All language subtitles for Super Senses 3of3 Scent 720p HDTV_Subtitles01.ENG

Our human senses are incredible.

We have excellent vision.

Precise hearing.

And can detect the slightest
fragrance drifting on the breeze.

But we only experience a tiny
fraction of what's out there.

Imagine a world where you
could see with sound.

These images are just phenomenal.

Hear thunderstorms from hundreds
of kilometres away.

That's incredible.
They've all stopped.

Imagine seeing the world
in slow motion.

Or through some of the sharpest
eyes in nature.

HE GASPS

He's so fast!

Travelling to some of the wildest
places on Earth...

We reveal the strange and wonderful
world of animal senses.

Light is emitted. Look at that!

Another one!

This is brilliant!

I'm Dr Helen Czerski.

I'm a physicist and I want to find
out how animals tap into an amazing

range of light, scent and sound.

I'm Patrick Aryee.

And as a biologist, I'm fascinated
by what the world appears like

through animal senses
far superior to our own.

In this episode,

we are on a journey through
the invisible world of scent.

To discover the bizarre
and extraordinary ways

creatures use their sense of smell
to survive.

Experience the world
through animal senses.

The plains of Africa.

As I walk through this landscape,
my eyes see the golden sunlight.

And my ears hear exotic birdsong.

But there's another sensory world
here that I can barely detect.

In the air are millions of minute
scent particles,

given off by the earth...

..by plants and by animals.

Our human noses pick up only a tiny
fraction of these smells.

But for any animal that lives here,
this is vital information.

In this landscape, scent is king.

On the plains of Africa,

smell is crucial to the survival
of most animals.

And over millions of years

life has tapped into this invisible
chemical world

in some extraordinary ways.

The Great Migration,

where more than a million wildebeest
journey across the savanna,

is driven by scent.

Each wildebeest leaves a trail
of a musky odour that others follow.

Scent keeps these herds
together on their epic journey.

Lions also produce
a distinctive scent

and cubs recognize their mothers
through her unique smell.

But there are some unlikely little
creatures that also survive out here

thanks to their amazing noses.

Meerkats.

I'm going to spend the day with them
to see just how they do it.

These meerkats have just come
out of their burrow.

The gang is made up of 14 adults
and four newly emerged pups,

and they're just heating
up as the sun rises.

These pups are just enchanting,

and they're only about
four weeks old.

You can see they are sticking
very close by.

With pups around, the gang must be
extra vigilant.

And whilst meerkats are known
for their excellent vision,

it's their long pointed noses that
can offer vital surveillance.

Meerkats are constantly alert.

And whilst this sentry is on the
lookout for any predators

in his visual range,

Meerkats can smell danger
long before they see it.

And that's their way of keeping
their pups safe.

Meerkats have many predators...

like jackals

and cobras.

Their predators may "appear"
camouflaged,

but they cannot hide their scent.

Wherever they go,
they leave minute traces.

To show how well their noses are
tuned into these dangerous smells

I've got a little test.

Now, this set up might seem a bit
strange, but inside this bag

I've got a small rock with a piece
of wildcat hair attached to it.

Now, wildcats are one of the major
predators of meerkats -

so let's see what happens
when I put it down here,

a few meters from where they're
foraging.

It takes just a few moments for the
scent to reach the meerkats' noses.

Ah, you can see they've definitely
picked up the scent

and now they're coming in.

And you can see that classic
mobbing behaviour -

their backs are arched,
their tails held high.

And they're all clustered
together as well.

It's a powerful display of how
finely tuned

the meerkats' noses are to danger.

But it's not the only way these
little gangsters

use their sense of smell.

They also use it to
defend their patch.

Meerkats spend their lives
constantly locked in a turf war

against rival gangs,

so it's absolutely crucial
they can identify friend from foe.

Meerkats are highly territorial.

Scraping out a living in this
arid desert is tough,

so staking claim to their patch and
food source is an absolute priority.

They do this by scent marking.

It's such a powerful instinct.

If anything new is placed in their
territory - like this stick -

they have an irresistible
urge to mark it.

OK, here we go. It looks like
one of the more dominant meerkats

is about to stake its claim.

And it's scenting all over
the post -

making clear that it
belongs to this group of meerkats.

Meerkats produce the scent
from glands just below their tails.

There it goes.

And there it goes, again.

Anything unfamiliar,
any object in their patch,

they'll want to claim as their own.

Now, I've got a rather
mischievous trick.

I'm going to take this post
and present it to another gang

to see if they recognize
their rival's scent.

This marks the border between two
rival gangs of meerkats.

And visually there's not much to
see,

but if you could enter
their olfactory world

you'd see this entire area awash
with odours and meerkat scent.

This heavily scented area is

a meerkat's equivalent
of a no trespassing sign.

For a passing meerkat from a rival
gang,

you'd cross this border at your
peril.

I set up the post close to the
rival's burrow.

Within minutes
they pick up the scent.

Here we go. We've got a meerkat
coming up to our post.

And now more of them are coming in.

So, they've detected that
the scent that's been left

is from a rival meerkat.

And now they're on high alert.

And one of them
is standing on its hind legs -

and its eyes are trained
on the horizon.

He's trying to see
if he can spot an intruder.

And if he were to see a rival
meerkat,

it would rally the rest of the
troops into a violent attack.

Using their noses,

meerkats detect dangers their eyes
and ears just can't pick up.

Scent is hugely
important in their world.

And there's a good reason for this.

Leave some water out in the open and
it quickly evaporates in the heat.

That's exactly what happens with
scent as it disperses into the air.

And that's why places with warmer
climates

have more smells in the atmosphere.

For the meerkats, this vital
source of sensory information

is key to keeping the gang safe.

The meerkats are back from their
days foraging,

safe and sound in their burrow

and the young pups are accounted for
as well.

And that's in part thanks
to their amazing little noses

that act as excellent early warning
systems.

Although meerkats are brilliant at
detecting lots of different smells,

their noses aren't very
sensitive to tiny traces of scent.

But in the frozen wilds of Alaska,

there's one mammal that can sniff out
food from more than a kilometre away.

That requires one of the most acute
noses on the planet.

You know those cold, clear days

where the world just seems to be
fresh and clean?

One of the reasons that everything
seems so clean is that

you actually can't
smell most of what's going on.

And that's because cold environments
like this one

make it a lot harder for those scent
molecules to evaporate

and to drift up into the atmosphere.

And just to show you how
cold it is, look at this.

I've got a beaker here full of just
boiled water. Watch.

At minus 20 degrees Celsius,

the boiling water freezes before it
hits the ground.

If you're a carnivore and
you can survive in this environment,

you need a really impressive
sense of smell.

And there's one tenacious mammal
that thrives here

thanks to its extraordinary nose.

It's the giant of the weasel family.

The wolverine.

Wolverines are scavengers,
and they're really good at it.

They can travel up to 25 miles a day

through terrain like this
looking for food,

and what they're
looking for is dead animals

that are buried underneath the snow.

Their Latin name is brilliant,

it's Gulo gulo,
which means the glutton,

and they're voracious eaters,

they chomp trough a carcass,
bones and all.

To find out how they locate their
food in this frozen wilderness,

I've come to meet one of the world's
only habituated wolverines.

A two-year-old orphan named Jasper.

Jasper was rescued by arctic
wildlife expert Steve Kroschel,

who exercises him on a lead to
contain his boundless energy.

So, he's sniffing around all
the time,

getting used to the environment?
Yes. Never a dull moment.

They're always very active,
their metabolism is very high.

No such thing really as a fat
wolverine.

And they don't hibernate,
like a bear.

So, they just keep going all winter?
That's right.

They don't have much time,
it's all about survival, you know,

and mother nature doesn't give an
animal like this

a lot of margin for error.

As scavengers, most of a wolverine's
diet is dead animals.

And to find their food,

wolverines take advantage of one
of nature's most destructive forces.

Avalanches.

As snow thunders
down the mountainside,

mammals are often buried beneath.

And it's thought that wolverines can
sniff out frozen carcasses

even deep beneath the snow.

I want to put this to the test,

so I'm going to bury some meat
and leave it for several hours.

Then, I'm going to see
if Jasper can sniff it out.

I could walk along this path now

and never know that the
chicken was down there.

But here's the amazing thing.

Even though it's frozen solid,
and it will stay frozen solid,

molecules of that chicken
are evaporating in tiny quantities.

They're drifting out through the
snow and out into the air just here.

I can't detect them, but a wolverine
could use them to find dinner.

Before we set Jasper his challenge,

I'm going to demonstration how our
noses and the wolverine's work.

To show you I'll need an orange.

When I sniff the orange...

It's really strong, this one.

..is that the scent molecules from
the orange are going up my nose

and they're going up to the top here,

and there's a structure up here
called the epithelial membrane

and that is where the odour detectors
are.

It's thought smell works like a lock
and key.

The scent molecule is the key
and will only fit certain "locks" -

the odour detectors.

We have 400 different types of locks.

But scent molecules can hit many
combinations of detectors

so we can identify
thousands of different smells.

And that's how its works
for everything you've ever smelt,

from new shoes to perfume to oranges,

it's all about the combination of
receptors that those molecules hit.

All mammals detect scent in this way.

But for wolverines
it's all about sensitivity.

Detecting the tiniest traces of
scent, even deep under the snow.

So, let's see how Jasper
gets on with finding the buried meat.

We start several hundred
meters away

and let the wolverine
choose his course.

He's smelling things right
now, Helen.

And it is not only what
is on the snow,

it's the air drifting past
that he's smelling.

Oh, having a bit of a sniff here.

He quickly picks up a scent,
but is it the right one?

He definitely knows there is
something here.

He's onto some scent there,
for sure.

Those big paws are pretty
efficient, aren't they?

Yes. He looks like nothing will
get in his way.

He's shifting a lot of snow. Yeah.

Oh, they're we go - he's got it!

He got it. He found it.

He might even recache it
if he's not all that hungry.

In the wild, wolverines cache,
or bury, their food

so they can eat it later.

He's heading for a hole over here.

Oh, he's going to put
it in there, isn't he?

Straight in there.
So, that's his larder now in there.

So, Jasper succeeded in sniffing
out the buried food.

I couldn't smell a thing.

But if their noses
work in the same way as ours,

why is their sense of smell
so much better?

It all comes down to an extraordinary
adaptation inside their noses.

This is the skull of a wolverine.

And the really interesting bit
is his nasal cavity, which is here.

If you look straight down it

what you see are these amazing
honeycomb structures.

This is where the scent
detectors are found.

The honeycomb pattern greatly
enlarges the surface area

so there's room for many more
detectors.

Unravelled, it would be the
size of a plate.

We have a similar structure,

but ours is only the size of a ten
pence piece.

It means that up the nose of a
wolverine

is an enormous detector for scent.

In fact, the wolverine's nose has
twice the surface area

of a bloodhound's -

a dog purposefully bred for its
amazing sense of smell.

That's how they're able to
track down frozen carcasses

even deep beneath the snow.

And it's their secret to
survival in this icy world.

But one creature has evolved an even
more precise way of detecting scent.

They can smell the world in stereo,

allowing them to pinpoint prey with
deadly accuracy.

Rattlesnakes.

For decades, a mystery has
surrounded exactly how these snakes

are able to hone in on their prey.

It's only now that we can
unlock their sensory secret.

The answer lies in the unique way
it smells the world

and the brilliant way it
uses its venom.

I've come to the great prairie
lands of Colorado

to see these snakes in action.

And I've teamed up with
Professor Steve Mackessy

who's advised me to wear snake-proof
boots.

Steve, where's the best
place to find some snakes?

Well, we have a rattlesnake den
site about 30 meters up ahead here.

And we're going to see
if the snakes are out and about.

So, watch your feet.

Right. So, how many snakes are we
likely to find today?

Well, we could find as many as...

HE GASPS

There's one! There's one there!
Look! Look!

Oh, my goodness. There it is.

They move so quickly.

That rattlesnake was perfectly
camouflaged,

we had no idea it was there.

Oh, lordy, lord.

I think it's pretty clear they're on
the move today. Yeah.

I'm going to be a bit more careful
because after seeing that snake

I can tell you I've got goosebumps
all over my skin.

But to show how rattlesnakes use
scent to hunt down prey

I need to get closer.

A lot closer.

Luckily, the next snake
we find is a little calmer.

And reveals its extraordinary
sensory trick.

Now, you can see that tongue
flickering in and out of it's mouth.

And what it's doing is using that
tongue to pick out

the scent molecules in the air.

Some of which I'll be giving
off right now.

So, he can taste my presence.

For the rattlesnake, its sense of
taste and smell are the same thing.

When it detects a scent, it brings
its tongue back into its mouth

and presses
it on a patch of sensory cells.

This highly sensitive area
identifies the smell.

It's called the Jacobson's organ,
and this is what gives

the rattlesnake its serpentine
supersense.

But this is just part of the story.

Many rattlesnakes are strike
and release predators.

They lie in wait,

strike their prey just once
then let them go.

But the venom doesn't kill
immediately,

so the prey can move a distance
away before the toxins take hold.

This presents a huge sensory
challenge for the rattlesnake

because now they must
track down their dinner

in these wide-open prairies.

And that can be like finding
a needle in a haystack.

Within these vast grasslands
are a complex and tangled network

of scent trails left by countless
mice and other small mammals.

So, even with this supersense,

a rattlesnake somehow needs to
distinguish between all

the other mice and the one that has
been injected with its venom.

How do they do this?

I'm hoping this test will offer
an intriguing clue.

Using sponges, I lay two trails in
the sand.

The one on the right contains
the scent of rattlesnake's venom.

The one on the left doesn't.

Which one will the snake follow?

So, you can see our snake is
already on the trail.

The forked tongue gives them
their directional sense of smell.

This snake is detecting more scent
molecules on the right fork,

so is moving in that direction.

He's using that forked tongue to
pick out the scented sponge.

Look, he's going the right way now.

It's a great demonstration of how
a rattlesnake

will find its prey in the wild.

There you go,
it's right by the sponge.

I really wasn't sure
if our experiment was going to work.

But it goes to show that the
rattlesnake's sense of smell

is absolutely remarkable.

The snake followed the trail that
containing the venom.

So, it seems there's something
in the deadly toxin that allows

the snake to track down its prey.

But what is it?

Steve has been carefully extracting
venom to unravel this mystery.

So, when you have them up
close here you can see fangs.

Yeah, I can see them.

So, using these capillary tubes

we should be able to get
some of that venom out. Right.

Prairie rattlesnakes have long,
delicate fangs.

That's why the snakes release their
prey as soon as they've struck.

It means the fangs don't get
damaged.

Wow.

So, I'm going to put
this in our tube here. Yes.

That's incredible.

HE EXHALES

Rattlesnake venom contains more than
100 different molecules.

By freeze-drying it and isolating
all the components, Steve discovered

a group of molecules that appear to
help the snake track its prey.

They're called disintegrins.

Well, the disintegrins seem to
act as a chemical tag,

so it's marking of prey that's
been bitten by the rattlesnake as

the envenomated prey, and that's
what lays down the chemical trail

that the snake is following. Yeah.

And so by using that very exquisite
sense of taste and smell,

the snake is able to follow the prey
very, very carefully and very,

very exactly to where
it's run off and expired.

Disintegrins are the mystery
molecules in the snake's venom

that allows them to track
down their prey with such precision.

In the rattlesnake's world, where
the ground is awash with scent,

this is how they find their dinner
in

the vastness of the great American
prairies.

So far we've seen how animals are
able to detect

tiny traces of scent
in the air around them.

But it's an amazing thought
that our oceans are also awash

with different smells.

And creatures beneath have developed

even more sophisticated ways
of sensing them.

I'm just off the Bahamas
and I'm here to show you one of

the most powerful
uses of scent in the natural world.

In our oceans, there's a complex mix
of thousands of chemical compounds

carried on swirling currents.

And I'm in search of a master
of this sensory world.

The shark.

These sharks are swimming through
a world that I just can't sense.

But they're masters at it.

The water all around me here is
full of tiny amounts of chemicals

that I can't detect.

But there's a huge amount of
information

just flowing around my head.

And these animals,

they're fantastically well equipped
to swim through this world

and to be able to decode that
information and use it to survive.

I want to discover the extraordinary
way sharks use scent

and debunk an age-old myth
about their thirst for blood.

But to start with,

I want to find out how they are able
to smell underwater.

For that I need to get
hands on with a baby lemon shark.

Look at this, I'm holding a shark.
I've never done this before.

He's quite calm down here,

but there is a trick where we can
calm him down a little bit more.

What I'm going to do is turn him
over.

If I turn the shark
upside down he becomes very passive.

It's called tonic immobility,

and it gives me a chance to look at
his nostrils.

As water flows through the nostrils,
or naries, it enters

the olfactory chamber, lined with
hundreds of thin membranes.

These are covered in odour detectors.

And the water is always flowing in
the same direction

so the sharks are smelling
continuously.

It's a brilliant system,
but just how sensitive is it?

To find out I've teamed up with
shark biologist Dr Tristan Guttridge

to test a scent that
sharks are renowned for detecting.

The smell of blood.

So, we're standing in a pen of lemon
sharks here.

Yup, these are semi-captive pens.

As you can see, they are exposed to
the ambient conditions,

and we have about 12 juvenile
lemon sharks.

And as they are swimming along,

they are continually sensing
the water around them.

Exactly,
so they will be swimming around

and they're determining whether
there is something interesting.

And if there is anything
interesting that smells good,

they'll then direct themselves
towards that source.

And what sort of thing interests
them?

These little lemon sharks,
they feed primarily on fishes.

So, they will be sniffing
around hunting for fish.

To start our experiment,
I take a sample of fish blood.

I'm going to release a tiny amount
into the water to see if they react.

We're looking for a corkscrewing
behaviour,

where the sharks turn repeatedly.

It's a sign they've
detected the smell

and are trying to find the source.

There you go.

Oh, he turned.

So they're all turning now, looking.
Yeah.

That guy in particular

just turned around at least
three or four times -

there you go, he's trying to find
it on the floor.

See this one here turning as well?

He knows what's going on.

And now all of them are interested.

Oh, they've all come in,
look at that. Yeah.

So just a few drops of fish blood
triggered this response.

But what about human blood?

It's been said that it can attract
sharks from many kilometres away.

So it's spreading out
just like the fish blood did.

Let's see what these guys do.

No change whatsoever -

still in their nice, big
circle formation.

Let's see if they come through
it again - these two here.

Yeah, they would have
picked it up by now.

So they're not interested in humans
or human blood at all.

No. We're intact and they didn't
react to the human blood.

Our simple test shows these sharks
are not attracted to my blood.

And despite many myths,

there's no evidence to suggest that
larger sharks - like great whites -

are interested in human blood either.

But there is one mysterious scent
that all sharks detest.

In fact, it's so reviled
by these predators

that it's currently being trialled
as a shark repellent.

So we've come to a reef where sharks
gather in large numbers...

and I've been
volunteered as a guinea pig.

There's a lot of sharks down there.

The plan is to go down to let
the sharks get used to my presence,

and then to release this
and watch how they react.

Three, two, one - jump.

The sharks come right up
to investigate.

Their noses are detecting the
minute chemical cues

I give off as I move
through the water.

Look at this!

They look bigger down here
than they looked up on the surface!

Oh...

I just love it being down here,

sitting in the middle of all this.

You can see their nostrils
right on the front of their snout.

Imagine water coming towards them -

so they're taking it into this
chemical laboratory

that's inside their nose.

They're amazing animals.

When the sharks are really close,
I release the scent.

They've gone.

All the other species are still here.

The sharks have vanished.

So why are sharks
so repulsed by this mystery smell?

Dr Patrick Rice is a marine biologist
who studies shark olfaction,

and he's helping to develop this
shark-repelling scent

called a necromone.

A necromone is a chemical signal

that tells sharks that there's
other predators in the area.

There's evidence from nature
that when a predator comes in

and eats another shark,

the little bits left behind
may start to decay

and emit this signal,

and that chemical signal

tells a shark that
there's a predator in the area.

So it's a protective thing -

so even though we think of sharks
as being invincible,

they're actually - even they have to
look out for themselves.

That's correct.

Necromones -
or the scent of dead shark -

are a sure sign
there's danger around.

So sharks are hardwired to flee
when they detect it.

It's believed this is a response
they've had since prehistoric times.

So this evolved at a time
when sharks weren't top predators -

they were just little
things in the sea,

and they were basically food for even
bigger animals. That's right.

There was a monster shark called
the megaladon -

a prehistoric great white shark
that was about 60 feet long,

and it preyed on everything,

and it was the king of the ocean
at the time.

And today they're still vulnerable.

Almost half of baby sharks don't
survive their first year -

many because they're
eaten by bigger species.

Even the most feared ocean predator -
the great white shark -

can be attacked by a pod
of killer whales.

So the ability to smell danger
is still key to their survival.

Although sharks detect scent
underwater,

their noses work in a similar way
to ours - and other mammals.

It's all about taking scent
inside the body

and analysing it.

But some creatures smell the world
through the outside of their bodies,

and that allows them to use
scent in even more complex ways.

BUZZING

Bees.

Their world is controlled by smell.

And if you can tap into this, you
can harness the power of the swarm.

I've come to Arizona's
Sonoran Desert

to show the overwhelming
power of scent in the bee's world.

This is a swarm of European
honeybees,

and there must about 5,000 of them.

And I'm going to move them
from here...into here.

And I'm going to do it simply by
tapping into their world of scent.

And this is my secret weapon.

This is amazing.

You can see all
the bees are reacting,

and they're instantly
swarming into the case.

And it's that sense of smell

that's driving that behaviour.

The bees are reacting to minute
traces of scent in the air.

A scent I can't pick up at all.

In humans, we smell by breathing,

but bees detect scent
in a completely different way.

They use their antennae
and that's what they are doing here.

Capturing that scent
and moving towards it.

Their antennae are packed
full of odour receptors,

which pick up scent molecules
as they fly though the air.

Just look at that -

virtually the entire swarm
is now in this case.

But what's the secret
to my bee trickery?

It's all to do with a group
of odours called pheromones

that bees use to communicate.

It's as if they can talk
through scent.

My secret weapon was
a synthetic pheromone

that exactly replicates the one
produced by the queen bee.

It encourages the workers to
surround her,

and that's what's happened here.

The bees have detected the scent
and moved into the case.

So there we have it -

5,000 bees in a briefcase,

simply by the power of scent.

This is just one example of how bees
use odour to talk to each other.

They have a language of scent -

with more than 15 pheromones

triggering wildly
different behaviours.

They use them to navigate,
find food and to reproduce.

But there's one pheromone that
triggers a response so dangerous

that it can only be studied
well away from human habitation.

To see this in action,

I've come to a remote research base
deep in the desert.

This is home to some of the most
dangerous insects on the planet.

Behind me are hives
full of Africanised bees,

also known as killer bees.

And to protect their home,

they'll wage war on anything
or anyone that approaches.

And they do this entirely
through their sense of smell.

I've teamed up with entomologist
Dr Steve Thoenes

who is studying what makes this
subspecies of bee so aggressive.

Once a month, he checks
on the health of the hives.

To do this, he has to get up close.

Here we have the research
apiary for Africanised bees.

Africanised bees have a
lot of good qualities.

They are very hard working,

they produce a lot of honey

and they don't get any of the
diseases that European bees do.

Their problem is

that they are really, really
defensive of their nest.

If you disturb one bee,
she will release alarm pheromone.

The alarm pheromone spreads,

and you have this whole cascade
where up to 50% of the workers

will come out to defend their
colony. Wow.

The main area that Africanised bees
are going to come is at your face

because they have been attacked
for millions of years by mammals.

And we all breathe in oxygen and
we breathe out CO2... CO2, yep.

..so they are going to come
right at the CO2 source,

which is your mouth and nose.

Just don't panic.

Let's get you all suited up,
and we'll go look.

In defence mode, the bees will find
any chink in our bee armour.

So nothing's left to chance.

Steve uses smoke to
keep the bees calm.

This blocks the scent
receptors on their antennae,

making them less sensitive
to alarm pheromone.

But it doesn't last long.

So, Steve, we've got our smoke,

which is going to pacify
the bees, yeah?

Yes, that's the best tool
a bee keeper has.

Gosh, I can feel my heart beat.

I've been nervous around bees
since I was a child,

so I'm going to have to overcome
one of my greatest fears.

How long do you think
we'll have here?

Couple of minutes.

Let's see what's inside of here.

OK, they're coming at me.

They're definitely
interested in what we're doing now.

They're getting very,
very defensive.

This is serious.
This is serious stuff.

This is just starting.

Oh, you're joking.

Steve needs to check
through the hive

to ensure the honey stocks are good,
and there's no sign of disease.

But his work triggers the bees
to start releasing alarm pheromone.

And when one starts -
others quickly join in.

Oh, whoa.

Oh, wow.

Wow!

Oh, Lord.

Oh...

Within minutes, thousands of bees
are in the air

and in full attack mode.

So this is the defence
of Africanised bees.

Where they've coordinated
all this by odour,

and there's an odour in the air.

You can smell a little of it.
That smells...

That smells just like... Bananas.
..off bananas, yeah. Right.

And that's the alarm pheromone
that the humans can smell.

And they're coordinating their
attack by releasing alarm pheromone

and responding to that.

How does it feel to be
a predator of bees?

I don't want to be
a predator of bees!

I want to leave them alone. OK.

Despite our hostile reception,
it seems all is well with the hive.

So the brood's good,
the honey stores are good

and the whole hive is thriving.

Great. It's time for us to, er,
get out of Dodge!

It's getting too much.
OK, I'll put it back together again

and we can head off down towards
the truck. Let's do that.

It's been a stark demonstration

of the power of scent
in the bees' world,

and I'm just happy
to be heading back.

That was overwhelming.

There must have been 5,000
Africanised bees

swarming all around us.

We've left the hives,
but they're still following.

This has got to be
one of the ultimate examples

of how an animal uses scent
to defend their home.

The intricate ways bees
use scent to communicate

have made them one of the most
successful insects on Earth.

But when it comes to detecting
tiny quantities of scent

from a long way away,

the ultimate prize goes to
another extraordinary insect.

Moths -

one of the planet's best smellers.

Their supersized antennae
are like feather dusters,

sieving the air for minute
molecules of scent.

Some species can pick up scents
from nearly five kilometres away.

I've come to meet one particular moth

renowned for an amazing
sense of smell.

This is the tobacco hawkmoth -

they're really large moths
that live in America,

and that thing that's really
distinctive about them

is that they're able to hover,

so they look a bit like the
hummingbirds of the insect world.

And the thing about the hovering
is that it's really energy expensive,

and so these moths need
a constant supply of food.

When they're active,

they need to feed every 15 minutes.

And they're capable of flying
80 miles in a single night

just to find food.

Which is a tall order

if you're only this big.

These hawkmoths
feed on nectar from flowers.

Like most moths,
they're only active at night.

So all they have to guide them
through the darkness

are minute wisps of scent
blowing from the flowers.

To reveal the fascinating
way they do this,

I've set up a hi-tech smell test.

Using a wind tunnel,

and their favourite food source -

a petunia flower -

I can recreate their natural
feeding conditions.

In pitch darkness,
with a night-vision camera,

I'm going to see how quickly these
moths can track down their food.

When I switch the wind tunnel on,

the breeze will carry odour
molecules downwind

and down there
a moth might detect them,

and then it's got some
detective work to do,

because it's got to solve the puzzle
of where the scent came from.

And that is not as simple
as it sounds.

The fans create swirling eddies

of turbulent air -

like a windy day.

If we could see
the flower's fragrance,

it would appear as delicate wisps
or patches of scent

constantly on the move.

So, for the moth, working out where
that smell is coming from

is a real challenge.

Once inside the wind tunnel
he zigzags back and forth,

trying to find the tiny
traces of scent.

The patches of odour
that the moths have to detect

could be just a few
millimetres across,

so at the speed these moths
are flying,

it would be really easy
to miss the signal.

So, for the moths,

it's not enough to be able to
smell well -

they've also got to be able to
smell at high speed.

We can identify
less than one smell a second.

That's because it takes time
for our noses to refresh

and detect something new.

But these moths smell
more than 30 times quicker.

And because their antennae
are constantly being refreshed

they can detect
and follow the tiniest traces scent.

And that's how they are able
to find the source of the smell

and feed on the sweet nectar

that's so valuable to them.

It's taking these moths
a lot of energy to stay in the air.

They're probably beating their wings

30 to 40 times a second.

For all organisms
there has to be a balance

between the energy they take in,
they eat,

and the energy they need
to expend to live -

and if you look at way these
moths are flying,

they're using up a huge amount
of energy just to stay in the air,

so they must need a lot of food.

And if you're in that situation,
the best thing you can do

is be as efficient as possible
about how you find it.

And that is what their sense
of smell is all about.

In the wild,
these amazing hovering moths

use their supersensitive antennae

to find flowers from several
kilometres away -

something they could never do
through sight or hearing.

For me, this is the most
incredible example

of how an animal uses scent
to survive.

Our journey through the world
of smell is almost complete.

But there's one creature that's
harnessed the power of scent

in a highly unusual
and unwelcome way.

They produce an odour so potent

it should only be handled
with extreme caution.

And the fumes it gives off
are so volatile

they light up with a bang.

So what animal produces this
unholy odour?

Meet the striped skunk -

one of the world's smelliest
creatures.

I've come to northern Arizona

to discover the amazing way
these little mammals use scent

to protect themselves.

To experience it first-hand,
I'm joining Kevin Overfield,

who rescues skunks

that have caused a bit of a stink.

Basically we go to homes,

people that are having nuisance,
animal problems -

like the skunks are living
under their house or under a deck.

We go over there, we set a live trap
so that the animal's not harmed,

and we trap 'em
and we bring 'em back to my home.

Once we know that they're healthy
and not sick

we take them out and release them
in the woods,

back in their natural habitat.

Kevin has a skunk
that's ready for release.

And he's kindly offered me
the chance to help him out.

So what can I expect when we
try and put this skunk in a cage?

You can expect to be sprayed.

OK. And what's that musk smell like?

It's really hard to explain -
there's no other smell like it.

You can taste it, you can smell it,

you know, you can almost feel it
sometimes, it's so powerful.

PATRICK CHUCKLES

So you know when you've been
sprayed by a skunk. Definitely.

You know when you've been sprayed.

OK. Well, here goes.

We're going to move up slow. Yep.

Be aware where the cage is -

the cage is going to be
right here, OK? OK.

Now, just kind of
move up on him real slow. Mm-hm.

OK.

OK, there's your chance.

There you go.

OK, now hold him there.

Hold him like I told you. Yep.

OK.
SKUNK SQUEALS

KEVIN LAUGHS
No, put him in the cage!

There you go, got him.

Oh... Oh, God, that's disgusting.

Good job.

PATRICK COUGHS

It smells of burning rubber,
stale urine and rotten eggs.

HE COUGHS HEARTILY

If you've got it on your face,
just keep spitting.

Ugh, right up my nose. Ugh.

Augh!

Straight in the face.

If you look at your glasses,
all the yellow on your glasses,

that's all skunk spray
and on your forehead.

They can aim.
They can aim very well.

I think you did a good job.
Oh, yeah...

I'll hire you.
PATRICK LAUGHS

But why do we find this smell
so unpleasant?

So, this is it.

This is the skunk's secret weapon.

It's made up of seven volatile
compounds called thiols.

But it's one element within these
that causes the stink.

The reason we find this substance
so repulsive

is because it contains sulphur -

now, from an evolutionary
point of view,

sulphur is associated with areas
of low concentrations of oxygen

and rotting food, so we do our best
to stay away from it.

Skunks use their sulphurous
scent to defend themselves

against predators -
like mountain lions.

They can spray it 15 feet,

and aim for the eyes,
causing temporary blindness...

..giving the skunk time to escape.

But their foul smell is precious.

They only carry enough
to spray about five times,

and then it takes ten days
to replenish.

So skunks only pull
the trigger as a last resort.

That's why they've come up
with an ingenious way

to advertise their potency.

Perhaps one of the most obvious
things you notice

when you first see a skunk
is that magnificent white stripe.

It's used as a warning
to other animals.

It says, "Stay away -
I am a skunk and I am toxic."

It's believed the skunk's odour
is so notorious

that their colouring alone
is enough to deter predators.

So what happens when an animal with
one of nature's most sensitive noses

spots those bold warning stripes?

I've come to a bear
park in Arizona to find out.

So here's the plan.

We've rustled up two decoy skunks -

one with that classic black
and white stripe

and one which we've dyed
completely black.

Now, in theory, any foraging bears
should have no problem

approaching our black skunk -

but they should avoid
this black and white one,

because they associate
these markings

with that foul-smelling musk.

The stunt skunks are placed
inside the bear enclosure

with on-board cameras.

And to lure the bears up close,
I'm leaving some tasty snacks.

We've got our decoy
skunks in position.

Now, let's see if those black
and white stripes

really are a deterrent.

After some time,
a big bear called Jack approaches.

OK, we've finally got a bear
coming in to investigate.

He's a really big one.

This big bear is definitely
approaching our black skunk.

You can see he's not bothered
in the slightest.

He's confident,

he's eating up all those berries -

that skunk is in big trouble.

Now he's just taking
the skunk apart.

OK, now he's turned around

and he's headed for
our black and white skunk

Bears use their sensitive
noses to sniff out food.

But such an acute sense of smell
would be overwhelmed by the skunk.

So, in theory, Jack should spot
that white stripe and steer clear.

I don't know if he's interested
or not -

but is he going to go for him?

Now he's turning around.

Looks like he's not interested
in the striped skunk at all.

It worked.

It may not be the most rigorous
of scientific tests,

but it illustrates the point

that the skunk's success is not
only down to their foul smell,

but also the brilliant way they
advertise their defensive weapon.

You take him right
down there by that creek.

And it's this that should
keep our rescued skunk safe

as he's released back into the wild.

Somewhere about here?
Yeah, that'll be good.

Skunks really do get a bad press,

but having the chance to get this
close to them,

you really can appreciate
what beautiful creatures they are.

And just like any other animal
out here,

all they're trying to do is survive.

In this episode we've seen
the most extraordinary ways

animals tap into the invisible
world of scent.

Smell is our most unfamiliar sense.

But in the wild it offers animals
vital information

that they just can't get
from sight or sound.

In nature, a keen nose
is essential for survival.