- Imagine walking down the street and then out of nowhere you just start getting pelted with bowling balls.

Sounds extremely not fun and actually kind of deadly, but this is what it's like for an insect caught in a rainstorm.

Now, for you and me getting caught in the rain is, I don't know, annoying maybe.

But for a mosquito or a dragonfly or a butterfly, or really any flying bug, this is a potentially dangerous problem that they've got to solve in order to survive.

Luckily, nature has given them a really cool secret weapon that basically makes them waterproof or what scientists call superhydrophobic.

And it's not just bugs either.

Birds, even Many plants have developed similar adaptations all in the name of making their bodies extremely unfriendly to water.

Today we're gonna take a close look at the insanely cool living nanotechnology that makes this work.

We're also gonna look at some of the strange ways that water behaves at super small scales.

And finally, how all of this is inspiring humans to develop super waterproof surfaces for everything from aircraft to solar panels.

Who knew butterflies were so high tech?

Welcome back smart people, Joe here.

Remember how a minute ago I said for a mosquito in a rainstorm, it's like you or I getting pelted with bowling balls?

Well, it's actually way worse.

Mosquitoes are really lightweight.

When a rain drop hits them.

It's the equivalent of a person getting hit by a Volkswagen Beetle.

So it's a, it's a big deal for them.

But unlike us, if we get hit with something that's 50 times our weight, we die.

But mosquitoes, they actually survive these raindrop impacts.

- And he's not wrong about those numbers.

A human size raindrop, say a meter in radius would be over four metric tons worth of water.

And if we scale up the velocity of that rain drop from mosquito to human scale, it's moving at several hundred body lengths per second.

If that hit you, then you would be the one who went splash.

Yet mosquitoes can fly in the rain, so how do they do it?

So when you get hit by a raindrop, what you are actually feeling is the equal and opposite force that your body is applying back to the raindrop.

Because you have lots of inertia, so you resist that tiny force.

But when a mosquito gets hit by a raindrop - Because they're so light when they get hit, they just go along with a ride.

They don't stop the raindrop because they're not resisting the force.

It just keeps on going and they get a much reduced force when they get hit by that large weight.

- That's really interesting.

Small insects like mosquitoes and flies deal with raindrops by basically not resisting them at all.

Here's an interesting way to think of this.

Imagine that you're trying to just pop a balloon by punching it.

That's impossible because the balloon doesn't resist your motion at all.

But this also isn't the whole answer.

Because water can deform around tiny insects and trap them.

That's deadly because at those small scales, the stickiness of water that's equivalent of you or I trying to pull ourselves out of molasses or something.

What what about bigger flying insects, like dragonflies or butterflies?

They are massive enough that unlike a mosquito, they don't just go flying the other direction when they get hit by a raindrop.

Instead, they've basically built their wings in a way that water can't stick to them.

Okay, I've got some just normal water here.

Watch what happens when I drip this onto a butterfly wing.

I mean, it just bounces right off like the water's like a little rubber ball or something.

It's totally weird.

And it's not just butterflies dragonfly wings too completely, just like a trampoline for water.

You can even see how water beads up on the surface.

It's so weird.

So what's happening here, - A lot of these insects, are hydrophobic.

They're water repellent by virtue of having all these little pockets of air on their skin.

They have all these little hairs and things like that, and when drops hit them, if they hit them fast enough, they don't have time to sort of go into these holes.

- So if you were to zoom way, way in on a butterfly's wing scales, what you'd see is that they're actually these grids and stacks of ridges and other shapes, basically lots of empty space.

These nanoscale structures are actually what give some butterflies, those brilliant blues and iridescent colors because of how they interfere with light.

But when it comes to repelling water, it's about what those structures don't do.

This is a sort of representative model of what it insects wing surface looks like at that microscopic scale.

All these little waffle rod like pockets here.

basically this surface is rough on the micro scale.

Now, if you imagine this is a tiny water droplet, well, it just sort of sits on top of that lattice there.

It never really goes in and well, that water droplet just ends up kind of rolling off the edges.

Now, a lot like the stretchy elastic on the outside of the balloon works to keep it from deforming.

Well, the water molecules in a droplet are attracted to each other and they want to pull that water droplet into the shape with the least surface area.

It's why water droplets try to form spheres.

It's the shape with the least surface area per volume.

This attraction of water molecules to other water molecules, that's called cohesion.

On the other hand, if I drop some water onto a glass plate like this, well, it doesn't form a sphere at all, does it?

It just kind of spreads out weird little lumps.

That's because water molecules are also attracted to the atoms in certain materials like glass, that is called adhesion water being attracted to things that aren't water.

If the water sticks to itself more strongly than it sticks to whatever surface that it's interacting with, if the cohesion outweighs the adhesion, you get a situation like this, you can actually measure the angle between the surface and the droplet.

If it's greater than 90 degrees, then we say that surface is hydrophobic.

If that angle's more than 150 degrees, then it's superhydrophobic.

And if it's less than 90 degrees like our water droplet on glass, that kind of surface is called hydrophilic.

So if we look at our little model of a droplet on an insect wing, again, because so little of the water droplet is actually in contact with the surface, with the cohesive forces of the water sticking to water, they outweigh the adhesion of water sticking to the wing.

And so the drop just pulls itself into this round shape and we get a really large superhydrophobic contact angle and that water just ends up rolling right off.

And this goes beyond insect wings too.

It's also how insects like water striders glide across the surface of a pond.

- And in fact, if you look at these insects that walk on water and you actually look really closely underneath, they look like they're staining on water because their hairs are so numerous.

They've got 10,000 hairs per square millimeter.

I mean, if you imagine a square millimeter and you pretty much take all the hairs on my head and put them in that little pot, that's what they have.

And you can imagine the water drop, if it's like a balloon and you're trying to push it into those little 10,000 little pinholes, it doesn't like to do that 'cause it's gotta conform to all those pinholes.

It would rather just sit on a little pocket of air.

- We even find these rough microscopic surfaces on some plants, many of which they can just beat up water and just rolls right off their leaves, even keeping them clean in the process.

Even bird feathers do this.

These are feathers from a kingfisher, a bird that pretty famously spends a good portion of its life in water.

Watch what happens when I drip water on these, just like the butterfly wing, it just bounces right off.

- If I look at .

.

.

you can't see me through this thing, right?

This doesn't look very porous, and the pores are, are close enough together that it can actually, you know, support the bird's weight while it's flapping.

But this is 70% air.

- Now, if you were to zoom in on this feather, well, it might remind you of a tree - branches that come off the main trunk splitting into smaller branches and even smaller subbranches which hook together literally like Velcro.

This creates another rough surface that's mostly air and water wants to stick to itself more than it wants to stick to air.

So the result is a naturally superhydrophobic feather surface.

Now, birds do also coat their feathers with some waxy oily secretions to make them even more water resistant.

But most of what makes water roll off a duck's back are these superhydrophobic microstructures.

The end result of what these microscopic structures do is that when a butterfly or a dragonfly or a bird gets hit with a droplet of water, all of this superhydrophobic magic minimizes the amount of time that droplet is in contact with the animal.

This is a really critical thing because the less time that a droplets in contact with the wing, the less momentum that it can transfer.

Keeping the insect more steady in the air, that also means less time for the water droplet to suck heat out of the animal so it doesn't get cold.

And if a droplet does hit the wing and splash, those microstructures can act like little blades kind of shredding the droplet apart as it thins, which takes even more of that kinetic energy, converts it into other kinds of energy instead of the insect taking a bowling ball level impact.

Being superhydrophobic has a ton of advantages.

Our skin is decidedly not hydrophobic.

When you step out of the shower, you might have as much as a pound of water spread across your skin, more like that glass than a butterfly wing.

But scientists are using these natural structures is inspiration to develop rough, superhydrophobic structures for everything from airplane parts to solar cells because not only does being superhydrophobic keep a surface dry or from accumulating ice, when those droplets fall off, they can pick up debris like a snowball rolling downhill and effectively make those surfaces self-cleaning.

I find myself constantly amazed at the incredible ways that nature and the living world have solved these extreme engineering problems, thanks to the power of evolution and natural selection and a few hundred million years of trial and error.

As for me, well, I'm still gonna remember my umbrella.

Stay curious.