Devious Defences Weird Nature

There was a time when myths and science were entwined...

..when mermaids and unicorns could mysteriously appear.

Nature was weird.

When science revealed the truth behind these imaginary creatures,

it found real animals lay behind the legends.

Today, science still makes astonishing discoveries,

but nature seems just as weird.

It's just that fact has broken free from fiction.

GROWLING

In nature, a good defence is key to survival.

But humans have no natural defences at all.

Even our most magical camouflage is no match for the real thing.

Vine snakes freeze motionless for hours

as they mimic the creepers that hide them.

In turn, snakes are impersonated

by the snakehead caterpillar.

Insects become leaves, finessed with details of damage.

A hunter's spotted coat conjures up dappled shade.

But in the arms race between predator and prey,

even the eyes of a killer are mimicked.

These false faces, complete with eyes and nose,

belong to eyespot frogs.

They frighten real predators.

Poison arrow frogs really are lethal.

So rather than hide, they use vivid colours

to warn against being eaten by mistake.

Their toxic secretions lace tribal darts.

The poison from just one frog can kill a man.

Weird Nature uses imaginary settings to showcase real animal behaviour.

This weird journey reveals

the strange ways animals protect themselves.

Full body armour is often the first line of defence.

The three-banded armadillos of Argentina are the masters.

Like medieval knights,

they use articulated armour.

Their protective shields, made from a double layer of horn and bone,

are hinged with leathery skin.

The plates cope with most of what nature throws at them,

but a polo match is exceptional.

This imaginary scene showcases the armadillo's extraordinary behaviour.

Its first defence is to run, but heavy armour slows it down.

Its second defence is to roll up,

interlocking its plates into a sealed ball...

..the strongest shape in nature.

It can open just a chink to check what's happening.

Even WE ball up for protection.

But helmets and padding can't compete with full body armour.

The only soft part of the armadillo is its face and underbelly.

Otherwise, it's a walking armoured tank.

It takes the knocks of real life just as easily in its stride.

This fantasy wreck displays the inventive defences of sea creatures.

The puffer fish has its own version of armour.

Instead of scales,

its leathery skin is armed with spines.

The spines erect to form a lethal pincushion

when the fish sucks in water.

With elasticated skin and no ribs to stop its body expanding,

it balloons to five times its normal size -

too big for most mouths to swallow.

The puffer's ultimate weapon is poison -

enough to kill 30 people.

There is no known antidote.

This wreck also shows how animal defences can adapt

to extraordinary circumstances.

For dresser crabs, the right dress code is everything.

They decorate their shells to fit in

wherever they go.

They select material from whatever is around.

A dressing room full of treasure is paradise.

They first chew their finds to make them frayed and fibrous.

They then attach the prepared fabrics to Velcro-like hooks

on their legs and shell.

The dresser crab uses its keen attention to detail

to fashion a camouflaged suit.

It usually adorns its costume with sponges and seaweed,

as these are most often to hand.

But given the chance, it improvises,

a trait that helps the dresser crab maintain perfect camouflage.

Their eclectic dress sense means they blend in anywhere,

safe from they eyes of predators like puffer fish.

To vanish, they freeze.

Making yourself bigger is not only a defence -

it can also send a message.

The spotted skunk is famed for its offensive body odour.

TECHNO MUSIC

Bold markings warn that it carries a concealed weapon.

If the skunk isn't shown respect, it ups the ante.

Handstanding exaggerates its size and shows off its markings.

It's a dance of defiance.

Foot-stomping drives home the threat.

If the message is missed, the skunk reveals its weapon.

Like an aerosol, anal glands spray sulphurous chemicals

through nozzles aimed at the eyes.

They cause temporary blindness and nausea.

Some defensive sprays are even deadlier.

Most give cobras

a wide berth.

But they say curiosity killed the cat.

Snakes prefer to conserve their venom.

So it spreads its hood as a warning.

The spitting cobra aims for the eyes.

Glands squeeze venom through hypodermic fangs.

The spray jets 3m.

A direct hit could have blinded for life.

Most animals fear snakes.

The horned frog of Central America is no exception.

A lookalike snake provokes the same bizarre reaction.

LOUD SCREECH

If puffing up and screaming like a banshee fails, it fights back.

It pays to have a wide repertoire. Danger is never far away.

A horned owl would soon make a meal of a frog,

even one with an inflated ego.

But owls are equally fooled by a snake in the grass.

They click their beaks and hiss and arch their wings

to puff themselves up.

If this bluff fails, they turn tail.

Changing shape has been perfected by many sea creatures.

The octopus's soft, malleable body helps it change shape easily,

but the price of having no skeleton is vulnerability.

One defence is to change texture to mimic its surroundings.

Another is reactive camouflage.

Its near-instantaneous colour change is under nervous control.

Pigment cells expand and contract

in waves of emotion.

The colour cells react quicker than those of any other animal.

But this quick-change artist has a rival.

The peacock flounder's skin

can make a near perfect facsimile of its surroundings.

A paper-thin profile helps its vanishing trick.

But how does it fare on a less familiar background?

Its stalked eyes have feature detectors,

primed to pick out patterns. It does a quick survey

and then it makes a match.

The eyes pass data to the brain

which adjusts the size and contrast of pigment cells

for the best possible copy.

Incredibly, it has to assume how the pattern would continue

if its body wasn't there.

On familiar ground the match is perfect.

If the octopus' camouflage fails, it has other tactics.

Throwing sand in the face is one.

So is whipping up a smokescreen.

The ink is made of the black pigment, melanin.

It escapes under the cover of darkness.

The octopus's last trick is that of a contortionist.

It can squeeze through a hole one tenth its body width.

Its shrink-to-fit routine is limited only by the size of its beak.

Once these hard mouth parts are through,

the rest is easy.

But the best shape-shifting act belongs to another of its kind.

This is the amazing vampire squid.

This rare, deep-sea octopus has an equally rare defence.

It turns itself inside-out.

The armoury of spines makes it seem impregnable.

But its spines are soft as jelly.

It seems this is just an amazing bluff.

Other creatures of the depths have equally odd defences.

In the cold fjords of Sweden,

crab fishermen occasionally dredge up more than they bargained for.

These are hagfish,

relics from before the age of dinosaurs.

Their peculiar miracle is turning seawater into slime.

Glands that line their body fire out protein pellets

that swell on contact with water.

Other glands fire explosive threads.

Together, they form an impenetrable slime barrier

that suffocates predators.

To avoid the same vile fate,

the hagfish can slip off its slimy coat

by passing a knot down its body.

One hagfish oozes enough gunge

to turn a whole bucket of water into slime.

As well as deterring predators,

this gloopy mucus keeps rival hagfish away,

as they scavenge on rotted carcasses.

Even hungry birds find this slippery fish too slimy to swallow.

In Scandinavia, fieldfares use equally foul play on intruders.

Fieldfares nest together, so one alarm call rallies the whole colony.

LOW-PITCHED CHIRPING

All who trespass are dealt the same dirty trick.

Even though humans have little natural protection,

we've made up for it with some deadly inventions.

But these birds have their own fire power.

GUNSHOT

The whole squadron is scrambled.

The hunter gets his comeuppance. On birds of prey the droppings

can be fatal, destroying the waterproofing of their plumage.

The fulmar's defence tactics are even more repulsive.

Its frontline defence is a mountain fortress

that keeps land predators from the breeding colony.

The young are left for hours on these sea stacks

as their parents make long fishing trips far offshore.

Wise climbers avoid nesting cliffs.

They know that chicks left home alone have a secret weapon.

But what happens if a climber takes the wrong route?

Chicks brew up an oily concoction in their stomachs from fish they eat.

They save this vile soup for the times they're left alone.

The chicks' usual threat is predatory birds,

but anything within spitting distance becomes a target.

It fires a warning shot, followed by a blast.

The vomit is made from fish oils,

separated in the stomach from other food.

What repels a climber could kill a bird. The vomit also damages plumage,

causing hypothermia or drowning.

Birds that use projectile vomiting may seem bizarre.

But humans are weirder. We evolved to have no natural defences at all.

Our safety net is our technology

and a brain that quickly learns from mistakes.

Few animals are so poorly equipped to defend themselves.

In nature's terms, it is WE who are weird.

Other animals even employ acting skills as a defence.

This is not what it seems.

These animals are far from dead.

They are putting on a remarkable performance.

Only a hint of movement gives the game away.

Birds enter this trance-like state quite readily.

Frogs appear to die if turned on their backs,

but it's just a bluff.

The hognose snake lolls its tongue to fake death throes

and gives off the stench of decay.

The opossum gave death-feigning a name.

As it plays possum,

anal secretions make it smell like a rotten corpse.

This behaviour is easily triggered

by harmless hypnosis techniques.

Strangely, the animals often wake up together.

Playing dead works because most predators won't touch carrion.

Danger gone, they quietly leave the stage.

Among nature's devious feats of deception,

playing possum must be as weird as it gets.

Our next weird journey looks at the bizarre ways animals breed.