Ultimate Swarms Page #5

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the river of food for anything else.

This swarm is taking over.

And the trouble with all this

is, it's a purely man-made problem.

These fish were

introduced 40 years ago to clean

the algae off commercial catfish

ponds.

When they escaped into nearby

rivers,

the carp found themselves

in the river full of food

and nothing to stand in their way.

With each carp able to produce up to

two million eggs a year,

it didn't take

long for the fish to become a swarm.

Something that doesn't happen

back in their native home, Asia,

where predators

keep their numbers in check.

They've just exploded.

This is a swarm of epic proportions.

Look at the size of that one.

That's got to be 30 pounds.

If that hit you, it would

break your jaw.

PEOPLE SHOU And although this may all look

a bit unconventional,

this event does play a small

part in a serious attempt

to control these fish.

By the end of the event,

over two tons of carp will have been

cleared from the river.

ALL CHEER:

And that's in addition to

the hundreds of tons caught

every

year through commercial fishing,

some of which is actually now

exported back as food

to the carp's original home, Asia.

But all this is just keeping

things in check.

It's not enough to actually defeat

the swarm and stop it spreading...

Because a dangerous

combination of unlimited food,

lots of space and freedom

from predators allows some animals

to swarm to biblical proportions.

And when swarms get to this scale,

they also have a dark side.

It doesn't take much to throw

hundreds

of carp into mass confusion.

In seconds,

fear passes from fish to fish...

even though most of them

won't know what they're afraid of.

Because in a swarm,

individuals are so closely connected

that they share moods and reactions.

In the event of danger, a quick,

united response like this

can mean the difference

between life or death.

But, occasionally,

the system goes wrong.

An event sends a contagious

emotion through the swarm

and causes complete chaos.

And, unfortunately, that's something

you see in humans, too.

CHEERING:

When thousands of strangers come

together for a shared experience,

it can create a powerful connection.

When everything's going well,

it can be an incredible experience.

But when the mood changes,

things can get very nasty.

It takes just one event

to cause a crowd

to stampede like wildebeest...

out of control

and with dangerous consequences.

SIREN BLARES:

Anger spreads person to person

till a peaceful demonstration

becomes a full-blown mob.

People stop thinking as individuals

and begin to follow the herd.

Emotions are high

and behaviour starts to change.

Within the group, people start

losing their inhibitions.

They do things they'd never consider

doing if they were on their own.

And because the group makes

individuals feel powerful

and less accountable,

normally responsible people start

acting completely out of character.

So, finding yourself in a crowd

can play a huge role in how you

behave as an individual.

SIREN BLARES:

Now, thankfully, most human

gatherings pass without incident.

But there is a swarm where big

crowds are nearly always fatal.

A plague of locusts is never

a welcome sight for farmers.

But when the numbers explode,

it's also bad news for the swarm.

At peak populations, the locusts

suddenly start craving protein...

..and the meat closest to hand is

the insect ahead.

To avoid being eaten

alive by their nearest neighbours,

the locusts need to keep moving.

This cannibalistic swarm is not just

tearing through the crops,

it's also at risk of devouring

itself.

But overcrowding doesn't always

work against the swarm.

The animal I'm off to see next

has turned

overcrowding into its greatest

asset.

This is a creature found in numbers

so high,

it brings people

out into the streets.

To join them, I'm heading south.

I'm in Texas, home to the largest

gathering

of mammals anywhere on the planet.

Every summer,

as night falls in Austin, Texas,

a seemingly endless swarm

fills the air.

Wow! Look at this. They're just like

flooding out of the bridge right now.

Wow! Look back into the distance,

guys.

It almost looks like a plume

of smoke.

The residents are outnumbered.

Over a million creatures

are swarming the skies.

This bridge is the biggest

urban roost

for Mexican free-tailed bats

anywhere in the world.

Oh, look at this. Look at this.

This has become a real spectacle.

There's just

hundreds of thousands of bats

and they're streaming

out from under the bridge.

This is a colony of biblical

proportions.

So what do the bright lights of

the city have to offer these bats?

Like many riverside cities,

there's a glut of insects

in the summer months.

But what really makes Austin

a bat hotspot is its architecture.

When Congress Bridge

was rebuilt in the '80s,

the new structure was full of deep,

narrow openings.

It was the ideal bat home

and they moved in en masse,

but this convenient city pad

isn't without problems.

Space is limited and the bats

are an easy target

for birds of prey

and other predators.

So, as impressive as this is,

a three-hour drive away, there's

a bat swarm ten times bigger.

And a swarm of this size can achieve

the seemingly impossible.

But getting a good view of it

isn't going to be easy.

This area of Texas is

riddled with caves,

making it the perfect

habitat for bats.

The caves offer them protection from

the elements and from aerial attack.

But to find the real reason

ten million bats flock to this

particular cave...

I need to get much

closer to the swarm.

This isn't going to be

a pleasant journey.

I'm now entering

one of the most overcrowded

and toxic places on Earth.

So, I've come prepared.

Wow. The smell.

Ammonia is actually quite intense.

The caves are piled high with bat

droppings, guano,

releasing dangerously high

levels of poisonous gases.

Levels of ammonia are so high

that it bleaches the bats' fur.

But, amazingly,

the bats themselves aren't harmed.

By slowing down their metabolism,

their bodies are able to

neutralise the toxic gas.

This pile of guano is

absolutely enormous -

it must be metres thick.

That roof is absolutely jam-packed

with bats and look at them.

It's every crevice.

There's a big group of them

right here.

The levels of ammonia are now

potentially fatal

and, without these masks, we'd be

unconscious in a matter of minutes.

Very little can survive these

lethal conditions...

apart from the bats, that is.

If you're wondering what a million

bats look like, it looks like this.

This is one of the most incredible

sights I think I've ever seen.

This is a giant bat creche.

Every year, ten million pregnant

female bats

fly to these caves to give birth.

It's more or less predator-free down

here, thanks to the deadly fumes,

so it's a safe place for mothers

to leave their young

while they go off and hunt.

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