0:00:19 > 0:00:24In this episode, an Australian town under attack from aerial invaders...
0:00:26 > 0:00:28It smells, the noise...
0:00:28 > 0:00:32..an exquisite piece of alien artwork...
0:00:32 > 0:00:34Oh, my God!
0:00:34 > 0:00:39..and the mystery of sperm whales washed up on the North Sea coast.
0:00:42 > 0:00:46But first, to the USA.
0:00:46 > 0:00:48Denison, Texas.
0:00:50 > 0:00:53Like most American towns, Denison has a main road.
0:00:53 > 0:00:55Nothing unusual about that.
0:00:58 > 0:01:02Well, that was until the morning of May 29th, 2015.
0:01:04 > 0:01:07Yeah, this one's not for the squeamish out there,
0:01:07 > 0:01:09but it's still fascinating.
0:01:11 > 0:01:14This highway became the scene of a very strange sighting.
0:01:19 > 0:01:24Balls of worms appeared overnight, squirming in circles,
0:01:24 > 0:01:28all lined up exactly between the centre lines.
0:01:34 > 0:01:37Piles of worms.
0:01:37 > 0:01:43And not small piles - I'm talking about massive piles of worms,
0:01:43 > 0:01:47hundreds piled together in the middle of a Texas road.
0:01:49 > 0:01:53But why had these animals come together in such unusual numbers?
0:01:57 > 0:02:00With no-one admitting to putting them there,
0:02:00 > 0:02:03the people of Denison were left baffled.
0:02:03 > 0:02:05So the footage was put online,
0:02:05 > 0:02:08where it caught the attention of an expert.
0:02:08 > 0:02:10It is really unusual to see them lined up
0:02:10 > 0:02:13in the middle of the road like that.
0:02:16 > 0:02:19I've never, ever seen that before.
0:02:19 > 0:02:22Now, Emma could think of some good reasons why the worms
0:02:22 > 0:02:24had clumped together like this.
0:02:24 > 0:02:28It's much, much safer for earthworms once they're on the surface
0:02:28 > 0:02:31to actually congregate into these big balls.
0:02:31 > 0:02:33Worms actually breathe through their skin,
0:02:33 > 0:02:36so they do need to stay moist at all times.
0:02:36 > 0:02:40So being up on the surface, being exposed to the sun's rays,
0:02:40 > 0:02:44is actually really, really harmful and they can die pretty quickly.
0:02:44 > 0:02:48But, of course, if they're encased around with other worms,
0:02:48 > 0:02:50that will actually keep them a lot safer.
0:02:52 > 0:02:55OK, so the worms had balled together for safety,
0:02:55 > 0:02:59but this doesn't explain why they were on the road in the first place.
0:03:01 > 0:03:05There just didn't seem to be a sensible answer.
0:03:05 > 0:03:07And whilst the residents were there scratching their heads,
0:03:07 > 0:03:11looking for clues, the day just got weirder and weirder,
0:03:11 > 0:03:15with reports coming in of something equally odd
0:03:15 > 0:03:1775 miles south in Dallas.
0:03:20 > 0:03:23Check this out. This is amazing!
0:03:24 > 0:03:29Andres Ruzo captured this bizarre footage of fish trapped dead
0:03:29 > 0:03:32in a fence a metre above the ground.
0:03:34 > 0:03:36Check that out!
0:03:37 > 0:03:39My first reaction when I saw all these fish in the fence was,
0:03:39 > 0:03:42"Holy cow! This is bizarre!"
0:03:49 > 0:03:50I didn't expect to see that at all.
0:03:50 > 0:03:53Suddenly, I'm walking around and these prehistoric-looking things
0:03:53 > 0:03:55with mouths full of teeth are suddenly right there
0:03:55 > 0:03:57and it was just, you know,
0:03:57 > 0:03:59immediately to the cellphone, "What is this?!"
0:04:02 > 0:04:05Well, these freaky-looking fish are gars,
0:04:05 > 0:04:08one of the largest freshwater fish in North America.
0:04:10 > 0:04:12Often called living fossils,
0:04:12 > 0:04:16they've remained virtually unchanged for the last 100 million years.
0:04:20 > 0:04:23Sharing the world with T-rex and velociraptors,
0:04:23 > 0:04:26these truly are prehistoric beasts.
0:04:29 > 0:04:31So Andres knew what these fish were,
0:04:31 > 0:04:36but why were these unfortunate few stuck so high and dry?
0:04:37 > 0:04:40- Well, that was a mystery. - It was just weird!
0:04:40 > 0:04:43You don't expect to see a bunch of fish randomly sitting in a fence
0:04:43 > 0:04:45and no-one's going to show up, "Oh, I've got a great idea.
0:04:45 > 0:04:48"Let me take all these dead fish and stick them in a fence."
0:04:48 > 0:04:50No-one's going to do that! So, how did they get there?
0:04:52 > 0:04:57So, we have two bizarre animal appearances 75 miles apart
0:04:57 > 0:05:00happening within hours of each other.
0:05:01 > 0:05:04Could these strange sightings be linked?
0:05:05 > 0:05:07What could they possibly have in common?
0:05:14 > 0:05:16In the month before these weird happenings,
0:05:16 > 0:05:22a whopping 37 trillion gallons of rain fell on Texas.
0:05:22 > 0:05:27It pushed the water table far beyond its normal range.
0:05:28 > 0:05:31Lakes spilled over, rivers burst their banks
0:05:31 > 0:05:34and large parts of Dallas experienced severe flooding,
0:05:34 > 0:05:38affecting not only the community living along the river,
0:05:38 > 0:05:41but also its fish.
0:05:41 > 0:05:44The entire field where I was had been flooded.
0:05:44 > 0:05:47It would have been about chest high for me.
0:05:47 > 0:05:50That's a significant amount of water.
0:05:50 > 0:05:52Significant indeed.
0:05:52 > 0:05:56Enough water for the fish to swim easily over the fence,
0:05:56 > 0:05:59across the flooded fields, looking for something to eat.
0:05:59 > 0:06:04But when the water level dropped, well, the way home was blocked.
0:06:06 > 0:06:09I imagine the small ones got through the holes in the fences no problem,
0:06:09 > 0:06:11but the bigger ones, they happened to get stuck.
0:06:17 > 0:06:21It was a miserable end for these fish in the fence.
0:06:22 > 0:06:25But what about those worm balls on the road?
0:06:25 > 0:06:29Could the extreme Texan weather provide the key?
0:06:31 > 0:06:34It had been raining really, really heavily.
0:06:34 > 0:06:37Everywhere was absolutely saturated, completely waterlogged.
0:06:37 > 0:06:41So basically, all these worms had to come up to the surface.
0:06:41 > 0:06:43And as they're trying to escape,
0:06:43 > 0:06:46they've all hit this big tarmac road.
0:06:48 > 0:06:51To avoid drowning, the worms took to higher ground.
0:06:53 > 0:06:56But this still doesn't explain why they lined themselves up
0:06:56 > 0:06:59in between the double yellow lines.
0:06:59 > 0:07:01Earthworms don't have eyes like we do,
0:07:01 > 0:07:05but they are very sensitive as to whether it's light or dark,
0:07:05 > 0:07:08so when they've got into this middle, black area,
0:07:08 > 0:07:11they've maybe stayed there and then not wanted to venture
0:07:11 > 0:07:14the other side either because of the other yellow line.
0:07:14 > 0:07:16So maybe it feels to them a little bit safer.
0:07:18 > 0:07:22And so the worms huddled together, safe from the floods,
0:07:22 > 0:07:24but trapped between the lines.
0:07:25 > 0:07:28No other parts of Texas had recorded the same nightmarish
0:07:28 > 0:07:33piles of worms, or weird fish stuck in fences.
0:07:33 > 0:07:37This was a very location-specific event,
0:07:37 > 0:07:41down to the unprecedented levels of rain that had come together
0:07:41 > 0:07:43to produce the perfect storm.
0:07:46 > 0:07:48Next, we travel down under,
0:07:48 > 0:07:51to a small town with its own set of strange invaders.
0:07:56 > 0:07:59New South Wales, Australia.
0:07:59 > 0:08:05The coastal town of Batemans Bay sees its fair share of tourists.
0:08:05 > 0:08:08People come to Batemans Bay to relax, to take it easy.
0:08:11 > 0:08:13They like the visual aspect of it, they like the clean beaches,
0:08:13 > 0:08:15they like the trees.
0:08:15 > 0:08:19But in 2016, the bay became famous for an invasion
0:08:19 > 0:08:21of much more unwelcome visitors.
0:08:26 > 0:08:29It's horrible. It smells. The noise.
0:08:29 > 0:08:31You can't hang your washing out.
0:08:31 > 0:08:33Everyone's moved out.
0:08:33 > 0:08:36There's only three of us left in this whole block of units now.
0:08:38 > 0:08:41Batemans Bay is under siege.
0:08:41 > 0:08:45The worst thing is when they go over night-time.
0:08:45 > 0:08:47They block out your TV.
0:08:47 > 0:08:49It's just all black.
0:08:51 > 0:08:54They need to get rid of them, otherwise, I don't know,
0:08:54 > 0:08:56bad things are going to happen.
0:08:57 > 0:08:59The people of Batemans Bay
0:08:59 > 0:09:03have had their peaceful lives turned upside down
0:09:03 > 0:09:05by an invasion of...
0:09:05 > 0:09:06bats.
0:09:08 > 0:09:11And not just any old bat, giant Australian fruit bats,
0:09:11 > 0:09:15otherwise known as the grey-headed flying fox.
0:09:15 > 0:09:17CHITTERING
0:09:21 > 0:09:25Grey-headed flying foxes are one of the largest bats in the world.
0:09:29 > 0:09:32Their wingspan is about a metre.
0:09:32 > 0:09:35That's the length of a large dog!
0:09:35 > 0:09:40Each bat weighs up to a kilogram, and they don't fly alone either.
0:09:40 > 0:09:42Flying foxes are highly colonial animals.
0:09:42 > 0:09:45They roost in large aggregations during the day
0:09:45 > 0:09:48in the open canopy of trees.
0:09:48 > 0:09:50Now, the area around Batemans Bay
0:09:50 > 0:09:52has always been a flying fox hot spot.
0:09:55 > 0:09:58Roosting out in the wilderness, beyond the town.
0:09:58 > 0:10:02But in 2011, these bats turned their backs on the bush
0:10:02 > 0:10:04and set their sights on the town centre.
0:10:05 > 0:10:08Year by year, their numbers have rocketed
0:10:08 > 0:10:12from around 10,000 to over 100,000.
0:10:12 > 0:10:16It's the largest number ever recorded in an urban area.
0:10:19 > 0:10:22And the reason behind this relocation?
0:10:22 > 0:10:25Well, it's all to do with this.
0:10:25 > 0:10:30Flying foxes are fruit bats and feed on fruit and nectar,
0:10:30 > 0:10:32and there's nothing they like more
0:10:32 > 0:10:34than the nectar-rich flowers of a gum tree.
0:10:36 > 0:10:38The forests around Batemans Bay contain
0:10:38 > 0:10:42a large number of a eucalyptus species known as spotted gum.
0:10:44 > 0:10:48It produces particularly rich nectar from its flowers.
0:10:48 > 0:10:52So spotted gum is almost like a magnet for flying foxes.
0:10:56 > 0:11:00Not only is the centre of Batemans Bay close to these tasty trees,
0:11:00 > 0:11:03but it's also got a good supply of fresh water
0:11:03 > 0:11:07and lots of trees to roost in during the daytime.
0:11:07 > 0:11:09This place is a bat heaven.
0:11:09 > 0:11:11And when you consider that large areas of forest
0:11:11 > 0:11:15in the surrounding area have been cut down for logging and farmland,
0:11:15 > 0:11:18well, bedding down in the centre of town
0:11:18 > 0:11:21makes perfect sense to the flying fox.
0:11:21 > 0:11:26It's just that the human population is not quite so happy about it.
0:11:29 > 0:11:33Everyone's had a dog that's barked a lot next door that drives you insane.
0:11:33 > 0:11:36Well, multiply it by 100,000 and then you actually get an idea
0:11:36 > 0:11:38of the physical and the mental stress
0:11:38 > 0:11:40that's placed on a community with that size of numbers.
0:11:40 > 0:11:43SQUAWKING
0:11:43 > 0:11:45It's not that the residents of Batemans Bay
0:11:45 > 0:11:48are entirely anti-bat, they're not.
0:11:48 > 0:11:51It's just that they'd rather they weren't living quite
0:11:51 > 0:11:54so close to their homes.
0:11:54 > 0:11:57So they've cut down a couple of the bats' favourite trees
0:11:57 > 0:11:59and they're using bright lights...
0:12:01 > 0:12:03..some loud noises... AIR HORN
0:12:03 > 0:12:05..and smoke...
0:12:06 > 0:12:11..to safely and humanely encourage the flying foxes back into the bush.
0:12:16 > 0:12:2080% of our shire is covered in national park and forest.
0:12:20 > 0:12:24And, um...flying foxes are more than welcome to go to that 80%
0:12:24 > 0:12:26and we need to encourage them to do that.
0:12:28 > 0:12:32It's not just a respect for nature that's motivating residents here.
0:12:32 > 0:12:36You see, bats play a vital role in the ecosystem.
0:12:38 > 0:12:42Every night when they're feeding in the bush, they collect pollen
0:12:42 > 0:12:43in their fur, on their heads,
0:12:43 > 0:12:47and they move it to each successive tree that they visit.
0:12:47 > 0:12:51And in doing that, they're providing an extraordinary service.
0:12:57 > 0:13:00Pollination. You see, keeping the forests alive.
0:13:00 > 0:13:04Good for the flying foxes and good for people, too.
0:13:04 > 0:13:08So let's hope that man and bat find a happy compromise
0:13:08 > 0:13:11and peace can return to Batemans Bay as soon as possible.
0:13:15 > 0:13:19Our next unusual animal sighting was reported much closer to home.
0:13:23 > 0:13:25January 9th, 2016.
0:13:27 > 0:13:28Germany.
0:13:28 > 0:13:31A sperm whale the size of a double-decker bus
0:13:31 > 0:13:34was washed up on the north coast.
0:13:38 > 0:13:42Then, within a few hours, another whale appeared.
0:13:42 > 0:13:43Then three more nearby.
0:13:47 > 0:13:52A few days later, six more sperm whales stranded.
0:13:52 > 0:13:56Unbelievably, the news got worse.
0:13:59 > 0:14:01Whales began appearing on English beaches.
0:14:02 > 0:14:05The world's media looked on horrified as
0:14:05 > 0:14:07over a period of three weeks
0:14:07 > 0:14:1029 sperm whales washed ashore,
0:14:10 > 0:14:13their bodies found all along the North Sea coast.
0:14:16 > 0:14:19It was the largest mass sperm whale stranding event
0:14:19 > 0:14:22in the North Sea since records began.
0:14:27 > 0:14:29The UK's leading whale-stranding expert
0:14:29 > 0:14:31rushed to the coast to investigate.
0:14:33 > 0:14:36I've never had to deal with anything like that before,
0:14:36 > 0:14:37both emotionally and physically.
0:14:40 > 0:14:43We haven't had an event of this magnitude
0:14:43 > 0:14:45with sperm whales for 100 years.
0:14:45 > 0:14:47The question for us is, what happened?
0:14:49 > 0:14:52What could possibly cause so many sperm whales to strand
0:14:52 > 0:14:55in such a short period of time?
0:14:58 > 0:15:02Well, whales do strand across the world every year.
0:15:04 > 0:15:09In 2004, 150 melon-headed whales came ashore in Hawaii.
0:15:09 > 0:15:14And in 2005, over 100 pilot whales stranded in Tasmania.
0:15:17 > 0:15:20But both of these events had one thing in common -
0:15:20 > 0:15:23they coincided with large sonic activities.
0:15:25 > 0:15:27Naval testing and minesweeping.
0:15:30 > 0:15:32Whales have particularly sensitive hearing,
0:15:32 > 0:15:37and loud, unnatural sounds can interfere with their navigation.
0:15:39 > 0:15:44But in 2016, there was no evidence of any naval exercises,
0:15:44 > 0:15:46or other loud underwater disturbance.
0:15:48 > 0:15:50Rob went back to the drawing board.
0:15:51 > 0:15:53Wind farms might be causing it...
0:15:53 > 0:15:55Then we have some more esoteric ones.
0:15:55 > 0:15:59Maybe the Large Hadron Collider might be impacting,
0:15:59 > 0:16:00or climatic factors.
0:16:00 > 0:16:04The El Nino's going on, that might be having an impact, too.
0:16:04 > 0:16:06Those things we have to consider.
0:16:07 > 0:16:09It was a case of back to the drawing board,
0:16:09 > 0:16:12or perhaps more pertinently, back to the history books.
0:16:12 > 0:16:15You see, although this stranding in 2016
0:16:15 > 0:16:17was the biggest in historical times -
0:16:17 > 0:16:19well, say, the last 100 years -
0:16:19 > 0:16:21if you go back further into the past,
0:16:21 > 0:16:24a very curious picture emerges.
0:16:26 > 0:16:30These works of art date from as far back as the 16th century.
0:16:31 > 0:16:33It's a very familiar scene, isn't it?
0:16:36 > 0:16:39The 2016 event was by no means
0:16:39 > 0:16:42the very first mass sperm whale stranding.
0:16:43 > 0:16:46There are many famous historical accounts of sperm whale strandings
0:16:46 > 0:16:51and mass strandings all around the North Sea.
0:16:51 > 0:16:52And, well, frankly,
0:16:52 > 0:16:57you can't help but notice that these whales are all males.
0:17:00 > 0:17:04But what about the 2016 whales? Is there a link?
0:17:05 > 0:17:08Well, what was startling about the latest stranding
0:17:08 > 0:17:10was that they, too, were all males.
0:17:10 > 0:17:13Every single one of them.
0:17:13 > 0:17:15And that wasn't all.
0:17:15 > 0:17:20These old works of art show the exact same stretches of coastline.
0:17:20 > 0:17:24Whales have been stranding here for centuries.
0:17:26 > 0:17:30So, what makes this coast so deadly for sperm whales?
0:17:35 > 0:17:39Sperm whales like to live in water thousands of metres deep.
0:17:41 > 0:17:44But this part of the North Sea is surprisingly shallow -
0:17:44 > 0:17:47in some places, only 50 metres deep.
0:17:49 > 0:17:54Sperm whales use an impressive biosonar to navigate and find food.
0:17:54 > 0:17:57It's the loudest sound produced by any living creature.
0:17:59 > 0:18:01It's perfect for deep water,
0:18:01 > 0:18:03but in this part of the North Sea,
0:18:03 > 0:18:05the sonar bounces against
0:18:05 > 0:18:06the shallow ocean floor.
0:18:09 > 0:18:13The whales become confused and they lose their way.
0:18:16 > 0:18:18Now, the North Sea is a deathtrap.
0:18:18 > 0:18:21There isn't anything to eat because the squid,
0:18:21 > 0:18:25their main prey species, is mainly found in much deeper water.
0:18:28 > 0:18:31And as sperm whales get all their fluid from their food,
0:18:31 > 0:18:34no food means no water.
0:18:36 > 0:18:40They become dehydrated, weak and confused.
0:18:46 > 0:18:48If they don't get out of there,
0:18:48 > 0:18:51their chances of stranding are probably quite high.
0:18:52 > 0:18:56But why do so many strand at once?
0:18:56 > 0:18:59And why are they always male?
0:19:02 > 0:19:06When young males grow up, they form groups called bachelor pods
0:19:06 > 0:19:08that migrate to colder waters in search of food.
0:19:10 > 0:19:13All 29 whales that stranded in the North Sea
0:19:13 > 0:19:16were most likely from the same bachelor pod.
0:19:18 > 0:19:21All it takes is for one to make a wrong turn
0:19:21 > 0:19:23and the entire pod will follow,
0:19:23 > 0:19:26even into a dangerously shallow sea.
0:19:31 > 0:19:34This was undeniably a horrible tragedy,
0:19:34 > 0:19:39but paradoxically, it might also be a sign of some good news.
0:19:39 > 0:19:42You see, since 1986, when most commercial whaling
0:19:42 > 0:19:46was outlawed, some whale populations have begun to increase.
0:19:46 > 0:19:48Now, we can't say for certain
0:19:48 > 0:19:51that that's the case with sperm whales, but it's likely.
0:19:51 > 0:19:54And, of course, if there are more sperm whales in the ocean,
0:19:54 > 0:19:58there are likely to be more sperm whale strandings.
0:19:58 > 0:20:01So, although this was a very sad event,
0:20:01 > 0:20:05we can perhaps look forward to some better things to come.
0:20:10 > 0:20:13Next, to North Africa,
0:20:13 > 0:20:17where a surprising discovery in the dunes could take us to other worlds.
0:20:20 > 0:20:222008, Morocco.
0:20:24 > 0:20:26On the edge of the Sahara,
0:20:26 > 0:20:30German professor Ingo Rechenberg made an astonishing discovery.
0:20:33 > 0:20:34I was very, very excited.
0:20:34 > 0:20:36Very excited. I was crying!
0:20:41 > 0:20:43Now, Professor Ingo Rechenberg has dedicated his life
0:20:43 > 0:20:47to designing machines inspired by nature.
0:20:48 > 0:20:51He loves the climate and the tranquillity of the Sahara
0:20:51 > 0:20:53and spends his winters living here.
0:20:53 > 0:20:59But one night, he was in for the shock of his life.
0:20:59 > 0:21:02I was going outside in the night
0:21:02 > 0:21:05and an animal was crossing near.
0:21:06 > 0:21:09I had the feeling it was a very large animal,
0:21:09 > 0:21:14maybe a jumping mouse, or maybe a lizard or something else.
0:21:16 > 0:21:20And then I looked and just before me, a spider was sitting down.
0:21:20 > 0:21:25The spider was the size of about 10cm. A very large spider.
0:21:26 > 0:21:31And as Ingo watched, the spider did something extraordinary.
0:21:31 > 0:21:34Suddenly, the spider was rolling away.
0:21:36 > 0:21:39I was crying, "Look, this spider is rolling!"
0:21:40 > 0:21:45Yes, the spider was indeed rolling, but that's not so strange,
0:21:45 > 0:21:49because there is, in fact, another spider that rolls -
0:21:49 > 0:21:51the golden wheel spider.
0:21:52 > 0:21:55It balls itself up to roll down the dunes.
0:21:56 > 0:22:00So, why was Ingo so excited?
0:22:00 > 0:22:04Well, this Moroccan spider was different.
0:22:05 > 0:22:09It wasn't just rolling downhill, but uphill.
0:22:09 > 0:22:13The spider was rolling up the dune! Up the dune!
0:22:13 > 0:22:16And so, I must say, I was very, very excited.
0:22:17 > 0:22:21It was a completely unique form of locomotion,
0:22:21 > 0:22:23totally new to science.
0:22:27 > 0:22:30But why would a spider want to do this?
0:22:32 > 0:22:35The velocity when rolling is twice the velocity
0:22:35 > 0:22:38when the spider is walking with eight feet.
0:22:38 > 0:22:40It has a big advantage.
0:22:43 > 0:22:47In the desert, this spider could be prey for larger and faster beasts,
0:22:47 > 0:22:50like the fennec fox or the pompilid wasp.
0:22:53 > 0:22:57When threatened, this amazing arachnid flips into rolling mode
0:22:57 > 0:23:00and doubles its speed for a fast getaway.
0:23:00 > 0:23:02It's just brilliant!
0:23:04 > 0:23:07And, of course, it's every biologist's dream
0:23:07 > 0:23:09to discover a new species.
0:23:09 > 0:23:13The strange thing is that Professor Rechenberg is not a biologist -
0:23:13 > 0:23:17he's a scientist with a very particular specialisation.
0:23:20 > 0:23:23My interest is mainly bionics.
0:23:23 > 0:23:25That means that we try to study
0:23:25 > 0:23:28the performance of biological systems,
0:23:28 > 0:23:31then, of course, we try to imitate this
0:23:31 > 0:23:34and to develop a new machine, or something else.
0:23:39 > 0:23:42He's being quite modest here.
0:23:42 > 0:23:45Professor Ingo Rechenberg is at the very top of his field,
0:23:45 > 0:23:50world-renowned for designing robots inspired by nature.
0:23:52 > 0:23:56So, after discovering the spider, Professor Ingo Rechenberg
0:23:56 > 0:23:59did what any world-renowned bionics engineer would do.
0:24:01 > 0:24:05So, we started to imitate the motion
0:24:05 > 0:24:08and our aim now is to design a robot
0:24:08 > 0:24:10which is able to do both,
0:24:10 > 0:24:14to walk and to move in the wheeling condition.
0:24:17 > 0:24:23And here it is. Yes, a robot that rolls just like the spider.
0:24:28 > 0:24:31It's certainly a very clever bit of engineering,
0:24:31 > 0:24:34but the question is, why?
0:24:35 > 0:24:39I mean, what possible purpose would there be for such an invention?
0:24:41 > 0:24:46Well, Professor Rechenberg has big plans for his little robot.
0:24:46 > 0:24:49You see, with this particular type of movement, it has the potential
0:24:49 > 0:24:54to boldly go where no robot spider has ever gone before.
0:24:58 > 0:25:01We hope that NASA, or also here ESA,
0:25:01 > 0:25:04will become interested when I finish the robot
0:25:04 > 0:25:06to design a larger one, yes,
0:25:06 > 0:25:12than we designed here for the use on the next Mars mission.
0:25:12 > 0:25:15A robot on Mars,
0:25:15 > 0:25:18able to walk and roll,
0:25:18 > 0:25:21adapting to even the most challenging alien landscape.
0:25:21 > 0:25:25So space really could be the final frontier
0:25:25 > 0:25:28for our little spider robot,
0:25:28 > 0:25:31crawling and rolling over the surface of Mars.
0:25:31 > 0:25:33And just to think that all of that came to pass
0:25:33 > 0:25:37because of a chance encounter with a real spider in the Sahara,
0:25:37 > 0:25:41one that now bears the name of the man who discovered it -
0:25:41 > 0:25:43Cebrennus rechenbergi.
0:25:46 > 0:25:49Next, the Amazon.
0:25:53 > 0:25:56South America, 2011.
0:25:56 > 0:25:59Field biologist Aaron Pomerantz was on an expedition
0:25:59 > 0:26:03in the deepest reaches of the Amazon rainforest.
0:26:03 > 0:26:06There is an insane amount of diversity out there.
0:26:11 > 0:26:14So I was walking down this trail, I was just covered in mud
0:26:14 > 0:26:18and I just sort of casually walked past this tree.
0:26:18 > 0:26:22When I took a closer look, I noticed something I wasn't really expecting.
0:26:23 > 0:26:28Hanging from a tree was something minute and extraordinary.
0:26:30 > 0:26:34A strange structure, delicate and complex.
0:26:34 > 0:26:38It was like nothing Aaron had ever seen before.
0:26:39 > 0:26:42This structure is really odd-looking,
0:26:42 > 0:26:44like a little hanging orange basket.
0:26:45 > 0:26:49It just looks like something 3-D printed.
0:26:51 > 0:26:53I was just like,
0:26:53 > 0:26:55"Oh, my God, I need to catch this."
0:26:55 > 0:26:57Like, "We need to look at this further."
0:27:00 > 0:27:04Just look...at that!
0:27:06 > 0:27:12It was bright orange, made out of a very delicate lattice.
0:27:15 > 0:27:18It's like a little alien basket.
0:27:19 > 0:27:23But what was even stranger is that when Aaron peered inside,
0:27:23 > 0:27:26he could see something in there.
0:27:28 > 0:27:33Something that any entomologist would easily recognise.
0:27:33 > 0:27:37It was a pupa, a moth chrysalis,
0:27:37 > 0:27:43which means the tiny alien structure Aaron found was, in fact, a cocoon.
0:27:49 > 0:27:51Cocoons are made to keep caterpillars safe
0:27:51 > 0:27:53as they transform into moths.
0:27:56 > 0:28:00They need to be weatherproof and to keep out any predators.
0:28:00 > 0:28:05So, why would a moth create such a fragile structure?
0:28:05 > 0:28:11Well, a pupa in the rainforest has one particularly prolific predator.
0:28:12 > 0:28:15Ants are everywhere in the Neotropics.
0:28:15 > 0:28:19And so we think that this adaptation, with this odd structure,
0:28:19 > 0:28:21allows the pupa to sort of hang there,
0:28:21 > 0:28:24where it's protected, away from ants.
0:28:27 > 0:28:31Yes. Suspending itself on a long, thin thread,
0:28:31 > 0:28:33the cocoon becomes ant-proof.
0:28:33 > 0:28:36Even the most persistent and hungry ant
0:28:36 > 0:28:40can't safely descend such a long, thin fibre.
0:28:43 > 0:28:45But, then, why the weird latticework?
0:28:45 > 0:28:50Surely the pupa would be safer completely enclosed.
0:28:50 > 0:28:52Well, you see, living on a long, thin thread
0:28:52 > 0:28:55is a very fragile existence.
0:28:55 > 0:28:58Too much weight or wind will snap the thread
0:28:58 > 0:29:01and it will be game over for the pupa.
0:29:02 > 0:29:04So the caterpillar that made this cocoon
0:29:04 > 0:29:08came up with an ingenious plan.
0:29:08 > 0:29:12But to understand it, we need to look at the structure more closely.
0:29:15 > 0:29:19The nearest we can get to making something so intricate
0:29:19 > 0:29:21is with a 3-D printer.
0:29:23 > 0:29:25And here is our cocoon copy.
0:29:26 > 0:29:29And here's a more classic-looking cocoon
0:29:29 > 0:29:31with nice, safe, closed sides.
0:29:34 > 0:29:38If we recreate rainforest conditions,
0:29:38 > 0:29:41the solid cocoon becomes waterlogged and heavy.
0:29:42 > 0:29:46But the lattice lets the rain drain straight through.
0:29:47 > 0:29:50This keeps the cocoon nice and light
0:29:50 > 0:29:53and prevents its anti-ant strand snapping.
0:29:55 > 0:29:58And then, if that wasn't clever enough,
0:29:58 > 0:30:01air can circulate through the lattice,
0:30:01 > 0:30:05keeping the pupa dry and preventing fungal infections.
0:30:06 > 0:30:09If it was just enclosed, like a lot of species that we have in,
0:30:09 > 0:30:11say, Europe or North America,
0:30:11 > 0:30:15there's not as much humidity and not as much rain in these environments.
0:30:15 > 0:30:20So in the rainforest, we think it's this open structure so it doesn't drown.
0:30:20 > 0:30:23This delicate, intricate structure
0:30:23 > 0:30:27is actually completely and wonderfully, well, practical.
0:30:29 > 0:30:32So you might expect that the moth that would emerge from this
0:30:32 > 0:30:36would be of great, mesmerising beauty,
0:30:36 > 0:30:39a paragon amongst moths.
0:30:39 > 0:30:43Well, ladies and gentlemen, young people,
0:30:43 > 0:30:46I give you the urodid moth.
0:30:48 > 0:30:51I'm afraid it's rather drab.
0:30:55 > 0:31:00But thankfully, our next weird discovery is far more colourful,
0:31:00 > 0:31:03as we venture into the rainforests of Borneo.
0:31:04 > 0:31:07Home to some very unusual plants.
0:31:10 > 0:31:14Hidden amongst the greenery are some hair-raising hunters -
0:31:14 > 0:31:15pitcher plants.
0:31:21 > 0:31:24Most plants get nutrients through their roots,
0:31:24 > 0:31:28but these peculiar plants have an altogether more sinister strategy.
0:31:32 > 0:31:34They eat meat.
0:31:43 > 0:31:45Now, all pitchers are pretty wonderfully weird,
0:31:45 > 0:31:48but there's one particular species
0:31:48 > 0:31:50that's puzzled botanists for decades -
0:31:50 > 0:31:53Nepenthes hemsleyana -
0:31:53 > 0:31:56because, well, it's a picky eater.
0:32:00 > 0:32:04This species catches seven times fewer insects
0:32:04 > 0:32:06than its closest relatives.
0:32:06 > 0:32:08It's practically a vegetarian.
0:32:08 > 0:32:12But if it isn't eating insects, what is it eating?
0:32:14 > 0:32:17In 2014, a scientific expedition to Borneo
0:32:17 > 0:32:20captured these incredible images.
0:32:26 > 0:32:29Bats, inside the pitcher plant.
0:32:31 > 0:32:35Could this be the first documented case of a bat-eating plant?
0:32:38 > 0:32:43Captivated by these images, bat experts Michael and Caroline Schoner
0:32:43 > 0:32:45travelled from Germany to the jungle
0:32:45 > 0:32:50to find out if the plant really had developed a taste for bats.
0:32:51 > 0:32:55We don't think that the plants have evolved to digest these kinds of animals.
0:32:55 > 0:32:58They have evolved to digest arthropods, insects, for example.
0:33:01 > 0:33:04Potentially, bats would be able to die inside,
0:33:04 > 0:33:06but it's more than unlikely, I would say.
0:33:06 > 0:33:11So, if the pitcher plant wasn't eating the bat, what was going on?
0:33:11 > 0:33:15Perhaps the bat was the one hoping for a meal.
0:33:17 > 0:33:19We had this idea at the beginning
0:33:19 > 0:33:22that the bats might steal insects from the pitchers,
0:33:22 > 0:33:24but actually, it's not working
0:33:24 > 0:33:27because the bats can never reach this fluid.
0:33:28 > 0:33:33No. These peculiar pitcher plants weren't providing a free lunch,
0:33:33 > 0:33:37they were offering something much more unusual.
0:33:37 > 0:33:40These pitchers, they have a very stable microclimate inside,
0:33:40 > 0:33:43so during the hottest hours of the day,
0:33:43 > 0:33:46they are cooler than the outside temperature.
0:33:46 > 0:33:49And this is something which bats absolutely like.
0:33:51 > 0:33:55So these pitcher plants make the perfect air-conditioned
0:33:55 > 0:33:58place to rest during the heat of the day.
0:33:58 > 0:34:00But what's in it for the plant?
0:34:00 > 0:34:04Why's this carnivore cuddling up to a bat?
0:34:04 > 0:34:08Well, this guest leaves a gift behind.
0:34:11 > 0:34:16Bat faeces contain a lot of nitrogen and phosphorus and also potassium.
0:34:20 > 0:34:23Those nutrients are missing in the areas where the plants are growing.
0:34:25 > 0:34:29This extraordinary pitcher plant has evolved to survive
0:34:29 > 0:34:33almost entirely on the poo of its guest,
0:34:33 > 0:34:36relying on the bat to bring it sustenance.
0:34:39 > 0:34:41I just love this.
0:34:41 > 0:34:44A perfectly strange symbiosis between a plant
0:34:44 > 0:34:46and its small, furry friend.
0:34:46 > 0:34:49And it's a win-win situation.
0:34:49 > 0:34:52The pitcher provides the perfect bat bag
0:34:52 > 0:34:54and, of course, the bat benefits.
0:34:54 > 0:34:58At the same time, the pitcher's thriving on the bat's poo.
0:34:58 > 0:35:02And their survival is intricately intertwined.
0:35:02 > 0:35:06There's just one last piece to the puzzle.
0:35:06 > 0:35:09How does the plant attract the bat?
0:35:10 > 0:35:13Well, we know that bats use echolocation
0:35:13 > 0:35:16to find their way around.
0:35:16 > 0:35:18They send out high-frequency calls
0:35:18 > 0:35:20and use the reflected sound waves
0:35:20 > 0:35:23to build up a picture of the forest around them.
0:35:25 > 0:35:29But Borneo has over 15,000 species of plants
0:35:29 > 0:35:32and more than 30 types of pitcher plant.
0:35:32 > 0:35:36So, how does this particular one make sure that the bats find it?
0:35:38 > 0:35:43Well, would you believe, the pitcher has evolved to become noisier.
0:35:43 > 0:35:47Its back wall is unusually wide and curved,
0:35:47 > 0:35:51just to reflect and amplify the bat's calls.
0:35:54 > 0:35:57It's the perfect bat beacon.
0:36:04 > 0:36:06And it works like a dream.
0:36:13 > 0:36:18Amazing! Not only has the pitcher evolved to fit the bat like a glove,
0:36:18 > 0:36:23it's also come up with a structure that acts as an advertisement
0:36:23 > 0:36:26which says, "This is the best bat hotel in town."
0:36:26 > 0:36:30Now, honestly, that's why I get up in the morning.
0:36:30 > 0:36:32That's proper biology.
0:36:35 > 0:36:38And finally, we investigate a very serious danger
0:36:38 > 0:36:40from the Australian bush.
0:36:41 > 0:36:43Danger from above.
0:36:43 > 0:36:46A-A-A-A-A-A-A-A-A-A-A-A-Argh!
0:36:48 > 0:36:50So, a Drop Bear is like a cross between a polar bear
0:36:50 > 0:36:53and a koala bear that potentially could drop out of a tree
0:36:53 > 0:36:55when you're out camping, for example.
0:36:58 > 0:37:01It's probably almost as deadly as the crocodile, but you just...
0:37:01 > 0:37:03Yeah, almost.
0:37:04 > 0:37:08'And remember, look up when in the outback.'
0:37:12 > 0:37:16The Drop Bear, a fearsome koala-like creature that
0:37:16 > 0:37:20preys on the weak and unsuspecting, but also just
0:37:20 > 0:37:22a piece of Australian folklore,
0:37:22 > 0:37:25the sort of thing you hear round the campfire
0:37:25 > 0:37:26to scare you if you're a tourist
0:37:26 > 0:37:28or give you nightmares if you're a kid.
0:37:28 > 0:37:31Couldn't possibly be any truth in it,
0:37:31 > 0:37:32or could there?
0:37:35 > 0:37:39In 2015, in a remote corner of Western Australia,
0:37:39 > 0:37:43researchers found weird scratch marks high up on a cave wall.
0:37:43 > 0:37:46Scratches that were vital clues,
0:37:46 > 0:37:51clues to shed a new light on the mysterious Drop Bear.
0:37:51 > 0:37:54You see, those scratches might actually point to some
0:37:54 > 0:37:58evidence that proves that the Drop Bear is more than a tall tale.
0:37:59 > 0:38:01Mm.
0:38:01 > 0:38:05Scratch marks on a cave wall that wouldn't mean much to you or I,
0:38:05 > 0:38:10but to one palaeontologist, this was a monumental discovery.
0:38:11 > 0:38:15Our story begins almost two centuries ago.
0:38:15 > 0:38:18With the settlement of Australia in the 1800s,
0:38:18 > 0:38:24pastoralism was moving out beyond the main centres of occupation
0:38:24 > 0:38:26like Sydney and Melbourne.
0:38:31 > 0:38:34In the process, people were stumbling on the remains of
0:38:34 > 0:38:37large animals that they knew nothing of.
0:38:37 > 0:38:42This was the Australian megafauna - giant animals.
0:38:43 > 0:38:46One of these early finds was a skull of
0:38:46 > 0:38:50a very strange-looking animal about the size of a leopard.
0:38:53 > 0:38:57It had the front teeth of a herbivorous marsupial like
0:38:57 > 0:38:59a kangaroo or a koala...
0:39:02 > 0:39:06..but its cheek teeth were huge, sharp blades,
0:39:06 > 0:39:09the kind you'd expect from a meat eater.
0:39:11 > 0:39:14A marsupial with carnivorous teeth?
0:39:14 > 0:39:17Now, that's a very weird find indeed.
0:39:21 > 0:39:26It was so unusual, like no other species ever seen.
0:39:28 > 0:39:31It was given a very fitting scientific name -
0:39:31 > 0:39:33Thylacoleo carnifex,
0:39:33 > 0:39:36which translates as the marsupial lion.
0:39:36 > 0:39:38The butcher.
0:39:41 > 0:39:44But what exactly was this mysterious beast?
0:39:47 > 0:39:49Well, with only a skull to go on,
0:39:49 > 0:39:53it was anyone's guess and would stay a mystery for 100 years.
0:39:56 > 0:40:02Until a young palaeontologist made a huge breakthrough.
0:40:02 > 0:40:08In 1969, I was exploring with a colleague, and we detected
0:40:08 > 0:40:12a gust of air coming out of a rock pile.
0:40:12 > 0:40:16So we wriggled through into a chamber and in that chamber
0:40:16 > 0:40:21there was a silt floor with these funny saw-tooth patterns.
0:40:22 > 0:40:26When my eyes got accustomed I looked down, and there at my feet
0:40:26 > 0:40:30was the upturned skull of the marsupial lion.
0:40:31 > 0:40:33Incredibly exciting.
0:40:33 > 0:40:35I still get excited telling you about it.
0:40:37 > 0:40:43To the side of that, there was the arm of the lion
0:40:43 > 0:40:48with the hand reaching up out of the sediment against the rock.
0:40:49 > 0:40:53And on the arm were long, sharp claws,
0:40:53 > 0:40:55exactly the sort a predator would use
0:40:55 > 0:40:57to catch and hold on to prey.
0:41:06 > 0:41:10Over the next few decades, more discoveries of complete skeletons
0:41:10 > 0:41:14helped flesh out a picture of a truly terrifying predator.
0:41:20 > 0:41:24This animal can produce the most powerful bite
0:41:24 > 0:41:26known for any living mammal.
0:41:30 > 0:41:33It could crush a skull in a single bite.
0:41:33 > 0:41:36It really is the stuff of nightmares,
0:41:36 > 0:41:39but can we say that this was the Drop Bear?
0:41:39 > 0:41:43Well, remember those scratches on the cave wall?
0:41:46 > 0:41:50In just recent times, a couple of my colleagues have been examining
0:41:50 > 0:41:54scratch marks on the walls of caves in which we've found
0:41:54 > 0:41:55the marsupial lion.
0:41:59 > 0:42:03This seems to suggest that they were actually actively climbing in
0:42:03 > 0:42:04and out of the cave.
0:42:06 > 0:42:09If it could climb out of a cave, then potentially
0:42:09 > 0:42:12it could climb a tree. And if it could climb a tree,
0:42:12 > 0:42:16then it could drop out of it onto unsuspecting prey.
0:42:16 > 0:42:18You can see where I'm going -
0:42:18 > 0:42:22it's beginning to sound more and more like the Drop Bear.
0:42:22 > 0:42:25I suppose the question then is, how could the legend pass
0:42:25 > 0:42:27into the present day?
0:42:30 > 0:42:34Well, just look at this rock art made by indigenous Australians
0:42:34 > 0:42:38more than 40,000 years ago.
0:42:38 > 0:42:41Are you seeing what I'm seeing?
0:42:41 > 0:42:46Experts believe this is most likely our marsupial lion.
0:42:47 > 0:42:53And if so, it's direct evidence that some people came face to face
0:42:53 > 0:42:56with it and lived to tell the tale.
0:42:57 > 0:43:01A tale that could make even the scariest campfire story
0:43:01 > 0:43:03imaginable, real, even.
0:43:03 > 0:43:07Perhaps memorable enough to pass on to the next generation
0:43:07 > 0:43:11and the next generation, all the way down to the present day.
0:43:11 > 0:43:14And you never know, it might still be out there.
0:43:14 > 0:43:17If ever you're camping in Australia, you might want to look up.
0:43:22 > 0:43:26I find it strangely reassuring that when we finally explain one of these
0:43:26 > 0:43:30weird mysteries, we become aware that there are still loads more
0:43:30 > 0:43:32out there to be solved.
0:43:32 > 0:43:35There's no doubt at all that there are plenty of puzzles
0:43:35 > 0:43:37left on our planet.