Episode 4 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, new stories reach us.

Stories that surprise us...

What is that?!

-..shock us...

-Whoa!

-That is so cool!

-Oh, my God!

..sometimes even scare us.

SCREAMING

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, an Australian town under attack from aerial invaders...

It smells, the noise...

..an exquisite piece of alien artwork...

Oh, my God!

..and the mystery of sperm whales washed up on the North Sea coast.

But first, to the USA.

Denison, Texas.

Like most American towns, Denison has a main road.

Nothing unusual about that.

Well, that was until the morning of May 29th, 2015.

Yeah, this one's not for the squeamish out there,

but it's still fascinating.

This highway became the scene of a very strange sighting.

Balls of worms appeared overnight, squirming in circles,

all lined up exactly between the centre lines.

Piles of worms.

And not small piles - I'm talking about massive piles of worms,

hundreds piled together in the middle of a Texas road.

But why had these animals come together in such unusual numbers?

With no-one admitting to putting them there,

the people of Denison were left baffled.

So the footage was put online,

where it caught the attention of an expert.

It is really unusual to see them lined up

in the middle of the road like that.

I've never, ever seen that before.

Now, Emma could think of some good reasons why the worms

had clumped together like this.

It's much, much safer for earthworms once they're on the surface

to actually congregate into these big balls.

Worms actually breathe through their skin,

so they do need to stay moist at all times.

So being up on the surface, being exposed to the sun's rays,

is actually really, really harmful and they can die pretty quickly.

But, of course, if they're encased around with other worms,

that will actually keep them a lot safer.

OK, so the worms had balled together for safety,

but this doesn't explain why they were on the road in the first place.

There just didn't seem to be a sensible answer.

And whilst the residents were there scratching their heads,

looking for clues, the day just got weirder and weirder,

with reports coming in of something equally odd

75 miles south in Dallas.

Check this out. This is amazing!

Andres Ruzo captured this bizarre footage of fish trapped dead

in a fence a metre above the ground.

Check that out!

My first reaction when I saw all these fish in the fence was,

"Holy cow! This is bizarre!"

Bizarre indeed.

I mean, it's not every day you see

a suspended fish stuck in the fence of a playing field.

I didn't expect to see that at all.

Suddenly, I'm walking around and these prehistoric-looking things

with mouths full of teeth are suddenly right there

and it was just, you know,

immediately to the cellphone, "What is this?!"

Well, these freaky-looking fish are gars,

one of the largest freshwater fish in North America.

Often called living fossils,

they've remained virtually unchanged for the last 100 million years.

Sharing the world with T-rex and velociraptors,

these truly are prehistoric beasts.

So Andres knew what these fish were,

but why were these unfortunate few stuck so high and dry?

-Well, that was a mystery.

-It was just weird!

You don't expect to see a bunch of fish randomly sitting in a fence

and no-one's going to show up, "Oh, I've got a great idea.

"Let me take all these dead fish and stick them in a fence."

No-one's going to do that! So, how did they get there?

So, we have two bizarre animal appearances 75 miles apart

happening within hours of each other.

Could these strange sightings be linked?

What could they possibly have in common?

Well, it turns out that May was a busy month for this corner of Texas.

While fish and worms made mysterious appearances,

a much more public event was making itself felt.

THUNDERCLAP

RAIN PELTS

In the month before these weird happenings,

a whopping 37 trillion gallons of rain fell on Texas.

It pushed the water table far beyond its normal range.

Lakes spilled over, rivers burst their banks

and large parts of Dallas experienced severe flooding,

affecting not only the community living along the river,

but also its fish.

The entire field where I was had been flooded.

It would have been about chest high for me.

That's a significant amount of water.

Significant indeed.

Enough water for the fish to swim easily over the fence,

across the flooded fields, looking for something to eat.

But when the water level dropped, well, the way home was blocked.

I imagine the small ones got through the holes in the fences no problem,

but the bigger ones, they happened to get stuck.

It was a miserable end for these fish in the fence.

But what about those worm balls on the road?

Could the extreme Texan weather provide the key?

It had been raining really, really heavily.

Everywhere was absolutely saturated, completely waterlogged.

So basically, all these worms had to come up to the surface.

And as they're trying to escape,

they've all hit this big tarmac road.

To avoid drowning, the worms took to higher ground.

But this still doesn't explain why they lined themselves up

in between the double yellow lines.

Earthworms don't have eyes like we do,

but they are very sensitive as to whether it's light or dark,

so when they've got into this middle, black area,

they've maybe stayed there and then not wanted to venture

the other side either because of the other yellow line.

So maybe it feels to them a little bit safer.

And so the worms huddled together, safe from the floods,

but trapped between the lines.

No other parts of Texas had recorded the same nightmarish

piles of worms, or weird fish stuck in fences.

This was a very location-specific event,

down to the unprecedented levels of rain that had come together

to produce the perfect storm.

Next, we travel down under,

to a small town with its own set of strange invaders.

New South Wales, Australia.

The coastal town of Batemans Bay sees its fair share of tourists.

People come to Batemans Bay to relax, to take it easy.

They like the visual aspect of it, they like the clean beaches,

they like the trees.

But in 2016, the bay became famous for an invasion

of much more unwelcome visitors.

It's horrible. It smells. The noise.

You can't hang your washing out.

Everyone's moved out.

There's only three of us left in this whole block of units now.

Batemans Bay is under siege.

The worst thing is when they go over night-time.

They block out your TV.

It's just all black.

They need to get rid of them, otherwise, I don't know,

bad things are going to happen.

The people of Batemans Bay

have had their peaceful lives turned upside down

by an invasion of...

bats.

And not just any old bat, giant Australian fruit bats,

otherwise known as the grey-headed flying fox.

CHITTERING

Grey-headed flying foxes are one of the largest bats in the world.

Their wingspan is about a metre.

That's the length of a large dog!

Each bat weighs up to a kilogram, and they don't fly alone either.

Flying foxes are highly colonial animals.

They roost in large aggregations during the day

in the open canopy of trees.

Now, the area around Batemans Bay

has always been a flying fox hot spot.

Roosting out in the wilderness, beyond the town.

But in 2011, these bats turned their backs on the bush

and set their sights on the town centre.

Year by year, their numbers have rocketed

from around 10,000 to over 100,000.

It's the largest number ever recorded in an urban area.

And the reason behind this relocation?

Well, it's all to do with this.

Flying foxes are fruit bats and feed on fruit and nectar,

and there's nothing they like more

than the nectar-rich flowers of a gum tree.

The forests around Batemans Bay contain

a large number of a eucalyptus species known as spotted gum.

It produces particularly rich nectar from its flowers.

So spotted gum is almost like a magnet for flying foxes.

Not only is the centre of Batemans Bay close to these tasty trees,

but it's also got a good supply of fresh water

and lots of trees to roost in during the daytime.

This place is a bat heaven.

And when you consider that large areas of forest

in the surrounding area have been cut down for logging and farmland,

well, bedding down in the centre of town

makes perfect sense to the flying fox.

It's just that the human population is not quite so happy about it.

Everyone's had a dog that's barked a lot next door that drives you insane.

Well, multiply it by 100,000 and then you actually get an idea

of the physical and the mental stress

that's placed on a community with that size of numbers.

SQUAWKING

It's not that the residents of Batemans Bay

are entirely anti-bat, they're not.

It's just that they'd rather they weren't living quite

so close to their homes.

So they've cut down a couple of the bats' favourite trees

and they're using bright lights...

..some loud noises... AIR HORN

..and smoke...

..to safely and humanely encourage the flying foxes back into the bush.

80% of our shire is covered in national park and forest.

And, um...flying foxes are more than welcome to go to that 80%

and we need to encourage them to do that.

It's not just a respect for nature that's motivating residents here.

You see, bats play a vital role in the ecosystem.

Every night when they're feeding in the bush, they collect pollen

in their fur, on their heads,

and they move it to each successive tree that they visit.

And in doing that, they're providing an extraordinary service.

Pollination. You see, keeping the forests alive.

Good for the flying foxes and good for people, too.

So let's hope that man and bat find a happy compromise

and peace can return to Batemans Bay as soon as possible.

Our next unusual animal sighting was reported much closer to home.

January 9th, 2016.

Germany.

A sperm whale the size of a double-decker bus

was washed up on the north coast.

Then, within a few hours, another whale appeared.

Then three more nearby.

A few days later, six more sperm whales stranded.

Unbelievably, the news got worse.

Whales began appearing on English beaches.

The world's media looked on horrified as

over a period of three weeks

29 sperm whales washed ashore,

their bodies found all along the North Sea coast.

It was the largest mass sperm whale stranding event

in the North Sea since records began.

The UK's leading whale-stranding expert

rushed to the coast to investigate.

I've never had to deal with anything like that before,

both emotionally and physically.

We haven't had an event of this magnitude

with sperm whales for 100 years.

The question for us is, what happened?

What could possibly cause so many sperm whales to strand

in such a short period of time?

Well, whales do strand across the world every year.

In 2004, 150 melon-headed whales came ashore in Hawaii.

And in 2005, over 100 pilot whales stranded in Tasmania.

But both of these events had one thing in common -

they coincided with large sonic activities.

Naval testing and minesweeping.

Whales have particularly sensitive hearing,

and loud, unnatural sounds can interfere with their navigation.

But in 2016, there was no evidence of any naval exercises,

or other loud underwater disturbance.

Rob went back to the drawing board.

Wind farms might be causing it...

Then we have some more esoteric ones.

Maybe the Large Hadron Collider might be impacting,

or climatic factors.

The El Nino's going on, that might be having an impact, too.

Those things we have to consider.

But then, more information arrived from Germany.

Postmortem examinations of sperm whales

revealed something disturbing.

Inside their stomachs was plastic.

A lot of plastic.

Plastic in the marine environment is a very, very serious issue,

and surely a whale with its stomach packed full of this stuff

would suffer some very serious health problems.

So, could it be that this oceanic litter

is responsible for the stranding?

That would be case closed.

Well, actually, no.

Because, you see, not every whale had a stomach full of plastic.

So plastic could not have been the cause of the stranding.

It was a case of back to the drawing board,

or perhaps more pertinently, back to the history books.

You see, although this stranding in 2016

was the biggest in historical times -

well, say, the last 100 years -

if you go back further into the past,

a very curious picture emerges.

These works of art date from as far back as the 16th century.

It's a very familiar scene, isn't it?

The 2016 event was by no means

the very first mass sperm whale stranding.

There are many famous historical accounts of sperm whale strandings

and mass strandings all around the North Sea.

And, well, frankly,

you can't help but notice that these whales are all males.

But what about the 2016 whales? Is there a link?

Well, what was startling about the latest stranding

was that they, too, were all males.

Every single one of them.

And that wasn't all.

These old works of art show the exact same stretches of coastline.

Whales have been stranding here for centuries.

So, what makes this coast so deadly for sperm whales?

Sperm whales like to live in water thousands of metres deep.

But this part of the North Sea is surprisingly shallow -

in some places, only 50 metres deep.

Sperm whales use an impressive biosonar to navigate and find food.

It's the loudest sound produced by any living creature.

It's perfect for deep water,

but in this part of the North Sea,

the sonar bounces against

the shallow ocean floor.

The whales become confused and they lose their way.

Now, the North Sea is a deathtrap.

There isn't anything to eat because the squid,

their main prey species, is mainly found in much deeper water.

And as sperm whales get all their fluid from their food,

no food means no water.

They become dehydrated, weak and confused.

If they don't get out of there,

their chances of stranding are probably quite high.

But why do so many strand at once?

And why are they always male?

When young males grow up, they form groups called bachelor pods

that migrate to colder waters in search of food.

All 29 whales that stranded in the North Sea

were most likely from the same bachelor pod.

All it takes is for one to make a wrong turn

and the entire pod will follow,

even into a dangerously shallow sea.

This was undeniably a horrible tragedy,

but paradoxically, it might also be a sign of some good news.

You see, since 1986, when most commercial whaling

was outlawed, some whale populations have begun to increase.

Now, we can't say for certain

that that's the case with sperm whales, but it's likely.

And, of course, if there are more sperm whales in the ocean,

there are likely to be more sperm whale strandings.

So, although this was a very sad event,

we can perhaps look forward to some better things to come.

So, from invasive invertebrates to stranded leviathans,

animals can turn up in the weirdest of places.

Coming up - what happens when technology and nature meet?

First up, let's find out how a robot could help save

one of the world's greatest natural wonders.

This is the Great Barrier Reef.

The world's largest living structure.

And it's under attack.

Tropical cyclones are becoming more frequent and severe,

battering and damaging the reef.

And warming seas have caused widespread bleaching of living coral.

But there is a much nastier threat.

The reef is being devoured by a lethal predator

that's multiplying at an alarming rate.

With a voracious appetite for living coral,

it leaves only death and destruction in its wake.

The culprit is something you may not expect.

We're in the midst of an outbreak of crown-of-thorns starfish right now.

Yes, the coral-killing culprits are starfish.

Crown-of-thorns starfish,

or COTS.

Growing to almost a metre across,

these things are coral-eating machines.

The big problem with crown-of-thorns starfish

is that they have voracious appetites.

Coral is their number one food.

And their appetite isn't the only problem.

A single female can generate

100 million eggs.

And so, they have an amazing capacity to multiply

and then spread from one reef to another.

In healthy reefs, there are only one or two starfish per acre.

But in outbreak areas, there can be thousands.

So, what has caused this invasive invertebrate

to swarm in such numbers?

Its natural predators, like the triton snail and humphead wrasse,

are in serious decline due to shell collecting and overfishing.

But there's an even more serious issue.

The release of pollution from agriculture, which is then

fertilising the water and helping these starfish propagate.

When excess nutrients run off farm fields and into the ocean,

plankton blooms,

and starfish larvae thrive on plankton.

With too much food and nothing to keeps COTS numbers in check,

the situation is desperate.

So, can anything be done to stop these coral-killers?

In the 1960s, when these outbreaks first occurred,

well-meaning divers went down,

collected the starfish and cut them into pieces.

The thing is, each of those pieces can regenerate

into a fully-formed starfish,

so this simply made matters worse.

Thankfully, after years of research,

scientists have come up with a far more precise method.

Teams of divers go out on a boat,

they'll take a solution of what are known as bile salts,

and you inject that single injection

into the body of the starfish.

And that can kill the starfish.

Bile salts dissolve the starfish from the inside out,

rapidly killing it, but without polluting the marine environment.

It's effective, but it's labour-intensive.

Mm. With such a massive reef,

there must be millions of crown-of-thorns starfish out there.

And, of course, human divers have got a limited amount of time

that they can spend under the water.

And they're limited to how deep they can go.

So to get rid of them that way would be a monumental task.

What they needed was a far more efficient solution

to this...thorny problem.

Introducing COTSbot.

A team at the Queensland University of Technology

have developed a dedicated starfish destroyer.

What we've actually done is designed a robot like a predator,

and it's a robot for killing crown-of-thorns starfish.

-How does it look? Pretty stable?

-One metre...

We've developed this system to manoeuvre around the reef by itself.

It has an onboard brain and it interprets the environment.

It has a vision system to be able to detect organisms on the sea floor.

And at that time,

it's actually looking for these crown-of-thorns starfish.

This robot can actively seek out its victim

using a state-of-the-art vision system.

It then manoeuvres itself for a closer look.

And with one stab of a needle, it's game over for the starfish.

You'll see the arm go down...

..it delivers the dose of 10mm of bile salts,

retracts, brings its arm back up

and then the robot moves on to the next starfish.

And this ingenious invention isn't just precise, it's also practical.

They don't get tired. We can go down to 100 metres.

Currently, occupational divers can only go to 30.

We can operate at night. So we could eradicate quite a few hundred a day.

This is actually going to make a big difference.

So it's something I'm very proud of

and hopefully we'll see more types of these solutions

to help protect our natural environment in the future.

It's hoped that in the future

there'll be a whole fleet of robots patrolling the reef,

helping to protect one of the world's greatest

and most fragile ecosystems.

But it's not just our oceans that are under attack.

Our skies are being invaded, too.

In 2016, more than 1.5 million drones were sold worldwide.

No-one is safe from these flying cameras.

SCREAMING

And with so many amateur film-makers now taking to the sky,

it's not just humans who are unhappy

with the aerial intrusion.

Drones are easy to come by these days.

Just watch this.

Look at that. This one only cost a few pounds.

And anyone can fly them.

Well, almost anyone.

But the fact that you can get them quite literally off the shelf,

and they're relatively easy to fly,

means that they are becoming a bit of a problem.

When wildlife takes on these aerial spies,

it can make entertaining viewing.

But in the wrong hands...

..drones become a very serious danger indeed.

As well as leisure use,

drones present the possibility of use for criminal purposes.

There's also the potential for drones to be used by terrorists

with spectacular consequences.

Certainly, this is an issue that's at the forefront

of governments' and defence corporations' thinking

about how we respond to the potential -

only the potential so far -

use of these things for what we call nefarious purposes.

The possibilities are too terrifying to imagine,

and it's a problem that needs to be solved.

The issue of how to deal with problem drones

has come up with a whole variety of novel solutions.

The manufacturers themselves have talked about geo-fencing -

building in software to the drone to prevent them going anywhere

where they could cause a real problem.

Airports, nuclear power stations.

The Japanese have developed a drone with a net underneath,

sort of a version of aerial lacrosse -

it scoops small drones out of the air.

All good solutions, but in the global fight

against dangerous drones, there's a more surprising strategy.

HIGH-PITCHED SCREECH

In 2014, a team of Dutch security experts

started employing a flyer even more skilled than the drones.

Other technologies have been investigated.

The most novel one of those is the potential use of eagles.

Yep, you heard it right, he said eagles.

The Dutch team believe that eagles might just be the perfect weapon

to combat dangerous drones.

Eagles clearly are supreme aerial predators.

With eyesight eight times better than ours, a drone has no chance.

Even the rotor blades are no problem for their immensely powerful talons.

And if large gatherings of people were under threat,

like at a sporting event,

a trained eagle could be THE perfect weapon

to safely neutralise a suspicious drone.

Eagles trained in anti-drone defence

are now being very seriously considered

by police forces all over the world.

I suppose we could think of this as a perfectly-evolved,

natural solution to a new hi-tech problem.

Next, to North Africa,

where a surprising discovery in the dunes could take us to other worlds.

2008, Morocco.

On the edge of the Sahara,

German professor Ingo Rechenberg made an astonishing discovery.

I was very, very excited.

Very excited. I was crying!

Now, Professor Ingo Rechenberg has dedicated his life

to designing machines inspired by nature.

He loves the climate and the tranquillity of the Sahara

and spends his winters living here.

But one night, he was in for the shock of his life.

I was going outside in the night

and an animal was crossing near.

I had the feeling it was a very large animal,

maybe a jumping mouse, or maybe a lizard or something else.

And then I looked and just before me, a spider was sitting down.

The spider was the size of about 10cm. A very large spider.

And as Ingo watched, the spider did something extraordinary.

Suddenly, the spider was rolling away.

I was crying, "Look, this spider is rolling!"

Yes, the spider was indeed rolling, but that's not so strange,

because there is, in fact, another spider that rolls -

the golden wheel spider.

It balls itself up to roll down the dunes.

So, why was Ingo so excited?

Well, this Moroccan spider was different.

It wasn't just rolling downhill, but uphill.

The spider was rolling up the dune! Up the dune!

And so, I must say, I was very, very excited.

It was a completely unique form of locomotion,

totally new to science.

But why would a spider want to do this?

The velocity when rolling is twice the velocity

when the spider is walking with eight feet.

It has a big advantage.

In the desert, this spider could be prey for larger and faster beasts,

like the fennec fox or the pompilid wasp.

When threatened, this amazing arachnid flips into rolling mode

and doubles its speed for a fast getaway.

It's just brilliant!

And, of course, it's every biologist's dream

to discover a new species.

The strange thing is that Professor Rechenberg is not a biologist -

he's a scientist with a very particular specialisation.

My interest is mainly bionics.

That means that we try to study

the performance of biological systems,

then, of course, we try to imitate this

and to develop a new machine, or something else.

He's being quite modest here.

Professor Ingo Rechenberg is at the very top of his field,

world-renowned for designing robots inspired by nature.

So, after discovering the spider, Professor Ingo Rechenberg

did what any world-renowned bionics engineer would do.

So, we started to imitate the motion

and our aim now is to design a robot

which is able to do both,

to walk and to move in the wheeling condition.

And here it is. Yes, a robot that rolls just like the spider.

It's certainly a very clever bit of engineering,

but the question is, why?

I mean, what possible purpose would there be for such an invention?

Well, Professor Rechenberg has big plans for his little robot.

You see, with this particular type of movement, it has the potential

to boldly go where no robot spider has ever gone before.

We hope that NASA, or also here ESA,

will become interested when I finish the robot

to design a larger one, yes,

than we designed here for the use on the next Mars mission.

A robot on Mars,

able to walk and roll,

adapting to even the most challenging alien landscape.

So space really could be the final frontier

for our little spider robot,

crawling and rolling over the surface of Mars.

And just to think that all of that came to pass

because of a chance encounter with a real spider in the Sahara,

one that now bears the name of the man who discovered it -

Cebrennus rechenbergi.

So, we've learned when nature and technology meet,

the results can be both ingenious and wonderful.

Coming up - a weird world of new discoveries.

First stop, though, the Amazon.

South America, 2011.

Field biologist Aaron Pomerantz was on an expedition

in the deepest reaches of the Amazon rainforest.

There is an insane amount of diversity out there.

So I was walking down this trail, I was just covered in mud

and I just sort of casually walked past this tree.

When I took a closer look, I noticed something I wasn't really expecting.

Hanging from a tree was something minute and extraordinary.

A strange structure, delicate and complex.

It was like nothing Aaron had ever seen before.

This structure is really odd-looking,

like a little hanging orange basket.

It just looks like something 3-D printed.

I was just like,

"Oh, my God, I need to catch this."

Like, "We need to look at this further."

Just look...at that!

It was bright orange, made out of a very delicate lattice.

It's like a little alien basket.

But what was even stranger is that when Aaron peered inside,

he could see something in there.

Something that any entomologist would easily recognise.

It was a pupa, a moth chrysalis,

which means the tiny alien structure Aaron found was, in fact, a cocoon.

Cocoons are made to keep caterpillars safe

as they transform into moths.

They need to be weatherproof and to keep out any predators.

So, why would a moth create such a fragile structure?

Well, a pupa in the rainforest has one particularly prolific predator.

Ants are everywhere in the Neotropics.

And so we think that this adaptation, with this odd structure,

allows the pupa to sort of hang there,

where it's protected, away from ants.

Yes. Suspending itself on a long, thin thread,

the cocoon becomes ant-proof.

Even the most persistent and hungry ant

can't safely descend such a long, thin fibre.

But, then, why the weird latticework?

Surely the pupa would be safer completely enclosed.

Well, you see, living on a long, thin thread

is a very fragile existence.

Too much weight or wind will snap the thread

and it will be game over for the pupa.

So the caterpillar that made this cocoon

came up with an ingenious plan.

But to understand it, we need to look at the structure more closely.

The nearest we can get to making something so intricate

is with a 3-D printer.

And here is our cocoon copy.

And here's a more classic-looking cocoon

with nice, safe, closed sides.

If we recreate rainforest conditions,

the solid cocoon becomes waterlogged and heavy.

But the lattice lets the rain drain straight through.

This keeps the cocoon nice and light

and prevents its anti-ant strand snapping.

And then, if that wasn't clever enough,

air can circulate through the lattice,

keeping the pupa dry and preventing fungal infections.

If it was just enclosed, like a lot of species that we have in,

say, Europe or North America,

there's not as much humidity and not as much rain in these environments.

So in the rainforest, we think it's this open structure so it doesn't drown.

This delicate, intricate structure

is actually completely and wonderfully, well, practical.

So you might expect that the moth that would emerge from this

would be of great, mesmerising beauty,

a paragon amongst moths.

Well, ladies and gentlemen, young people,

I give you the urodid moth.

I'm afraid it's rather drab.

But thankfully, our next weird discovery is far more colourful,

as we venture into the rainforests of Borneo.

Home to some very unusual plants.

Hidden amongst the greenery are some hair-raising hunters -

pitcher plants.

Most plants get nutrients through their roots,

but these peculiar plants have an altogether more sinister strategy.

They eat meat.

Now, all pitchers are pretty wonderfully weird,

but there's one particular species

that's puzzled botanists for decades -

Nepenthes hemsleyana -

because, well, it's a picky eater.

This species catches seven times fewer insects

than its closest relatives.

It's practically a vegetarian.

But if it isn't eating insects, what is it eating?

In 2014, a scientific expedition to Borneo

captured these incredible images.

Bats, inside the pitcher plant.

Could this be the first documented case of a bat-eating plant?

Captivated by these images, bat experts Michael and Caroline Schoner

travelled from Germany to the jungle

to find out if the plant really had developed a taste for bats.

We don't think that the plants have evolved to digest these kinds of animals.

They have evolved to digest arthropods, insects, for example.

Potentially, bats would be able to die inside,

but it's more than unlikely, I would say.

So, if the pitcher plant wasn't eating the bat, what was going on?

Perhaps the bat was the one hoping for a meal.

We had this idea at the beginning

that the bats might steal insects from the pitchers,

but actually, it's not working

because the bats can never reach this fluid.

No. These peculiar pitcher plants weren't providing a free lunch,

they were offering something much more unusual.

These pitchers, they have a very stable microclimate inside,

so during the hottest hours of the day,

they are cooler than the outside temperature.

And this is something which bats absolutely like.

So these pitcher plants make the perfect air-conditioned

place to rest during the heat of the day.

But what's in it for the plant?

Why's this carnivore cuddling up to a bat?

Well, this guest leaves a gift behind.

Bat faeces contain a lot of nitrogen and phosphorus and also potassium.

Those nutrients are missing in the areas where the plants are growing.

This extraordinary pitcher plant has evolved to survive

almost entirely on the poo of its guest,

relying on the bat to bring it sustenance.

I just love this.

A perfectly strange symbiosis between a plant

and its small, furry friend.

And it's a win-win situation.

The pitcher provides the perfect bat bag

and, of course, the bat benefits.

At the same time, the pitcher's thriving on the bat's poo.

And their survival is intricately intertwined.

There's just one last piece to the puzzle.

How does the plant attract the bat?

Well, we know that bats use echolocation

to find their way around.

They send out high-frequency calls

and use the reflected sound waves

to build up a picture of the forest around them.

But Borneo has over 15,000 species of plants

and more than 30 types of pitcher plant.

So, how does this particular one make sure that the bats find it?

Well, would you believe, the pitcher has evolved to become noisier.

Its back wall is unusually wide and curved,

just to reflect and amplify the bat's calls.

It's the perfect bat beacon.

And it works like a dream.

Amazing! Not only has the pitcher evolved to fit the bat like a glove,

it's also come up with a structure that acts as an advertisement

which says, "This is the best bat hotel in town."

Now, honestly, that's why I get up in the morning.

That's proper biology.

And finally, we investigate a very serious danger

from the Australian bush.

Danger from above.

A-A-A-A-A-A-A-A-A-A-A-A-Argh!

So, a Drop Bear is like a cross between a polar bear

and a koala bear that potentially could drop out of a tree

when you're out camping, for example.

It's probably almost as deadly as the crocodile, but you just...

Yeah, almost.

'And remember, look up when in the outback.'

Many places around the world have their own legends of mythical creatures.

Scotland has the Loch Ness monster,

North America has Bigfoot

and Australia has the Drop Bear.

The Drop what?

A truly terrifying beast that can climb trees and drop down

on you from above.

SCREAMS

The Drop Bear, a fearsome koala-like creature that

preys on the weak and unsuspecting, but also just

a piece of Australian folklore,

the sort of thing you hear round the campfire

to scare you if you're a tourist

or give you nightmares if you're a kid.

Couldn't possibly be any truth in it,

or could there?

In 2015, in a remote corner of Western Australia,

researchers found weird scratch marks high up on a cave wall.

Scratches that were vital clues,

clues to shed a new light on the mysterious Drop Bear.

You see, those scratches might actually point to some

evidence that proves that the Drop Bear is more than a tall tale.

Mm.

Scratch marks on a cave wall that wouldn't mean much to you or I,

but to one palaeontologist, this was a monumental discovery.

Our story begins almost two centuries ago.

With the settlement of Australia in the 1800s,

pastoralism was moving out beyond the main centres of occupation

like Sydney and Melbourne.

In the process, people were stumbling on the remains of

large animals that they knew nothing of.

This was the Australian megafauna - giant animals.

One of these early finds was a skull of

a very strange-looking animal about the size of a leopard.

It had the front teeth of a herbivorous marsupial like

a kangaroo or a koala...

..but its cheek teeth were huge, sharp blades,

the kind you'd expect from a meat eater.

A marsupial with carnivorous teeth?

Now, that's a very weird find indeed.

It was so unusual, like no other species ever seen.

It was given a very fitting scientific name -

Thylacoleo carnifex,

which translates as the marsupial lion.

The butcher.

But what exactly was this mysterious beast?

Well, with only a skull to go on,

it was anyone's guess and would stay a mystery for 100 years.

Until a young palaeontologist made a huge breakthrough.

In 1969, I was exploring with a colleague, and we detected

a gust of air coming out of a rock pile.

So we wriggled through into a chamber and in that chamber

there was a silt floor with these funny saw-tooth patterns.

When my eyes got accustomed I looked down, and there at my feet

was the upturned skull of the marsupial lion.

Incredibly exciting.

I still get excited telling you about it.

To the side of that, there was the arm of the lion

with the hand reaching up out of the sediment against the rock.

And on the arm were long, sharp claws,

exactly the sort a predator would use

to catch and hold on to prey.

Over the next few decades, more discoveries of complete skeletons

helped flesh out a picture of a truly terrifying predator.

This animal can produce the most powerful bite

known for any living mammal.

It could crush a skull in a single bite.

It really is the stuff of nightmares,

but can we say that this was the Drop Bear?

Well, remember those scratches on the cave wall?

In just recent times, a couple of my colleagues have been examining

scratch marks on the walls of caves in which we've found

the marsupial lion.

This seems to suggest that they were actually actively climbing in

and out of the cave.

If it could climb out of a cave, then potentially

it could climb a tree. And if it could climb a tree,

then it could drop out of it onto unsuspecting prey.

You can see where I'm going -

it's beginning to sound more and more like the Drop Bear.

I suppose the question then is, how could the legend pass

into the present day?

Well, just look at this rock art made by indigenous Australians

more than 40,000 years ago.

Are you seeing what I'm seeing?

Experts believe this is most likely our marsupial lion.

And if so, it's direct evidence that some people came face to face

with it and lived to tell the tale.

A tale that could make even the scariest campfire story

imaginable, real, even.

Perhaps memorable enough to pass on to the next generation

and the next generation, all the way down to the present day.

And you never know, it might still be out there.

If ever you're camping in Australia, you might want to look up.

From the discovery of an alien cocoon to a plant that makes

a home for a bat and the unravelling of an ancient legend.

I find it strangely reassuring that when we finally explain one of these

weird mysteries, we become aware that there are still loads more

out there to be solved.

There's no doubt at all that there are plenty of puzzles

left on our planet.

Next time, we investigate vampire fish,

head-banging sharks and some very weird waves.