
Contrary to popular wisdom, bats are not actually blind.
But they do use sound to locate their prey.
They emit high-pitched squeals--
[bats squealing]
--which bounce off other objects.
They
they hear it, and they can discern information
about the object, like its location.
Thus it's called echolocation.
You can actually do this, too, if you go to a cave
or a really big room or somewhere
and you-- [shouting] echo! Echo!
You're discerning information about the size of that space.
Maybe you don't do it as well as, say, a bat,
but it still does give you more info
on the size of the room you're standing in.
And this is a biological analogue to radar,
except for instead of radio waves, we're using sound waves.
Actually, come to think of it, bats and moths
do have this kind of fighter-jet,
Top-Gunny thing going, right?
They're flying, they're-- whoosh, whoosh!
Trying to get radar and get locks on and stuff.
That's kind of cool.
You would think it'd be like an eagle
or a falcon or something that would be like a Top Gun,
but, nah, it's just bats and moths.
And what are bats eating?
What is the "MiG-28" of our mammalian Top Gun?
It is the moth.
Between these two animals, nature is in the middle
of a full-scale sonic arms race.
And some of the strategies that these animals are using
aren't that different from what we humans have come up with
in our more literal arms races.
So the bats are using these ultra-sonic,
echolocating shrieks,
and moths-- they need a defense.
As they are eaten and eaten and eaten,
some moths adapted a slightly better sound-absorbing wing,
and that baffled the bats' radar.
Then, as more and more bats were baffled,
one of the bats adapted a slightly better
echolocation system.
I mean, it's an arms race. But that's not all they do.
Moths can also hear when bats are echolocating nearby
thanks to a tympanic membrane that they evolved
that vibrates when sound hits it,
sort of like your eardrum.
When they sense that approaching bat,
the moth takes evasive action,
upping their chances of survival by 40%.
So not only do they have a counter to the radar
with absorption, but they can also tell
when they are being locked onto.
But the bats aren't going to be "goosed,"
so eventually some bats change their calls
to combat the moths' ability to hear them.
They changed to different frequencies
or they made the calls quieter
in an effort to stay undetected.
So moths evolved another defensive technology--
sound-absorbing scales.
And this is what I'm talking about, y'all.
Windmill high-five!
Self high-five.
These scales are incredible at absorbing sound.
Like, even beyond what we humans can do.
So much so that the researchers studying them
call them "natural metamaterials."
You-you're not as excited about that as I am?
Let me explain.
Metamaterials are typically engineered
synthetic materials which are designed to take advantage
of a property that is not found in nature.
So, when nature makes it
and it's a metamaterial, that's mind-blowing.
Think
But if you put it into one-atom-thick sheets,
it's super strong, conductive, biodegradable.
You roll that sheet into a tube, you got a carbon nanotube,
some of the strongest things humans know how to make.
Again, it's just plain old carbon--
the stuff you get when you burn wood.
These moths, they did that, but they did it with evolution.
And that's extremely rare in nature.
And it might be the only example we know of
of a natural acoustic metamaterial.
When sound hits these scales on a moth's wings,
it absorbs it, even though the scales
are 100 times thinner, at least,
than the sound waves they're absorbing.
Put more technically, when a 78 kilohertz wave
hit the wing, it absorbed it at 72%,
meaning it absorbed most of the sound that hit it
even though it was ultra-thin.
And different-sized scales on the wings work together
to make the moth wings behave like this metamaterial,
allowing it to absorb different wavelengths.
You could put it this way--
moths have evolved an acoustic invisibility cloak
which makes them harder targets for bats to spot.
Stealth planes, by the way,
are coated with radar-absorbing materials
much for the same reason.
Again, whoosh, whoosh! Top Gun.
When I, a human, want to stop sound--
I already mentioned this-- I have to use squashy
or angled physical barriers.
That's the tech we got.
And the thicker those barriers, the more broadband sound,
as it's called, it's going to absorb.
If I just want to block one frequency,
sure, I can use a thin layer
that absorbs just that wavelength,
but I'd need more layers for more wavelengths.
Or I have to switch and put a big, thick foam blanket
to physically block the sound.
These moths use a variety of scales
to soak up that broad range of frequencies
and remain ultra-thin--
I don't know how else I can put it.
It's mind-blowing.
In the future, the researchers think,
if we can figure out how this works well enough,
they could use this tech to make a wallpaper
that absorbs so much broadband sound.
And thanks to bats and moths, we might be able to make
trains, planes, automobiles, homes, buildings quieter
with just a super-thin layer of moth-inspired sound paper.
I know!
"But that's not all!" as they used to say.
Other moth species have taken an even more active approach
to this sonic warfare.
When certain tiger moths sense a bat coming,
they'll actually chirp back at the bat--
clap back at it.
Some species of tiger moths do it to warn the bat
that they're toxic-- basically saying,
"I'm not delicious! Don't eat me!
Trust me, it's disgusting."
Which is actually my strategy as well
when, you know, people come running at me.
I'm just like, "No, leave me alone! I'm awful."
Other tiger moths make ultrasonic clicks
fast enough to jam the bats' echolocation.
And, yes, jamming radar with confounding waves
is also a tactic of some
specialized electronic warfare jets,
one of which I actually rode in once, you know--
not to brag. [coughs]
Anyway, once you're aware that this sonic arms race exists,
you start to see it everywhere.
Bats are not the only echolocators
out there in nature; another group of animals
famously use echolocation as well.
Do you know what that would be?
(voices) Marshmallows! Tigers!
Dolphins! I'm hungry! Santa Claus.
That's right!
Toothed whales.
I mean, "dolphins" is also right.
They're just a subset of toothed whales.
Two different genres-- ones are baleen whales,
the other are toothed whales,
and all the toothed whales use echolocation.
Strangely, while we've discovered a lot of adaptations
that insects use to elude bats,
there don't seem to be that many specific adaptations
that the prey animals to these toothed whales use.
There are a few species that can pick up
on the clicks and whistles of dolphins--
shad, for instance, will turn tail and bolt
when they detect sonar,
which makes them harder to spot and puts some distance
between them and a hungry dolphin.
Toadfish, which use mating calls
that sound like your phone on vibrate, uh,
will switch to silent if they get pinged by sonar.
No, ew.
Ech, no, no thank you.
Other marine animals can't detect sonar, per se,
but may have some natural defenses against it.
Some deep-water cephalopods have very low muscle mass;
that helps hide their presence under water from sonar.
They're way less muscle-y than some of their cousins,
so if you're ever self-conscious, just remember
that you're safer from a sperm whale attack
if you're scrawny like a deep-water cephalopod.
Put that on your inspirational poster
and hang it. [coughs]
For the most part, though,
it seems like aquatic prey animals have no real counter
to echolocation.
That may be because water is a different medium than air.
You know, they evolved differently;
they have a tough time picking up sound at all
because without swim bladders,
their bodies don't impede the sound,
so it just kind of moves through their body
and they can't sense that physical pressure change,
which is a real issue.
And even if they did have swim bladders,
that doesn't really help pick up the frequency of the clicks
because that's a very high frequency,
and on top of that, the predators in this area,
you know, they don't actually use echolocation that much,
anyway, so why would you evolve a fool-proof way
to counter an attack that doesn't actually
get used that often?
The best choice might be
just listen for John Williams' soundtrack
with the London Symphony, because something crazy
is happening any time that comes around, right?
Or they could just listen to the low-frequency whoosh
of water predators as they barrel toward them
with jaws that snap...
Cephalopods
thanks to literal stones in their ears.
Yeah, they actually do have little calcium pebbles
in their ears.
And so do you... because common ancestor.
Isn't that awesome? I love learning something new.
Sometimes I'm just at my computer--
that was one of those moments--
and I just go, "What?"
My mom always said that was me
getting another wrinkle in my brain,
and my coworkers always said that meant it was going
to be a good video, so must be really wrinkly now.
If you love that feeling, too,
and you want to learn something new every day,
which is my favorite thing,
you should try Brilliant.
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like in between when I release my videos
or when you're hanging out waiting for the bus.
Let's say you're intrigued by sound waves
and wave propagation that we've been talking about
and how they might be canceled out by moth wings.
You hit up lessons on Brilliant about waves
in the Trigonometry section.
Brilliant is cool because it's not just a static quiz;
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You can learn and retake bits. You can get hints and tips.
If I'd had this tool when I was learning math
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Having that basic understanding of math and science
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Once again, brilliant.org/Trace.
You can learn something new anytime,
and thanks for considering it.
By the way-- the little stones in your ears?
They're called
Nature is both incredible and rudimentary.
Why make it complicated?
If I can just have some little stones rolling around in there,
I can tell which way is up.
But the mind-blowing thing is
all bony fish have otoliths,
which is again why you have otoliths--
because we evolved from a common ancestor.
Otoliths tell you which way is up,
they translate acceleration changes,
and all of these species need to know that.
But you and fish inherited something
from a common ancestor.
Just let that sink in for a minute.
It may look fairly Stone Age--
pun intended-- when you consider
that bat vs. moth metamaterial comparison
to literal fighter jets,
but whether the adaptations are complex metamaterials
or, you know, rocks in your head,
the way sound influenced the predator/prey evolution
is absolutely fascinating.
And who knows what cool survival strategy
or countermeasures nature is going to devise next.
I'll probably make a video about it.
Speaking of that, I do have more videos coming at you soon.
Thank you to all of my patrons
who help keep this channel afloat.
That is a fish pun there, I guess.
If you have an idea for a future video,
please drop me a line on Twitter, in the comments.
I read all the comments.
Please consider subscribing.
Keep on learning.
I'm Trace. Thanks again.
I'll see you in the future.