Nature (1982–…): Season 33, Episode 14 - Animal Homes: Animal Cities - full transcript

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.

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...

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.

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.

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.

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!

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!

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.

I'm much more familiar
with animals that live on land.

It's meant to be an
emergency release.

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.

Hey, Chris, take
a look at this nest.

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.

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.

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.

Now, this is the
really fun part,

because these fish have an
amazingly complex sex life.

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.

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.

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.

Yeah, he doesn't have to do
any work around the house.

Just sex.

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.

Yeah, it's like a soap
opera sometimes.

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.

So, this is a fairly big mound.

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!

It is.

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.

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.

Thanks for telling
me about that earlier!

Oh, yeah! Yes.

Oh, yeah! So, that's
the guard to the ants.

Look at the soldiers coming.

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!

It's their job to defend the
homeland against any threat.

All right, I'm gonna let her go.

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!
- Look at that.

That's incredible.
What a structure.

The white is the fungus,
and the darker color

is the leaf fragments

that have been embedded
in the fungus garden.

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.

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.

That's a great comparison.

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.

This is their refuse dump.

So, they're... as you can see...
Bringing the waste material

from this garden out.

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.

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.

Oh, wow, they think of
everything, don't they?

Yeah.

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,