Original subtitles

Narrator: Spiders normally hang out on webs.

So why are these guys disco dancing?

There is a lot more to this display than meets the eye.

Narrator: What mysterious creature

Is killing europe's sheep?

Some predator is ruthlessly tearing apart livestock.

Narrator: And what in the world is the foamy stuff

Taking over this town?

I can't tell whether it's terrifying or fun.

Narrator: Nature is awe-inspiring.

But sometimes it just doesn't make sense.

Man: I have never seen anything like this.

Our team of experts investigate the weirdest animal behavior...

That's amazing.

...And the most unexpected events...

What is causing that?

...Ever caught on camera.

My god!

These are...

You might have seen a fair number of spiders

Hanging out, poised in webs,

Walking on walls, or hiding in a corner.

But some of these arachnids have a magnificent talent

You probably haven't witnessed.

They like to boogie.

Burke: This is absolutely incredible footage.

I really -- I've seen a lot of things about spiders,

But this is new to me.

They'll sort of shimmy to the left, shimmy to the right.

They do these really rapid leg moves.

They sway from side to side.

Narrator: Scientists have found over 6,000 species that dance.

Some of the most impressive are the peacock spiders.

They have this vibrant color.

And they also have this very elaborate dance.

Narrator: So, why do these guys look like they're auditioning

For a part in "Saturday night fever"?

Burke: Is this some strange courtship ritual?

And certainly there are loads of examples in the natural world

Of animals doing some pretty crazy things to impress females.

Elias: Males do a lot of very elaborate dance moves.

One of the classic examples

Is birds of paradise from new guinea

And also manakins from central and south america.

These birds are brilliantly colored

And have all these really spectacular feathers,

And they dance around in these really impressive ways.

Narrator: Scientists found that when spiders dance,

It is, in fact, the males performing to attract a mate,

And they'll need to put on quite a show.

Dancing spider females can store male sperm,

So they only have to mate once over their whole lifetime.

Elias: Females really hold the keys

To the entire mating process.

70% of females in many species will reject males.

♪

Narrator: But it seems the mating ritual

Is not quite as straightforward as it looks.

In this footage, what we find

Is something really quite remarkable,

Which is that the female doesn't seem to be --

Not even that she's not impressed.

She's not actually watching,

Despite this incredible visual display.

Narrator: In one study,

Scientists found the females pay attention

For less than 30% of the performance.

Burke: So it begs the question,

Why do the males work so hard for a visual display

If the females aren't even watching?

Narrator: Researchers speculate

That the females have other priorities,

Like not getting killed by one of their many predators.

Elias: A spider's life is very dangerous.

So females need to be attuned to their environment at all times.

So males are trying to keep that attention to themselves.

Narrator: The males face the exact same predators,

With one addition,

One that poses a rather more immediate threat.

There is a risk that the female will actually eat the male

Before reproduction.

So that male has to make sure his dancing is on form

To reduce the risk of being eaten alive.

Narrator: So it could be mating success

Or death.

It's quite literally murder on the dance floor.

But when researchers looked more closely,

They discovered there's even more to this arachnid mystery.

Damian elias was studying some of these mating rituals

When he noticed something weird.

Elias: I work on the genus habronattus.

And they have some of the most spectacular colors

And spectacular dances known.

One of the things that became evident

Was as they were dancing,

They were also moving parts of their body

That the female would never be able to look at.

Narrator: The spider was shaking his booty

Even though it was completely obscured from the female's view.

Damian wondered, could the spider's wiggling butt

Actually be making a noise?

Now, to the human ear,

Most of these dancing spiders produce no sound.

But are the males actually singing to the females

In a way we just can't hear?

After all, spiders sense sound quite differently to how we do.

Burke: Spiders famously have these hairy legs,

And some of them are very specifically designed

To pick up vibrations.

Elias: They're able to detect very small motions,

Whether they be on a spider web or on a leaf,

And they're able to detect movements of those surfaces,

And that's the way that they do the equivalent of hearing.

Narrator: Damian uses some tech called a laser vibrometer,

Which measures tiny vibrations on a material's surface

And turns it into sound.

He uses a brush

To move two habronattus spiders into position

So we can hear what happens during the mating ritual.

[ buzzing ]

Burke: So there is a lot more to this display than meets the eye.

He is also doing a song, not just a dance.

Narrator: The question is, has he done enough to win her over?

Or will he get eaten?

Elias: Once she was looking at the male displaying,

She was staring right at him.

And then so that let the male know

That he could get further and further along in his display.

[ buzzing ]

Then finally you saw the male get on top of the female

And start to copulate with her.

Now, one of the things that's really interesting

Is that they continue to sing while they're copulating.

At that point, he wants to get off the female

Without being eaten.

And so you had this kind of big burst of buzzing

And then -- right before the male jumped off and ran away.

[ buzzing ]

Narrator: When damian prevented the males from making sound

By covering their rear ends in wax,

He made a startling discovery.

He found they were much less likely to copulate

And much more likely to get eaten.

So it seems like sound is crucial to their success.

Who knew?

Some spider species can make music with their butts.

And the reason they sing and dance isn't just to mate.

It's to keep stayin' alive.

♪

July 2017, europe,

The luxembourg state agency for nature conservation.

This is an amazing mystery.

This one is quite creepy, actually.

Narrator: The hotline buzzes regularly

With sightings of strange animals

And possible mysterious attacks.

We get a lot of funny phone calls

Of people having seen various animals which don't exist here.

Narrator: Generally these calls turn out to be false alarms.

But then laurent gets one that sounds different.

Schley: On a Saturday evening, I got a phone call from a farmer

Who's telling me about a few sheep

That had been killed in one of his pastures.

The way he was describing it made me feel quite alert,

And so I went myself to his pasture to have a look.

[ insects buzzing ]

We saw a few sheep lying all over this pasture.

One of those sheep was more or less completely eaten up.

The others had just been killed.

Narrator: Luxembourg's only sheep predators

Are dogs and foxes,

And laurent has seen lots of these attacks.

But the nature of the injuries here looks different.

Schley: There were very clear bite wounds at the throat.

There was no bite wounds at the hind legs

Or at other parts of the body, which is more typical for dogs.

I did have the feeling immediately

That there was something odd.

Narrator: It was a real mystery.

Did luxembourg have a brand-new predator on the prowl.

Narrator: Sheep have been found dead in luxembourg,

And the local predators, foxes and dogs, have been ruled out.

So who is the mystery killer?

Some wonder if bears could be responsible.

They're found in austria, Italy, and Spain, as well as France,

Where attacks on sheep in the pyrenees

Have doubled recently.

As a bear expert, I can tell you

This is not consistent with a bear attack.

Bears attack with both paws and biting.

So you often see very heavy club-like injuries,

But there was no clubbing action consistent with a bear.

No, this was something much more targeted.

The throats were torn out,

The animal consumed almost in its entirety.

Nobody knows what's doing it.

All the usual suspects have been ruled out.

Greive: As for the actual predator doing the killing,

All we know is that they're very, very good at it.

Narrator: Could luxembourg's sheep be under attack

From a new predator?

Greive: The actual manner

In which these animals were slaughtered,

Having their throats torn out,

Is consistent with a wolf attack.

But there's been no wolves in luxembourg for over a century,

Leaving everyone baffled and afraid.

Narrator: By 1900,

European wolves were hunted to the brink of extinction

Because of the threat they posed to livestock.

Surviving populations are mainly found

In pockets of Spain and eastern europe.

So had they returned?

So we took samples from the bite wounds

That we sent in to the lab

Where they could try to identify the dna from the predator.

And the results confirmed, indeed,

That the predator had been a wolf.

[ wolf howls ]

These attacks were by wolves.

Wolves were back.

Schley: We were quite excited that this could well be

The first wolf presence in luxembourg for 124 years.

Narrator: With wolves confirmed as the killers,

The mystery deepened.

Where did they come from, and how did they get here?

Burke: So these aren't just isolated killings.

There's a real trend emerging here.

And the sightings of wolves across the continent

Where they were once thought to be extinct is also on the up.

Narrator: In France, 300 wolves slaughter 10,000 sheep

In just a single year.

In germany, the story is similar.

Europe is so unprepared for the wolves' invasion,

Workmen mistakenly rescue a drowning wolf,

Thinking it's a dog.

No wonder he looks sheepish.

We've rested on our laurels so long in western europe.

We're not ready for the wolves. They suddenly appear.

I mean, they literally have appeared almost overnight

In these countries.

Narrator: By 2017, wolves have established populations

In nearly all western european countries.

So there's a real mystery here,

Is where have these wolves come from?

The most obvious place to look was in eastern europe,

Where wolf populations have been doing quite well there.

Narrator: But wolves are known for being very territorial,

Often only hunting within fixed boundaries

And fighting other wolves that encroach on their space.

Greive: But that is not the case in europe at all.

They are covering greater and greater distances,

And the livestock casualties are mounting up.

Narrator: If wolves are so territorial,

Why have they suddenly abandoned their home

And traveled a thousand miles to attack sheep in luxembourg?

Narrator: Sheep have been turning up dead in luxembourg,

And wolves are the culprit. [ wolves howling ]

But wolves haven't inhabited this region for over a century.

Could they have really traveled a thousand miles

From their eastern european home?

Baker: That's the interesting part of this story

Because what they're effectively doing is reclaiming lost land.

The big surprise is why they are suddenly doing it.

Narrator: One factor could be a change that occurred

In the political landscape several decades ago --

The collapse and breakup of the former soviet union in 1991.

Now, this didn't just affect people.

This affected the animals and the wildlife.

Greive: The collapse of the soviet union

Also meant the collapse

Of state-sponsored culling programs,

Meaning there was absolutely nothing

To keep wolf population numbers in check.

Narrator: In 10 years, the wolf population more than doubled.

And more hungry mouths meant greater competition

For both food and territory.

So this forced the wolves to go on the move,

And it's very likely that they headed west.

Narrator: Yet this fact alone

Is unlikely to account for europe's wolf invasion.

Investigators suspect there must be more to the story.

The redistribution of wolf populations

Is utterly mind-blowing.

The map has been completely redrawn.

Narrator: The answer, it appears, dates back to 1992.

After wolf hunting is banned across much of europe,

The eastern european wolves are, in effect,

Handed a free pass to seek out new hunting grounds

All over the continent.

Baker: Just take them as a species.

They can be found right up in the arctic circle.

They are the perfect wandering animal.

So we shouldn't be surprised when we hear them

Doing these amazing journeys

And appearing where we've not seen wolves

For hundreds of years.

The usual main question that always comes up from people

Is, "what do I do if I meet a wolf in the forest?"

Don't run. Just stay calm.

Be happy that you have this lucky moment, actually,

To see a wolf.

Narrator: Lucky indeed

For an animal once on the edge of extinction.

Not so good if you happen to be a sheep.

[ wolves howling ]

♪

February 2016.

The inhabitants of penmarch in France

Wake up to discover their town is covered in this stuff.

It's as if everybody's washing machine

Was just overflowing with suds

And just covering the entire town.

Franks: It's like a blob from the ocean attacked this village.

You know, if you got a car parked in the parking lot,

You might have a hard time finding it afterwards.

Honestly, I can't tell whether it's terrifying or fun.

But the question is, where did it come from?

Narrator: Penmarch is on the coast,

And the white foam appears to be coming from the ocean.

Bubbles in crashing waves are common.

They're created when air gets churned into the water.

Normally these bubbles quickly disappear.

To understand why, we need to go back to some bubble basics.

Water molecules are attracted to each other, a bit like magnets.

This attracting force is called surface tension.

It holds a bubble's skin together.

But surface tension is also the reason bubbles pop.

Other water molecules are drawn to the bubble's outer layer,

Stretching it apart until it bursts.

So why aren't these bubbles disappearing?

If you had a straw and a cup of water,

You could blow bubbles into it, and what happens?

The bubbles come to the surface and pop.

You put that same straw into a cup of milk and blow bubbles,

Now we've got bubbles flowing over the top.

The bubbles are not popping.

So what's the big difference between the milk and the water?

The milk has all kinds of things dissolved in it,

All kinds of proteins and fats.

Narrator: This suggests there must be something unusual

In the seawater

Altering the surface tension of the bubbles

So that they last much longer.

It would take something to change the water chemistry

Or the water quality in such a way

That would make it more viscous and allow these bubbles to form.

It could be pollution,

But pollution isn't usually an event.

Pollution is something that's ongoing.

It's chronic. It's happening a lot.

It's not usually this overnight sensation

Where this stuff forms like this.

Narrator: There are no reports of any chemical spills nearby.

So what else could change the water enough

To create the weird frothy sea foam

That engulfed an entire town?

Narrator: Strange foam has covered a french town.

And it appears to be coming from the sea.

Something must have changed the water chemistry.

If it wasn't pollution, what could it be?

Well, animals and fish in the ocean

Can alter the water's composition.

Normally when you look at seawater,

It can look pretty clear, especially in the tropics,

But even in places like that, there's still tons of --

Tons and tons of life within each drop of water in the ocean.

It's filled with decaying plant life,

With newly emerging plant life

And biological material of all kinds.

Narrator: Occasionally, population explosions

Can alter water chemistry dramatically.

Phytoplankton are tiny marine organisms

That live in the upper layers of the ocean

And can reproduce rapidly.

Phytoplankton, which are pretty much like small plants,

They photosynthesize, they live off the sunlight.

And these plankton go through cycles

Where they'll sometimes achieve huge abundances.

They can actually color the water.

Narrator: In high densities, they're known as an algal bloom.

Some are so big, they can even be seen from space.

Conley: All these things have life cycles,

And when they die, their bodies degrade,

And these all produce these organic chemicals.

Narrator: It's possible that an algal bloom like this

Could have altered the water enough to make bubbles last.

They allow for more foam to be built

And allow for more bubbles to form,

And instead of breaking down, they stick around.

Narrator: But hang on.

Something else would have to happen

To whip this water into a bubble frenzy.

So if you were to take that tiny little drop of ocean water

With all that life in it

And were to shake it up and agitate it,

That's where you'd get that foam from.

So what would be an agitator?

What would cause that foam to form?

Narrator: Storm imogen was sweeping through northern europe

At this time,

And reports show it did pass by penmarch.

Storm imogen created a tremendous amount of damage

In the way of wind speed, in the way of storm surge,

In the way of rainfall.

Franks: It's exactly the same as whipping air into egg whites.

It's like a giant egg beater.

Midcap: Voilà! That's your agitation.

And that's where you get your foam.

Narrator: Incredible.

Seawater plus algae

And, of course, a hurricane-force wind

Is all it takes to turn a small french town

Into a cappuccino coast.

-- Captions by vitac -- www.Vitac.Com

Captions paid for by discovery communications