Original subtitles

Animals can sometimes reach such numbers they defy our understanding.

They seem to rise up and invade our lives.

They become Superswarms -

So immense, they are impossible to ignore.

From the outside, they can be the stuff of nightmares.

From the inside, they are a thing of extraordinary beauty.

Among the apparent chaos, something remarkable is going on.

A weird kind of intelligence controls the swarm.

Right now, 8:30 sharp.

It's like swarms right now,

you see, they look like black clouds going across the sky.

At Congress Bridge in Austin, Texas,

100,000 tourists visit each year

to watch an incredible natural spectacle -

1.5 million free-tailed bats leaving their roost for the night.

It's an awe-inspiring sight, that to our eyes looks chaotic.

Inside the swarm, it's a very different picture.

The bats fly in perfect unison, always aware of their nearest

neighbour, chatting together as they stream from the roost.

The tourists sometimes spot a bird diving among the bats,

trying to grab a meal -

this gives even more of a clue as to what is going on.

Slow down the action and what's happening becomes clearer.

For the peregrine to succeed, she must single out a bat from

the masses - an almost impossible task amongst all the confusion.

A red-tailed hawk tries his luck, but faces the same problem.

BATS SQUEAK

The bats' alarm calls warn of danger - they work together.

They drop like stones from the sky

- the sudden change of direction wrong-footing their attackers.

Bats on their own are easier to pick out.

And there is no-one to watch their backs.

By sharing information,

the bats effectively increase their intelligence.

LOUD SQUEAKING

Just 60 miles away, at Bracken Cave, a mothers' meeting is taking place.

Here, female bats gather to give birth.

40 million bats in all - the largest swarm of mammals on earth.

The bats migrate to these maternity caves

from South and Central America.

It's like a giant creche and the mothers don't stop talking.

But this isn't idle gossip - they are exchanging information.

At dusk, the females and young take to the air with a purpose.

It may seem disorganised, but this is flight school for bats.

The young learn from their mother how to catch insects.

Among the millions, she can recognise her own young's call

and they stay together as they fly.

At normal speed, you get a sense of how difficult this must be.

But this Superswarm doesn't exist in any time world we know.

They react many times faster than we can.

The older, more experienced females act like scouts,

leaving the cave first to check that all is clear.

The novices follow, swirling together to form a bat tornado.

This vortex grows rapidly, always spinning in the same direction.

It acts as a beacon, signalling to others that it's time to leave.

The bats also use the vortex to exchange information.

They collectively make informed decisions on where they should go,

based on their experiences from the previous night.

In this gathering, a kind of swarm intelligence is being created

and spread among the individuals.

Other swarms use this behaviour too.

The vortexes created by fish can be so spectacular

they appear almost like an alien organism.

They move like one too -

a creature that shape-shifts before our eyes.

Fish have a lateral line system, sensitive to pressure waves,

that runs like a series of hidden ears along the body.

This picks up the tiny movements of neighbouring fish so they can

mirror each other's actions in perfect synchrony.

The lateral line also detects predators.

Sailfish are built to deal with this super-organism.

They are the fastest fish in the ocean.

But, like birds, they find that dealing with the swarm isn't easy.

If any member of the shoal detects danger,

they use pheromones to warn the others.

With so many individuals on the lockout, their senses are amplified.

It's difficult for predators to take them by surprise.

The Sailfish's gameplan is to divide and rule. Smaller shoals are easier.

They slice through the mass, breaking them into smaller targets.

But chasing even these mini-swarms is difficult.

Only the weak or diseased usually get taken.

The fragmented shoal seeks safety with the master swarm.

In this fish whirlpool, they communicate by resonating

their swim bladders or grinding their teeth.

Together, they become more than the sum of their parts.

It's as if each fish adds its intelligence to the other,

to create a single mind.

The root of such complex behaviour lies with far simpler animals.

This is Mono Lake in California,

a hauntingly beautiful location made famous by it's pumice towers.

Appearances are deceptive - below its calm surface

is a caustic chemical brew in which almost no life survives.

Except, that is, for flies. Brine Flies.

There are billions of them.

Often so deep they blacken the ground.

Their young live in the lake and when they emerge,

they eat nothing but algae.

Visitors can't help but notice

the flies' extraordinary swarming behaviour.

They ripple away from whoever approaches.

It's a game of chasing shadows.

Gulls chasing the flies create the same reaction.

The flies react in a wave,

sensing their neighbour's movements and reacting instantly.

Against such organisation,

the gull's response is about as basic as it gets.

They open their mouths, run, and hope for the best.

It's frustrating work -

for most of the time the flies keep tantalisingly out of reach.

These apparently simple animals have complex behaviour

and are capable of learning.

Working as a swarm, the flies increase their awareness of the world,

making it difficult for predators to catch them.

Fortunately, the flies are so high in protein

the gulls don't actually need to catch that many.

Just 20 flies a day gives them all the calories they need.

The flies are so nutritious,

65,000 Californian gulls come here to breed each year.

In Rome, yellow-legged gulls also adapt their

behaviour to feed on a swarm.

As 10 million starlings stream into the city to roost,

they outnumber the human residents four to one.

Most are young, inexperienced birds.

By flocking together, they benefit from each other's knowledge.

For the gulls, it's like chasing fish shoals in the sky.

They act like fish shoals too -

forever changing shape and re-forming.

The gull attacks, trying to split the flock. The flock regroups.

The starlings' manoeuvres are too quick for a single predator.

The gulls try to turn the odds in their favour by working as a team.

Together, they corral the starlings and try to split the flock.

But the flock grows more powerful by the minute.

As more birds join, they gain strength in numbers.

A peregrine falcon is a greater challenge -

it reaches 220mph in a dive.

The starlings snap together in close formation.

They become a blockade of birds.

The peregrine risks serious injury if it attacks now.

The flock is like quicksilver,

forever splitting and reforming to confuse their attackers.

It's impossible to target a single bird.

Like other swarms, birds create this distracting display

by watching their companions.

Amazingly, each starling tracks the movements

of seven of its neighbours at a time.

By monitoring these seven birds and keeping in formation with them, each

individual helps keep the swarm as a cohesive force.

All this happens ten times faster than a human can think.

We are only just discovering how much information is exchanged

when birds gather in huge numbers.

It's May in Delaware Bay on the east coast of America.

These waders have flown all the way from South America

to coincide with a very special swarming event.

As the birds roost, the invasion begins, cued by the cycle of the moon.

Human visitors usually see them first.

Well, I tell you, this is creepy...

not creepy, but just freaky!

I don't know what they're doing -

are they battling or something over a female? Holy mackerel!

Here's a guy swimming along.

And I just... I love them, they're just so, so, s0...

oh, my God, it's cold! ...So cool.

You know, you're cool and all, but I really don't want you that close to me.

I think I could stay out here longer now my feet have gone numb - Ahhhh!

Dawn reveals the true scale of the spectacle.

It's an event that has been happening for the last 250 million years.

The horseshoe crab is truly prehistoric.

They are more closely related to spiders than crabs.

They chew with their legs and their digestive tract

passes through their brain.

Sometimes known as King crabs, they, appropriately, have blue blood.

Their timing is precise.

They always appear in early May, on the highest tides of the month.

They use an internal body clock.

This is set by watching the cycles of the moon.

Their eyes are a thousand times more sensitive than ours.

They have ten in all and a couple on their tail for good measure.

Good time-keeping ensures that a half a million crabs synchronise

their egg-laying with the high spring tides.

The smaller males cluster around the larger females, fertilising the eggs

that she buries deep in the sand.

Laid high up the beach, the eggs are out of the reach of fish

predators for most of the month.

But these prehistoric creatures hadn't reckoned on the birds.

Horseshoe crabs once walked alongside dinosaurs, long

before birds appeared on Earth.

Evolution never prepared them for this.

The birds snatch any eggs they can.

Fortunately, as each crab lays 100,000 eggs,

there are plenty to spare.

The crabs prefer to sneak ashore under the cover of darkness, but

if the weather is bad, they have to take their chance in the day.

One million shore birds use the eggs as fuel to

power their journey onwards to their Arctic breeding ground. Some travel

ten thousand miles to get here.

Sand-pipers rely on the surf to reveal the nutritious crab caviar.

Although the horseshoe crabs' emergence is remarkable,

the birds' appearance here is even more extraordinary.

Their journeys are governed by a knowledge held by all the birds

- a swarm intelligence based on the collective experience of all.

It is this kind of shared intelligence that drives

one of the most famous migrations on the planet.

Wildebeest may seem familiar,

but look at them from a different perspective

and it's clear that they act as a swarm.

As they cross the plains of East Africa,

following the seasonal rains, they do everything together.

Like starlings, they are hyper-sensitive

to their immediate neighbours and their interactions connect the herd together like a web.

From the air, it's possible to gain a sense of how far the network spreads.

Dotted among the wildebeest are smaller groups of zebra.

They exist as small family groups, even within bigger herds.

Each member reacts intelligently to events. As they join the wildebeest

migration, it's possible to see their different strategies in action.

In common with other swarms, migrating wildebeest are gripped by a collective urge -

nothing stands in their way.

Driven by the will of the herd, they make decisions

that, on the face of it, seem quite stupid.

The river stops them in their tracks

- it's as if the whole herd has to decide together

when it's safe to take the plunge.

Gradually, pressure builds from the ones behind until the front-runners

are left with no option.

Someone has to go first -

but it's the herd that makes the decision.

This is the moment the crocodiles have been waiting for -

with thousands of floundering prey, they should have a field day.

But the crocs soon discover it's not that easy.

Among the mass of bodies and flailing hooves,

the crocs can't single out a target.

Faced by overwhelming numbers, they beat a retreat.

Jumping in feet first has actually worked for the swarm.

The zebras arrive.

Unlike the wildebeest, they prefer to make a plan.

They carefully consider all options before they join the throng.

They deliberately avoid the apparently mindless masses.

Meanwhile, the wildebeest have led themselves up a blind alley.

They are pinned against a wall that is impossible to climb.

The zebra appear to have chosen more wisely,

but independence has its own dangers.

Their well-considered plan didn't account for the crocodiles.

On their own, the zebra are an easy target.

The wildebeest may be floundering, but the mass of bodies pushing

from behind has helped some to start scaling the wall -

probing it for escape routes.

The remaining zebra make it to the other side,

but their problems continue.

The bank is too high to get out.

The wildebeest spread along the bank, testing each section for a possible way out.

Their vast numbers increase the chance of one of them

finding an escape route.

Eventually, some of them are successful.

The masses follow their lead.

Swarm intelligence finally pays off.

The zebra are still paying the price for their independence of mind.

The whole wildebeest herd funnels up the escape route.

As they break down the bank, they make it easier for those that follow.

This fact hasn't been lost on the zebra -

they now have to join the wildebeest.

Despite their apparently mindless approach,

all the wildebeest survived.

The zebra weren't so lucky.

Here it's not brain versus brawn -

it is individual brains versus the intelligence of the swarm.

Although each zebra has a higher intellect, by working together,

the wildebeest herd gains greater wisdom.

It's surely no coincidence that wildebeest outnumber zebra

by nearly ten to one.

This swarm is joined by another - red-billed quelea -

the most numerous bird on the planet.

When they flock together, they also act with one mind.

Although they feed in small flocks, they join up to become a mega-flock

as they make their way to roost sites or waterholes.

The flocks are mixed ages. Most are this year's young -

fledgling birds, just a few weeks old.

LOUD CHIRPING

They are still very inexperienced - their naivety makes them vulnerable.

Their biggest enemy is the lanner falcon.

It soon learns where their watering holes are.

The lanner reaches 150 miles per hour in a stoop.

Taken by surprise, the youngster didn't stand a chance.

The survivors may have had their feathers ruffled,

but they've learned an important lesson.

They are in a quandary.

It's dangerous to drink,

but they won't survive the night without water.

This is where their collective intelligence starts to work.

The flock start to share roles.

The more adventurous resume drinking, but this time,

the more nervous birds act as lookouts.

They watch the braver ones' backs as they drink.

The falcon tries again.

FRANTIC CHIRPING

Quickly spotted, a wave of panic alerts the flock.

Such group tactics work well because every bird has a slightly different personality.

Some are wary and hold back,

others throw caution to the wind, risking all for a drink.

Once the daredevils have finished, they take over lookout duties.

By rotating roles, the flock increases its overall awareness.

Together, they outsmart the lanner falcon.

Safely refreshed, the flock returns to its roost.

But this is not simply a dormitory,

it's a meeting room where almost a million birds exchange information.

In a way not yet understood, the quelea learn from each other.

Prime feeding spots that yesterday

were only known by a select few, become today's star attractions.

They leave the roost with a clear mission on their collective mind.

A deluge of birds now descends on the ripe grass seeds.

The leading edge of the flock lands and begins to feed.

Birds at the back leapfrog to the front of the queue.

This creates a wave of continuous motion -

a rolling flock that devours every seed in its path.

Both wildebeest and quelea show the wisdom of the crowd in action.

But swarm intelligence actually reaches perfection in insects.

A fact some of us may have suspected all along.

Ew...This is gross.

OK, go and move the pillow.

Ah, this is disgusting! Mum, look at...

how many do you think there are?

What do you think these guys are thinking?

We have reason to be in awe of ants.

Slowed down forty times,

these African driver ants are moving house.

The 20 million individuals that make up the colony

have collectively made the decision to move.

They carry their eggs, larvae and pupae with them,

dividing up their tasks according to size.

The workers carry the larvae, while the soldiers hold

the much larger pupae that will ultimately become new soldiers.

It's a huge undertaking, but many claws make light work,

and the entire colony of 20 million individuals relocates

over the course of 48 hours.

The heavily fortified trail can stretch a hundred metres from the

old nest - the equivalent of 11 miles in the human world.

As we all know, moving house is never easy

and the ants' journey is fraught with problems.

A twig blocking their path is like a tree blocking a main road.

Their first job is to identify the problem.

Those first at the scene call for back-up, releasing a pheromone.

The heavy mob arrive and immediately set to work -

they can lift 50 times their own weight.

As well as brute strength, this needs supreme organisation.

They somehow have to all lift and push at the same time -

a challenge that even we find difficult.

Obstruction removed, the traffic soon starts flowing again.

In defence of the trail, the ants take no prisoners,

but even an innocuous-looking insect can be surprisingly dangerous.

The soil millipede is killed quickly, but the soldier's highly-

sensitive antennae immediately reveal that it's poisonous.

The message soon reaches nearby ants. They know exactly what to do.

They gather lumps of mud and bury the problem.

With the millipede out of harm's way, the trail can safely

continue its journey.

But more dangers await the trailblazers.

A praying mantis plucks unsuspecting ants from the column.

He seems to have the upper hand,

but the ants he kills send out a dying message.

Reacting to this pheromone, reinforcements arrive.

The mantis is a deadly predator,

but the ants know exactly what they're dealing with.

One soldier grabs the mantis' jaws,

stopping it from doing any more damage.

Other ants swarm over the mantis,

butchering it with surgical precision.

The mantis' fate is sealed by a clinical decapitation.

The eggs and pupae are taken into the new nest.

Here, they are safe.

The millions of interlocking ants that make up the nest's

superstructure create an impenetrable barrier.

Only from the outside is it possible to get an idea

of the nest's huge scale.

Literally millions of individuals

form a nervous network that communicates using pheromones.

As ants pass messages to each other, they effectively act like brain cells.

Through the millions of inter-connections

they arrive at a decision that works for the benefit of the colony.

Like human brain cells, individual ants are not "intelligent”,

but the links between them create a mind - an ant superbrain.

Deep inside is the queen.

Her role is to replenish the colony by laying 2 million eggs a month.

She is merely an egg-laying machine, under the collective command of all

the ants that make up the mind of the hive.

The ants create a different kind of intelligence -

a brain that exists outside any single body.

Other social insects work in a similar way.

One of the most well-studied is the honey bee.

Like ants, individual bees communicate with others in

the hive and their experiences add together to make decisions

for the benefit of the colony.

This is most apparent when bees create swarms, as they do when looking for a new home.

In their searches, they can turn up just about anywhere

- a disconcerting fact for anyone caught in their path.

They're all right here, man.

Every single one of them.

We'll end up with a whole hive on the thing. Oh yeah.

What seems to us an odd choice is just part of an efficient process

that ultimately results in the swarm finding the right place to settle permanently.

So, choosing a car or a bike isn't necessarily a mistake.

It has plenty of nooks and crannies where they can build their combs.

The first bees to land release a pheromone that guides the others in.

They cluster together in a protective mass.

But as the sun beats down and temperatures soar, they begin

to question their choice.

There is only so much shade to go around.

They fan their wings to keep cool.

But the over-heating bees release a chemical signal

that tells the scout bees that they aren't happy.

The scouts quickly get the message, and set off to find an alternative.

With the sun beating down, it's a race against time.

The scouts look for a cavity large enough to contain the hive.

This shows distinct possibilities.

She inspects the property -

pacing the floor and measuring up, just like a human surveyor.

Once the scout is happy, she leaves to let the swarm know.

Back at the temporary bivouac, she announces the good news by dancing.

But this is a dance with a precise meaning.

The straight part of the dance shows the angle

they must fly to find the cavity.

The duration of her waggle dance shows how far they have to go.

A second's worth of waggles equals half a mile of flying.

Other scouts watch the dance,

following her every move, taking in her directions.

When she leaves, the scouts follow.

With her guidance, this advance party makes a beeline to the exact spot.

Now it's their turn to check it out.

They too pace out the cavity, checking whether they agree or not.

Having all made their assessment,

they hold a committee meeting to consider their findings.

How they arrive at a consensus is uncertain,

but eventually they do.

They let the swarm know the good news.

The scouts rush through the swarm, vibrating their wings

in what is called a buzz run.

This tells the swarm one thing...

It's time to leave.

100,000 bees take to the air in less than two minutes.

The swarm follows the scouts, leading them to their new home.

As more and more bees settle in,

they release a scent that attracts in any stragglers.

Communal thinking is the secret to the swarm's success.

But this kind of intelligence has its problems.

It works best when things stay as nature intended.

But it can't think out of the box.

Even this might not be the disaster it seems.

Many swarms have become successful by being transported

as stowaways around the world.

...Traffic heavy, one mile south of the airport...

These are Fireants. They originated in the jungles of Brazil and arrived

in North America on cargo vessels.

They now infest many airports, homes and public buildings across the southern states of America.

Despite their tiny size, they have the power to close down

airports, traffic control systems and server networks.

Their destructive influence continues to grow.

Computers are especially vulnerable.

Remarkably, it's the electricity that they like.

Their antennae are electro-sensitive and the ants react

to electrical charges by attacking them with their jaws.

The soldier ants also like the sweet taste of the terminals

and they can't resist having a nibble.

All this activity creates problems and leads to dangerous

short circuits as their jaws and legs touch exposed circuitry.

They are now creating havoc

over vast areas of the southern states of America.

Having come from the rainforest, the ants are used to this kind of weather.

But unknowingly, the ants have built their nest in a drainage ditch.

Flooding is a challenge for even the most intelligent swarm.

The ants start an evacuation, moving the nest to higher ground.

It's women and children first,

as the ants carry the queen and her pupae to safety.

But still the water rises.

The ants react by linking arms together, forming a mesh of inter-connected bodies.

Between them, they are making a life-raft.

The ants' most precious cargo,

the eggs and remaining pupae, are safely stowed on top.

Flying ants also board - like helicopters on

an aircraft carrier, ready to lift off to start a new colony

if the raft gets into trouble.

Remarkably, some of the pupae are set aside to

act as flotation devices, to help keep the raft afloat.

As the water level rises further, the raft detaches

from its moorings - it is now at the mercy of the wind and water.

Some of the workers paddle with their front legs,

giving the elements a helping hand.

On the top deck, the workers tend the pupae and larvae.

Below deck, workers clean and maintain the underside of the raft.

As the raft approaches land, it begins to change shape.

The ants start building a pontoon from the raft that

reaches towards the bank.

The individuals are working as a unified team

for the benefit of the whole colony.

As fingers of ants reach out,

they show swarm intelligence working to perfection.

As more ants add to the pontoon's length,

it becomes a bridge to the land.

Once contact is made, the most precious cargo is unloaded first.

Like a team of porters, they ferry the pupae to the shore.

The next generation is safe.

The queen is next to disembark - the colony's future is assured.

Using their incredible swarm intelligence, fireants are taking on the world.

As well as invading America, they have started to colonize Australia.

With global warming, they are likely to invade Europe,

as far north as southern England.

They are the swarm of the future.

As we have explored the world of the swarm,

we discovered how they profit on the back of our success.

How they feed off our agriculture

and take advantage of the new environments we create.

We have seen how they can erupt at any time - taking us by surprise.

And how they have hitched a ride with us around the world.

We have seen how even simple organisms can create spectacles

that can be awe-inspiring and beautiful.

And also how they can become the stuff of nightmares.

We have seen how swarms can learn from their collective experience.

And how they can act as a single organism.

We have even seen how looking at swarms is like looking

into the inner workings of an alien brain.

But this is one swarm that we have yet to feature -

one that may even help to save the world.

These little known creatures are salps - a sea creature that

in fact is more closely related to us than the jellyfish it resembles.

They come in many bizarre shape and sizes.

Many are joined together to create daisy chains - some a mile long.

At night, all across the oceans of the world,

they rise to the surface in their billions to feed.

Recently, their numbers have started to increase

and swarms now cover thousands of square miles.

They eat the algae that absorb our greenhouse gasses and then

safely lock the carbon away at the bottom of the ocean.

An average swarm removes an incredible 4,000 tons of carbon each night.

They are a growing swarm with the power to help save our planet and

their significance has only just been discovered.

They are living proof that we should never underestimate the power of the swarm.