0:00:02 > 0:00:05We live in a very weird world.
0:00:09 > 0:00:13And the more we discover about our planet, the stranger it gets.
0:00:15 > 0:00:17Every day, new stories reach us.
0:00:17 > 0:00:19Stories that surprise us...
0:00:19 > 0:00:22What is that?!
0:00:22 > 0:00:26- ..shock us...- Whoa! - That is so cool!- Oh, my God!
0:00:26 > 0:00:29..sometimes even scare us.
0:00:29 > 0:00:30SCREAMING
0:00:30 > 0:00:32Oh, my God!
0:00:32 > 0:00:36We've scoured the globe to bring you the most curious creatures...
0:00:38 > 0:00:41..the most extraordinary people...
0:00:41 > 0:00:44I can stick almost anything to my skin without no glue.
0:00:44 > 0:00:46..and the most bizarre behaviour...
0:00:49 > 0:00:52..using eyewitness accounts and expert opinion
0:00:52 > 0:00:55to explore a weird world
0:00:55 > 0:00:57of unexplained underwater blobs...
0:00:59 > 0:01:01..flying goats,
0:01:01 > 0:01:04and glow-in-the-dark fish.
0:01:06 > 0:01:08We examine the evidence,
0:01:08 > 0:01:10test the theories...
0:01:12 > 0:01:15..to work out what on earth is going on.
0:01:35 > 0:01:41In this episode, an Australian town under attack from aerial invaders...
0:01:43 > 0:01:45It smells, the noise...
0:01:45 > 0:01:49..an exquisite piece of alien artwork...
0:01:49 > 0:01:51Oh, my God!
0:01:51 > 0:01:55..and the mystery of sperm whales washed up on the North Sea coast.
0:01:59 > 0:02:03But first, to the USA.
0:02:03 > 0:02:04Denison, Texas.
0:02:07 > 0:02:10Like most American towns, Denison has a main road.
0:02:10 > 0:02:12Nothing unusual about that.
0:02:15 > 0:02:19Well, that was until the morning of May 29th, 2015.
0:02:21 > 0:02:24Yeah, this one's not for the squeamish out there,
0:02:24 > 0:02:26but it's still fascinating.
0:02:27 > 0:02:31This highway became the scene of a very strange sighting.
0:02:36 > 0:02:41Balls of worms appeared overnight, squirming in circles,
0:02:41 > 0:02:45all lined up exactly between the centre lines.
0:02:50 > 0:02:53Piles of worms.
0:02:53 > 0:02:59And not small piles - I'm talking about massive piles of worms,
0:02:59 > 0:03:04hundreds piled together in the middle of a Texas road.
0:03:05 > 0:03:10But why had these animals come together in such unusual numbers?
0:03:14 > 0:03:16With no-one admitting to putting them there,
0:03:16 > 0:03:19the people of Denison were left baffled.
0:03:19 > 0:03:21So the footage was put online,
0:03:21 > 0:03:24where it caught the attention of an expert.
0:03:24 > 0:03:26It is really unusual to see them lined up
0:03:26 > 0:03:29in the middle of the road like that.
0:03:32 > 0:03:35I've never, ever seen that before.
0:03:35 > 0:03:38Now, Emma could think of some good reasons why the worms
0:03:38 > 0:03:40had clumped together like this.
0:03:40 > 0:03:44It's much, much safer for earthworms once they're on the surface
0:03:44 > 0:03:47to actually congregate into these big balls.
0:03:47 > 0:03:50Worms actually breathe through their skin,
0:03:50 > 0:03:53so they do need to stay moist at all times.
0:03:53 > 0:03:56So being up on the surface, being exposed to the sun's rays,
0:03:56 > 0:04:01is actually really, really harmful and they can die pretty quickly.
0:04:01 > 0:04:04But, of course, if they're encased around with other worms,
0:04:04 > 0:04:06that will actually keep them a lot safer.
0:04:08 > 0:04:11OK, so the worms had balled together for safety,
0:04:11 > 0:04:15but this doesn't explain why they were on the road in the first place.
0:04:17 > 0:04:21There just didn't seem to be a sensible answer.
0:04:21 > 0:04:24And whilst the residents were there scratching their heads,
0:04:24 > 0:04:27looking for clues, the day just got weirder and weirder,
0:04:27 > 0:04:31with reports coming in of something equally odd
0:04:31 > 0:04:3375 miles south in Dallas.
0:04:36 > 0:04:39Check this out. This is amazing!
0:04:40 > 0:04:45Andres Ruzo captured this bizarre footage of fish trapped dead
0:04:45 > 0:04:48in a fence a metre above the ground.
0:04:50 > 0:04:52Check that out!
0:04:53 > 0:04:56My first reaction when I saw all these fish in the fence was,
0:04:56 > 0:04:59"Holy cow! This is bizarre!"
0:05:03 > 0:05:04Bizarre indeed.
0:05:04 > 0:05:06I mean, it's not every day you see
0:05:06 > 0:05:09a suspended fish stuck in the fence of a playing field.
0:05:12 > 0:05:14I didn't expect to see that at all.
0:05:14 > 0:05:17Suddenly, I'm walking around and these prehistoric-looking things
0:05:17 > 0:05:19with mouths full of teeth are suddenly right there
0:05:19 > 0:05:20and it was just, you know,
0:05:20 > 0:05:22immediately to the cellphone, "What is this?!"
0:05:26 > 0:05:29Well, these freaky-looking fish are gars,
0:05:29 > 0:05:32one of the largest freshwater fish in North America.
0:05:34 > 0:05:35Often called living fossils,
0:05:35 > 0:05:40they've remained virtually unchanged for the last 100 million years.
0:05:44 > 0:05:46Sharing the world with T-rex and velociraptors,
0:05:46 > 0:05:49these truly are prehistoric beasts.
0:05:52 > 0:05:54So Andres knew what these fish were,
0:05:54 > 0:05:59but why were these unfortunate few stuck so high and dry?
0:06:01 > 0:06:03- Well, that was a mystery. - It was just weird!
0:06:03 > 0:06:06You don't expect to see a bunch of fish randomly sitting in a fence
0:06:06 > 0:06:08and no-one's going to show up, "Oh, I've got a great idea.
0:06:08 > 0:06:11"Let me take all these dead fish and stick them in a fence."
0:06:11 > 0:06:14No-one's going to do that! So, how did they get there?
0:06:16 > 0:06:21So, we have two bizarre animal appearances 75 miles apart
0:06:21 > 0:06:23happening within hours of each other.
0:06:25 > 0:06:27Could these strange sightings be linked?
0:06:28 > 0:06:30What could they possibly have in common?
0:06:34 > 0:06:38Well, it turns out that May was a busy month for this corner of Texas.
0:06:41 > 0:06:44While fish and worms made mysterious appearances,
0:06:44 > 0:06:48a much more public event was making itself felt.
0:06:49 > 0:06:52THUNDERCLAP
0:06:52 > 0:06:54RAIN PELTS
0:06:56 > 0:06:59In the month before these weird happenings,
0:06:59 > 0:07:05a whopping 37 trillion gallons of rain fell on Texas.
0:07:05 > 0:07:10It pushed the water table far beyond its normal range.
0:07:11 > 0:07:14Lakes spilled over, rivers burst their banks
0:07:14 > 0:07:17and large parts of Dallas experienced severe flooding,
0:07:17 > 0:07:21affecting not only the community living along the river,
0:07:21 > 0:07:24but also its fish.
0:07:24 > 0:07:27The entire field where I was had been flooded.
0:07:27 > 0:07:30It would have been about chest high for me.
0:07:30 > 0:07:33That's a significant amount of water.
0:07:33 > 0:07:35Significant indeed.
0:07:35 > 0:07:38Enough water for the fish to swim easily over the fence,
0:07:38 > 0:07:42across the flooded fields, looking for something to eat.
0:07:42 > 0:07:47But when the water level dropped, well, the way home was blocked.
0:07:49 > 0:07:52I imagine the small ones got through the holes in the fences no problem,
0:07:52 > 0:07:54but the bigger ones, they happened to get stuck.
0:08:00 > 0:08:04It was a miserable end for these fish in the fence.
0:08:05 > 0:08:08But what about those worm balls on the road?
0:08:08 > 0:08:12Could the extreme Texan weather provide the key?
0:08:14 > 0:08:17It had been raining really, really heavily.
0:08:17 > 0:08:20Everywhere was absolutely saturated, completely waterlogged.
0:08:20 > 0:08:24So basically, all these worms had to come up to the surface.
0:08:24 > 0:08:26And as they're trying to escape,
0:08:26 > 0:08:29they've all hit this big tarmac road.
0:08:31 > 0:08:34To avoid drowning, the worms took to higher ground.
0:08:36 > 0:08:39But this still doesn't explain why they lined themselves up
0:08:39 > 0:08:42in between the double yellow lines.
0:08:42 > 0:08:44Earthworms don't have eyes like we do,
0:08:44 > 0:08:48but they are very sensitive as to whether it's light or dark,
0:08:48 > 0:08:51so when they've got into this middle, black area,
0:08:51 > 0:08:54they've maybe stayed there and then not wanted to venture
0:08:54 > 0:08:57the other side either because of the other yellow line.
0:08:57 > 0:08:59So maybe it feels to them a little bit safer.
0:09:01 > 0:09:05And so the worms huddled together, safe from the floods,
0:09:05 > 0:09:07but trapped between the lines.
0:09:14 > 0:09:17No other parts of Texas had recorded the same nightmarish
0:09:17 > 0:09:22piles of worms, or weird fish stuck in fences.
0:09:22 > 0:09:26This was a very location-specific event,
0:09:26 > 0:09:29down to the unprecedented levels of rain that had come together
0:09:29 > 0:09:31to produce the perfect storm.
0:09:35 > 0:09:37Next, we travel down under,
0:09:37 > 0:09:40to a small town with its own set of strange invaders.
0:09:44 > 0:09:46New South Wales, Australia.
0:09:48 > 0:09:51The coastal town of Batemans Bay sees its fair share of tourists.
0:09:53 > 0:09:56People come to Batemans Bay to relax, to take it easy.
0:09:59 > 0:10:01They like the visual aspect of it, they like the clean beaches,
0:10:01 > 0:10:03they like the trees.
0:10:03 > 0:10:07But in 2016, the bay became famous for an invasion
0:10:07 > 0:10:09of much more unwelcome visitors.
0:10:14 > 0:10:17It's horrible. It smells. The noise.
0:10:17 > 0:10:19You can't hang your washing out.
0:10:19 > 0:10:21Everyone's moved out.
0:10:21 > 0:10:24There's only three of us left in this whole block of units now.
0:10:26 > 0:10:29Batemans Bay is under siege.
0:10:29 > 0:10:33The worst thing is when they go over night-time.
0:10:33 > 0:10:35They block out your TV.
0:10:35 > 0:10:37It's just all black.
0:10:39 > 0:10:42They need to get rid of them, otherwise, I don't know,
0:10:42 > 0:10:44bad things are going to happen.
0:10:45 > 0:10:47The people of Batemans Bay
0:10:47 > 0:10:51have had their peaceful lives turned upside down
0:10:51 > 0:10:53by an invasion of...
0:10:53 > 0:10:54bats.
0:10:56 > 0:10:59And not just any old bat, giant Australian fruit bats,
0:10:59 > 0:11:03otherwise known as the grey-headed flying fox.
0:11:03 > 0:11:05CHITTERING
0:11:09 > 0:11:13Grey-headed flying foxes are one of the largest bats in the world.
0:11:17 > 0:11:20Their wingspan is about a metre.
0:11:20 > 0:11:23That's the length of a large dog!
0:11:23 > 0:11:28Each bat weighs up to a kilogram, and they don't fly alone either.
0:11:28 > 0:11:30Flying foxes are highly colonial animals.
0:11:30 > 0:11:33They roost in large aggregations during the day
0:11:33 > 0:11:36in the open canopy of trees.
0:11:36 > 0:11:38Now, the area around Batemans Bay
0:11:38 > 0:11:40has always been a flying fox hot spot.
0:11:43 > 0:11:46Roosting out in the wilderness, beyond the town.
0:11:46 > 0:11:50But in 2011, these bats turned their backs on the bush
0:11:50 > 0:11:52and set their sights on the town centre.
0:11:53 > 0:11:56Year by year, their numbers have rocketed
0:11:56 > 0:12:00from around 10,000 to over 100,000.
0:12:00 > 0:12:04It's the largest number ever recorded in an urban area.
0:12:07 > 0:12:10And the reason behind this relocation?
0:12:10 > 0:12:13Well, it's all to do with this.
0:12:13 > 0:12:18Flying foxes are fruit bats and feed on fruit and nectar,
0:12:18 > 0:12:20and there's nothing they like more
0:12:20 > 0:12:22than the nectar-rich flowers of a gum tree.
0:12:24 > 0:12:26The forests around Batemans Bay contain
0:12:26 > 0:12:30a large number of a eucalyptus species known as spotted gum.
0:12:32 > 0:12:36It produces particularly rich nectar from its flowers.
0:12:36 > 0:12:40So spotted gum is almost like a magnet for flying foxes.
0:12:44 > 0:12:48Not only is the centre of Batemans Bay close to these tasty trees,
0:12:48 > 0:12:51but it's also got a good supply of fresh water
0:12:51 > 0:12:55and lots of trees to roost in during the daytime.
0:12:55 > 0:12:57This place is a bat heaven.
0:12:57 > 0:12:59And when you consider that large areas of forest
0:12:59 > 0:13:03in the surrounding area have been cut down for logging and farmland,
0:13:03 > 0:13:06well, bedding down in the centre of town
0:13:06 > 0:13:09makes perfect sense to the flying fox.
0:13:09 > 0:13:14It's just that the human population is not quite so happy about it.
0:13:17 > 0:13:21Everyone's had a dog that's barked a lot next door that drives you insane.
0:13:21 > 0:13:24Well, multiply it by 100,000 and then you actually get an idea
0:13:24 > 0:13:26of the physical and the mental stress
0:13:26 > 0:13:28that's placed on a community with that size of numbers.
0:13:28 > 0:13:31SQUAWKING
0:13:31 > 0:13:33It's not that the residents of Batemans Bay
0:13:33 > 0:13:36are entirely anti-bat, they're not.
0:13:36 > 0:13:39It's just that they'd rather they weren't living quite
0:13:39 > 0:13:42so close to their homes.
0:13:42 > 0:13:45So they've cut down a couple of the bats' favourite trees
0:13:45 > 0:13:47and they're using bright lights...
0:13:49 > 0:13:51..some loud noises... AIR HORN
0:13:51 > 0:13:53..and smoke...
0:13:54 > 0:13:59..to safely and humanely encourage the flying foxes back into the bush.
0:14:04 > 0:14:0880% of our shire is covered in national park and forest.
0:14:08 > 0:14:12And, um...flying foxes are more than welcome to go to that 80%
0:14:12 > 0:14:14and we need to encourage them to do that.
0:14:16 > 0:14:20It's not just a respect for nature that's motivating residents here.
0:14:20 > 0:14:24You see, bats play a vital role in the ecosystem.
0:14:26 > 0:14:30Every night when they're feeding in the bush, they collect pollen
0:14:30 > 0:14:31in their fur, on their heads,
0:14:31 > 0:14:35and they move it to each successive tree that they visit.
0:14:35 > 0:14:39And in doing that, they're providing an extraordinary service.
0:14:45 > 0:14:48Pollination. You see, keeping the forests alive.
0:14:48 > 0:14:52Good for the flying foxes and good for people, too.
0:14:52 > 0:14:56So let's hope that man and bat find a happy compromise
0:14:56 > 0:14:59and peace can return to Batemans Bay as soon as possible.
0:15:03 > 0:15:07Our next unusual animal sighting was reported much closer to home.
0:15:11 > 0:15:13January 9th, 2016.
0:15:15 > 0:15:16Germany.
0:15:16 > 0:15:19A sperm whale the size of a double-decker bus
0:15:19 > 0:15:22was washed up on the north coast.
0:15:26 > 0:15:30Then, within a few hours, another whale appeared.
0:15:30 > 0:15:31Then three more nearby.
0:15:35 > 0:15:40A few days later, six more sperm whales stranded.
0:15:40 > 0:15:44Unbelievably, the news got worse.
0:15:47 > 0:15:49Whales began appearing on English beaches.
0:15:50 > 0:15:53The world's media looked on horrified as
0:15:53 > 0:15:55over a period of three weeks
0:15:55 > 0:15:5829 sperm whales washed ashore,
0:15:58 > 0:16:01their bodies found all along the North Sea coast.
0:16:04 > 0:16:07It was the largest mass sperm whale stranding event
0:16:07 > 0:16:10in the North Sea since records began.
0:16:15 > 0:16:17The UK's leading whale-stranding expert
0:16:17 > 0:16:19rushed to the coast to investigate.
0:16:21 > 0:16:24I've never had to deal with anything like that before,
0:16:24 > 0:16:25both emotionally and physically.
0:16:28 > 0:16:31We haven't had an event of this magnitude
0:16:31 > 0:16:33with sperm whales for 100 years.
0:16:33 > 0:16:35The question for us is, what happened?
0:16:37 > 0:16:40What could possibly cause so many sperm whales to strand
0:16:40 > 0:16:43in such a short period of time?
0:16:46 > 0:16:50Well, whales do strand across the world every year.
0:16:52 > 0:16:57In 2004, 150 melon-headed whales came ashore in Hawaii.
0:16:57 > 0:17:02And in 2005, over 100 pilot whales stranded in Tasmania.
0:17:05 > 0:17:08But both of these events had one thing in common -
0:17:08 > 0:17:11they coincided with large sonic activities.
0:17:13 > 0:17:15Naval testing and minesweeping.
0:17:18 > 0:17:20Whales have particularly sensitive hearing,
0:17:20 > 0:17:25and loud, unnatural sounds can interfere with their navigation.
0:17:27 > 0:17:32But in 2016, there was no evidence of any naval exercises,
0:17:32 > 0:17:34or other loud underwater disturbance.
0:17:36 > 0:17:38Rob went back to the drawing board.
0:17:39 > 0:17:41Wind farms might be causing it...
0:17:41 > 0:17:43Then we have some more esoteric ones.
0:17:43 > 0:17:47Maybe the Large Hadron Collider might be impacting,
0:17:47 > 0:17:48or climatic factors.
0:17:48 > 0:17:52The El Nino's going on, that might be having an impact, too.
0:17:52 > 0:17:54Those things we have to consider.
0:17:56 > 0:18:00But then, more information arrived from Germany.
0:18:01 > 0:18:04Postmortem examinations of sperm whales
0:18:04 > 0:18:06revealed something disturbing.
0:18:10 > 0:18:15Inside their stomachs was plastic.
0:18:15 > 0:18:17A lot of plastic.
0:18:23 > 0:18:29Plastic in the marine environment is a very, very serious issue,
0:18:29 > 0:18:34and surely a whale with its stomach packed full of this stuff
0:18:34 > 0:18:38would suffer some very serious health problems.
0:18:38 > 0:18:41So, could it be that this oceanic litter
0:18:41 > 0:18:44is responsible for the stranding?
0:18:44 > 0:18:46That would be case closed.
0:18:46 > 0:18:49Well, actually, no.
0:18:50 > 0:18:55Because, you see, not every whale had a stomach full of plastic.
0:18:58 > 0:19:02So plastic could not have been the cause of the stranding.
0:19:02 > 0:19:03It was a case of back to the drawing board,
0:19:03 > 0:19:07or perhaps more pertinently, back to the history books.
0:19:07 > 0:19:09You see, although this stranding in 2016
0:19:09 > 0:19:12was the biggest in historical times -
0:19:12 > 0:19:13well, say, the last 100 years -
0:19:13 > 0:19:16if you go back further into the past,
0:19:16 > 0:19:19a very curious picture emerges.
0:19:21 > 0:19:25These works of art date from as far back as the 16th century.
0:19:26 > 0:19:28It's a very familiar scene, isn't it?
0:19:31 > 0:19:33The 2016 event was by no means
0:19:33 > 0:19:37the very first mass sperm whale stranding.
0:19:38 > 0:19:41There are many famous historical accounts of sperm whale strandings
0:19:41 > 0:19:46and mass strandings all around the North Sea.
0:19:46 > 0:19:47And, well, frankly,
0:19:47 > 0:19:52you can't help but notice that these whales are all males.
0:19:55 > 0:19:58But what about the 2016 whales? Is there a link?
0:20:00 > 0:20:03Well, what was startling about the latest stranding
0:20:03 > 0:20:05was that they, too, were all males.
0:20:05 > 0:20:08Every single one of them.
0:20:08 > 0:20:10And that wasn't all.
0:20:10 > 0:20:15These old works of art show the exact same stretches of coastline.
0:20:15 > 0:20:19Whales have been stranding here for centuries.
0:20:21 > 0:20:25So, what makes this coast so deadly for sperm whales?
0:20:30 > 0:20:33Sperm whales like to live in water thousands of metres deep.
0:20:36 > 0:20:39But this part of the North Sea is surprisingly shallow -
0:20:39 > 0:20:42in some places, only 50 metres deep.
0:20:44 > 0:20:49Sperm whales use an impressive biosonar to navigate and find food.
0:20:49 > 0:20:52It's the loudest sound produced by any living creature.
0:20:54 > 0:20:56It's perfect for deep water,
0:20:56 > 0:20:58but in this part of the North Sea,
0:20:58 > 0:21:00the sonar bounces against
0:21:00 > 0:21:01the shallow ocean floor.
0:21:04 > 0:21:08The whales become confused and they lose their way.
0:21:10 > 0:21:13Now, the North Sea is a deathtrap.
0:21:13 > 0:21:16There isn't anything to eat because the squid,
0:21:16 > 0:21:20their main prey species, is mainly found in much deeper water.
0:21:23 > 0:21:26And as sperm whales get all their fluid from their food,
0:21:26 > 0:21:29no food means no water.
0:21:31 > 0:21:35They become dehydrated, weak and confused.
0:21:41 > 0:21:43If they don't get out of there,
0:21:43 > 0:21:46their chances of stranding are probably quite high.
0:21:47 > 0:21:51But why do so many strand at once?
0:21:51 > 0:21:54And why are they always male?
0:21:56 > 0:22:00When young males grow up, they form groups called bachelor pods
0:22:00 > 0:22:03that migrate to colder waters in search of food.
0:22:05 > 0:22:08All 29 whales that stranded in the North Sea
0:22:08 > 0:22:11were most likely from the same bachelor pod.
0:22:13 > 0:22:16All it takes is for one to make a wrong turn
0:22:16 > 0:22:18and the entire pod will follow,
0:22:18 > 0:22:21even into a dangerously shallow sea.
0:22:26 > 0:22:29This was undeniably a horrible tragedy,
0:22:29 > 0:22:34but paradoxically, it might also be a sign of some good news.
0:22:34 > 0:22:37You see, since 1986, when most commercial whaling
0:22:37 > 0:22:41was outlawed, some whale populations have begun to increase.
0:22:41 > 0:22:43Now, we can't say for certain
0:22:43 > 0:22:46that that's the case with sperm whales, but it's likely.
0:22:46 > 0:22:49And, of course, if there are more sperm whales in the ocean,
0:22:49 > 0:22:53there are likely to be more sperm whale strandings.
0:22:53 > 0:22:56So, although this was a very sad event,
0:22:56 > 0:23:00we can perhaps look forward to some better things to come.
0:23:03 > 0:23:07So, from invasive invertebrates to stranded leviathans,
0:23:07 > 0:23:11animals can turn up in the weirdest of places.
0:23:15 > 0:23:19Coming up - what happens when technology and nature meet?
0:23:23 > 0:23:27First up, let's find out how a robot could help save
0:23:27 > 0:23:29one of the world's greatest natural wonders.
0:23:32 > 0:23:34This is the Great Barrier Reef.
0:23:36 > 0:23:38The world's largest living structure.
0:23:39 > 0:23:41And it's under attack.
0:23:43 > 0:23:46Tropical cyclones are becoming more frequent and severe,
0:23:46 > 0:23:49battering and damaging the reef.
0:23:50 > 0:23:54And warming seas have caused widespread bleaching of living coral.
0:23:57 > 0:24:00But there is a much nastier threat.
0:24:03 > 0:24:06The reef is being devoured by a lethal predator
0:24:06 > 0:24:08that's multiplying at an alarming rate.
0:24:10 > 0:24:13With a voracious appetite for living coral,
0:24:13 > 0:24:16it leaves only death and destruction in its wake.
0:24:20 > 0:24:23The culprit is something you may not expect.
0:24:24 > 0:24:28We're in the midst of an outbreak of crown-of-thorns starfish right now.
0:24:30 > 0:24:35Yes, the coral-killing culprits are starfish.
0:24:35 > 0:24:38Crown-of-thorns starfish,
0:24:38 > 0:24:40or COTS.
0:24:40 > 0:24:42Growing to almost a metre across,
0:24:42 > 0:24:46these things are coral-eating machines.
0:24:46 > 0:24:48The big problem with crown-of-thorns starfish
0:24:48 > 0:24:50is that they have voracious appetites.
0:24:53 > 0:24:54Coral is their number one food.
0:24:56 > 0:24:59And their appetite isn't the only problem.
0:24:59 > 0:25:03A single female can generate
0:25:03 > 0:25:05100 million eggs.
0:25:05 > 0:25:09And so, they have an amazing capacity to multiply
0:25:09 > 0:25:12and then spread from one reef to another.
0:25:13 > 0:25:17In healthy reefs, there are only one or two starfish per acre.
0:25:17 > 0:25:21But in outbreak areas, there can be thousands.
0:25:23 > 0:25:26So, what has caused this invasive invertebrate
0:25:26 > 0:25:28to swarm in such numbers?
0:25:30 > 0:25:34Its natural predators, like the triton snail and humphead wrasse,
0:25:34 > 0:25:37are in serious decline due to shell collecting and overfishing.
0:25:39 > 0:25:41But there's an even more serious issue.
0:25:43 > 0:25:47The release of pollution from agriculture, which is then
0:25:47 > 0:25:50fertilising the water and helping these starfish propagate.
0:25:52 > 0:25:56When excess nutrients run off farm fields and into the ocean,
0:25:56 > 0:25:58plankton blooms,
0:25:58 > 0:26:02and starfish larvae thrive on plankton.
0:26:06 > 0:26:09With too much food and nothing to keeps COTS numbers in check,
0:26:09 > 0:26:12the situation is desperate.
0:26:13 > 0:26:17So, can anything be done to stop these coral-killers?
0:26:20 > 0:26:24In the 1960s, when these outbreaks first occurred,
0:26:24 > 0:26:26well-meaning divers went down,
0:26:26 > 0:26:30collected the starfish and cut them into pieces.
0:26:31 > 0:26:34The thing is, each of those pieces can regenerate
0:26:34 > 0:26:37into a fully-formed starfish,
0:26:37 > 0:26:40so this simply made matters worse.
0:26:40 > 0:26:43Thankfully, after years of research,
0:26:43 > 0:26:46scientists have come up with a far more precise method.
0:26:48 > 0:26:50Teams of divers go out on a boat,
0:26:50 > 0:26:54they'll take a solution of what are known as bile salts,
0:26:54 > 0:26:56and you inject that single injection
0:26:56 > 0:26:59into the body of the starfish.
0:26:59 > 0:27:00And that can kill the starfish.
0:27:02 > 0:27:06Bile salts dissolve the starfish from the inside out,
0:27:06 > 0:27:11rapidly killing it, but without polluting the marine environment.
0:27:11 > 0:27:14It's effective, but it's labour-intensive.
0:27:18 > 0:27:21Mm. With such a massive reef,
0:27:21 > 0:27:25there must be millions of crown-of-thorns starfish out there.
0:27:25 > 0:27:28And, of course, human divers have got a limited amount of time
0:27:28 > 0:27:30that they can spend under the water.
0:27:30 > 0:27:33And they're limited to how deep they can go.
0:27:33 > 0:27:37So to get rid of them that way would be a monumental task.
0:27:37 > 0:27:41What they needed was a far more efficient solution
0:27:41 > 0:27:44to this...thorny problem.
0:27:47 > 0:27:51Introducing COTSbot.
0:27:53 > 0:27:56A team at the Queensland University of Technology
0:27:56 > 0:28:00have developed a dedicated starfish destroyer.
0:28:02 > 0:28:06What we've actually done is designed a robot like a predator,
0:28:06 > 0:28:09and it's a robot for killing crown-of-thorns starfish.
0:28:11 > 0:28:14- How does it look? Pretty stable?- One metre...
0:28:14 > 0:28:17We've developed this system to manoeuvre around the reef by itself.
0:28:17 > 0:28:21It has an onboard brain and it interprets the environment.
0:28:21 > 0:28:25It has a vision system to be able to detect organisms on the sea floor.
0:28:25 > 0:28:26And at that time,
0:28:26 > 0:28:29it's actually looking for these crown-of-thorns starfish.
0:28:32 > 0:28:36This robot can actively seek out its victim
0:28:36 > 0:28:39using a state-of-the-art vision system.
0:28:40 > 0:28:42It then manoeuvres itself for a closer look.
0:28:43 > 0:28:49And with one stab of a needle, it's game over for the starfish.
0:28:49 > 0:28:51You'll see the arm go down...
0:28:52 > 0:28:56..it delivers the dose of 10mm of bile salts,
0:28:56 > 0:28:58retracts, brings its arm back up
0:28:58 > 0:29:01and then the robot moves on to the next starfish.
0:29:02 > 0:29:08And this ingenious invention isn't just precise, it's also practical.
0:29:08 > 0:29:11They don't get tired. We can go down to 100 metres.
0:29:11 > 0:29:14Currently, occupational divers can only go to 30.
0:29:14 > 0:29:19We can operate at night. So we could eradicate quite a few hundred a day.
0:29:19 > 0:29:22This is actually going to make a big difference.
0:29:22 > 0:29:24So it's something I'm very proud of
0:29:24 > 0:29:26and hopefully we'll see more types of these solutions
0:29:26 > 0:29:29to help protect our natural environment in the future.
0:29:33 > 0:29:35It's hoped that in the future
0:29:35 > 0:29:38there'll be a whole fleet of robots patrolling the reef,
0:29:38 > 0:29:41helping to protect one of the world's greatest
0:29:41 > 0:29:43and most fragile ecosystems.
0:29:46 > 0:29:49But it's not just our oceans that are under attack.
0:29:53 > 0:29:55Our skies are being invaded, too.
0:29:57 > 0:30:04In 2016, more than 1.5 million drones were sold worldwide.
0:30:04 > 0:30:07No-one is safe from these flying cameras.
0:30:07 > 0:30:09SCREAMING
0:30:09 > 0:30:13And with so many amateur film-makers now taking to the sky,
0:30:13 > 0:30:17it's not just humans who are unhappy
0:30:17 > 0:30:20with the aerial intrusion.
0:30:25 > 0:30:27Drones are easy to come by these days.
0:30:27 > 0:30:29Just watch this.
0:30:29 > 0:30:31Look at that. This one only cost a few pounds.
0:30:31 > 0:30:33And anyone can fly them.
0:30:38 > 0:30:41Well, almost anyone.
0:30:41 > 0:30:44But the fact that you can get them quite literally off the shelf,
0:30:44 > 0:30:47and they're relatively easy to fly,
0:30:47 > 0:30:49means that they are becoming a bit of a problem.
0:30:51 > 0:30:54When wildlife takes on these aerial spies,
0:30:54 > 0:30:56it can make entertaining viewing.
0:30:58 > 0:30:59But in the wrong hands...
0:31:01 > 0:31:04..drones become a very serious danger indeed.
0:31:08 > 0:31:09As well as leisure use,
0:31:09 > 0:31:13drones present the possibility of use for criminal purposes.
0:31:16 > 0:31:19There's also the potential for drones to be used by terrorists
0:31:19 > 0:31:21with spectacular consequences.
0:31:24 > 0:31:27Certainly, this is an issue that's at the forefront
0:31:27 > 0:31:30of governments' and defence corporations' thinking
0:31:30 > 0:31:33about how we respond to the potential -
0:31:33 > 0:31:34only the potential so far -
0:31:34 > 0:31:38use of these things for what we call nefarious purposes.
0:31:40 > 0:31:42The possibilities are too terrifying to imagine,
0:31:42 > 0:31:45and it's a problem that needs to be solved.
0:31:47 > 0:31:49The issue of how to deal with problem drones
0:31:49 > 0:31:52has come up with a whole variety of novel solutions.
0:31:52 > 0:31:55The manufacturers themselves have talked about geo-fencing -
0:31:55 > 0:31:58building in software to the drone to prevent them going anywhere
0:31:58 > 0:32:00where they could cause a real problem.
0:32:00 > 0:32:04Airports, nuclear power stations.
0:32:04 > 0:32:07The Japanese have developed a drone with a net underneath,
0:32:07 > 0:32:09sort of a version of aerial lacrosse -
0:32:09 > 0:32:12it scoops small drones out of the air.
0:32:17 > 0:32:19All good solutions, but in the global fight
0:32:19 > 0:32:23against dangerous drones, there's a more surprising strategy.
0:32:23 > 0:32:26HIGH-PITCHED SCREECH
0:32:26 > 0:32:30In 2014, a team of Dutch security experts
0:32:30 > 0:32:34started employing a flyer even more skilled than the drones.
0:32:36 > 0:32:39Other technologies have been investigated.
0:32:39 > 0:32:43The most novel one of those is the potential use of eagles.
0:32:44 > 0:32:48Yep, you heard it right, he said eagles.
0:32:50 > 0:32:54The Dutch team believe that eagles might just be the perfect weapon
0:32:54 > 0:32:56to combat dangerous drones.
0:33:01 > 0:33:05Eagles clearly are supreme aerial predators.
0:33:05 > 0:33:10With eyesight eight times better than ours, a drone has no chance.
0:33:10 > 0:33:15Even the rotor blades are no problem for their immensely powerful talons.
0:33:17 > 0:33:20And if large gatherings of people were under threat,
0:33:20 > 0:33:22like at a sporting event,
0:33:22 > 0:33:25a trained eagle could be THE perfect weapon
0:33:25 > 0:33:28to safely neutralise a suspicious drone.
0:33:35 > 0:33:37Eagles trained in anti-drone defence
0:33:37 > 0:33:39are now being very seriously considered
0:33:39 > 0:33:42by police forces all over the world.
0:33:42 > 0:33:45I suppose we could think of this as a perfectly-evolved,
0:33:45 > 0:33:48natural solution to a new hi-tech problem.
0:33:53 > 0:33:56Next, to North Africa,
0:33:56 > 0:34:00where a surprising discovery in the dunes could take us to other worlds.
0:34:03 > 0:34:062008, Morocco.
0:34:07 > 0:34:09On the edge of the Sahara,
0:34:09 > 0:34:13German professor Ingo Rechenberg made an astonishing discovery.
0:34:16 > 0:34:17I was very, very excited.
0:34:17 > 0:34:19Very excited. I was crying!
0:34:24 > 0:34:27Now, Professor Ingo Rechenberg has dedicated his life
0:34:27 > 0:34:30to designing machines inspired by nature.
0:34:31 > 0:34:35He loves the climate and the tranquillity of the Sahara
0:34:35 > 0:34:37and spends his winters living here.
0:34:37 > 0:34:42But one night, he was in for the shock of his life.
0:34:42 > 0:34:45I was going outside in the night
0:34:45 > 0:34:48and an animal was crossing near.
0:34:49 > 0:34:52I had the feeling it was a very large animal,
0:34:52 > 0:34:57maybe a jumping mouse, or maybe a lizard or something else.
0:34:59 > 0:35:03And then I looked and just before me, a spider was sitting down.
0:35:03 > 0:35:08The spider was the size of about 10cm. A very large spider.
0:35:09 > 0:35:14And as Ingo watched, the spider did something extraordinary.
0:35:14 > 0:35:17Suddenly, the spider was rolling away.
0:35:19 > 0:35:22I was crying, "Look, this spider is rolling!"
0:35:23 > 0:35:28Yes, the spider was indeed rolling, but that's not so strange,
0:35:28 > 0:35:32because there is, in fact, another spider that rolls -
0:35:32 > 0:35:34the golden wheel spider.
0:35:36 > 0:35:38It balls itself up to roll down the dunes.
0:35:40 > 0:35:43So, why was Ingo so excited?
0:35:43 > 0:35:47Well, this Moroccan spider was different.
0:35:48 > 0:35:52It wasn't just rolling downhill, but uphill.
0:35:52 > 0:35:56The spider was rolling up the dune! Up the dune!
0:35:56 > 0:35:59And so, I must say, I was very, very excited.
0:36:00 > 0:36:04It was a completely unique form of locomotion,
0:36:04 > 0:36:06totally new to science.
0:36:10 > 0:36:13But why would a spider want to do this?
0:36:15 > 0:36:19The velocity when rolling is twice the velocity
0:36:19 > 0:36:21when the spider is walking with eight feet.
0:36:21 > 0:36:23It has a big advantage.
0:36:26 > 0:36:31In the desert, this spider could be prey for larger and faster beasts,
0:36:31 > 0:36:33like the fennec fox or the pompilid wasp.
0:36:36 > 0:36:40When threatened, this amazing arachnid flips into rolling mode
0:36:40 > 0:36:43and doubles its speed for a fast getaway.
0:36:43 > 0:36:45It's just brilliant!
0:36:47 > 0:36:50And, of course, it's every biologist's dream
0:36:50 > 0:36:52to discover a new species.
0:36:52 > 0:36:56The strange thing is that Professor Rechenberg is not a biologist -
0:36:56 > 0:37:00he's a scientist with a very particular specialisation.
0:37:03 > 0:37:06My interest is mainly bionics.
0:37:06 > 0:37:08That means that we try to study
0:37:08 > 0:37:12the performance of biological systems,
0:37:12 > 0:37:15then, of course, we try to imitate this
0:37:15 > 0:37:18and to develop a new machine, or something else.
0:37:23 > 0:37:25He's being quite modest here.
0:37:25 > 0:37:28Professor Ingo Rechenberg is at the very top of his field,
0:37:28 > 0:37:33world-renowned for designing robots inspired by nature.
0:37:35 > 0:37:39So, after discovering the spider, Professor Ingo Rechenberg
0:37:39 > 0:37:42did what any world-renowned bionics engineer would do.
0:37:44 > 0:37:48So, we started to imitate the motion
0:37:48 > 0:37:51and our aim now is to design a robot
0:37:51 > 0:37:53which is able to do both,
0:37:53 > 0:37:57to walk and to move in the wheeling condition.
0:38:01 > 0:38:06And here it is. Yes, a robot that rolls just like the spider.
0:38:11 > 0:38:14It's certainly a very clever bit of engineering,
0:38:14 > 0:38:17but the question is, why?
0:38:19 > 0:38:22I mean, what possible purpose would there be for such an invention?
0:38:24 > 0:38:29Well, Professor Rechenberg has big plans for his little robot.
0:38:29 > 0:38:32You see, with this particular type of movement, it has the potential
0:38:32 > 0:38:37to boldly go where no robot spider has ever gone before.
0:38:41 > 0:38:44We hope that NASA, or also here ESA,
0:38:44 > 0:38:47will become interested when I finish the robot
0:38:47 > 0:38:50to design a larger one, yes,
0:38:50 > 0:38:55than we designed here for the use on the next Mars mission.
0:38:55 > 0:38:58A robot on Mars,
0:38:58 > 0:39:01able to walk and roll,
0:39:01 > 0:39:05adapting to even the most challenging alien landscape.
0:39:05 > 0:39:08So space really could be the final frontier
0:39:08 > 0:39:11for our little spider robot,
0:39:11 > 0:39:14crawling and rolling over the surface of Mars.
0:39:14 > 0:39:16And just to think that all of that came to pass
0:39:16 > 0:39:20because of a chance encounter with a real spider in the Sahara,
0:39:20 > 0:39:24one that now bears the name of the man who discovered it -
0:39:24 > 0:39:26Cebrennus rechenbergi.
0:39:31 > 0:39:34So, we've learned when nature and technology meet,
0:39:34 > 0:39:39the results can be both ingenious and wonderful.
0:39:40 > 0:39:43Coming up - a weird world of new discoveries.
0:39:47 > 0:39:50First stop, though, the Amazon.
0:39:54 > 0:39:58South America, 2011.
0:39:58 > 0:40:01Field biologist Aaron Pomerantz was on an expedition
0:40:01 > 0:40:03in the deepest reaches of the Amazon rainforest.
0:40:05 > 0:40:08There is an insane amount of diversity out there.
0:40:13 > 0:40:16So I was walking down this trail, I was just covered in mud
0:40:16 > 0:40:20and I just sort of casually walked past this tree.
0:40:20 > 0:40:24When I took a closer look, I noticed something I wasn't really expecting.
0:40:25 > 0:40:30Hanging from a tree was something minute and extraordinary.
0:40:32 > 0:40:36A strange structure, delicate and complex.
0:40:36 > 0:40:40It was like nothing Aaron had ever seen before.
0:40:41 > 0:40:44This structure is really odd-looking,
0:40:44 > 0:40:46like a little hanging orange basket.
0:40:48 > 0:40:51It just looks like something 3-D printed.
0:40:53 > 0:40:55I was just like,
0:40:55 > 0:40:57"Oh, my God, I need to catch this."
0:40:57 > 0:40:59Like, "We need to look at this further."
0:41:02 > 0:41:06Just look...at that!
0:41:08 > 0:41:14It was bright orange, made out of a very delicate lattice.
0:41:17 > 0:41:20It's like a little alien basket.
0:41:21 > 0:41:25But what was even stranger is that when Aaron peered inside,
0:41:25 > 0:41:28he could see something in there.
0:41:30 > 0:41:35Something that any entomologist would easily recognise.
0:41:35 > 0:41:39It was a pupa, a moth chrysalis,
0:41:39 > 0:41:45which means the tiny alien structure Aaron found was, in fact, a cocoon.
0:41:51 > 0:41:54Cocoons are made to keep caterpillars safe
0:41:54 > 0:41:55as they transform into moths.
0:41:58 > 0:42:02They need to be weatherproof and to keep out any predators.
0:42:02 > 0:42:07So, why would a moth create such a fragile structure?
0:42:07 > 0:42:13Well, a pupa in the rainforest has one particularly prolific predator.
0:42:14 > 0:42:17Ants are everywhere in the Neotropics.
0:42:17 > 0:42:21And so we think that this adaptation, with this odd structure,
0:42:21 > 0:42:23allows the pupa to sort of hang there,
0:42:23 > 0:42:26where it's protected, away from ants.
0:42:29 > 0:42:33Yes. Suspending itself on a long, thin thread,
0:42:33 > 0:42:35the cocoon becomes ant-proof.
0:42:35 > 0:42:38Even the most persistent and hungry ant
0:42:38 > 0:42:42can't safely descend such a long, thin fibre.
0:42:45 > 0:42:47But, then, why the weird latticework?
0:42:47 > 0:42:52Surely the pupa would be safer completely enclosed.
0:42:52 > 0:42:55Well, you see, living on a long, thin thread
0:42:55 > 0:42:57is a very fragile existence.
0:42:57 > 0:43:00Too much weight or wind will snap the thread
0:43:00 > 0:43:03and it will be game over for the pupa.
0:43:04 > 0:43:06So the caterpillar that made this cocoon
0:43:06 > 0:43:10came up with an ingenious plan.
0:43:10 > 0:43:14But to understand it, we need to look at the structure more closely.
0:43:18 > 0:43:21The nearest we can get to making something so intricate
0:43:21 > 0:43:23is with a 3-D printer.
0:43:25 > 0:43:27And here is our cocoon copy.
0:43:28 > 0:43:31And here's a more classic-looking cocoon
0:43:31 > 0:43:33with nice, safe, closed sides.
0:43:36 > 0:43:40If we recreate rainforest conditions,
0:43:40 > 0:43:43the solid cocoon becomes waterlogged and heavy.
0:43:44 > 0:43:48But the lattice lets the rain drain straight through.
0:43:50 > 0:43:52This keeps the cocoon nice and light
0:43:52 > 0:43:55and prevents its anti-ant strand snapping.
0:43:57 > 0:44:00And then, if that wasn't clever enough,
0:44:00 > 0:44:03air can circulate through the lattice,
0:44:03 > 0:44:07keeping the pupa dry and preventing fungal infections.
0:44:08 > 0:44:11If it was just enclosed, like a lot of species that we have in,
0:44:11 > 0:44:13say, Europe or North America,
0:44:13 > 0:44:17there's not as much humidity and not as much rain in these environments.
0:44:17 > 0:44:22So in the rainforest, we think it's this open structure so it doesn't drown.
0:44:22 > 0:44:25This delicate, intricate structure
0:44:25 > 0:44:29is actually completely and wonderfully, well, practical.
0:44:32 > 0:44:34So you might expect that the moth that would emerge from this
0:44:34 > 0:44:38would be of great, mesmerising beauty,
0:44:38 > 0:44:41a paragon amongst moths.
0:44:41 > 0:44:45Well, ladies and gentlemen, young people,
0:44:45 > 0:44:48I give you the urodid moth.
0:44:51 > 0:44:53I'm afraid it's rather drab.
0:44:57 > 0:45:02But thankfully, our next weird discovery is far more colourful,
0:45:02 > 0:45:05as we venture into the rainforests of Borneo.
0:45:06 > 0:45:09Home to some very unusual plants.
0:45:12 > 0:45:16Hidden amongst the greenery are some hair-raising hunters -
0:45:16 > 0:45:17pitcher plants.
0:45:23 > 0:45:26Most plants get nutrients through their roots,
0:45:26 > 0:45:30but these peculiar plants have an altogether more sinister strategy.
0:45:34 > 0:45:36They eat meat.
0:45:45 > 0:45:47Now, all pitchers are pretty wonderfully weird,
0:45:47 > 0:45:50but there's one particular species
0:45:50 > 0:45:52that's puzzled botanists for decades -
0:45:52 > 0:45:55Nepenthes hemsleyana -
0:45:55 > 0:45:58because, well, it's a picky eater.
0:46:02 > 0:46:06This species catches seven times fewer insects
0:46:06 > 0:46:08than its closest relatives.
0:46:08 > 0:46:10It's practically a vegetarian.
0:46:10 > 0:46:14But if it isn't eating insects, what is it eating?
0:46:16 > 0:46:20In 2014, a scientific expedition to Borneo
0:46:20 > 0:46:22captured these incredible images.
0:46:28 > 0:46:31Bats, inside the pitcher plant.
0:46:33 > 0:46:37Could this be the first documented case of a bat-eating plant?
0:46:40 > 0:46:45Captivated by these images, bat experts Michael and Caroline Schoner
0:46:45 > 0:46:47travelled from Germany to the jungle
0:46:47 > 0:46:52to find out if the plant really had developed a taste for bats.
0:46:53 > 0:46:57We don't think that the plants have evolved to digest these kinds of animals.
0:46:57 > 0:47:00They have evolved to digest arthropods, insects, for example.
0:47:03 > 0:47:06Potentially, bats would be able to die inside,
0:47:06 > 0:47:09but it's more than unlikely, I would say.
0:47:09 > 0:47:13So, if the pitcher plant wasn't eating the bat, what was going on?
0:47:13 > 0:47:17Perhaps the bat was the one hoping for a meal.
0:47:19 > 0:47:21We had this idea at the beginning
0:47:21 > 0:47:24that the bats might steal insects from the pitchers,
0:47:24 > 0:47:26but actually, it's not working
0:47:26 > 0:47:29because the bats can never reach this fluid.
0:47:30 > 0:47:35No. These peculiar pitcher plants weren't providing a free lunch,
0:47:35 > 0:47:39they were offering something much more unusual.
0:47:39 > 0:47:43These pitchers, they have a very stable microclimate inside,
0:47:43 > 0:47:45so during the hottest hours of the day,
0:47:45 > 0:47:48they are cooler than the outside temperature.
0:47:48 > 0:47:51And this is something which bats absolutely like.
0:47:53 > 0:47:57So these pitcher plants make the perfect air-conditioned
0:47:57 > 0:48:00place to rest during the heat of the day.
0:48:00 > 0:48:02But what's in it for the plant?
0:48:02 > 0:48:06Why's this carnivore cuddling up to a bat?
0:48:06 > 0:48:11Well, this guest leaves a gift behind.
0:48:13 > 0:48:18Bat faeces contain a lot of nitrogen and phosphorus and also potassium.
0:48:22 > 0:48:25Those nutrients are missing in the areas where the plants are growing.
0:48:27 > 0:48:31This extraordinary pitcher plant has evolved to survive
0:48:31 > 0:48:35almost entirely on the poo of its guest,
0:48:35 > 0:48:38relying on the bat to bring it sustenance.
0:48:41 > 0:48:43I just love this.
0:48:43 > 0:48:46A perfectly strange symbiosis between a plant
0:48:46 > 0:48:49and its small, furry friend.
0:48:49 > 0:48:51And it's a win-win situation.
0:48:51 > 0:48:54The pitcher provides the perfect bat bag
0:48:54 > 0:48:57and, of course, the bat benefits.
0:48:57 > 0:49:00At the same time, the pitcher's thriving on the bat's poo.
0:49:00 > 0:49:04And their survival is intricately intertwined.
0:49:04 > 0:49:08There's just one last piece to the puzzle.
0:49:08 > 0:49:11How does the plant attract the bat?
0:49:12 > 0:49:15Well, we know that bats use echolocation
0:49:15 > 0:49:18to find their way around.
0:49:18 > 0:49:20They send out high-frequency calls
0:49:20 > 0:49:22and use the reflected sound waves
0:49:22 > 0:49:25to build up a picture of the forest around them.
0:49:28 > 0:49:31But Borneo has over 15,000 species of plants
0:49:31 > 0:49:34and more than 30 types of pitcher plant.
0:49:34 > 0:49:38So, how does this particular one make sure that the bats find it?
0:49:40 > 0:49:45Well, would you believe, the pitcher has evolved to become noisier.
0:49:45 > 0:49:49Its back wall is unusually wide and curved,
0:49:49 > 0:49:53just to reflect and amplify the bat's calls.
0:49:56 > 0:49:59It's the perfect bat beacon.
0:50:06 > 0:50:08And it works like a dream.
0:50:15 > 0:50:20Amazing! Not only has the pitcher evolved to fit the bat like a glove,
0:50:20 > 0:50:25it's also come up with a structure that acts as an advertisement
0:50:25 > 0:50:28which says, "This is the best bat hotel in town."
0:50:28 > 0:50:32Now, honestly, that's why I get up in the morning.
0:50:32 > 0:50:34That's proper biology.
0:50:37 > 0:50:40And finally, we investigate a very serious danger
0:50:40 > 0:50:42from the Australian bush.
0:50:43 > 0:50:45Danger from above.
0:50:45 > 0:50:48A-A-A-A-A-A-A-A-A-A-A-A-Argh!
0:50:50 > 0:50:53So, a Drop Bear is like a cross between a polar bear
0:50:53 > 0:50:55and a koala bear that potentially could drop out of a tree
0:50:55 > 0:50:57when you're out camping, for example.
0:51:00 > 0:51:03It's probably almost as deadly as the crocodile, but you just...
0:51:03 > 0:51:05Yeah, almost.
0:51:06 > 0:51:10'And remember, look up when in the outback.'
0:51:13 > 0:51:18Many places around the world have their own legends of mythical creatures.
0:51:18 > 0:51:20Scotland has the Loch Ness monster,
0:51:20 > 0:51:23North America has Bigfoot
0:51:23 > 0:51:27and Australia has the Drop Bear.
0:51:27 > 0:51:29The Drop what?
0:51:30 > 0:51:34A truly terrifying beast that can climb trees and drop down
0:51:34 > 0:51:36on you from above.
0:51:36 > 0:51:37SCREAMS
0:51:39 > 0:51:43The Drop Bear, a fearsome koala-like creature that
0:51:43 > 0:51:48preys on the weak and unsuspecting, but also just
0:51:48 > 0:51:50a piece of Australian folklore,
0:51:50 > 0:51:52the sort of thing you hear round the campfire
0:51:52 > 0:51:54to scare you if you're a tourist
0:51:54 > 0:51:56or give you nightmares if you're a kid.
0:51:56 > 0:51:58Couldn't possibly be any truth in it,
0:51:58 > 0:52:00or could there?
0:52:02 > 0:52:06In 2015, in a remote corner of Western Australia,
0:52:06 > 0:52:11researchers found weird scratch marks high up on a cave wall.
0:52:11 > 0:52:14Scratches that were vital clues,
0:52:14 > 0:52:18clues to shed a new light on the mysterious Drop Bear.
0:52:18 > 0:52:21You see, those scratches might actually point to some
0:52:21 > 0:52:26evidence that proves that the Drop Bear is more than a tall tale.
0:52:27 > 0:52:29Mm.
0:52:29 > 0:52:32Scratch marks on a cave wall that wouldn't mean much to you or I,
0:52:32 > 0:52:37but to one palaeontologist, this was a monumental discovery.
0:52:39 > 0:52:42Our story begins almost two centuries ago.
0:52:42 > 0:52:46With the settlement of Australia in the 1800s,
0:52:46 > 0:52:52pastoralism was moving out beyond the main centres of occupation
0:52:52 > 0:52:53like Sydney and Melbourne.
0:52:59 > 0:53:02In the process, people were stumbling on the remains of
0:53:02 > 0:53:04large animals that they knew nothing of.
0:53:04 > 0:53:09This was the Australian megafauna - giant animals.
0:53:11 > 0:53:13One of these early finds was a skull of
0:53:13 > 0:53:17a very strange-looking animal about the size of a leopard.
0:53:21 > 0:53:24It had the front teeth of a herbivorous marsupial like
0:53:24 > 0:53:26a kangaroo or a koala...
0:53:30 > 0:53:34..but its cheek teeth were huge, sharp blades,
0:53:34 > 0:53:37the kind you'd expect from a meat eater.
0:53:39 > 0:53:41A marsupial with carnivorous teeth?
0:53:41 > 0:53:45Now, that's a very weird find indeed.
0:53:49 > 0:53:54It was so unusual, like no other species ever seen.
0:53:55 > 0:53:58It was given a very fitting scientific name -
0:53:58 > 0:54:01Thylacoleo carnifex,
0:54:01 > 0:54:04which translates as the marsupial lion.
0:54:04 > 0:54:05The butcher.
0:54:09 > 0:54:12But what exactly was this mysterious beast?
0:54:14 > 0:54:16Well, with only a skull to go on,
0:54:16 > 0:54:21it was anyone's guess and would stay a mystery for 100 years.
0:54:23 > 0:54:29Until a young palaeontologist made a huge breakthrough.
0:54:29 > 0:54:36In 1969, I was exploring with a colleague, and we detected
0:54:36 > 0:54:39a gust of air coming out of a rock pile.
0:54:39 > 0:54:43So we wriggled through into a chamber and in that chamber
0:54:43 > 0:54:48there was a silt floor with these funny saw-tooth patterns.
0:54:50 > 0:54:54When my eyes got accustomed I looked down, and there at my feet
0:54:54 > 0:54:57was the upturned skull of the marsupial lion.
0:54:59 > 0:55:01Incredibly exciting.
0:55:01 > 0:55:03I still get excited telling you about it.
0:55:05 > 0:55:10To the side of that, there was the arm of the lion
0:55:10 > 0:55:15with the hand reaching up out of the sediment against the rock.
0:55:17 > 0:55:20And on the arm were long, sharp claws,
0:55:20 > 0:55:23exactly the sort a predator would use
0:55:23 > 0:55:25to catch and hold on to prey.
0:55:33 > 0:55:37Over the next few decades, more discoveries of complete skeletons
0:55:37 > 0:55:41helped flesh out a picture of a truly terrifying predator.
0:55:47 > 0:55:51This animal can produce the most powerful bite
0:55:51 > 0:55:54known for any living mammal.
0:55:57 > 0:56:00It could crush a skull in a single bite.
0:56:00 > 0:56:03It really is the stuff of nightmares,
0:56:03 > 0:56:06but can we say that this was the Drop Bear?
0:56:06 > 0:56:10Well, remember those scratches on the cave wall?
0:56:13 > 0:56:18In just recent times, a couple of my colleagues have been examining
0:56:18 > 0:56:22scratch marks on the walls of caves in which we've found
0:56:22 > 0:56:23the marsupial lion.
0:56:26 > 0:56:30This seems to suggest that they were actually actively climbing in
0:56:30 > 0:56:32and out of the cave.
0:56:34 > 0:56:36If it could climb out of a cave, then potentially
0:56:36 > 0:56:39it could climb a tree. And if it could climb a tree,
0:56:39 > 0:56:43then it could drop out of it onto unsuspecting prey.
0:56:43 > 0:56:45You can see where I'm going -
0:56:45 > 0:56:49it's beginning to sound more and more like the Drop Bear.
0:56:49 > 0:56:53I suppose the question then is, how could the legend pass
0:56:53 > 0:56:54into the present day?
0:56:57 > 0:57:02Well, just look at this rock art made by indigenous Australians
0:57:02 > 0:57:06more than 40,000 years ago.
0:57:06 > 0:57:08Are you seeing what I'm seeing?
0:57:08 > 0:57:13Experts believe this is most likely our marsupial lion.
0:57:14 > 0:57:20And if so, it's direct evidence that some people came face to face
0:57:20 > 0:57:23with it and lived to tell the tale.
0:57:24 > 0:57:28A tale that could make even the scariest campfire story
0:57:28 > 0:57:31imaginable, real, even.
0:57:31 > 0:57:34Perhaps memorable enough to pass on to the next generation
0:57:34 > 0:57:39and the next generation, all the way down to the present day.
0:57:39 > 0:57:41And you never know, it might still be out there.
0:57:41 > 0:57:45If ever you're camping in Australia, you might want to look up.
0:57:49 > 0:57:53From the discovery of an alien cocoon to a plant that makes
0:57:53 > 0:57:57a home for a bat and the unravelling of an ancient legend.
0:58:01 > 0:58:06I find it strangely reassuring that when we finally explain one of these
0:58:06 > 0:58:10weird mysteries, we become aware that there are still loads more
0:58:10 > 0:58:12out there to be solved.
0:58:12 > 0:58:15There's no doubt at all that there are plenty of puzzles
0:58:15 > 0:58:16left on our planet.
0:58:20 > 0:58:26Next time, we investigate vampire fish,
0:58:26 > 0:58:30head-banging sharks and some very weird waves.