Episode 3 Nature's Weirdest Events

No matter how well we think we know our planet,

the natural world still has the ability to surprise us,

to shock us and maybe, sometimes, even to scare us

with its extraordinary events and bizarre behaviour.

And new technology means that nature's weirdest phenomena

are being caught evermore readily on camera.

So, we're going to bring you the strangest stories

our world has to offer.

A specialist skill can help an animal get ahead.

Our stories show that the ability to create a superstructure

can be crucial...

..from an oozing slime clogging fishing nets,

to the mystery of elaborate works of art

appearing on the seabed.

But first...

to the heart of Pakistan,

where, during the summer of 2010,

reports of devastating floods spread throughout the world's media.

Tens of thousands of people are being forced to leave their homes.

Today brought new flood warnings in the southern Sindh Province.

But from amongst all these news reports

emerged an altogether different set of images.

Russell Watkins, from the Department for International Development,

was travelling to Sindh Province

when he came across a scene so surreal

it stopped him in his tracks.

Nothing really prepared us for what we saw when we got there.

What we were confronted with was quite spectacular.

Every tree you could see, every piece of vegetation that you

could see, for miles on end, was just cloaked in these enormous webs.

Russell had the photographic evidence but not the explanation.

So, who, or what, had turned these trees,

in a remote corner of Pakistan, into giant, spooky cocoons?

Silk specialist Chris Holland thinks he has the answer.

Whilst these trees completely covered in silk may seem

really unusual to the vast majority of us,

there's actually a very simple, natural process occurring here.

For Chris, there's only one culprit capable of spinning these

sinister structures.

Spiders.

Just as the human population was forced from their homes

by rising waters,

so arachnid refugees were pushed back to the only dry land in sight.

It just happens to be that when you have flooding events,

they have very few places to go, and they usually go for high ground,

and, in this case, it would be the trees.

So, the types of spiders that you see in these trees

are most likely the sheet-web building spiders.

These are the spiders that you tend to find in the

back of your garden, under your shed, or in your kitchen cupboards.

But these were big enough to entomb your entire kitchen.

Just how had these webs got so vast?

Ironically, the answer lay in the very water

that had trapped the spiders.

A stagnant breeding ground for mosquitoes.

So, when you get a few spiders confined to this really small space,

but a lot of food around,

for example, mosquitoes from these floodwaters,

you suddenly would generate a huge population explosion,

where all these spiders are having babies, these spiderlings,

running amok around these trees,

creating lots and lots of sheet-webs,

which creates these huge, beautiful covering of silk,

as we see in these photos.

So, what Russell saw in Pakistan

was really just normal spider behaviour pushed to extremes.

And, as it turned out, it wasn't the only example.

In March 2012,

thousands of spiders escaped floods in Wagga Wagga, Australia,

covering farmland in a creepy-crawly shroud.

And what you're seeing in these photographs aren't actually webs,

but millions of strands of dragline.

That's the silk that spiders lay as their safety net

and it's one of the most remarkable fibres in the natural world.

So, spider silk isn't actually stored already reeled up

like a fire hose inside the spider.

It's actually stored as a gel and this gel is made up of proteins.

As these proteins are pulled, they align into a hard, solid fibre.

And it's the alignment, and how these proteins go

together as building blocks, that gives silk it's amazing properties.

This protein reshuffle creates one of the toughest

fibres on the planet.

A natural material so strong it can outperform steel.

In the case of these spiders,

the ability to spin their own safety line proved to be a life-saver.

But our next superstructure has a much more poetic purpose.

We are travelling to the waters off Japan,

where, in September 2012,

underwater photographer Yoji Ookata

spotted something remarkable.

An intricate, circular pattern carved into the sand.

A peaked ring of ridges and waves, perfectly executed.

Yoji began a stakeout, hoping to unmask the culprit.

The artist responsible is a pufferfish.

Yoji saw a male work tirelessly...

..sculpting and perfecting his pattern over a number of days.

And no-one in the scientific community had ever seen

anything like it.

Biologists like Dan Da Costa were blown away by its behaviour.

Pufferfish are not well-known for swimming fast,

or moving fast at all.

And the way this pufferfish is moving,

and moving his fins to make this nest,

is just out of this world.

But why does the pufferfish go to all of this effort?

Well, the circle acts as a kind of oceanic love token.

The female is drawn into the patterns

and she lays her eggs in the central depression,

where they're protected from currents.

There's fish that do things to attract females,

but not a single tiny fish like that

builds a huge nest just to attract the female.

And there's little pieces of corals

and pieces of shells in it just to make it more attractive.

That's quite unique. It's incredible.

Talk about a grand romantic gesture.

Even though scientists have discovered more

than 120 different types of pufferfish,

in both tropical and fresh water,

they've never seen anything like that sculpturing ever before.

When you think about it, more than 70% of our planet's surface

is covered in water, much of it little explored,

so there must be many more phenomenal things out there

to be discovered.

Whilst the pufferfish nest is a work of art,

not all superstructures are quite so appealing.

This next strange substance is unlikely to win any

popularity contests.

There is a very sticky situation facing fishermen in the Atlantic.

'So, how do you get rid of all that slime?'

They are pulling up their nets and pots, only to find them

covered in slime.

Armfuls of this colourless gloop is appearing in any one catch.

With often more slime than fish,

removing it from a haul is an absolute nightmare.

Now, it's too common a complaint to be attributed

to some freak event or rare natural phenomena.

Something is creating enough of this substance to drive fisherman crazy.

The question is...

what?

Well, the source of this mystery mucus

can be found on the deep sea floor.

The repugnant perpetrator...

..is the hagfish.

It's the undertaker of the deep, searching the murky bed for corpses.

It uses a rasping tongue to pull flesh from bone.

It will even wriggle inside a rotting corpse

to devour the soft flesh under the skin...

..literally eating the victim inside out.

But nasty eating habits aside, the question remains,

why would a creature that lives on the seabed need to produce slime?

Well, aside from its willingness to eat sea floor scraps,

the hagfish doesn't seem to have very much going for it.

It's pretty much blind, has no jaws or tough scales.

It looks vulnerable.

But, in fact, the hagfish really is quite a success story.

It's been around for a whopping 300 million years,

which makes it one of the oldest fishes in the sea.

And the secret to its success is slime.

It's a defensive strategy so brilliant

that it makes the hagfish, quite literally, untouchable.

Professor Doug Fudge studies these master-slimers.

So, the hagfish is essentially covered with slime glands,

and when an animal is attacked by a predator...

there is muscle in the area where it is touched

that cause those slime glands to release their contents.

There's actually a little mini-volcano of slime

that comes out of the gland.

It's reinforced with tens of thousands

of silk-like protein fibres

that we call slime threads.

And it mixes with seawater, and it forms this large volume

of very unusual, fibre-reinforced slime.

A single hagfish can turn a bucket of water into slime in seconds.

Ew! That is so gross!

Which proves to be a pretty fantastic underwater weapon.

In a recent study that was published by a group in New Zealand,

they showed hagfish using their slime in a wild situation.

The fibrous mucus is designed to choke a predator

by clogging up its airways.

The shark is left gagging as its gills fill with mucus.

Every assailant is repulsed by a wall of slime.

And the technique is so effective

that the hagfish seems utterly unperturbed by the assault.

So both predators and unsuspecting fishermen

are getting the same treatment.

But how does the hagfish prevent itself from becoming

the victim of its own slimy strategy?

They have an ingenious way of getting out of the slime.

They'll tie their body in an overhand knot,

and then they'll pass their body through the knot,

and that will wipe the slime off of their body.

A necessary skill

for the ocean's most slippery character.

Now, you may not like this, but humans produce slime too,

in the form of snot.

And what's remarkable is that hagfish slime

and human snot are actually composed of very similar proteins.

Now, hagfish use their slime

to protect themselves from predators,

and humans use their snot to trap

harmful substances and then expel them from the body,

so, when you think about it, both hagfish

and humans are using slime as a front-line defence.

These animals have proved that, in the natural world,

it pays to be a master-craftsman.

Whether you're a silk-spinner escaping the rising tide,

a slime-producer defending yourself from attack,

or a sand-sculptor looking for love...

..a superstructure is crucial to success.