Episode 3 Nature's Weirdest Events

No matter how well we think we know our planet,

the natural world still has the ability to

surprise us, to shock us, and maybe sometimes even to scare us

with its extraordinary events and bizarre behaviour.

And new technology means that nature's weirdest phenomena

are being caught ever more readily on camera.

So we're going to bring you the strangest stories our world

has to offer.

I've never seen anything like that before.

From bizarre body snatchers...

..to some rather surprise guests.

There's the mystery of oozing ocean slime.

And a butterfly blizzard.

Do you see that, guys?

With the help of scientists, experts and eye witnesses,

we are going to try and unravel exactly what on Earth is going on.

So, let's get cracking.

First up, we reveal some astonishing super powers - specialist

skills that help animals succeed in the toughest of environments.

There's a group of insect jet-setters.

A tiny amphibian so tough, it can cheat death.

But our first weird event takes us to Zambia.

and to the South Luanga National Park, where

the star attraction is undoubtedly the African elephant.

This charismatic animal is a must see for all of the visitors.

But this is the largest land mammal

and it doesn't take kindly to invasion of its private space.

So, imagine the shock when, in 2009, a luxurious safari lodge received

some surprise visitors.

Staff and guests scattered as a herd of elephants

sauntered straight through reception and out into the central courtyard,

only stopping for a quick nose around the gift shop.

What had brought these normally elusive animals straight

through the lodge without a reservation?

Elephant specialist Dr Kate Evans was surprised to hear about

the elephants' sudden appearance.

These are normally creatures of habit.

Anywhere you go in Africa you often see

these animal paths through the bush.

Elephants do like to stay on these paths.

It's obviously the route of least resistance.

Been worn away over thousands of years.

These paths guide the elephants to favourite food and water spots.

The older individuals that have been around for 50-60 years potentially

would have learnt from their mothers a long, long time ago that

this is the route we need to travel to get to water in time of need.

And so the youngsters over time will pick up this information.

And it's this collective memory that keeps the elephants coming back

to the same water holes year after year, generation after generation.

So, if elephant movement is predictable,

why the impromptu check-in at the lodge?

Well, that's just it, you see, for this elephant herd it was

the lodge, not themselves, that was the surprise arrival.

I believe they've built the lodge on old elephant migration paths

and the migration path went through the middle of the lodge and that's why they're

choosing to go there rather than around.

With a memory stretching back this far, it can be hard to adjust

when suddenly things change.

So what do you do when a lodge springs up

right in the way of the route to your favourite mango tree?

You go straight through it, of course, stairs and all.

And now the elephants have become seasoned guests.

It would appear that these elephants have somehow learned that

they're not threatened here.

And this small group of elephants have chosen to

carry on with their migration route and go straight through the lodge.

So, elephants aren't ones to let obstacles change

the habits of a lifetime.

Even the construction of a hydroelectric dam couldn't

phase them.

When Lake Kareba was built, in between Zimbabwe

and Zambia, they found elephants swimming across these vast

distances to get to the other side.

And some well meaning people went out to try to bring them

back with boats, and sort of head them off,

but the elephant kept trying to get across.

And eventually got to the other side.

Discussion started amongst the community and they realised

they were following their old migration routes to get from A to B.

Collective memory is essential to the survival of elephants.

It's been proven that in times of drought,

an older member of the herd will lead that herd to a waterhole

that hasn't been visited for years. Perhaps decades.

And this is why poaching is so devastating.

It's not only about the loss of the animal,

it's about the loss of its knowledge, of its memories.

And this is why elephants as a species have a very healthy

respect for their elders.

So the largest land mammal has a suitably super memory.

But our next group of extreme jet-setters prove that when it comes to

super powers, size isn't everything.

In early October 2011, the Denning family

were hiking through woodland in central Mexico when they became

part of one of most extraordinary events in the natural world.

Look at them all. Do you see that, guys?

Millions of Monarch butterflies.

-Wow!

-A vision in orange, carpeting small stands of pines.

This is awesome.

Grant Sonnex found himself at the centre

of a butterfly blizzard.

Monarchs in their millions, that descend on very certain areas

of trees in Mexico and California like clockwork, every year.

Days before, these trees would have been bare.

So where have all of these swathes of butterflies come from?

And why are they here?

Monarchs can be found throughout the United States,

wherever their staple food, milkweed, is plentiful.

This food source can take them as far north as Canada.

Which, when the seasons change, can be a brutal place for a butterfly.

Richard Fox has spent years studying the intricacies of butterfly behaviour.

Basically, it's too cold in the winter time

across most of the United States and certainly in Canada

for these butterflies to survive.

So they've got to move or die.

The Monarchs are quite literally flying for their lives

away from the cold north.

But to reach these warm winter hideouts,

well, that's a seriously long haul flight.

These butterflies cover over 2,000 miles,

and fly for anything up to ten weeks to reach these winter roosts.

It's the kind of journey usually undertaken by birds or great herds

of mammals.

So how does a tiny insect manage it?

Well, these are butterflies with super powers.

We tend to think of butterflies as delicate creatures, blown around by the wind.

But these Monarchs are serious flying machines.

They have a brain the size of a pin head

and yet they are able to navigate across a continent

and they can fly at very high altitude, indeed people have

seen them from aeroplane windows.

And they're not flying blind.

Monarchs come equipped with some serious inbuilt GPS.

They have a time-compensated sun compass.

In their brains they have a compass which uses

sunshine as a way of working out north and south.

And in their antennae, their feelers, they have a clock which enables them to take account

for the passage of the sun across the sky.

As they travel further south,

these millions of Monarchs from all over the United States

are funnelled together by the Gulf Coast and the Rocky Mountains.

In a good year, it might be 150 million Monarchs.

And rather than spread throughout the forest, they huddle close

together, warmth in numbers against the cooler nights.

But as the sun rises, and the day heats up,

the butterflies leave the branches in an orange explosion!

Not surprisingly, these winter roosts have become tourist hotspots.

And for the people that live in these special areas

the arrival of the Monarchs is cause for celebration.

Lori Mannel is the director of the Museum of Natural History,

in Pacific Grove, California.

Also known as Butterfly Town USA.

Pacific Grove takes its Monarchs very seriously.

The first Saturday of October of every year all the school children in Pacific Grove gather together

to welcome the Monarchs back to the town.

The butterflies are the cultural icon of this town.

But just how they find the exact spot that their family member

travelled to the year before is still not fully understood.

Nor is why they chose these particular stands of trees.

When it comes to these extraordinary migrators,

there are still more super powers left to be discovered.

That Monarch migration is truly remarkable.

Did you know that you witness a similarly Herculean butterfly

effort here in the UK?

You see, Painted Ladies like these move from Africa up through

Europe every summer,

and end up in our gardens.

And we used to think that they just died here.

Recently, however, we've spotted them flying back to Africa.

So when you take in all of the generations, that's a round trip of more than 9,000 miles.

Not bad for an insect that weighs less than a gram.

Those butterflies are super migrators.

But what do you do if you can't escape the cold?

Let's travel to Canada, where we find an amphibian with

an incredible survival strategy.

Winters in the furthest reaches of the northern hemisphere

are seriously tough.

Only the hardiest animals can see though a season of snow and ice.

But in this frozen world, where only the toughest survive, is one

rather surprising resident.

Rana Sylvatica, a wood frog.

The only amphibian to be found north of the Arctic Circle.

Now, you'd be forgiven for thinking that the idea of an Arctic frog

is rather absurd.

Other animals hibernate or migrate to warmer climes,

but the frog can't do either.

And being cold-blooded and fundamentally rather wet,

you'd think that when winter came the frog would freeze.

And you'd be right. It freezes solid.

An ice block with no heartbeat or measurable brain activity - for all intents and purposes, it's dead.

But this frog has a secret super power.

Come the spring, it will come back to life.

So, a Frankenstein frog that

freezes solid in the winter only to come back to life in the spring.

How on Earth could this be possible?

For almost any other cold-blooded creature the cold is a killer.

Their core temperature mimics that of their surroundings

and if this falls too low, the water inside their blood will freeze.

Forming ice crystals, daggers that tear cells and tissue apart.

Some cold-blooded animals have emergency survival methods.

Take the red-sided garter snake, for example.

It produces a natural anti-freeze that can protect its major

organs for several hours at a time.

It's a lifesaver if it gets caught out in the cold.

But the wood frog needs to survive freezing

temperatures for months at a time.

When winter comes, it must meet it, head on.

As the first ice crystals begin to form on the frog's damp skin,

its core temperature plummets.

But it's at this life-or-death moment that the frog does something

very clever.

Firstly, its liver goes into overdrive,

producing masses of glucose, a type of sugar,

which it pumps into its cells to act as a type of anti-freeze.

At the same time, it releases a protein which attaches to

the water molecules between those cells

so that when they freeze, ice crystals are too small to do any damage.

Up to 65% of the frog's body is now ice, and its heart flat-lines.

For most other animals, this would mean certain death.

But not the wood frog.

It can stay in this suspended animation for weeks on end

until a change in temperature allows it to slowly thaw.

But there's still no heart beat, no brain activity, it's not breathing.

For all intents and purposes, this frog is just dead.

So what will provide the vital spark?

What's going to fuel its Frankenstein moment?

The heart muscle, whose cells have been protected by glucose,

starts to stretch.

Energy is released, thousands of tiny static sparks that, like

an internal defibrillator, create enough energy to shock the heart.

Blood rushes around the frog's body.

Within minutes, it's moving.

All of the frog's senses have been

restored and its time in the freezer is just a very cold dream.

Now THAT is a super power!

Clearly an amazing adaptation, which allows this frog to survive in extreme environments.

Now, we like to complain about the cold, and we should,

because extreme cold can be very dangerous to us humans.

You see, our tissue lacks the frog's glucose-producing properties

so when we get frostbite, the cells in our tissue freeze,

and then die, and then rot.

A very good reason to always remember your gloves.

These stories reveal the extraordinary lengths that animals will go to to survive.

Whether it's an elephant with food on the brain.

A sub-zero frog frozen solid.

Or a Monarch butterfly collecting some serious air miles.

It just goes to show that sometimes it takes super powers to succeed.

Although these stories have proved that what's on the inside really

does count,

having a super power is not the only way to survive.

Our next set of stories show that the ability to create

a super structure can be just as crucial, and just as weird.

From an oozing slime clogging fishing nets...

..to the mystery of elaborate works of art appearing on the sea bed.

But first, to the heart of Pakistan,

where, during the summer of 2010,

reports of devastating floods spread throughout the world's media.

Tens of thousands of people have been forced to leave their homes...

Today brought new flood warnings in the southern Sindh province...

But, from amongst all these news reports,

emerged an altogether different set of images.

Russell Watkins, from the Department for International Development,

was travelling to Sindh province

when he came across a scene so surreal it stopped him

in his tracks.

Nothing really prepared us for what we saw when we got there.

What we were confronted with was quite spectacular.

Every tree that you could see,

every piece of vegetation you could see for miles and miles on end,

was just cloaked in these enormous webs.

The trees just looked like they were wrapped in candyfloss.

It was very, very surreal, quite spooky in a way.

Russell had the photographic evidence, but not the explanation.

So who, or what, had turned these trees in

a remote corner of Pakistan into giant, spooky cocoons?

Silk specialist Chris Holland thinks he has the answer.

Whilst these trees completely covered in silk may seem

really unusual to the vast majority of us,

there's actually a very simple natural process occurring here.

For Chris, there's only one culprit capable of spinning

these sinister structures - spiders.

Just as the human population was forced from their homes

by rising waters,

so arachnid refugees were pushed back to the only dry land in sight.

It just happens to be that when you have flooding events

they have very few places to go, and they usually go for high ground,

and in this case, the trees.

So the types of spiders you see in these trees

are most likely the sheet web building spiders.

These are the spiders that you would tend to find

in the back of your garden, under your shed, or in your kitchen cupboards.

But these were big enough to entomb your entire kitchen.

Just how had these webs got so vast?

Ironically, the answer lay in the very water that trapped the spiders.

A stagnant breeding ground for mosquitoes.

So when you get a few spiders confined to this really small space,

but a lot of food around, for example mosquitoes from these flood waters,

you suddenly would generate a huge population explosion.

Where all theses spiders are having babies, these spiderlings are running amok around these trees,

creating lots and lots of sheet webs, which creates this huge beautiful coverings

of silk, as we see in these photos.

So what Russell saw in Pakistan was really just normal spider behaviour

pushed to extremes.

And, as it turned out, it wasn't the only example.

In March 2012, thousands of spiders escaped floods

in Wagga Wagga, Australia, covering farmland in a creepy-crawly shroud.

What you're seeing in these photographs aren't actually webs, but millions

of strands of dragline -

that's the silk that spiders lay as their safety net.

It's one of the most remarkable fibres in the natural world.

Spider silk isn't actually stored already reeled up like a fire hose inside the spider.

It's actually stored as a gel, and this gel is made up of proteins.

And as these proteins are pulled, they align into a hard, solid fibre.

And it's the alignment and how these proteins go together as building blocks that gives

silk its amazing properties.

This protein re-shuffle creates one of the toughest

fibres on the planet.

A natural material so strong it can outperform steel.

It saved the spiders from flood water and now scientists

are working on ways in which it might save the lives of humans too.

If we really understand how spider silk is spun and processed,

we may be able to reprocess it into types of shapes

and structures that we can use inside the body,

for example, making artificial bone, cartilage, or even trying to regenerate our nerves.

Silk could act as a kind of scaffold on which new nerves cells can

grow, bridging damage.

So the concept of a Spiderman might not be

so comic after all.

But whilst this is exciting new science, as usual,

we are lagging a long way behind nature.

Birds, for instance, have been using spider silk for millennia

and one species that you might know of that does is the very pretty

little long-tailed tit.

It uses spider silk to makes its fabulous little nest.

What a thing!

In the case of these spiders,

the ability to spin their own safety line proved to be a life-saver.

But our next super structure has a much more poetic purpose.

We're travelling to the waters off Japan,

where, in September 2012, underwater photographer Yoji Ookata

spotted something remarkable.

An intricate circular pattern carved into the sand.

A peaked ring of ridges and waves, perfectly executed.

In 50 years of diving, Yoji had never seen anything like it.

But was this a scientific discovery?

Or some sort of underwater hoax?

Yoji began a stakeout, hoping to unmask the culprit.

Who turned out to be more sub-aqua than extraterrestrial.

The artist responsible is a pufferfish.

Yoji saw a male work tirelessly - sculpting

and perfecting his pattern over a number of days.

No-one in the scientific community had ever seen anything like it.

Biologists like Dan de Costa were blown away by its behaviour.

Pufferfish are not known for swimming fast.

Or moving fast at all. And the way this pufferfish is moving

and moving his fins to make this nest, is just out of this world.

But why does the pufferfish go to all this effort?

Well, the circle acts as a kind of oceanic love token.

The female is drawn into the patterns

and lays her eggs in the central depression,

where they are protected from currents.

There's fish that do things to attract females, but not a single, tiny fish like that,

builds a huge nest, just to attract the female.

And lays little pieces of corals and little pieces of shells in it just to make it more attractive.

That's quite unique, its incredible.

Talk about a grand, romantic gesture.

Even though scientists have discovered more than 120 different types of pufferfish,

in both tropical and fresh water, they've never seen anything like that sculpturing ever before.

When you think about it, more than 70% of our planet's surface is covered in water,

much of it little explored, so there must be many more phenomenal things

out there to be discovered.

Whilst the pufferfish nest is a work of art,

not all super structures are quite so appealing.

This next strange substance

is unlikely to win any popularity contests.

There's a very sticky situation facing fishermen in the Atlantic.

How do you get rid of all that slime?

They're pulling up their nets and pots

only to find them covered in slime.

So does it ruin your prawns?

An oceanic ooze is clogging their nets

and having to be bailed from boats.

Armfuls of this colourless goop

is appearing in any one catch.

With often more slime than fish,

removing it from the haul is an absolute nightmare.

It's too common a complaint to be attributed to some freak event,

or rare natural phenomena.

Something is creating enough of this substance

to drive fishermen crazy.

The question is, what?

Well, the source of this mystery mucus

can be found on the deep sea floor.

The repugnant perpetrator is the hagfish.

It's the undertaker of the deep, searching the murky bed for corpses.

It uses a rasping tongue to pull flesh from bone.

It will even wriggle inside a rotting corpse

to devour the soft flesh under the skin,

literally eating the victim inside out.

But nasty eating habits aside, the question remains -

why would a creature that lives on the sea bed need to produce slime?

Well, aside from its willingness to eat sea-floor scraps,

the hagfish doesn't seem to have very much going for it.

It's pretty much blind, has no jaws or tough scales.

It looks vulnerable.

But in fact, the hagfish really is quite a success story.

It's been around for a whopping 300 million years,

which makes it one of the oldest fishes in the sea.

And the secret to its success is slime.

It's a defensive strategy so brilliant

that it makes the hagfish quite literally untouchable.

Professor Doug Fudge studies these master slimers.

So the hagfish is essentially covered with slime glands.

And when an animal is attacked by a predator,

there's a muscle in the area where it's touched

that causes those slime glands to release their contents.

There's actually a little mini volcano of slime

that comes out of the gland.

It's reinforced with tens of thousands

of silk-like protein fibres that we call slime threads

and it mixes with seawater

and it forms this large volume

of very unusual fibre-reinforced slime.

A single hagfish can turn a bucket of water into slime in seconds.

Eww, that is so gross.

Which proves to be a pretty fantastic underwater weapon.

In a recent study that was published by a group in New Zealand

they showed hagfish using their slime in a wild situation.

The fibrous mucus is designed to choke a predator

by clogging up its airways.

The shark is left gagging as its gills fill with mucus.

Every assailant is repulsed by a wall of slime.

And the technique is so effective

that the hagfish seems utterly unperturbed by the assault.

So both predators and unsuspecting fishermen

are getting the same treatment.

But how does the hagfish prevent itself from becoming

the victim of its own slimy strategy?

They have an ingenious way of getting out of the slime.

They'll tie their body in an overhand knot

and then pass their body through the knot,

and that'll wipe the slime off their body.

A necessary skill for the ocean's most slippery character.

Now you may not like this, but humans produce slime, too.

In the form of snot.

And what's remarkable is that hagfish slime and human snot

are actually composed of very similar proteins.

Now hagfish use their slime to protect themselves from predators

and humans use their snot to trap harmful substances

and then expel them from the body.

So when you think about it, both hagfish and humans

are using slime as a front-line defence.

These animals have proved that in the natural world,

it pays to be a master craftsman.

Whether you're a silk spinner escaping the rising tide,

a slime producer defending yourself from attack,

or a sand sculptor looking for love,

a super structure is crucial to success.

So a specialist skill can help an animal get ahead,

but what if you just can't survive on your own?

Rather than admit defeat, this next selection of weirdness

shows that enlisting some help can hold the key.

There's a strange subterranean structure

created by remarkable teamwork.

But first, a chilling tale of some real-life zombies.

Eric Williams from Delaware was mopping his kitchen floor

when a dead beetle began to mutate in front of his eyes.

From its body, something long and wormlike was emerging.

And Eric wasn't the only one to witness this miniature horror.

No idea what those things are.

I see all these strange hairs moving around.

What do you think that is?

It's a cockroach.

Look at the string coming out of it.

Oh, my God!

All of these records had that one thing in common.

Be it a mopped floor or nearby puddle,

the presence of water was triggering these writhing worms.

That's disgusting.

But what were they,

and how had they got into the bodies of these insects?

Biologist Janice Moore has spent a lifetime

fascinated by this particular weird event.

Whenever I was a child I used to see these long worms

sort of squiggling around my grandfather's horse trough.

And I was told they were horsehair worms,

and that is their common name

because legend has it that these worms come from horse hairs.

Well, in reality, they're parasites, and they're parasites

of crickets, grasshoppers, that sort of animal.

These parasites live inside, say, the cricket,

and grow up to be huge compared to the cricket.

All coiled up. The cricket is almost total parasite.

The hairworm larva develops snug inside the host insect's body.

But to complete the life cycle, it has to breed,

and to do this it needs to find water.

And rather than leave the safety of the host,

the hairworm has no qualms

with making the poor insect do all of the legwork.

This fiendish parasite alters the host's behaviour.

So at that point the cricket

becomes almost suicidally attracted to water.

And they've been reported to jump into toilets,

into dog watering bowls.

And if the hairworm's big enough,

the merest hint of moisture can be enough to tempt it out.

-What is it?

-I have never seen anything like that before.

Keep an eye out for these miniature body snatchers,

because they're found here in the UK too.

In fact, in every corner of the globe, super sneaky parasite species

have found ways to get others to do the hard work for them.

For example, the mind controller that lurks in German gardens.

So there's a really fun parasite.

The scientific name is Leucochloridium.

And it actually lives in the intestinal tract

of a variety of songbirds.

The parasitic flatworm reaches maturity

inside the digestive system of the bird

and casts out its eggs in the bird's droppings.

This would be the end of the cycle for Leucochloridium

if it weren't for the garden snail

that finds bird droppings irresistible.

When they eat these eggs,

the egg hatches and the little larval parasite,

a flatworm called a trematode,

moves into the tentacles of the snail.

And there it grows up into a kind of striped mass.

The snail's tentacle is now one enormous,

pulsating flatworm brood sac.

But here our parasitic mastermind encounters a problem.

Just like the hairworm, it can't breed in the snail.

To lay its eggs, it once again

needs to be back inside a bird's intestinal tract.

So how does the fickle flatworm complete the cycle?

Mind control.

It forces the usually reclusive snail upward toward the light.

Once exposed, the snail's tentacle is a pulsating grub on a plate.

Birds will look at this and say, "A-ha! Good to eat!"

and they'll eat it.

And in that way, the lifecycle is complete.

Now, the poor snail is the middleman,

it might just get out alive - minus a tentacle.

But other hosts are not so lucky.

Our next parasite requires its host to make the ultimate sacrifice.

So one of the most spectacular examples of zombie behaviour

is that of ants infected with a fungus.

If you're battling for space in the rainforest,

hitching a ride on the back of an ant would seem like a clever tactic.

But it's not nearly clever enough for the cordyceps fungus,

which is a bit of a control freak -

mind control, that is.

The fungus enters the body through the ant's windpipe

where it begins to extract nutrients from all but its major organs.

As the fungus grows, it eats the ant alive,

whilst leaving it with just enough of its faculties to move.

And the reason why it does this is brilliantly devious.

To cast spores, the fungus needs to be high.

So it floods the ant's brain with chemicals,

forcing it on an upward march.

Having reached an optimum height,

the ant has served its purpose and cordyceps devours its brain.

Before, with a final flourish,

it bursts through the exoskeleton and casts spores into the air.

It's really a wonderful story if you happen to be reading about it

and a really nasty story if you happen to be an ant.

One of my favourite types of bodysnatcher

actually lives in UK waters.

The larvae of a species of tapeworm inhabits the stickleback.

And just like all the other parasites we've been looking at,

when it needs to breed, it needs another host - in this case, birds.

Quite obviously, it doesn't leap out of the mouth of the stickleback

into a passing bird. No.

What it does is very cleverly modify the stickleback's behaviour,

causing it to flip over onto its back

and reveal its bright white belly,

making it far more obvious to predators like herons.

I know it's a sad end for the old stickleback,

but you've got to admit that when it comes to parasites,

mind control is a fiendishly effective survival technique.

Bending the will of others for your own gain

is not exactly the most altruistic of survival methods.

Thankfully, our next story shows you just what can be achieved

when you choose to work together.

In May 2004, a group of scientists gathered in South America.

At a very particular spot in rural Brazil

they took up tools and began to dig.

Over the next few days, they painstakingly excavated the area.

And from the soil, something incredible began to emerge.

They uncovered a vast network,

some 50 metres squared,

an architectural maze of different shapes and structures

branching out into the ground.

This subterranean design was precise,

and too complex to have been created by chance.

It had been engineered.

But by what?

What could have created this underground architecture?

What the scientists had uncovered was a secret city.

A giant home created for some of the smallest animals on the planet.

Ants.

For ant biologists like Ross Kirby,

this experiment brought theory to life.

This is the first time that we can literally

see the bare bones of what they've actually built.

They poured ten tonnes of cement into an empty leaf-cutter next

over the course of three days.

And once the cement had set,

the scientists could cut away and reveal the underground metropolis

of this leaf-cutter ant kingdom.

This wasn't just your average ant nest.

This was an entire ant city,

going as deep as eight metres into the ground

and masterminded by an estimated population

of up to seven million leaf-cutter ants.

But why does an ant need such an impressively complex home?

There's brood chambers which are important

because this is where the eggs develop.

There's waste disposal chambers.

There's also many different tunnels,

not just to take the ants from chamber to chamber,

but also to allow air

to be completely circulated throughout the nest.

Ants use pheromones to organise construction work

and to guide them to and from foraging sites.

These chemical trails help them work efficiently

and stop them from getting lost.

They ensure a steady stream of grass into the nest.

But it's not to eat.

The ants can't digest grass.

Instead, they use the blades to feed a fungus,

cultivated in special garden chambers.

This fungus is the ants' preferred main meal,

and when you've got seven million mouths to feed,

that's a lot of fungus farming.

A nest needs to be this size to support such a large colony.

But it's almost inconceivable that something as small

and simple as an ant could have created such an amazing structure.

When looking at an entire ant colony,

you shouldn't be thinking of it as seven million different individuals,

it should be thought of as one great collective unit.

A single ant by itself isn't really up to much.

However, when you get up to seven million of them,

interacting together, their behaviour can be quite complex.

All of these ants working together for the good of the whole colony

transform from individuals into a single living being.

A super organism. One brain, seven million ants strong.

It's this organisation that makes one of the smallest animals

capable of such incredible engineering.

So, clearly, being part of a super organism is beneficial.

But a group mentality can also have its drawbacks.

Kayla Brown was travelling through Peru in June 2008

when she came across some ants behaving strangely.

These army ants were spinning round and round in a constant circle.

Kayla watched them spiralling for hours.

Before, one by one, the ants began to collapse and die.

And she wasn't the only one to have witnessed these peculiar

death circles.

But why were the usually organised ants on self-destruct?

Well, it's most likely that these ants were out foraging

when they got separated from the rest of their party.

With the pheromone trail lost, the ants began to panic

and follow each other's pheromones.

This confused game of Follow My Leader forced them

into a never-ending circle.

And because ants aren't programmed to think like individuals,

they didn't save themselves.

Instead, the circle became tighter and faster

until the ants simply died of exhaustion.

Thankfully, these ant death circles are relatively rare events.

Clearly proving that the benefits of teamwork must outweigh

the potential for disaster.

And of course, ants aren't the only animals that form super organisms.

Take bees, for example.

For a hive to be successful,

thousands of bee brains must work together tirelessly and selflessly.

And the benefits are security, bed and board.

Clearly, when it comes to super organisms,

great minds must think alike.

These stories show the importance of enlisting some help.

Whether it's a devious parasite controlling

a host against its will...

or an ant colony combining forces to build

a subterranean megatropolis.

Two brains, or seven million if you can manage it, are better than one.

We've seen that the will to succeed can bring out the most

ingenious in animal behaviour.

But our final set of stories show that this survival drive can

also have unwanted side effects.

There are some reclusive rainforest residents with a sobering habit.

But first, to Sweden,

and an unfortunate case of animal inebriation.

In September, 2011, local resident Per Johansson went out

to investigate some unusual noises emanating from next door's garden.

It was late evening when I came home from work in Gothenburg.

And it was a very stormy, windy night. Much rain.

When I heard a scream, it was like "Rrrrr". The sound was spooky.

So I went in a bit more, I heard the scream again.

Something was moving in a nearby tree.

Then I took a few steps more and it was a moose.

Eurasian elk, to give them their proper name,

are a common sight in and among the forests that surround Saro.

To find one lodged in your neighbour's apple tree,

however, is perhaps less common.

It was like this, you know.

and it tried to get free then. "Rrrrrr!"

So what had happened to this unfortunate elk?

Per Johansson had his own theory.

It had walked around the neighbourhood,

eating a lot of apples. And it fermented in the stomach, you know.

The elk was accused of being under the influence. And why was that?

Well, getting stuck in an apple tree was a bit of a giveaway.

Very red eyes. You know, "Rrrrr". It looks drunk!

When the inebriated animal had tried to reach for more,

it had slipped and got itself wedged into the tree.

The story of a boozy moose was perfect front page fodder.

But what's the truth behind this headline?

Could eating fermented fruit make a wild animal drunk enough

to get itself into such a compromising position?

Well, fruit is a fantastic source of energy for animals,

because it's full of sugars.

But when yeasts, which are found on the skins of these fruits, react

with all of the sugar, fermentation occurs and alcohol is produced.

Professor Robert Dudley from Berkeley University studies

the surprising relationship between animals and alcohol.

Alcohol is a reliable indicator of the presence of sugar.

And fruit-eating animals, they need to find sugar

and if they don't eat over several days, they die.

It's life or death.

And if alcohol modules alert them to the presence of sugars,

they can find it faster and consume it faster.

Then they don't have to deal with the competition.

So if alcohol is found in most fruits and nectar,

then why aren't we seeing drunk animals everywhere?

They're not drinking liquid alcohol,

they're eating fruit which also happens to contain alcohol.

So as they consume more alcohol, they're actually filing their gut

with carbohydrates and lipids

and all kinds of structural things associated with fruit.

So they get full. They probably get full before they can get drunk.

So, without hitting the bottle, it would be difficult

for an animal to become drunk on naturally occurring alcohol.

But it can happen.

In the United States in 2007, necropsies carried out

on some cedar waxwings found high levels of alcohol in their blood.

These birds had gorged themselves on so much food

that it had begun to ferment inside their bodies.

The birds were illegally drunk, according to state law.

There are actually a few cases of documented death by ethanol

and true drunkenness in the animal kingdom.

If the apples in that Swedish garden had been fermenting

for long enough, then they could have produced enough

alcohol for the unsuspecting elk to feel the effects.

And its behaviour had all the hallmarks of drunkenness.

Once stuck in the tree, the elk wasn't coming down quietly.

It was time to call in reinforcements.

Urban Bomgren from the fire department assessed the scene.

-TRANSLATION:

-We decided to use our winch at the front of the truck.

And we tied a big rope around the tree and so we pulled it down.

The tree was nearly 90 degrees, you know. When the moose fell out, pop.

And just lay down. It pulled up its head and looked at us.

It looked very tired and looks maybe a little bit hungover.

Whilst its exploits became big news,

the unfortunate elk had no choice but to sleep off the escapade.

And a few days later, left the village none the worse for wear,

although presumably it was off the apples for a while.

Well, it's certainly a fun story.

But sadly, because no tests were ever done,

we can't be sure that the apples were to blame.

And of course, you can't breathalyse an elk.

But there has been another report recently of more drunken birds.

This one much closer to home and one that's also been proved.

A set of blackbirds were picked up in Cumbria in November, 2012.

and the post-mortem results showed some typical signs.

A belly full of berries and a high blood alcohol level.

And what we think happened was, it was winter.

There was a shortage of food,

so they gorged on the fermenting berries,

with no idea of the potential side effects.

Then, they were killed in mid-air collisions,

just going to prove that you shouldn't drink and fly!

In the case of these birds, fermenting berries proved deadly.

But what if alcohol in your diet is unavoidable?

Our next story takes us to the rainforests of Malaysia,

where we find two little mammals who are serious binge drinkers.

One of the really interesting examples of alcohol exposure

came out by German researchers working in Malaysia.

And they described the slow loris.

As well as pen-tailed tree shrews, these animals drink fermenting

nectar all night from a certain kind of palm tree.

So the flowers produce copious nectar

and it then ferments in the warm, humid tropical environment.

The animals come in and lap it up all night.

Scientists studied these tiny mammals consuming the equivalent

of beer-strength alcohol for hours on end every night.

And this wasn't accidental.

These animals were actively seeking alcohol.

But if the side-effects of alcohol can be deadly, then why would

wild animals choose such a potentially dangerous food source?

Well, that's just it.

Despite the mighty binge,

the scientists could find no obvious signs of drunkenness.

No strange behaviour, no dangerous side effects.

So they tested hair samples, which confirmed that these animals

had indeed been consuming alcohol long-term.

In fact, the results drew a surprising parallel.

There is a biochemical marker for alcoholism in modern humans.

It's called Ethyl glucuronide

and it turns up in hair samples of alcoholics.

Otherwise, nobody exhibits this molecule.

Except for the pen-tailed tree shrew and the slow loris

and none of the other mammals in the rainforests have this marker.

So their genetics confirmed that they were definitely consuming

alcohol, but showed no signs of getting drunk.

So what's their secret?

Well, their bodies have evolved to process alcohol much more

efficiently than our own.

Which means that they can make the most of the calorie-rich

nectar without any drunken side-effects.

So the tree shrew could drink you under the table

and never get a hangover.

Whether you're an unfortunate elk, a boozy blackbird,

or a sozzled cedar waxwing, the desire to fill your belly

can have some very dangerous side-effects.

Unless, of course, you're lucky enough to be a tree shrew.

So there we are.

We've delved into a catalogue of the most fun, the most foul,

the most morbid and marvellous stories

that our planet has to offer.

And whether it's been bizarre animal behaviour

or weird natural phenomena,

it's had the very best of our brains completely baffled.

But then, given the natural world's ability to astound,

this only really leaves us with one final and inevitable question.

What next?

Subtitles by Red Bee Media Ltd