(host)  The Serengeti is one  of the richest ecosystems on Earth, but surviving out here is not easy.
You got lions, cheetahs, leopards, hyenas, crocs, and that's just the stuff with sharp teeth.
You've also got giant elephants, rhinos, buffalo to worry about too.
The hippos-- man, you definitely don't want to run into hippos.
They kill more people every year than sharks, which is a fact that continues to blow my mind.
(Joe)  And that's just the big stuff.
There are  countless little bugs who'd just love  the opportunity to take a big old belly  full of your blood, or maybe lay a few  parasite eggs under your skin.
(speaker) At least I know-- (speaker)  Wha--what's going on?
Swarm of Tsetse flies inside the vehicle.
Nothing to worry about.
Out, out.
(Joe)  Surviving out here  is hardcore, but it's easier if you don't go it alone.
Today, we're going to look  at some stories where species cooperate to help each other survive.
If you know what you're looking for, you can find these relationships everywhere.
And we're also going to look at what happens when these alliances get a little out of balance.
Teamwork makes the dream work, and it's a good way not to die.
[gentle music] You guys know what makes this show work?
Post-production team.
Yeah, I was going to say producer Amanda.
I'll acknowledge my jokes are a big part of it, guys, I know.
But it's teamwork, and what makes teamwork work?
Like, I can't just ask you guys to do stuff for me.
I have to do something for you in return.
You scratch my back.
I'll scratch yours, you know.
Not really comfortable with scratching your back, Trace.
Joe, it's an-- I'm not actually-- it's an expression.
Cooperation within species-- that's one thing, right?
But what about cooperation between species?
Insects pollinating flowers and that kind of thing?
(Joe) Totally.
I mean, that's a classic example, right?
The flower gives the insect,  like, some pollen and nectar to eat, and the insect helps  the flower make baby flowers.
The technical term  for this kind of relationship actually is calledmutualism.
It's sort of any relationship where both species  get a benefit.
And if you go looking for these mutualisms in just about any ecosystem on Earth, you can get some pretty weird examples.
Acacia trees  are an iconic sight across the African savannah.
These almost fractal,  river-like branches and broad, wide canopies with all their leaves  clustered up top as if they're reaching  for the sun.
Do you guys know how they get that shape?
The gardener does it.
One of those snippers that you can get at the hardware store, the really big ones.
There's just one person doing that all day long.
I want that job.
It's actually because of this.
Nature's hedge trimmers.
(Joe)  Acacia trees look like that because that's how high  a giraffe can reach.
Those are  the only leaves left.
Once you get up close  to an acacia, you really going to wonder  why anything would go to the trouble  of trying to eat it.
Out here, we are surrounded by acacias.
And the one thing I've noticed about them is, they are covered in thorns, but the giraffe are still eating on them.
Like, it's like,  it's not a problem.
They just don't care.
(Jahawi)  I mean, giraffes are so well adapted  with that long tongue, and they sort of get  that tongue through the thorns and can still  get at the leaves.
In the Serengeti, everything is mean.
(Joe)  And some acacias are  a little meaner than others.
It's not a meal I would take.
No.
But we have another type of acacia over here.
Yeah.
I mean, it's still covered in thorns.
I mean, this one's really interesting.
This is called thewhistling thorn, and it's adapted a really interesting kind  of relationship with ants.
(Joe)  So these are--these  are little ant houses?
(Jahawi) Yeah, basically.
These?
Yeah, you can see them all around.
(Joe)  Ant houses built  right into the tree.
This little acacia  grows these nodules, especially when they're young like this, and inside  of those nodules live ants, an entire colony of ants in this tree.
You got ants in your plants?
Dad joke, check.
You only have to change one word in "dad joke" to make it a bad joke.
One letter, even.
You know, young plants need all the protection they can get out here with all the--and the browsers.
And this is like a super evolution of protection.
And this is just swarming with ants.
And this would send  a very clear signal if you're a giraffe trying to munch on this.
I have a feeling you'd, like,  just pick a different plant.
You'd go pick a different breakfast.
I mean, the minute you kind of, you know, disturb the plant, all these ants are going to come rushing out.
(Joe)  I mean, the thorns  are a--a big message, but the ants  are a double no for me.
(Emily)  So let me make sure  I've got this.
You said mutualism requires  both species to get a benefit.
The plant gets protection from hungry stuff, and the ants get a treehouse.
(Joe) Exactly.
And there's even more going on here.
(Joe) That's incredible.
So the plant gives them a place to live-- (Jahawi)  Yeah, and in return,  it gets protection, but there's even more,  because the plant-- if you kind of look, yeah, look down there, it actually provides  little nodules that secrete sugar.
Just came in and took a little-- took a little drop of nectar off the base of this leaf.
It's incredible.
So not only does this acacia  give the ants a place to live, it actually feeds them, too,  in return for protection.
(Trace)  What's really crazy to me is neither of these organisms  is conscious that they're in this kind of mutualistic relationship.
The plants--  they don't even have brains.
(Joe)  I know.
Like, they  just evolved this way, adapting and trying to  survive, and you get this--  it's crazy.
I love natural selection.
Should get that on a T-shirt.
So anything that tries to take a bite, these ants are going to say, "No, thanks, not at our house."
This is a great example  of mutualism.
(Jahawi)  Mutualism, exactly.
(Joe)  Species cooperating,  and both getting a benefit.
(Jahawi) Yes.
(Joe) And when there's so many other things to eat, like, why--why would you waste your time-- (Jahawi)  Yeah, I mean the last thing you'd want is ants  on your tongue.
We'll leave them alone.
We're not hungry.
Go about your ant business.
But why is it called a--a whistling thorn?
Excellent question.
So it turns out, in addition to being  an awesome photographer and filmmaker and safari guide, Jahawi is also a really talented musician, too.
The interesting thing is that when wind-- when you get really good wind coming through here, through these little nodules, it acts like a whistle.
So all of a sudden, the whole tree starts to whistle.
All those little holes that the ants are coming in and out of are like--like a little flute.
It creates, like, a flute.
That's why it's called  the whistling thorn.
[whistling] I'm fooled.
Guys, okay.
It wasn't very windy.
I'm sorry.
I don't control the weather.
But it is totally true.
I would never lie to my--my teammates.
Mm.
(Joe)  So the Serengeti is also home to one of the most iconic and awesome mutualisms  in the animal kingdom.
There are these birds.
They're calledhoneyguides.
And I guess their name kind of  tells you what they do.
The bird locates a beehive,  but it can't get to the honey on account  of all the angry bees.
So it calls  to the honey badger in...however honey badgers  and honeyguides communicate.
I don't know.
I don't speak bird.
Come on over, I've got some food.
(huskily) I'll be right there.
And the honey badger follows the honeyguide  over to the hive.
Somehow, both species know that there are  these delicious treats at the end of this trip.
So the honey badger  breaks open the hive, eats its fill  of delicious honey.
Then the bird comes in, gets its own meal of wax and larvae and honey all because the honey badger did the hard work.
Sure, the honey badger don't give a you-know-what, but it can lend a helping hand.
A helping paw.
Classic mutualism.
Each species is getting a benefit.
Okay, I've got one more.
And this one gets at a big unanswered question underlying all of these mutualistic relationships.
So you guys ever wonder how  a giraffe scratches its neck?
(Emily)  Wait, that is  your big unanswered question?
(Joe) Okay, actually, no, no, that is not the question, but I'm asking this one before I get to the important one.
How do they scratch their neck?
They don't.
They--they actually have these little birds do it for them.
These cute little flappy flaps--flappy flaps?
I don't think we call birds flappy flaps, do we?
Flappy flaps.
Like it.
(Joe) These cute little feathery friends are called oxpeckers,  and their name also kind of  tells you what they do, but they don't just live on oxen.
You'll pretty much find them  on the backs of any four-legged,  plant-eating animal on the savannah.
So they sit on the backs of grazing animals, and they eat ticks and worms and even gross stuff  like scabs and earwax, and those little boogers you get in the corner of your eye.
I mean, that happens to animals too.
Yes, fun facts, they actually will roost in the nether regions of giraffes too.
That is a very fun fact.
So the oxpecker gets  their food and their yummies, and the host gets cleaned off  and stays healthy.
And sometimes the oxpeckers  will even warn their hosts that predators are nearby.
"Hey, there's--there's a lion."
But in, like, bird speak.
This is an obvious win-win mutualism, right?
Well, it's actually  not always that simple.
And this is  the big unanswered question.
What keeps these mutualisms going?
(Emily) Yeah, I mean, now that you mention it, it seems like it would be pretty easy for one half  of the relationship to become a freeloader, right?
Getting a benefit without having to do any of the work.
Yeah, I was thinking the same thing.
Like if a butterfly decides  to get the nectar, but you know, it doesn't do  any pollinating, or if the ants, they live  rent-free inside the acacia, but they stopped  protecting the plant from hungry animals somehow.
Right, mutualisms require a balance.
But it might sometimes be easier to cheat.
Actually, when scientists study these oxpeckers, they noticed when there wasn't  enough bugs and worms and nasty stuff to eat, they would peck new wounds  in the backs of their hosts and drink their blood.
(Emily)  What?
Like vampire birds?
We're talking about "Nos-bird-atu"?
(laughs) But there is a way to keep this in balance.
See, the host never quite lets the oxpecker get comfortable enough  to do its job.
They're kind of always  swatting and shaking and, like, flicking their ear.
So the bird never gets  totally comfortable unless it's doing  its good grooming behavior.
So the host keeps the relationship as a mutualism and doesn't let the bird become a parasite.
Right, and we can totally see these organisms working together, but not all of the mutualisms that are out there are easy to find.
Some of them are a little more complex.
Easy ones are like trees, right?
They grow fruit so animals will eat them  and distribute seeds.
Yes, something that you can't see, but there's, like, plants give off oxygen and animals give off  carbon dioxide.
(Trace)  Exactly--  all of these relationships are pretty easy to find, easy to understand, but some mutualisms aren't so easy to see, and they can be way more intricate and complex.
Just off the 101 highway, around San Francisco,  lives this butterfly.
It's beautiful.
It's shimmery.
Flits around flower to flower, living  its little butterfly life.
I didn't know something so pretty can be so tiny.
It is a cute little butterfly.
(Trace) Yes, it's called theMission Blue.
And if you see one in  the wild, you're super lucky.
But what I want to show you today doesn't really involve looking  for the adult butterfly.
It's about the caterpillar.
To find these caterpillars, we had to go to one of only three places in the world where these butterflies live.
Not actually that hill.
It's--it's this other hill over here, San Bruno Mountain.
We're talking about a seriously rare habitat, and you couldn't just go there any time.
Mission Blue caterpillars-- they're only feeding for a few weeks of their year-long life cycle.
So we had to come to this specific mountain on this specific day,  and we would check in daily to see if volunteers  and park rangers had spotted any Mission Blue caterpillars on the three species of plant that they live on for their entire lives.
This is like the definition of a microhabitat.
Yes, and everything had to come together perfectly.
So one day, we got this call from our guide, Kirra.
She found caterpillars  on the lupines-- that's the type of plant-- and the next day,  we're on San Bruno Mountain on a caterpillar hunt.
(Kirra) I like to be this close to the ground.
I don't think I've ever spent this much time looking at one plant.
(Kirra) Welcome to my world.
I have no idea what I'm looking for, but I feel like I should at least try to look.
We spent the next half-day  down in the dirt, looking for a very well- camouflaged caterpillar that was, like, the size of my pinky nail.
And, luckily for us,  we found some.
These creatures spend almost their entire existence on a single plant.
So when you see an adult Mission Blue flying around, that part of its life  is maybe, like, two weeks max.
It's been alive for a year.
It's been alive for a year on the same plant.
So its entire life  is wrapped up on what's going on  in this one plant.
(Trace) Whoa.
Talk about small world.
(Trace)  So these caterpillars are on these lupines,  but they weren't alone.
They have this mutualistic  secret weapon.
These guys.
These are native  California formicine ants.
And if you watch closely, you can see them tapping their little antennae on the caterpillar's back;  that's like a little massage, and it stimulates the caterpillar to squeeze out  some sweet honeydew.
It's a nutritious  amino acid cocktail that the ants--  they eat it to survive.
Feel like honeydew is a very generous word for what that looks like.
They're squeezing sugar juice out of their butts.
Some sweet, sweet honeydew.
Talk about "pour some sugar on me."
Def Leppard was--caterpillars-- okay, but that is not all that is going on here.
The caterpillars really only have one job.
(Kirra) Which is to eat, and get fat and poop,  like babies do.
(Joe) As a dad, I'm very familiar with the concept.
(Trace)  These big, fat,  juicy caterpillars are delicious for predators,  not just as a snack, but also for  caterpillar-shaped incubators for parasitic wasps.
The wasps will actually lay  eggs inside the caterpillar, and when they hatch, the wasp larvae  eat their way out.
Amazing.
The caterpillars  actually keep the ants around and give them the honeydew because the ants will fight  off the parasitic wasps, thus protecting the caterpillars and their honeydew goodness.
Okay, so let me get this straight.
You've got this caterpillar  lives on this one hillside on this very specific plant that is friends with ants that are fighting off parasitic wasp that just want to lay eggs  in its big, chunky body?
Yes, that's it, yep.
And the caterpillar then grows up big and strong to become a tiny butterfly and start the whole cycle  again, thanks to the ants.
But it gets even weirder,  because if you think about it, the caterpillar is a parasite  on the lupine because it's eating  the lupine's leaves.
Once the caterpillar pupates  and becomes a butterfly, it then switches its relationship to mutualistic, drinking the nectar  and pollinating the plants.
It's super complex and cool.
And if any one thread  of this little web disappears, everything falls apart.
Well, that is amazing.
What, Trace, how did you even get this footage?
(Trace)  We have a friend  up in the Bay Area who--this is all he does.
It's incredible stuff.
And to be able to see  this interaction and to get it on camera-- it's pretty darn rare.
While we were putting  this piece together, I kept asking experts  and local, you know, volunteers and guides about footage and clips.
And it's not really something  that people film.
This story that we're telling,  these images of that ant tending its caterpillar teammate, this might be some of the best footage of this interaction  in existence.
And it's an important record  of this relationship because these butterflies are actually at risk.
I don't want to touch it or disturb it too much 'cause they are endangered.
We have to watch where we step.
We have to watch where all of our body parts are because we don't want to crush them.
One of the things that actually helped make them endangered: not just human activity in terms of development, but also trampling is one of the ways that you can kill them.
I gotta be really careful.
I mean, that legitimately gave me chills.
Did I forget to say that part?
Yes, it's endangered too.
And not only does the Mission Blue have this super complex web  of relationships that all hinge on each other  in this one place on the whole planet, but MB, too, has been on the endangered species list since 1976.
And it's hanging on by a thread.
In 1998, this unknown fungus  attacked the lupines, the one plant that it lives on, and almost wiped out the  whole Mission Blue species.
It's been super tough.
The Mission Blue  was actually named for San Francisco's  Mission district, now one of the most popular  neighborhoods in the city, and we humans have  sort of stranded it on the outskirts  of human developments and these little islands of nature.
And now, to keep them  in existence, we have to step in and take  some responsibility for them and their mutualistic web of partners.
Today, park rangers with the  San Mateo Parks Department, the Golden Gate National Recreation Area, the National Park Service, and volunteers  all over the place are trying to save the Mission Blue.
Every year,  they plant lupines, and in that tiny window of time where the adults are flying around  but haven't laid eggs yet, the rangers capture them and release them  in other parts of the Bay Area to spread them around.
It is complicated because, you know, you're out, you are chasing around butterflies with a butterfly net,  and then it's a matter of, you know, very, very carefully  containing them, putting them on ice,  like in coolers, and then driving them, moving them from one island of wild space in the Bay Area to another because they can't cross these swathes of city.
They need our help.
So one of the things  we've been focusing on in terms of conservation is getting more of these  different species of lupines planted and growing so that if and when  a meltdown like that happens, that there's an alternative  food source available and that the butterflies don't plummet.
The butterflies track  right along with what the plants  are doing.
So there's some variation throughout the site, and that's what you want, is more variability, more diversity.
That builds for, sort of like, a stronger, more resilient butterfly population.
(Emily) So, by protecting the butterflies, they're protecting  the lupines, the ants.
It's everything.
Yeah, choosing which species to save from extinction isn't just about the species.
It's also about these relationships.
Without the butterflies, the lupines suffer, the ants suffer, and you could argue the wasps might suffer too.
Their larvae--they need to eat.
They're all connected.
(Emily)  When I watch this,  I'm thinking, what is this footage  going to be in the future?
Is it a time capsule  of a future extinct species, or is this capturing  the efforts that saved the Mission Blue?
It's when people start to develop a more intimate connection with the landscape around them, with these wild spaces, it really reduces  any sense of loneliness because if you can look around  and you say, "Oh, I know that that's  a lupine.
"and I know that  the butterflies live here, "and I know that that's  a California poppy, "or I know that that's,  you know, this golden violet, and there's another rare butterfly that utilizes that," then all of a sudden, you're not just out here walking along the trail, you're out here with  thousands of other things, doing their thing.
And it's-- it's a much more exciting place to be.
It's, like-- it's an alive place.
Mutualism and symbiosis is really the lifeblood of billions of individual life forms all over our planet.
And I could even argue that you, Emily, and you, Joe--you are walking examples of mutualism.
Your gut bacteria needs a nice place to live and some food, and in exchange, you get help digesting your lunch.
(Joe)  These relationships-- they give me  so much more respect for the power of natural selection and evolution.
I mean, there's no direction  or intent, right?
I mean, these ants and these caterpillars-- they're not conscious that  they're helping each other, yet nature is still able to weave these beautiful and intricate webs.
Absolutely, and one of the reasons that we made the series is that we wanted to look at nature more holistically, right?
It's not just individual  animals or specific places, but relationships.
Even conservationists have forgotten this  in the past, sometimes looking at things species by species.
And we can't forget these links.
It's not just lions.
It's not just bison.
It's not just humans.
We are all connected.
When you look at a small thing and you're like, "Well, that must be simple."
But in reality, they're both kind of equally complicated.
'Cause it requires the entire mountain for them to exist.
So they're big.
They're the size of a mountain.
[gentle music] And next time, we'll be bringing you another story of these intricate webs in nature, one that connects a pile of elephant dung in Africa to a football stadium  in California.
[making skittering noises] There's bugs.
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