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...

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 superpowers - specialist

skills that help animals succeed in the toughest of environments.

But our next group of extreme jet-setters prove

that when it comes to superpowers, 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 superpowers.

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 in-built 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 schoolchildren 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 choose these particular stands of trees.

When it comes to these extraordinary migrators,

there are still more superpowers left to be discovered.

That Monarch migration is truly remarkable.

Did you know that you can 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.

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 seabed 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 muscle in the area where it's touched

that cause 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 life cycle 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

to be 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 nest

over the course of three days.

And once this 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.

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?