Episode 8 Nature's Weirdest Events

We live in a very weird world.

And the more we discover about our planet, the stranger it gets.

Every day, news stories reach us.

Stories that surprise us.

What is that?

-Shock us.

-Wow.

Sometimes, even scare us.

Oh, my God.

We've scoured the globe to bring you the most curious creatures,

the most extraordinary people...

I can stick almost anything to my skin without no glue.

..and the most bizarre behaviour.

Using eyewitness accounts and expert opinion to explore a weird world

of unexplained underwater blobs...

..flying goats...

and glow-in-the-dark fish,

we examine the evidence, test the theories...

..to work out what on earth is going on.

In this episode,

we lift the lid on some of nature's most confounding conundrums.

We discover holes ripped out of the sky...

Oh, Jeez.

..see all that glitters is not gold,

before finding out why these weird rock formations

might just hold the key to finding alien life.

But first, we're delving into the complex world of conspiracies,

where weird events bring bizarre theories.

May 2015.

A television crew from the UK are in Kazakhstan expecting to film a

gathering on an epic scale.

The annual breeding congregation of a herd of 250,000 saiga antelope.

With their distinctive bulbous noses,

this grassland grazer might look like

it's walked off the set of Star Wars,

but it once roamed in vast herds all the way from Europe to Mongolia.

This was supposed to be the story of the incredible survival of this

ancient species.

Now, on our first morning we went out.

We dug a deep hole in the ground

and camouflaged our cameraman and then backed off

and waited for the sun to come up.

But as the light fell across the plain,

the sight that awaited them

was truly shocking.

What we started seeing was more and more dead saiga on the horizon.

We went up and had a look at a few of the bodies,

and we noticed some were frothing at the mouth,

some of them had diarrhoea.

Most of them were fully dead,

so whatever had killed them had happened really, really quick.

Over just three days,

what started as a few dead individuals

quickly turned into hundreds and then thousands.

We were a bit concerned for our safety.

We're in the middle of nowhere with no medical help,

and you're looking at these large mammals that are dying on the spot,

going from healthy to dead within hours.

And of course nobody knew what it was,

so everybody's looking at each other thinking, "Are we diseased?

"Are we infected? Is this something from the X-Files?

"Can we get out of here?"

So what on earth was going on?

What could explain the sudden death

of hundreds of thousands of these animals?

Getting answers was proving increasingly difficult.

The authorities came in.

At first, it was completely shut down.

Nobody wanted the media to know.

Nobody wanted us to film it.

We basically were told to keep our mouths shut and not report this.

Well, this is the scene that the Kazakhstan government

didn't want us to see, or film.

We felt very tortured.

You almost felt like a war journalist on the front line,

watching genocide before your very eyes.

But we weren't really allowed to cover it.

So was there something sinister the authorities were trying to cover up?

We talked to the scientists,

the researchers all had different theories.

Some people thought that it might have been nuclear testing

that had been done in the area.

Other people started talking about diseases like anthrax.

None of us had answers.

None of us had any idea what was going on.

As the Kazak government turned to the rest of the world for help,

news teams were finally allowed in,

and the true scale of the event started to become apparent.

Scientists are not sure exactly why

the species is dying off in such huge numbers.

The saiga have been dying out in large numbers and nobody knows why.

Entire herds have been found dead.

About 135,000 animals in total,

or 40% of a species that was already critically endangered.

And as the journalists arrived,

other evidence started coming to light.

Many locals believe the mystery disease has fallen from the sky,

linking it with failed launches of

Russia's Proton-M rocket at Kazakhstan's Baikonur Cosmodrome.

So could a rocket fuel leak really be to blame?

Baikonur space station is right in the steppe,

quite close to where the saigas give birth,

and that's where the Russian space launches happen.

When a space launch happens,

then sometimes you can have a discharge of really,

really toxic rocket fuel called heptyl.

And if that goes on the grass, that could poison the animals.

But sifting through the evidence, EJ began to see flaws in the timeline.

Firstly, the timing was wrong.

So they started dying before the space launch,

a couple of days beforehand.

And secondly, it would be quite a constrained area.

Because it was such a large area,

what we need is something that acts over that kind of landscape scale.

To put this into perspective,

the saiga apocalypse was taking place

over an area of land the same as England and Wales combined.

So it's highly unlikely that a single external factor

could have been killing these animals over such a large area.

The obvious next step was to examine the antelope internally.

We could tell that this was really nasty.

And so when we saw these vets arrive covered in biohazard suits,

and masks and rubber gloves, taking very careful samples,

most of the team were fairly freaked out.

Dozens of postmortems all revealed the same gruesome cause of death.

What actually happened was that there was internal bleeding,

so they were bleeding everywhere inside,

which is what caused them to die.

But it couldn't be a contagious disease.

There simply wasn't time for one to spread

from individual to individual.

After months of tests,

scientists were finally confident

they'd identified the cause of death.

What we found was it's a bacterium

which is called Pasteurella multocida.

It seems that within hours

the whole herd had contracted a deadly infection.

Something happened to trigger that bacterium

to suddenly become virulent,

so produce these toxins and kill the animals very, very quickly.

But how on earth did this happen?

Well, this is where it gets very weird.

You see, this bacteria wasn't a new threat.

Just like in many ruminants, it occurs naturally,

normally residing harmlessly in the saigas' lungs

and those massive bulbous noses.

But something had caused its population to explode,

leading to septicaemia, internal bleeding,

respiratory complications and rapidly death.

So the thought is it would've had to be a short-term drop in temperature.

Or a short-term change in, for example, wind chill.

That would compromise their immune system and made them weaker,

that might have allowed the bacterium to take hold.

If EJ is right and there was a severe temperature drop

at the beginning of May, after a month of unseasonably wet weather,

it was the worst possible moment.

You see, the saiga had just shed their winter coats.

Mothers were weakened from giving birth.

Combined, it was a perfect storm,

turning the normally harmless bacteria into lethal pathogens.

But there is some hope.

When our colleagues went out and did an expedition after the deaths

to see what they could find,

they found a few herds of partially-grown babies,

and it seems like perhaps they had managed to get independent

before their mothers died,

so miraculously some babies survived.

In total, more than 88% of the herd's population,

200,000 animals have been lost.

But it's not the end for this extraordinary animal.

The saiga population is remarkable

in that, if weather conditions are right,

it can increase by 60% in a single year.

So these saiga survivors may well live to fight another day.

From one conspiracy theory to another.

Throughout history, man has looked up to the skies for answers.

But in November 2010,

a strange shape in the sky left onlookers with only questions.

Look at this. What the hell?

Look at that sky.

What looked like a perfect hole,

punched out of the clouds above Arizona.

-Look at that. That is freaking bizarre.

-Very weird.

But this wasn't a one-off.

In September 2012, this one was filmed above Moscow.

And this one showed up in Ontario, Canada.

That's weird.

But what are these bizarre clouds?

What could be causing these perfect patterns?

Well, the internet, of course, is awash with strange theories.

I've seen people speculate that it's UFOs,

or perhaps some covert government operation that's given rise to these

strange, you know, holes punched out of the cloud.

OK, so these cloud formations might seem utterly bizarre

but they are known to science.

They're called fallstreak holes, and their existence has

generated one particularly out-there conspiracy.

To believers, their existence is connected to a US Air Force and Navy

research facility known as Haarp.

Set up to study the upper atmosphere

for communication and surveillance purposes,

the rumour goes that the site's real aim is to control catastrophic

weather events,

turning everything from earthquakes to hurricanes into weapons.

And the fallstreak holes?

Well, some believe they are evidence of these experiments at work.

Sound unlikely?

I think so.

Here's another more logical and scientific explanation.

A fallstreak hole is a dramatic cloud feature

and it looks like a layer of cloud has had a hole cut out of it,

almost like a cookie cutter has been placed on it.

And below this hole is a streak,

rather like the tendrils of a jellyfish,

hanging down below and petering out into the blue.

Whilst the clouds around these weird holes may look fairly normal,

your average white fluffy kind,

there is actually far more to them than meets the eye.

You see, the water droplets suspended in them have a superpower.

One of these formations can form

when a layer of cloud is made of droplets,

but droplets that are very, very cold,

and they're known as supercooled droplets of water.

The key to understanding this supercooling superpower

is to realise that one of the most basic scientific experiments

that we are taught is actually wrong.

You see, at school, we are told that water freezes

at zero degrees centigrade.

But it's simply not true.

Only impure water freezes at zero degrees centigrade.

Pure water, like that found in these clouds,

freezes much lower - much, much lower.

The tiny droplets can actually go down to -15 degrees Celsius, -20.

In fact, they can go down as cold as -40 degrees Celsius without starting

to freeze, unless there's something for them to get started on.

This supercooled water can remain suspended in the cloud indefinitely,

until a tiny speck of dirt or a shard of impure ice

falls from a cloud above...

..and boom!

One particle triggers the freeze in a chain reaction that

spreads out in a perfect circle.

And the streak below?

Well, that's just the ice crystals falling,

leaving a beautiful rainbow tendril beneath.

Absolutely bizarre.

That's way cool.

So, if it's not a government conspiracy,

why exactly have we been seeing more and more of these strange holes

appearing in recent decades?

Well, there's a logical explanation for that, too.

One thing that can set off the freezing is,

surprisingly, an aeroplane.

When an aircraft flies up through a layer of supercooled droplets,

it can be just the trigger needed to start the freezing.

Many fallstreak holes are in fact caused by polluting particles from

the aircraft's exhaust,

or by a rapid drop in temperature around the wing,

acting as a trigger for the freeze.

So this is not a case of UFOs, it's a case of EFOs,

explained flying objects,

in the form of planes,

which are producing these bizarre clouds all over the world.

From one set of bizarre theories to another.

Only these are so extraordinary

they are verging on the extra-terrestrial.

The Peruvian desert,

with vast swathes of arid scrub and massive sand dunes,

it might look like a barren,

uninspiring place, but this is a land rich in ancient oddities.

From strange skulls found in nearby Paracas, resembling alien coneheads,

to the Nazca Lines,

bizarre drawings hundreds of metres long carved out of the desert scrub.

But one curious construction, first recorded in 1931,

has baffled visitors ever since.

As you can see,

this is the most amazing discovery in the history of mankind.

I don't know what it is, the scientists don't know what it is.

It's just an amazing, amazing thing.

Known as the Band Of Holes,

these 7,000 two-meter wide pits

carved out of the barren rock stretch along

a ridge for more than one-and-a-half kilometres.

And their purpose has been linked to everything,

from alien hatching pods to UFO launchpads.

Well, there are a lot of crazy theories in archaeology

about just about everything.

Maybe some of the craziest are that these are some kind of

constructions by aliens as guideposts.

It's kind of silly.

Probably, if you can fly from Alpha Centauri to Earth,

you probably don't need a guidepost.

All those nonmainstream theories really don't stand up to any kind of

serious scientific scrutiny.

For over 80 years,

visitor after visitor has tried to work out just what these strange,

now partially collapsed holes could possibly have been used for.

Look at that. That's a skull right there.

Unreal, man.

It's, like, an Inca burial site?

No!

Hm...

So, had our enthusiastic tourists

stumbled across the missing evidence?

Were they a long line of graves?

Well, ancient Peruvians did bury their dead in a crouched,

sitting position, facing the rising sun.

But the theory just didn't stand up.

Only a handful of bones had been found,

certainly not enough to justify 7,000 graves.

So if it's not graves, what could it be?

In 2015, archaeologist Charles Stanish

went to investigate for himself.

Well, it's a fascinating site.

It really... It's what we live for as archaeologists.

We find a mystery, we love mysteries.

We started to look around

and we noticed that the holes look very similar

to storage pit constructions

that were typical of the Inca and pre-Inca times.

With an encyclopaedic knowledge of prehistoric Peruvian culture,

Charles started to see clues all around him.

And then below we found a road,

an Inca road, classic Inca road construction.

They are very like Roman roads, you can pick them up right away.

And they're 5km from

the major Inca administrative site of Tambo Colorado.

And it's right up valley from one of the richest agricultural areas

in the world, for that matter.

Charles had spotted an ancient road running right alongside the holes,

leading to the main road below.

With the Incan administrative site of Tambo Colorado

just 5km to the east and rich farmlands to the west,

Charles was onto something.

But he still needed to explain

exactly what the holes were used for.

And the answer to this complex conundrum

was to be found in the pattern of the pits.

The thing that really intrigued us was that the holes were in lines,

and there appeared to be numerical patterning of the holes,

so we started to count them and it was like,

"One, two, three, four, five, six, seven.

"Seven, eight, eight, nine, nine."

And at that point we said, "OK, something much

"more interesting is going on."

One, two, three, four.

What we've got here is a very precise pattern

of numerically ordered holes.

So we have to suppose that the Inca were counting.

But what exactly where they counting?

Well, it wasn't money, that's for sure.

Well, in the Inca Empire, people paid tribute in commodities.

There was no money. So people had to pay with labour

and with commodities.

And so every village or every kin group, or every taxpaying unit was

required to pay with labour or in kind.

And the holes would fit that model of a

non-monetary Inca tribute system.

And once Charles had all of his clues lined up in a row, the answer,

to him at least, was obvious.

The Pisco holes are most likely an accounting device

devised by the Inca state.

You come up the valley,

you stop right before you get to the last big Inca site before you go up

into the highlands.

And this is where you would leave your materials.

So every community,

every taxpaying group, would be responsible

to fill up so many of these holes.

And once your block was filled, then you would move on.

So the Pisco holes were not evidence of an alien invasion

or a ceremonial burial site.

They were a method of paying taxes.

Yes, as the farmers passed by,

they would deposit a percentage of their produce in each of the holes

as a means of paying their annual tax to the state.

What about that? It's accountancy but without the paperwork.

And that's got to be a good idea.

From a saiga apocalypse in Kazakhstan,

weird holes punched in the sky,

to bizarre pits carved in the Peruvian desert,

a potential conspiracy can pop up anywhere.

And strange theories often lead to stranger explanations.

Coming up...

a selection of bizarre invasions,

from glowing, glittering, scary spiders,

to a mystery threat terrorising sea birds.

But first, we're investigating the last invasion force

from a very Cold War indeed.

2016, Norway.

A beautiful landscape of dramatic fjords and majestic coastlines.

But under the waves, all is not well.

You see, Norwegian waters are under attack.

It's a voracious animal, it spreads far and fast.

An army over 20 million strong has invaded this stretch of coastline.

These are red king crabs.

And they're on the rampage.

What a leg.

What an extraordinary appendage this is.

You know, these crabs can grow to 10kg in weight

and their leg span can be 1.8 metres across.

They are monstrous, monstrous.

But unfortunately,

they're equally having a monstrous effect beneath the waves.

Now, you've heard the phrase, "an army marches on its stomach".

Well, the red king crab is far from a picky eater.

It eats pretty much everything.

So it can eat worms, slugs, sea urchins, starfish, which means that,

you know, anywhere it goes it will

find a type of food source that it can eat.

And fuelled by their insatiable appetites,

this invasion force is growing.

One female red king crab can lay over half a million eggs every year.

And this has allowed this army to triple its numbers

in the last ten years.

It's very bad news for Norway's marine life.

It can be quite disastrous.

It has had huge impacts on the ecosystem.

Just how have these massive marauders got so out of hand?

Well, the weird thing is

these crabs, they haven't always been here.

The story goes that in the sleepy village of Burgoynes,

in northern Norway,

the first crabs were pulled from the depths in 1977.

So where had they come from?

The thing is, these king crabs didn't come from Norway.

In fact, they didn't even originate in Scandinavia or indeed Europe.

No, no, no. They came from all the way over here - Alaska.

That's 6,000km away.

It seems like an impossible journey.

But it obviously wasn't.

So how did the crabs get there?

Back in the 1930s, with Russians around the Barents Sea starving,

Soviet dictator Joseph Stalin was on the lookout for a transportable,

quick-growing, nourishing food source

and the red king crab fitted the bill perfectly.

But it wasn't as easy as just shipping them across the country.

Several attempts failed.

But the scientists weren't about to give up.

It took 30 years for Stalin's plan to be implemented.

Crabs finally making the journey from Alaska to Murmansk by plane.

But once there,

with predators like the sea otter left far behind in Alaska,

they thrived.

And in 1977, when those crabs washed up in Bargoynes, 170 miles away,

the Norwegians knew that Stalin's Red Army had spread,

and their waters were now under attack.

40 years on, and the battle is still raging.

The problem with the king crab is, once they're first established,

it becomes really, really difficult to remove them.

Even if we were able to virtually decimate them from Norwegian waters,

the challenge would be that the Russians still want to keep them,

so we would still have a constant influx of crabs

coming in from Russia,

and it's not like we can establish any borders underneath the ocean.

So it's going to be really, really hard to ever get rid of this animal.

Maybe, but the Norwegians are very practical people.

They may not been able to win the war,

but luckily this enemy is delicious.

Yes, those huge legs are considered a delicacy, and fetch top dollar in

Japan and America.

The best thing that we can do is to intensify the fishing,

and just allow open access to the resource,

to allow as many people as possible to fish for the crab,

and then restrict its further spread.

So it seems that Stalin's last Red Army, the red king crabs,

are about to do something that the Soviet Union could never do -

invade Western Europe.

What a terrible thought.

And the only thing we can do to stop them is to carry on fishing,

which means, in turn, that we've got to carry on eating them.

It is a seafood lover's dream.

It's an invasion we've really got to get our teeth into...

From a giant, armoured intruder taking over Norwegian waters,

to a chilling encounter with the creepiest of crawlies...

Spiders.

Now, I love them, of course, but let's be honest,

they do have a serious image problem.

Arachnophobia is common the world over.

Almost a third of Americans claim to suffer from it.

And the reason?

Well, depending on who you ask,

is down to a few million years of evolution,

a terrifying personal experience, or to a barrage of cultural references

telling us that spiders are scary.

For shocking, skin-crawling excitement,

meet, face to face, 50 creeping tonnes of black horror.

See...The Spider.

But when this weird intruder comes knocking,

you've got every right to take fright.

Oh, my. Jeez. Look at that.

In summer 2016,

police detective Jared Marshall's Louisiana home

was invaded by one particularly arresting arachnid.

Oh, my Lord. What the heck?

It's so strange.

So just what had invaded Jared's privacy?

Had he stumbled upon Peter Parker's radioactive spider?

Well, clearly not.

But Jared had his own theory.

What the heck is that lighting up?

What is that?

-Holy

-BLEEP.

-It's like it's bioluminescent or something.

Oh, my gosh.

Oh, that is freaky.

Glowing, glittering green spiders.

It doesn't get much freakier than that, does it?

But is our American friend right?

Is this down to bioluminescence?

From the night sky to the ocean's depths,

animals are using a light-emitting compound called luciferin,

combined with an enzyme catalyst to illuminate the darkness.

Some do it to attract mates,

whilst for others it's to entice prey.

So could this footage be the first-ever documented case

of arachnid bioluminescence?

Well, no.

So the spider's not glowing.

It's not producing its own light.

If you look very carefully here you can see what it's doing is actually

reflecting light.

You can see the reflection changing as the light source moves.

They are beautifully weird, aren't they?

But could the clue to this dazzling display

be found in another spider species?

We know spiders from the coastlines up to 7,000 metres in the Himalayas.

You have lots of spiders with these guanine crystals in the abdomen,

and you can call them mirror spiders because they reflect the light.

So these guanine crystals are firstly good for making a pattern.

This could be good for camouflaging.

And then it is also good for preventing the spiders

from overheating in the sun,

when they sit during the daytime in their web.

A mirror spider with his own mirrors.

What a thing.

But is this sequinned stunner

related to our mystery sparkling spider?

Well, the answer to this reflecting riddle isn't quite that simple.

You see, the spider in Jared's film is a wolf spider,

a nomadic night hunter constantly on the move,

with no need for protection from the sun nor this kind of camouflage.

But Jared's film wasn't a one-off.

Take a look at this.

What in the heck is that?

And as you look closely at these films you may start to notice some

similarities.

All of them have been filmed in the dark

with the camera's flashlight on,

and in these conditions our eyes struggle

but the spiders have evolved a solution.

Many spiders have a reflecting layer in their eyes.

Spiders have usually eight eyes, two eyes in the front, the main eyes,

and all the other six are secondary eyes and these eyes may have these

tapetum, a so-called tapetum, which reflects the light,

which makes them like shining diamonds in the night.

Yes, just like many nocturnal animals,

these spiders have a group of reflective cells

in their eyes behind the retina,

that do something incredible.

Light enters the eye,

passes over the retina and hits this reflective layer

known as the tapetum.

It then concentrates what little light there is,

and reflects it back,

allowing the spider's retina a second chance to process

any light it missed the first time,

enabling it to see in near darkness.

Quite useful for a nocturnal hunter.

So that explains why the spider's eyes are glowing.

But the mystery remains.

Why are their bodies ablaze, too?

Well, this piece of footage might just unravel that mystery.

SCREAMS AND LAUGHTER

Oh!

Oh, my God...

So what on earth is going on?

Well, the truth is just about as weird as it looks.

SCREAMS AND LAUGHTER

Wolf spiders are distributed around the world,

and they have special brood care behaviours,

and the mother is carrying them around and taking care of them.

It can be ten spiderlings or probably hundreds of spiderlings.

And it's this special brood care,

combined with their remarkable eye design,

that holds the key to understanding this strange event.

When we know the fact that we have six eyes

with these reflecting layers,

then it's just a matter of likelihood

that we get one eye particularly in this right angle

to see the eye shine.

And if you have then more spiderlings on the mother's back,

then the likelihood is quite high

to see some of the eyes shining the light back.

All her eyes are, like, glowing.

Her eyes are shining and all the little baby eyes

are shining, too, like looking in the mirror.

So there you have it.

The glitter spider is in fact just a

mother carrying her babies on her back and it's their eyes

you see glittering back at you.

How sweet.

Well, no, not entirely.

So the wolf spider mother is caring for their brood

probably for a few weeks.

Then the mother will die

and the brood, in a positive case, will eat her.

Or feed on her. So the nutrition is not wasted.

Yes, the mother spider is about to make

the ultimate sacrifice to ensure that her young survive.

But they'd better move on quickly before

these siblings start seeing each other as their next course.

Spiders, they'll explode like a firework.

The explanation may be simple but the result is truly spectacular.

From a scary invasion in the American suburbs,

to a far more sinister one miles from home.

Two islands far from the coast of South Africa, Gough and Marion,

are home to millions of nesting sea birds,

but they share a sinister bond.

Something truly terrifying.

We thought it was a safe haven but something drastically wrong was

happening on the island.

In September 2000,

ornithologists Richard and Erica Cuthbert's dream placement

quickly became a nightmare.

So we're on the island really to set up

monitoring protocols for these birds.

And during the year we started finding some very strange signs.

A lot of the eggs had been successfully incubated,

but when they hatched they just disappeared overnight.

And then we started finding carcasses,

chicks that had been healthy the day before were just dead.

We were walking around,

and nest after nest had a dead chick or the remains of a

dead chick in and we realised right then that, actually,

there's something really bad going on on this island.

On both islands, scientists were finding young chicks with horrific

injuries, wounds all over the body and most disturbingly, to the head.

Richard needed to find out what was doing this, and fast.

And his biggest clue was to be found in one particularly gruesome detail.

It's quite hard to see what might have done this,

but looking at some of them carefully we could also see these

bite marks, little nibble marks.

So what was eating the sea birds?

Richard scoured the island for culprits.

We knew the animals that were on the island.

Other birds, subantarctic skuas and giant petrels,

which will occasionally take a chick,

but not to the extent that we were seeing.

So, if it wasn't one of the usual suspects, who else could it be?

We were scratching our heads as to what was going on.

We were looking around and wondering whether rats or cats had come in on

the island, but couldn't find any trace of those.

But there was one resident that had previously been ignored.

One that arrived with sailors less than 200 years ago.

During the summer there are mice everywhere.

We'd have mice burrowing into the tent at night after the food,

mice in your pots and pans in the morning.

I mean, it's horrific.

A few breeding pairs had become thousands.

But surely the common house mouse couldn't be responsible, could it?

Typically, mice eat seeds, they eat insects,

they eat bits of vegetation.

They don't eat sea birds.

A sweet little mouse eating a bird?

Oh, come on.

Nowhere on Earth had anyone witnessed anything like this.

And yet all the evidence seemed to point right at them.

Richard's theory was way too radical for some.

As ornithologist Ross Wanless could well understand.

Mice are probably the most widespread mammal on earth

after human beings.

They've co-existed with humans on islands all over the place.

How come, after all of these years, someone pitches up and says,

"Oh, by the way, mice are eating their way through

"these giant sea birds"?

No. That's not going to be a plausible situation.

Surely, we would have figured that out long ago.

Ross had to find out for himself.

Writing his PhD thesis on invasive species,

he travelled to Gough Island,

determined to gather evidence to prove their suspicions.

So he set up night-vision cameras and waited.

At first, all was well.

But then...

As the night fell,

the first mouse came out and started running around,

and then more mice came and they started

climbing all over the chick and eating it.

It just... It was a scene from a horror movie.

To witness this really gruesome brutal death is gut-wrenching.

It's really, really difficult.

This footage was irrefutable proof

that the mice where eating these poor chicks alive.

Feasting on the most accessible parts,

the rump, the body and the head.

So how did these islands become overrun with bird-eating mice?

Typically, you see, the size of a mouse is controlled by its diet.

So if it's eating seeds and grain you get a mouse-sized mouse.

But here on these islands,

they switched their diet to feed on birds, full of proteins and fats

and, as a consequence, they got bigger and bigger.

In fact, some of them even doubled their size.

The reason we don't see mice attacks of this nature elsewhere

is because mice are not alone on the islands.

They are with rats or cats or other things which keep

their numbers down,

and keep their behaviour really quite subdued

and wary of these other bigger things.

On Gough, one of the few islands where

mice are the only introduced mammal,

under those circumstances, they can...

Well, cat's away, mice will play.

And play they did.

Wiping out well over one million chicks

every year on Gough Island alone.

The scale of the carnage was really pretty phenomenal.

Beyond a shade of a doubt,

the mice are doing enough damage to drive both the

albatross and the Atlantic petrel extinct.

There are so few chicks fledged from either species in a year that

the populations are not sustained on their own.

There are other sources of mortality,

but even if we fixed those the mice alone are driving them extinct.

But there is one thing we can do.

Wipe out the mice entirely,

by dropping poisoned pellets from the air.

With 10 million needed to clear just one island,

intense fundraising is in full swing.

But it will be worth it to stop these rare birds

going the way of the dodo.

Now, don't get me wrong. I like mice very much indeed.

But the only way to deal with this savage,

bird-eating strain is to poison them.

And the hope is that, by doing so,

we can finally bring this horror story to an end.

From giant crabs in Norwegian waters,

spiderlings clinging to their mothers' backs,

to killer mice,

when animals invade, the results can be truly terrifying.

Coming up...

a bizarre discovery deep underground.

But first...

Uganda.

Kibale National Park...

..and a group of our closest relatives

have been caught doing something very strange.

Researchers have been studying this one troop since the early '90s.

After about 20 minutes of being with chimpanzees you realise that you're

in the presence of something that is different from other animals.

As Richard got to know the chimpanzees,

he began to notice that certain members

were doing something very subtle but very strange.

There's lots and lots of play going on,

and then all of a sudden what you will see is that somebody is just

sitting there with a rock on his back.

And you say, "Oh, what's going on there?"

Certain individuals seem to have taken a bit of a shine to, well...

rocks.

They will pick up one of these objects and then keep it with them.

And this wasn't just a quirk or a one-off.

Over 15 years,

Richard saw more and more chimpanzees

indulging in this strange behaviour.

They don't do anything with it other than keep it with them and make

it sometimes seem comfortable.

Just look at this.

This young chimp has a rock carefully balanced on its back.

Then it rolls off and it hurries to find it.

And this one puts the rock very carefully in the crook of its leg.

But it wasn't just rocks.

Sometimes twigs and logs were treated in the same way.

These objects were very clearly special.

But why?

Well, there's plenty of evidence that chimps are tool users.

Rocks and twigs create perfect food-finding utensils.

But these special objects weren't being used to get a snack.

No. Their use pointed to something much stranger.

I was following a mother and her son.

He was eight years old and she was pregnant...

..and as we went through the forest,

he fell on a log deliberately and then kept it.

Sometimes he'd put it on his back,

sometimes he dragged it along

like Christopher Robin carrying Winnie the Pooh.

After a couple of hours his mother went up a tree.

She relaxed by making a nest in the canopy,

and he relaxed by making his own nest in the canopy.

And then, a few minutes later,

what he did was to make a new nest which was really,

really small and then he went and got the log

and brought it to the new nest and put it in the nest,

and then he went back to his nest and went to sleep.

There was a very, very striking example

of how much attention they pay to an object

when they picked one up like this.

But the impression was that he was

substituting an object for an infant.

Yes, Richard believes that this is evidence that these chimps play with

rocks and sticks like children play with dolls.

It's absolutely incredible.

But could it possibly be true?

Well, for over a decade, Richard watched out

for this extraordinary behaviour

and began to notice a pattern.

Firstly, it was only ever seen in young chimps.

But that wasn't all.

So as the observations mounted over the years,

what we came to realise is that the

females are doing this a lot more than the males.

About three times as often.

And the males will be rougher and the females will be more caring.

They were carrying the rock dolls on their backs

just as they would a chimpanzee baby.

Like it or not, the types of toys that children are typically drawn to

is dependent upon that child's gender.

And now it seems that the same can be said for our chimpanzee cousins.

Just like other youngsters, the girls play with rock dolls.

And the boys, well, they're less interested in playing mum.

But it's what this behaviour tells us

about chimpanzee intelligence that is truly mind-blowing.

It's a behaviour that the juveniles are copying from each other.

It's a bit like, you know, conkers or something, or some of these

children's games that can go on for generations

without adults remembering how to do it,

but the kids are passing it on to each other while they are kids.

What this tells us about chimpanzees is that they share an enormously

important trait with us humans.

And that is imagination.

You see, these chimps are pretending that a rock is a baby and that

pretence wouldn't work without imagination.

And when it comes to the study of animal cognition,

this is a massive leap forward in terms of our understanding

of just how intelligent chimpanzees really are.

From proof that chimpanzees have imaginations...

..to an unimaginable alien discovery.

Caves.

The Earth's crust is riddled with them.

From tiny cracks to great caverns,

some extending for hundreds of miles into the darkness.

In these dark, dank places the weird thrives.

Bizarre rock formations and extraordinary species.

The darkness is alive with strange sights.

But in September 2014,

a research team delved deep under southern France and

found a piece of pure science fiction.

It was really like being in a Jules Verne book or something,

that you arrive in this room and you find this fully unexpected

spectacular thing.

I'm not an experienced caver and so already to get there it was quite an

adventure for me.

It's hard. It's not, like, easy,

you can't just walk in and get to the room.

I was almost scared.

It was a kind of an inhospitable environment.

But it was exactly these harsh, inhospitable conditions

that inspired Tomaso

to spend two long hours squeezing through the gloom.

I'm a geo-biologist.

The main goal of my research is that of looking or studying the earliest

evidence of life on Earth.

Caves are a very good analogue for early Earth,

because the conditions are very extreme, very inhospitable.

Tomaso wasn't just looking for a new species deep underground.

He was searching for a life form

that might have existed at the beginning of life on Earth.

And what he found blew him away.

When I saw it, I really had the feeling

that I was seeing a new creature like in

one of these movies of Cronenberg, this horror movie from the '80s.

It's really like if you find

a mysterious creature.

What they discovered were thousands of bizarrely beautiful mineral

deposits called speleothems - strange, sparkling structures.

I realised that some of these speleothems,

some of the stalactites had very unusual shapes that are very

difficult to explain. Very weird shapes.

So what were they?

First, he had to disprove the more simple explanations.

A colleague proposed to me that these may have been roots

because, in fact, they looked like roots coming from above,

from the soil on top of the cave.

And that maybe they were just encrusted

by this calcium carbonate.

But it was impossible because

the surface is so far away

that it was very unlikely that you would have roots

that go so deep into the ground.

So, if they weren't roots, what else could they be?

Well, it wasn't just the shape that was mystifying.

Then there was the other thing that, to me,

was simply impossible to explain.

In some cases you could see two of these branches merging in the

middle of the room and this cannot be a coincidence.

These weird things weren't just hanging from the roof,

they seemed to be defying gravity.

Tomaso was convinced they were growing towards each other.

These weren't just rock formations, they were alive.

But it was such a bizarre theory he needed to prove it.

So Tomaso took a sample back to his lab at ETH, Zurich,

and examined them at the molecular level.

It was really possible

to see that within this apparently completely dead

abiotic branch or piece of speleothem

there was some biomass, some organic material.

Yes, organic material means living material.

These deposits were created by tiny micro-organisms,

the kind that could have once existed

when life first evolved on Earth.

Now, that's pretty exciting, but the scope of this discovery is huge.

In fact, you could say that it's out of this world.

You could imagine that something similar

may exist or may form in another planet.

Maybe it will not be so complete a structure,

but when we find a tube on Mars we may say,

"We know, we recognise that.

"It's similar to what we've seen in the cave."

Yes, with life on other planets likely to exist underground,

protected from the sun's intense UV radiation,

Tomaso might just have found a clue

that could lead to the discovery of extra-terrestrial life.

Amazing.

From chimps with stone dolls,

to rocks alive with intergalactic possibilities,

we've discovered that imagination really is the key

to all great discoveries.

What a catalogue of the bizarre we've now enjoyed.

And with strange tales and bemusing events

coming from every corner of our planet,

I think you've got to agree - the natural world, well,

it's just plain weird.