- Oh, hello, look at you.

Oh, aren't you a deadly little hunter?

So fuzzy, so cute.

No, no!

Zoom in you fools.

That's better.

Oh, look at those eyes.

Oh, you such a cutie.

Who's your cute little spider?

That's right you are, yeah!

Hey, smart people, Joe here.

Behold my children.

I mean, my pets.

I used to hate spiders okay, but jumping spiders, these are the ones that made me change my mind.

Like I legitimately love spiders now.

It's because of these guys, and it's the eyes, that's what did it for me.

They're so curious.

They look up at you, they follow you.

They're genuinely so stinkin' cute.

But beyond their cuteness, jumping spiders possess one of the most advanced and highly tuned visual systems in the animal kingdom.

I remember a few years ago I read an article that said Jumping spiders might be able to see the moon in detail.

I was like, are you kidding me?

Nothing else that's this small can see anywhere near that kind of resolution.

So how do they do it?

I made this video to find the answer to that question.

We are gonna get up close and personal with these guys so that we can see some of the really cool things that they can do.

And how their one-of-a kind visual system makes that possible.

And I visited a lab to see how real scientists study these things.

(light music) Okay but first things first, what is a jumping spider?

Spiders come in a lot of shapes and forms, but about one in eight known spider species is a jumping spider, making them the biggest family of spiders on earth.

There are more jumping spider species than species of mammals.

They're officially known as salticidae or salticids.

That comes from the Latin word to jump.

And jumpers come in a lot of shapes in sizes too.

Unless you live in Antarctica there's probably a jumping spider near you right now.

You should be honored.

So this is kind of a weird thing to study.

- Usually when I tell people that I study spiders I get sort of a very shocked reaction.

First, people didn't even really know that there are people that do spend a lot of their time watching spiders and seeing how they behave.

But I think especially in the case of jumping spiders, because of their large charismatic eyes, a lot of people start to become really intrigued and ask questions and you know what do they see?

- What is it like to be a jumping spider?

What's your day like?

What's your environment like?

What do you do?

- So the sensory sort of world of jumping spiders is very different than ours.

Well a jumping spider detects a lot of cues in its environment through vibrations.

They're also tasting things with their feet.

Their visual world is also very different because us and many other vertebrates we have two eyes that look around our world, but their eyes are set up very very differently.

- Okay, most spiders have eight eyes.

It's like the second thing you learn after spiders have eight legs.

But most types of spiders don't actually rely on vision as their number one sense.

They detect vibrations in their surroundings using tiny hairs, or they smell chemicals in their environment.

But vision is number one for jumping spiders, it's what makes them such deadly hunters.

And we're about to put that to the test with this little cricket.

Circle of life guys.

The idea is that this spider is going to eat this cricket and we're gonna get the pounce in slow motion.

All you gotta do okay is just go eat that okay, go eat that.

It's right there in front of you, just take it.

Please jump, please jump, please jump.

Oh, I hate you so much.

Please back up.

Oh my god, oh my god, go.

Yes, yes, yes, yes, yes.

(dramatic music) Oh my gosh, that took like a whole day.

(Joe laughs) When your hunting strategy involves flinging yourself at your prey, you need eyes with really good depth perception, sensitivity, and detail.

Now just like a camera, there's usually a trade off.

More sensitivity typically means less detail and vice versa.

- Basically the more light that a single cell or single photo receptor can take in it reduces a resolution.

So if you sort of think of it like a TV screen with the number of pixels you have, if you have really large pixels, each individual one could be bright but less pixels make up the whole image.

There's constantly a trade off between how many photons you can take in versus how small details you can resolve in your environment.

- If you want more sensitivity you can make bigger sensory cells to sample a lot of light but then you can't fit as many in your eye so you lose detail.

If you want more detail you make your sensors smaller so you have more of 'em, but then they're less sensitive.

Different animals have evolved different kinds of eyes to solve this trade off.

Insects obviously have very tiny peepers, but they solved the detail problem using compound eyes.

Every facet on a compound eye acts kinda like its own eyeball.

So the more they pack in their head, the more detail.

Each one only samples a super tiny area, but they add up to give a kind of mosaic view of the world.

Dragonflies have pretty much the best compound eyes out there with around 30,000 of those little units per eye.

To get that level of detail though, their head is like all eyes.

They've run out of eye real estate, that's their limit.

For a compound eye to see as much detail as the human eye can, it'd have to be the size of a basketball which would make it pretty hard to fly.

Humans and other animals went for a totally different solution.

Round eyes with a lens up front that focuses light on a big layer of cells at the back.

Packing lots of those cells back there means a crisp detailed picture.

We've got hundreds of millions of those light sensing cells in our eyes.

And some birds of prey have like 10 times more than we do.

Things with backbones and skulls can support huge eyes, but jumping spiders are not huge.

Most of them can fit on like a pencil eraser.

You can't fit big eyes or millions of light sensing cells in this guy.

Yeah when it comes to detail and sensitivity they have the best eyes of anything without a backbone on land.

But they don't have compound eyes and they don't have eyes like humans.

So the big question is how do they do it?

It all starts with those two big adorable eyes up front.

They're not actually round, they're tubes, kinda like telescopes.

Lens on the front to focus light onto a retina in the back.

- The front two eyes, they're called the principle eyes.

But with jumping spiders, although their eyes are big relative to their body size, they're still very, very, very small.

- To get high detail out of those tiny eyes these guys have a really cool trick up their eight sleeves.

They can move those telescope eyes inside their heads.

- Each eye tube has its own set of muscles, and what they can do is they can independently move each of them.

- Jumping spider eyes are only big enough to fit a few hundred light sensing cells, but as each little telescope eye moves it samples little bits of the larger image, almost like shining a flashlight at different parts of a picture until you can make out the whole thing.

So they get amazing vision in a fraction of the space that around eye would require.

Telescopes for eyes.

Are you kidding me?

But that telescope scanning trick is only part of the story.

Wonder if these guys would chase a laser pointer like a cat does?

There's only one way to find out.

Oh, what'd you see?

See this over here?

What's this?

What's this?

Oh, you see it?

Over here.

Over here.

Over here.

Look what's this?

Oh, what's this?

Now most jumping spiders only have two types of color sensing cells in their big old cute main eyes.

Cells sensitive mainly to green light and cells sensitive mainly to ultraviolet light.

But weird physics happens to light when you're at really small scales.

And jumping spider eyes are actually built to correct for that.

See different wavelengths or colors of light, they get bent by a lens at slightly different angles.

It leads into what's known as chromatic aberration.

Now this is not that big of a deal in a big eye like yours, but in an itsy bitsy spider eye it means different colors of light are coming into focus at totally different distances from the lens.

- And when we find when you look inside the jumping spider retina you'll find photo receptors that are more sensitive to UV or ultraviolet wavelengths closer, and then deeper or potentially longer wavelength.

Photo receptors that are sensitive to certain colors are actually at different depths.

So all colors can be in focus at the same time.

- Like that's ridiculously cool.

They can even use those stacked cells to see how out of focus different parts of an image are in different layers.

And they can use that to calculate depth perception.

We need two eyes to get depth perception, but jumping spiders can judge distance with just one eye.

Did you see what happened when I shined that laser pointer behind the spider?

It always turns to point its two big telescope eyes at whatever is interesting, and that is what those other six eyes are for.

These other eyes are a jumping spider's motion detection system.

- [Alex] The motion detecting eyes called secondary eyes, they have a nearly 360 degree view around the hemisphere of the spider.

- Those secondary eyes are much more simple than the spiders to telescope eyes.

They don't see color, they're super low resolution, but they are great at sensing motion.

- So you can't sneak up on a jumping spider.

- [Joe] It just automatically is like motion, turn body.

- Turn body.

- Wow.

Whenever those six other eyes detect motion, the spider instinctually turns its big eyes to face it and get a more detailed picture.

As soon as I learned about this, something really big just clicked in my brain, because these eight tiny spider eyes do the same thing that we do with two eyes.

We use the center of the light sensing part of our eye to make out detail and color.

On the other hand, most of our peripheral vision is really low detail but really sensitive to motion.

Jumping spider eyes do the same thing.

Those telescope eyes make out detail and color, but all those secondary eyes, well they sense motion without much detail.

They've divided all that work up into eight parts instead of two like us.

All eight eyes combined, jumping spider eyes see better than dragonflies, as good as pigeons, and actually about one fifth as good as us.

All with peepers that are no bigger than a pinhead.

But how do we know any of this anyway?

I mean it's not like you can give a spider an eye test.

Well, actually yes, you can.

Show me where you keep your babies.

This is like the Ritz Carlton of spider habitats.

- Oh yeah.

Show them anything you want.

- You didn't tell me spiders are just watching TV all the time in here.

Can we go see it?

I wanna give a spider and eye exam.

- Yeah let's do it.

- [Joe] To get a spider ready for their eye exam Alex applies some melted wax and mounts a little stick hat which he'll remove later.

Next the spider holds onto a little ball.

Alex can track the ball's motion to measure how the spider turns and moves while looking into the eye tracking microscope.

- What we have here is a special camera that allows us to pick up light that's reflected off the retinas.

So what we're left with is what the spider is viewing and where they are actually looking.

- So just like the doctor like looks in my eye can see my retina and stuff when I go get an eye exam, you're doing the same thing here?

- Yeah, exactly.

And as the spider gets fatigued or less interested you see this exploratory movement where it's looking around but once-- - So it's just getting bored.

- It's getting bored.

(Joe laughs) But when the cube moves again the spider gets interested and tracks it.

- And they're doing this all by moving their eyes inside their head.

- Inside their head yep.

- And so sometimes I even see the eyes seem to almost point different directions for a minute.

Like they come apart there and then they're back together.

- [Alex] If they're really interested in something like a cube moving in front of them, they bring the retinas together to get a better view of it.

- We should give them something really interesting to look at, like some YouTube videos.

- Yeah, definitely.

- [Joe] I couldn't think of anything better to watch.

And our good friends from Deep Look, let's see if spiders like Deep Look.

- [Alex] Yeah, let's check it out.

- [Joe] Okays so the fly's moving and the retinas look right at it.

What must be hungry.

- [Alex] Oh yeah.

(Joe laughs) - This might be the first time a spider has ever watched a YouTube video, except for the one that's right behind you right now.

Getting up close and personal with my spider friends has really made me wonder why do jumping spiders need a visual system that's this complicated?

I mean their world is so small.

But these tiny feats of biology and physics have allowed them to interact with that world, with their prey, with their habitat, even with each other, in some super interesting ways.

- Maybe if you were thinking about sort of a classical representation of a spider, you imagine a large web, and insects flying in and getting trapped, and the spider running over and detecting the vibrations in their web.

But jumping spiders are a lot more like cat-like predators.

So they walk around, they stalk prey, they pounce on it.

- Their visual system also comes in handy during mating displays, which are pretty impressive.

When a male spider approaches a female (accordion music) trying to mate he never knows if he's gonna end up getting eaten or getting lucky.

So many jumping spiders perform elaborate dances as a way to attract female attention from a safe distance.

Researchers have used the spider eye tracking machine to see where females look during these dances and which parts they find most attractive.

In mammal eyes and jumping spider eyes nature's solved the same problem using totally different hardware.

I think that's pretty cool considering that we're separated by hundreds of millions of years of evolution.

And this is just one family of spiders.

Spider eyes come in lots of different numbers, arrangements, shapes, and sizes.

Each combination is perfectly suited to a unique way of living spider life.

But jumping spider eyes with those highly adapted telescopes and powerful motion sensors, they're unique not just among their eight legged cousins but really all animals.

Now that I've learned how they see, I think these guys might have the best eyes like of all the eyes.

It's just one example of how nature can fit some pretty surprising things in really small packages.

I mean literally right under our noses.

They are adorable and awesome and I hope everyone else appreciates them a little bit more.

Maybe like me, you've fallen in love with the cats of the spider world.