NARRATOR: They're our planet's first builders,
nature's architects and engineers,
crafting homes of spectacular design
in every corner of the globe.
Some are elegantly simple, other surprisingly complex.
Sort of looks like a teenager's bedroom from the outside,
but if you were to cut this right down the middle
and look inside...
Whether they were made by beaks or paws,
these homes have a universal purpose --
to keep their owners safe from a dangerous world
as they give birth and raise a family.
...but it makes it a perfect bear home.
It's secure, it's dry.
While many homeowners seek privacy, others band together.
Small villages can spring up in a single tree.
Then competition and cooperation set to work,
giving rise to complex societies
where millions of citizens build a metropolis
like nothing else on Earth.
The puffin -- it's a charming little bird
with its short wings and big, colorful beak.
It digs an underground retreat
to hide its nest and raise its young.
But it's far from reclusive.
In fact, puffins always nest near other puffins --
lots of them...
tens of thousands of them.
Wow.
That's why I'm here,
trying my best to blend into this puffin city
in the Hebrides off northwestern Scotland.
I'm Chris Morgan.
As an ecologist,
I'm interested in how animals make their homes
and what drives some of them to live with others of their kind.
Every spring, puffins congregate in giant nesting colonies.
This one has at least 40,000 puffins.
There are dozens of colonies on rocky islands
scattered all across the North Atlantic.
The locations are far from random.
Puffins spend most of the year out at sea,
living mainly on
a diet of small fish, like herring and sand eels.
When they nest,
puffins need easy access to their food supply.
This one's got a beak full of smelt.
They're all starting to come back in now
from their fishing expedition,
which takes them miles out to sea.
It's like a scene out of a Hitchcock movie.
[Laughs]
Whoa, you just hear this "whoosh" every so often.
They just come wheeling right by your head.
And you just really feel like
you're sitting in the middle of a bird neighborhood.
It really feels like a community here.
When puffins first arrive in the colony,
they go through the formalities --
greeting old acquaintances.
And somehow they locate their mates,
even after eight months apart.
But eventually, they have to get down to the business at hand --
repairing and refurbishing their burrows --
the same ones they use year after year.
It's a messy job, but somebody's got to do it --
because this is why they're here --
to nest and breed and bring a new puffin into the world.
On this rocky island,
the real-estate market can be very competitive.
And a choice nesting site is worth fighting for.
Soon everyone's hard at work,
giving their burrows a makeover
and a fresh lining of soft grass.
One couple has picked a good spot
right in the heart of the colony.
Their front porch even has a roof.
That comes in handy when it rains.
Others prefer a hideaway nestled in the rocks.
But they all have great ocean views.
They're looking for several features
when they're choosing where to be.
They're close to the sea --
that's where they have to go fishing.
They also are at a good elevation,
because they need to take flight with those tiny little wings,
which isn't easy -- it would be very difficult from flat ground.
And then they want to be packed in with lots of neighbors
because it's kind of a "safety in numbers" thing.
And you'll see them all looking into the sky
in a really paranoid way, watching every move
of every bird that comes by in case it's a gull or a skua.
And the second one of them sees a threat, they all take flight.
So, it's definitely a good neighborhood watch system.
And these things go really deep.
Let's see if I can get my arm in there.
If I get pecked on the finger, I'll deserve it.
The puffin's burrow is a simple hole in the ground
with a nesting chamber at the end.
Some are quite short.
Others extend for yards.
But they all provide a secure hideaway
for the mating pair's single egg.
And there are thousands of burrows all over this hillside.
But the interesting thing is that they don't break through
from one neighbor to the next.
And one of the theories is
that they have this deep, guttural sound...
[Puffin grumbling]
that helps prevent neighbors from bursting through the wall
as they're excavating their own places.
It's a good arrangement, and it affords mum and dad
the privacy that all new parents want,
even in this crowded neighborhood.
For the next six weeks,
they'll take turns incubating their egg
and feeding out at sea.
That same routine is followed by the whole community,
and it's why they've all come together here.
Most animals, whether they're birds or beavers,
make their homes
and raise their families all alone...
or with just one partner.
They crave isolation
and strict boundaries
to avoid competing with others for space or food,
or mates.
And so they can keep their young under wraps.
But many other species
face challenges they can only overcome by living in a group.
Take marmots, for instance.
They live in small colonies
with several families sharing burrows hidden in the rocks.
Any time they leave
the burrows, they're at risk,
so they maintain an early warning system.
[Screeching]
That protects the whole neighborhood.
Wildebeests spend their entire lives
on the move, looking for greener pastures.
The herd is their home,
the only shelter they need.
Calves can walk within minutes of birth,
and in a few days, they can keep up with the herd.
That's their best defense against predators.
Honeybees work together to provide a hive,
where they store food for lean times.
And together, they can mount a powerful defense
against anybody that tries to steal their honey.
For these and many other creatures,
sharing a home is the best strategy for survival.
[Penguins squawking]
This longleaf pine forest in the state of Georgia
is an incredibly rich wildlife habitat --
one of the most diverse ecosystems
in North America.
But living here carries risks --
these pine forests have a tendency to burn.
Fire is how the habitat renews itself.
The dense brush and scrub oaks in the understory burn off,
so they don't take over...
While the pine trees themselves have evolved to tolerate fires.
But for all the ground-dwelling animals that live here,
a burning forest can be a death trap.
The gopher tortoise has this problem licked.
He lives in a burrow that he digs deep into the sandy soil.
At the first whiff of smoke,
the tortoise can retreat to safety underground.
A gopher tortoise burrow can stretch for more than 40 feet
and up to 10 feet deep,
and is always just as wide as the tortoise is long
to ensure that he can turn around inside.
A single tortoise may dig as many as 35 burrows
in his small territory.
And all those burrows provide a refuge for other animals, too.
A rattlesnake
would bake to a crisp in the burning grass.
So it finds a convenient gopher tortoise burrow
where it can wait until the flames die down.
The little Florida mouse hides out down here, too.
He runs the risk of a fatal encounter with a snake.
But with the flames licking at his heels,
the burrow is still his best option.
Many of his neighbors agree.
More than 350 species --
birds, reptiles, amphibians, mammals, and insects,
spend time in tortoise burrows.
And not just during a fire.
There are regular visitors,
like the aptly named gopher tortoise copris beetle,
who serves as a janitor, cleaning up after his host.
And the little gopher frog
really appreciates these cool, damp surroundings.
The tortoise doesn't seem to mind their company one bit.
He's a vegetarian, so he's no threat to his guests.
And with that hard shell,
an adult tortoise is safe from predators.
When the forest burns,
the tortoise's burrows provide an emergency shelter.
So, the entire community owes a debt of gratitude
to its most generous citizen.
For many of them,
it's the only way they can live in this combustible environment.
Fire is less of a threat in the rainforest.
This is a place where resources and, of course, rain,
are abundant.
But in order to harvest that bounty
and deal with the weather,
some animals find that it helps to live together.
Most spiders are not what you'd call sociable.
In fact, they're usually downright hostile
toward their own kind.
But here in the rainforest,
there are exceptions to that rule --
spiders that share big, communal nests.
Now, if you don't like spiders, you might not like this species.
It's called
Anelosimus eximius.
It's harmless to humans,
but where you find one of these spiders,
you'll likely find a lot of them.
They're social spiders -- a rare breed.
Out of nearly
40,000 spider species, only a couple of dozen do this.
Their tangled,
three-dimensional nests
can be more than 20 feet across
and house 10,000 residents.
90% of them are females.
The smaller males don't contribute much.
It's the females that do all the work --
tending each other's egg sacks,
looking after the spiderlings,
and building and maintaining their home.
[Thunder rumbling]
Here in the rainforest, it can rain really hard.
And that can wreck any spider's web.
Repairing the damage is easier
when you have lots of willing workers to pitch in.
That's what makes it possible
to live in a big house made of silk in a rainy climate.
But this animal house is more than a home --
it's also a hunting ground.
From the top of their nest,
the spiders cast sticky lines of silk
that drift on the breeze to catch on nearby vegetation.
That creates a trap
that can bring a flying insect to a dead halt.
When the spiders feel a wiggle on the lines,
they investigate.
After subduing their prey with a dose of venom
and bundling it up in silk,
they cart it down to the nest for a communal feast.
Tropical rainforests are home to some very large insects.
Since social spiders can build enormous traps
and overwhelm their prey by strength of numbers,
they're perfectly positioned to take advantage of this resource.
So, bigger is better --
but only up to a point.
If the colony grows too large,
they just can't catch prey fast enough to feed everyone.
When that happens,
the spiders will have to abandon this nest
and go their separate ways,
to build new homes with new housemates.
Group living can help animals meet all sorts of challenges,
whether they face an abundance of resources, or a scarcity.
The east African savanna seems like
a wildlife paradise, but it can be a hard place to live.
The climate here is notoriously unpredictable.
The dry season is a brutal time of hunger,
and the rains may come late -- or not at all.
Add to that the presence of big predators,
and you've got a hazardous situation,
especially if you're trying to raise a family.
That may explain why so many animals in this region,
including some of the biggest and most familiar,
are so cooperative,
sharing the duties of
homemaking and parenting.
And that includes many east African birds.
One superb example
is the superb starling.
These stunning, iridescent songbirds
make their homes in acacia trees.
The thorns are a good way to ward off predators.
And they've evolved a lifestyle
that solves two other urgent problems --
building a nest and gathering food.
Superb starlings never nest alone.
Their relatives help them
with the duties of parenting.
It's a big extended family --
parents and cousins, uncles and aunts,
nieces and nephews.
But only a few of them win the right to breed.
The rest divide up the household chores.
Some scour the countryside
for insects and fruits so the chicks get enough to eat.
Others help with home repairs
or nest cleaning.
This kind of cooperative breeding
is pretty rare.
It's practiced by less than 9% of all bird species.
But here on the African savanna,
where food and weather are so unreliable,
it's relatively common.
Just one tree over,
a community of grey-capped social weavers
takes this team approach to the next level.
This tree is shared by several dozen nesting pairs.
It's a veritable village,
and there's plenty of help available
to care for the chicks.
It's the males who weave the nest out of grass and twigs.
The entrance hole faces downwards
to keep out water and evade predators hunting from above.
And it's narrow enough
to discourage all but the most determined snakes.
The chicks are tended by their two parents,
and also by a retinue of assistants --
mostly young males who delay heading off
to start their own households.
The nesting birds depend on them.
There are other benefits to living in a large community.
Like any village, this one
is an information hub.
Whenever a bird flies off to forage,
his neighbors take note of his trajectory.
If he comes back with food, they can figure out
where he found it and head to the source.
Their motto seems to be "share and share alike."
And that's their key to survival.
Wherever survival
is the most precarious and conditions the most extreme,
you're liable to find animals banding together to face them.
Australia's Great Sandy Desert is much dryer than east Africa.
It's bone-dry.
The temperature can soar to 120° in the afternoon
and plunge below freezing at night.
For any animal to make it here
takes special adaptations.
And for the great desert skink, it takes teamwork.
Lizards, by and large, are solitary creatures,
but not the great desert skink.
He leads a completely different kind of lifestyle,
and scientists have only recently learned about it.
Unlike most lizards,
great desert skinks remain faithful to their mates.
Together, they form big, extended family groups.
There's a good reason for it.
Because they're cold-blooded, skinks can't handle
the temperature extremes up above,
so they burrow deep into the red desert soil,
where conditions are more stable.
And to build and maintain their burrows,
it helps to have lots of helping hands -- or feet.
Young skinks live with their parents for several years.
Like grey-capped weavers,
they delay leaving home and lend their efforts
to extending the family compound.
The skinks need a lot of underground space
to accommodate their ever-growing clan.
One family's network of interconnected tunnels
can measure 40 feet across
with as many as 20 separate entrances.
Out of 5,000 species of lizards worldwide,
great desert skinks are the only ones that build a communal home.
But it's no wonder,
because out here,
the family that digs together,
survives together.
Back in Scotland,
each of the thousands of nesting pairs
have spent weeks taking turns
sitting on their egg.
But now that their chick has finally hatched,
the hard work of parenting has just begun.
And here's what that looks like --
a puffin returning to the burrow
with its beak stuffed full of fish
for the hungry chick waiting inside.
Wow, this whole slope is covered.
I'm really keen to get a look
in one of these burrows,
to observe the hidden life of puffins.
And there are certainly plenty to choose from.
All right, I found this perfect spot
to hide a camera actually in the burrow.
So, I'm thinking,
if I put a camera in there,
you might be able to see what's going on underground.
Fingers crossed.
Unfortunately for the puffins,
they aren't the only birds on this island.
And their neighbors aren't all friendly.
The gulls, for instance --
they nest here for the same reasons as the puffins --
because the fish in these waters are so plentiful.
But they also have another motive...
They prey on puffins.
The gulls patrol the puffin colony,
looking for a chance to steal
any unguarded eggs or chicks.
When the adult puffins return from their fishing trips...
they have to run a gauntlet of big, marauding birds.
So, they fly together
in a huge circular formation called a puffin wheel.
It's a way to overwhelm and confuse the predators.
Each puffin may circle around several times
before it drops out of the wheel
when it gets close to its burrow.
But here,
isolated and exposed, it's more vulnerable to attack.
Most gulls can't eat an adult puffin,
but they can force it to drop its load of fish...
...which the gull is happy to retrieve.
For the gull, it's a free meal.
For the puffin, a lot of wasted effort.
With its chick growing fast,
there's no choice but to head right back out to sea
for more fish.
Underground, inside the burrow,
that camera I set up should give us a chance to see
how things are progressing.
It's so interesting to see the inside of this.
The chick is huge! [Laughs]
Unreal.
This guy must be going stir-crazy by now -- I would be.
Six weeks in that little dark hole
and you don't know what the outside world is about,
and every so often, mum or dad appears at the front doorway
with a mouth full of fish -- and that's all you know.
They've been fishing out at sea
for 10 or 20 or 30 miles away.
And they come back,
and they're desperate to deliver those fish to the chick.
Oh, yeah. There she goes.
Oh...Wow!
Oh, my goodness!
It's got a beak full of fish.
Oh, the chick's pulling them out of its mouth!
The adult's just kind of sitting there,
not really helping.
And the chick is just swallowing them down headfirst.
Look at that!
[Laughs]
That is crazy!
I can't believe how quickly he ate those fish.
I think they were four, maybe five.
The chick is almost the size of the adult at this point.
Oh, that is just beautiful.
I mean, we've been watching them in the sky,
watching them on land,
and now seeing this underground world is magic.
It's magic.
This feeding routine will continue for weeks to come.
When the chicks are finally ready to fledge,
they'll emerge under cover of darkness
to avoid those gulls and take off.
Each young puffin will remain at sea,
all alone, for years,
before it returns to this island,
the place where its own life began,
to rejoin the company of its kind.
Like puffins, albatrosses spend most of their lives at sea.
And they have to come down to earth to breed.
They, too, return to the same big, crowded colonies
where they were hatched
to rejoin their mates
and nest alongside thousands of neighbors.
This albatross colony, though, is different.
For one thing,
it has a lot fewer birds.
That's because it's pretty new, by albatross standards.
It's located at Kaena Point on the Hawaiian island of Oahu.
Many of the birds that nest here
hatched in a colony that has disappeared
on an island that eroded beneath the waves.
So, they were forced to find a new place to nest.
Some made their way to Kaena Point,
where they pioneered this colony.
It's like they're homesteading on the frontier.
And just as in any frontier town,
they've had to bend a few rules to make a go of it.
You see, there's a problem at Kaena Point --
a problem with demographics.
Of the albatrosses that journeyed here
from that lost colony,
nearly two-thirds were female.
That means there aren't enough males to go around,
and there's just no way
a single female can raise a chick.
Incubating an egg and rearing a hatchling
is such a long commitment --
at least 30 weeks --
an albatross can't do it all alone.
It takes two.
So, what can they do about it?
The answer began to emerge just a few years ago.
And for the researchers here at Kaena Point,
it was completely unexpected.
They were shocked that at some of the nests,
there were two eggs.
One was inside,
while the other had been pushed out.
But an albatross never lays more than a single egg
in a breeding season.
Where did those extra eggs come from?
Genetic testing reveals that
the eggs were laid by two different females --
two females that were sharing the nest
in a same-sex partnership, like these two.
This same-sex couple
does almost everything a male-female couple would do.
They take their time getting re-acquainted
after leading separate lives for months.
They have to be in sync.
Of course, at least one of them has to mate with a male.
If both females end up laying eggs,
they'll keep one and reject the other,
though we have no idea how they make the choice.
An albatross nest is a simple affair --
little more than a scooped-out spot in the sand.
A brood patch on the belly provides plenty of warmth.
With their nests so exposed to the elements and to predators,
one parent has to keep a constant vigil
while the other is off at sea for weeks at a time.
But after being nestbound for so long,
sometimes it's hard to tear yourself away.
The changing of the guard can be a trifle awkward.
There's really no choice, though --
the sitter has to go.
These two come back here year after year
to share nest duties -- and they're far from unique.
Genetic testing revealed that
more than 30% of the breeding pairs at Kaena Point
are same-sex female couples.
It's not a perfect solution --
only one of the pairings
gets to pass on her genes to their chick.
But for the next breeding season,
they may swap roles and incubate the other partner's egg.
Someday, when their chick is grown,
she'll return to this colony to meet her partner,
male or female,
and together they'll rear a young one of their own.
As we've seen, when it comes to reproduction,
no animal wants to be shut out of the process.
But how far will they go for the privilege of breeding?
To find out, I'm headed to the French island of Corsica
to meet a little fish called the ocellated wrasse.
We're going over here, yeah?
The male is at the center of
a tangled social web of intrigue,
subterfuge, and sex.
[Air hissing]
I'm much more familiar with animals that live on land.
It's meant to be an emergency release.
MORGAN: That's why I'm teaming up with
Dr. Suzanne Alonzo.
She's an expert on the ocellated wrasse.
It's not unusual to find fish that live together
and swim together in schools
because they know that there's safety in numbers.
Ocellated wrasse hang out with other wrasse, too,
but for a different reason.
ALONZO: Hey, Chris, take a look at this nest.
MORGAN: This male wrasse
is a handsome guy in his neon breeding colors.
And surprisingly, this male fish has built himself
a nest.
It's tucked into a depression in the rocks.
He carefully selects
perfect little pieces of algae,
carries them over in his mouth,
and weaves them together.
Once his nest is built,
the male swims back and forth to attract females.
They're the smaller fish circling around --
the ones without the bright colors.
He's trying to persuade them to lay their eggs here
so he can fertilize them --
and that's what just happened.
With a flick of their tails,
the eggs are released and fertilized.
And the other females
keep an eye on what's going on,
because female wrasse are inclined to
put all their eggs in one basket.
ALONZO: The females actually prefer to spawn
where other females are present.
So, they copy their choice.
And so, once a nesting male gets a couple of females,
he gets more and more and more.
MORGAN: So, that's why we see
these masses of fish around one nest,
'cause they're all like,
"Oh, what's going on over there?"
The females seem to know that if the nest is full of eggs,
this male will take good care of their offspring.
So, it makes sense for them to share the same male
and to take advantage of his ready made nursery.
He is certainly conscientious,
fanning the microscopic eggs
to make sure they get enough oxygen,
while at the same time, he wards off
all the egg-eating predators that might try to invade.
He's the perfect stay-at-home dad.
Having a nest full of eggs sounds ideal,
but it creates a big problem for our male.
He'd like to attract even more females,
but he doesn't have the time.
He's too busy being a parent -- so, he hires an assistant.
ALONZO: Now, this is the really fun part,
because these fish have an amazingly complex sex life.
MORGAN: In fact, it's so complex,
you can't tell the players without a scorecard,
because male ocellated wrasse
can look quite different from each other.
Here's our dashing hero, the nest-building male.
And here's the assistant.
He's smaller, and he's called a satellite.
The satellite does the nesting male a favor
by swimming around to advertise this excellent nest
and draw in more females.
But once the females arrive to spawn,
the satellite seizes the chance
to fertilize some of those eggs, himself.
Perhaps he considers it payment for services rendered.
His boss might not agree.
ALONZO: The satellite male isn't just a helper,
he's a competitor.
So, when a female releases her eggs,
the nesting male wants to be the father.
But the satellite might also father some of them.
So, they're cooperating to get as many eggs as possible,
but they're also competing.
MORGAN: With all that activity around the nest
and everyone so busy,
a third kind of male wrasse shows up.
He's called a sneaker.
He's must smaller than the nest builder or the satellite,
and he lives up to his name.
Sneakers dart into the nest when no one's looking
to fertilize as many eggs as they can.
Sneaky little fish.
ALONZO: Yeah, he doesn't have to do any work around the house.
Just sex.
MORGAN: It's incredible to think that this one nest
is such a swirling mass of contradictory behaviors --
rivalry, teamwork, and plain old cheating.
There seems to be a lot going on down here.
ALONZO: Yeah, it's like a soap opera sometimes.
MORGAN: And next year,
some of these actors may swap roles.
A sneaker can bulk up and become a nest builder.
Or a nest builder could find himself serving as a satellite.
This is one of the most complicated breeding behaviors
that scientists have ever studied.
And this intricate arrangement
evolved to give everyone a shot a reproducing.
The females get to lay their eggs in a safe place;
the satellites and sneakers
get the chance to fertilize some of them.
And as for the nesting male, even though he didn't sire
every egg in his nest, enough are his
that it makes sense for him to give them all
the nurturing home life they need.
We've seen animals that live together,
share parenting duties,
even welcome strangers into their home.
But here in the rainforest,
there's one species that takes communal living
to the ultimate extreme.
These animals don't just share a home --
they seem to share a single mind.
They are leaf cutter ants.
They live in giant underground colonies
that can house millions.
But this is the behavior that sets them apart from other ants
and earns them their name -- cutting and collecting leaves.
Wow.
Incredible.
A whole stream of ants
up and down this tree.
But notice the leaves.
The leaves are only going one way, and that's down.
The ants use their serrated mandibles
to chew big sections out of the leaves.
Then they haul their harvest back down the tree,
like flag bearers in a miniature parade.
As they march through the forest,
they travel on specially cleared paths
that stretch for hundreds of yards.
That's a tremendous distance
when you're only half an inch long.
They find their way by following a trail of pheromones --
chemical signals left by other ants
to mark the path to a good leafy tree, and back home again.
They're all females, by the way --
the entire colony.
And all sisters -- the offspring of one mother.
And there's something even more surprising...
These ants don't eat leaves.
So, they're not bringing them back to feed the family.
They have a very different purpose.
And to find out what that is, we need to follow them home.
Cameron Currie, a biologist for the University of Wisconsin,
is an expert on leaf cutters --
and he can show me where they live.
CURRIE: So, this is a fairly big mound.
MORGAN: Oh, wow! I see what you mean.
Look at the size of that!
All we can see of the ant colony is the part that's above ground.
The earth looks like it's been plowed up here
into a low bank that stretches 40 feet across.
Wow, this is huge!
CURRIE: It is.
MORGAN: But it's just the tip of the iceberg.
Underneath lies a vast ant city.
And to get a look at it,
we have to dig.
Cameron assures me we're not causing any permanent damage.
We'll just excavate one shallow portion
of this huge colony.
The ants can repair it in a few days.
I've notice you're not kneeling on the ground like I am.
CURRIE: No, 'cause when we hit a tunnel,
soldiers will come out.
And if I have my knee on the ground,
they'll use that as a route to get up to my neck.
MORGAN: Thanks for telling me about that earlier!
CURRIE: Oh, yeah! Yes.
Oh, yeah! So, that's the guard to the ants.
Look at the soldiers coming.
MORGAN: Oh! Look at them come now -- wow!
The soldiers are the biggest, baddest ants in the colony.
-That's a soldier. -Oh, she's already got me!
MORGAN: It's their job to defend the homeland against any threat.
All right, I'm gonna let her go.
CURRIE: Yes, that was smart.
Oh, wow!
Once we're inside,
we can see what the soldiers are protecting.
This is the heart of the colony.
Each of its thousands of chambers
is constructed from leaves that are cut and collected
by the foraging ants.
But the walls are more than just structural,
because the colony is an indoor garden,
and the leaves are a medium for growing fungus.
That fungus is what the ants eat.
-Look at that! -CURRIE: Look at that.
MORGAN: That's incredible. What a structure.
CURRIE: The white is the fungus, and the darker color
is the leaf fragments
that have been embedded in the fungus garden.
MORGAN: The labyrinth of garden chambers
is connected by tunnels.
The workers that tend to the fungus also act as nurses,
caring for the countless eggs
that can be found throughout the colony.
Those eggs were all laid by one female --
the queen.
She lives in her own protected nest chamber,
where she's constantly groomed
and fed by some of the smallest workers.
She has her own job --
laying about 30,000 eggs every day --
more than 10 million a year --
to produce all the workers and foragers
and soldiers and gardeners
that the colony needs to survive.
CURRIE: This is a massive farm.
That's what's allowed them to reach colonies of this size.
How many ants in a colony like this?
There are gonna be millions of ants below ground here.
Wow. That's unimaginable.
It's almost like standing on top of Chicago or something.
CURRIE: That's a great comparison.
MORGAN: To manage their farm,
the ants use what can only be described as biotechnology.
Sensors on their antennae monitor temperature
and CO2 inside the chambers
to maintain ideal growing conditions.
And on their bodies,
they carry bacteria that produce antibiotics
to halt the spread of parasites on their fungus crop.
Incredible to think these ants evolved to build cities
and practice sophisticated agriculture
50 million years before we even showed up.
Like every big city,
this one generates a lot of trash.
Oh, wow. Cool!
And of course, the ants have a clever way to get rid of it.
CURRIE: This is their refuse dump.
So, they're -- as you can see -- bringing the waste material
from this garden out.
MORGAN: That's amazing.
They all get to the edge of the cliff here
and carrying that giant load and just hawk it off
into the landfill.
CURRIE: The dumps are always down-slope of the nest,
and we think that's because it keeps it hygienic
and the microbes that are in the dump
are washed away from the nest when it rains.
MORGAN: Oh, wow, they think of everything, don't they?
CURRIE: Yeah.
MORGAN: I've been into ants
since I was about the size of an ant.
Since I was a little kid. So this is a complete treat.
Individually, these ants would be nothing,
but five or ten million of them together, and suddenly,
they are a force to be reckoned with.
Their movements are so perfectly choreographed,
their collaboration so seamless,
many scientists consider a leaf cutter ant colony
to be a superorganism,
because they act as if they were
a single animal with a single purpose --
to preserve the home that they all live in together.
Animals live together for so many different reasons.
They've come up with
such creative ways to meet life's challenges,
and it all starts right at home.
My grand tour of animal homes
has given me new insights
into one of the most important aspects of life.
Oh, my goodness!
To say, "Home is where the heart is,"
may sound a bit sentimental...
It's fantastic!
...but it's kind of true.
A home is a lot more than a place to sleep
or lay an egg --
it really conveys the essence
of what every animal is all about,
and how every animal is different.
Whether it's the particular way they weave a nest...
or care for their young...
their choice of a home site,
how they alter their surroundings...
and who they choose to live with --
whether it's one partner,
or an entire city --
in every case, these traits are shaped by
millions of years of evolution,
and handed down from one generation to the next.
So, a home really is a window into every animal's past,
its present,
and its future.
To learn more about what you've seen on this "Nature" program,
visit pbs.org.