Sophisticated Serpents Life in Cold Blood

Whatever your feelings about snakes,

you can't deny that they have an extraordinary beauty.

Their lack of limbs compels them to deal with life's problems in ways that are utterly different from ours.

But nonetheless, the techniques they've developed

are spectacularly successful.

Snakes have one of the simplest of body shapes,

essentially just a long, thin tube,

but they have some remarkably effective ways of getting around.

They can climb a tree simply by embracing its trunk.

Some can flatten their bodies

so that they catch the air beneath them and glide.

By hitching up their undersides,

they can inch themselves forward in a straight line.

A sinuous wriggle enables them to skate across loose sand.

And the same action works equally well in water.

There, some swim close to the surface.

Others explore the depths and can stay underwater for hours on end.

One, believe it or not, can jump.

So, leglessness hardly seems such a handicap,

but how did snakes get that way?

Well, their remote ancestors 100 million years ago,

at the time of the dinosaurs, did have legs,

rather like today's lizards.

Doubtless they were very effective runners,

but some also started to burrow in search of prey.

Below ground, legs are a hindrance,

and over generations, they became smaller.

Today, burrowing lizards such as skinks

seem to be going through the same process.

Many have tiny but recognisable legs.

In others, the limbs have become nothing more than functionless flaps.

In this burrowing lizard, the process has gone even further.

The animal still has the face of a lizard...

but its legs have disappeared totally.

It seems that the ancestral snakes went through just such a process

way back in geological history, some 95 million years ago.

So, what did these very first snakes look like?

Well, the answer can be found in Asian jungles,

in American woodlands and gardens,

and even in flowerpots like this.

It may look like an earthworm, but actually it's a flowerpot snake,

and it's completely blind.

It doesn't need to see because it spends all its life underground.

I'll put it back in its flowerpot,

put a flower on top and it will live perfectly happily there

in this flowerpot, all by itself, providing it has enough food.

And there's a surprising amount for a small snake to eat underground.

Ant larvae, for example.

These early legless reptiles

flourished and remained underground for a long time.

Then, around 50 million years ago, some of them returned to the surface.

Why? Well, by this time the dinosaurs had disappeared

and the early mammals had arrived.

They were more nutritious than beetles and worms,

so the snakes began to catch them instead,

and became so good at doing so that today,

they are among the most skilful hunters on earth.

Here in North America, there's a snake

that combines its great speed and extraordinary senses

in a remarkable hunting strategy

we are only just beginning to understand.

A timber rattlesnake.

The morning sun has warmed its body,

giving it energy, and it starts to move.

It's searching for a place where it can conceal itself,

and wait for prey to come within striking distance.

A little chipmunk. It's in no danger yet.

The rattlesnake can't move fast enough to chase and catch it.

But small mammals tend to use the same paths

as they run over the forest floor,

and they leave behind a faint trail of scent.

The rattlesnake can detect that scent with its tongue.

It can also locate the warm-blooded chipmunk if it's nearby,

with heat detectors in a pair of pits beneath its eyes.

As it moves, it carefully holds its rattle above the ground

so it makes no noise.

It's chosen the place to wait at the bottom of this tree stump.

Its colouration matches the ground so closely

it needs no further concealment.

Now, it's just a matter of time.

Seeing a rattlesnake actually catching its prey

is a very, very difficult thing to observe.

In fact, some scientists have watched rattlesnakes for years

without seeing that particular crucial moment.

But we have a chance, partly because rattlesnakes are ambush hunters

so we know exactly where to put up our gear,

and partly because in that gear,

we've got the very latest in surveillance equipment.

There are remotely controlled cameras,

and infra-red lights on stands.

And there are motion detectors

that will switch on the cameras if anything moves.

So I needn't wait alongside.

If anything happens, the cameras will switch on automatically.

Later, I check the replay.

There's a mouse,

just along that log.

That obviously came to nothing,

but the cameras have started recording again

and the snake is moving.

He's checking out the trail with his tongue.

See, that's exactly where that mouse was running.

It's pitch dark and the mouse clearly has no idea that the snake is there.

But the snake is well aware of the mouse,

thanks, no doubt, to those heat-detecting pits.

The snake strikes by suddenly straightening the curve in its neck,

but at the moment, the mouse is not within range.

He's worked out that that is the path

along which the mice run.

And he's getting himself properly adjusted

so he can strike when he next gets a chance.

Now once again, waiting.

That's what snakes are so good at.

Oh, my goodness!

That's a dead mouse, all right.

Slow down that shot,

and you can see that the snake stabs the mouse just once.

After three convulsive kicks, the mouse is dead.

Snake is moving again.

He's going back now

to look for the one that he knows is dead back there.

Where is it?

Ah, now it looks as though he's really got it.

That's his dinner,

and that can last him

for...three weeks,

four weeks if necessary.

Rattlesnakes are among the least obtrusive inhabitants

of the forests of North America,

and they're probably far more numerous than many people realise.

Like many other animals, snakes use their nostrils to detect smells,

but the most sensitive and accurate information

about the world around them

comes from that constantly flickering tongue.

With this, a snake gathers molecules from the air

and carries them back for evaluation

to a pair of extremely sensitive organs in the roof of its mouth.

To see just how important scent can be to a snake,

I've come here to Carnac Island, just off the coast of Western Australia.

It's home to a large population of highly venomous tiger snakes.

Snakes have been established here for many years,

but there's something odd about this particular population.

Many of them have damaged heads, and some of them are actually blind,

like this one.

And yet, puzzlingly, in spite of the fact that they're blind,

they all appear to be very well fed.

So how do their heads get damaged,

and how, in that condition when they can't see anything,

can they catch all the prey they need?

The snakes, of course, are not the only inhabitants of the island.

It's also home for a large colony of silver gulls.

The gulls breed throughout the year,

so their chicks are a source of food for the snakes that never ends.

In fact, the snakes eat pretty well nothing else.

But the snakes don't get it all their own way.

The gulls are valiant defenders of their nests and their chicks.

Their stabbing beaks are powerful,

sharp and strong, and the gulls always go for the snake's head.

One in ten of the snakes are totally blinded.

Tiger snakes don't have those heat-sensitive pits

that rattlesnakes have,

so these blinded hunters are guided entirely by their forked tongue.

It's a superb direction-finding device.

The snake can measure the strength of the smell separately

on each of the two forks of its tongue.

And if it wishes to follow up a smell, then it simply detects the one

which has the stronger smell, and goes in that direction.

Gull chicks are an ideal prey for a blinded snake,

because they are programmed to stay on their nests.

Once a snake has located it, a chick is doomed.

Snakes, it must be admitted, have had a bad reputation

ever since one appeared in the Garden of Eden.

But in reality, even the most aggressive venomous snake

will avoid biting a human being if it can.

Why waste venom and risk a violent retribution

by biting something you're not going to eat?

To prevent misunderstanding,

most venomous snakes warn other animals, including human beings,

to keep out of their way.

RATTLING

Some snakes do that with sound.

HISS!

Others, such as cobras, give a visual signal,

by expanding the skin around their heads to form a conspicuous hood.

The threat of a bite

is far better defence for a snake than the bite itself.

However, there are some snakes

that not only use their venom to kill their prey,

but have also found a way of using it

to deter their enemies without even biting them.

This Mozambique cobra has a very special way of doing that.

To demonstrate this with some degree of safety,

I'm going to wear this visor which has been coated with a substance

that turns pink in contact with venom.

See what happens.

It's watching me, waiting to see if I get too close for its liking.

Venom spurts from its fangs.

As it spits, it turns its head from side to side

so that the jets have the best chance of hitting my eyes.

Well, I was well and truly sprayed.

Every one of those pink dots is a bead of venom,

and if any one of them had gone in my eye,

I would be now blind and in extreme pain.

So it's a fair warning from that snake to me not to get any closer,

and I daresay if I did

I would deserve what I would get, which would be a bite.

I have no intention of doing that.

On the other hand, some snakes which may appear to be venomous

are in reality quite harmless.

These two snakes look very, very similar, and they both occur here

in the southern United States,

so you are quite likely to meet one or the other here.

One of them, however, is harmless. It's called a king snake.

The other one is a coral snake and highly venomous.

One bite, certain death.

The question is, which is which?

Well, the key lies in the order of the colour rings.

People here have a local saying - "Red and black, venom lack.

"Red and yellow can kill a fellow."

This one has red and black,

so I guess that's a king snake.

We'll see.

So far, so good.

Yeah, this is a king snake.

And what a beautiful snake it is.

A really lovely reptile.

The king snake pretends to be venomous when it's not,

and there's another snake that pretends to be dead when it isn't.

Snakes, being cold-blooded, seem to relish the warmth of sun-baked roads

and often bask on them, and as a result, of course, many get run over.

But things aren't always exactly what they seem.

He looks fairly dead.

But in fact, this hog-nosed snake is perfectly all right.

He was just feigning death

so that things that might have been

interested in a living snake

are not, and what's more,

he's produced rather a remarkable smell.

In fact the smell, as it were,

of rotting flesh.

Maybe he was pretending, too, that he was not only dead but decomposing.

Very convincing. Off you go.

The lack of limbs that might seem to us to be such a huge handicap

has not stopped snakes from getting around in all kinds of ways,

and neither does it prevent them from tackling all kinds of meals.

This South African snake

has become a specialist in swallowing a particularly awkward mouthful.

It's as accomplished a tree-climber as you'll find among snakes.

The trees it frequents

also hold colonies of masked weaver birds,

that suspend their nests from the very tip of the branches.

But the snake is a skilled enough climber to reach them.

The weaver birds know it well and recognise it as a threat.

BIRDS TWITTER

It's well accustomed to these attacks.

These defenders, however, are just too determined, and it retreats.

But it doesn't give up altogether.

This nest is unguarded.

And this is what the snake is after, the eggs.

Each is several times bigger than the snake's head

but its jaws are linked by ligaments that are amazingly elastic.

Once the egg is engulfed by the snake's jaws,

powerful throat muscles push it down its gullet.

Moving X-rays enable us to see exactly what's happening.

Soon, the egg reaches a part of the backbone

that has downward-pointing spines on it.

The snake arches its backbone and then squeezes.

The shell cracks and the spines on the backbone slit the membrane.

The shell is crushed

and rich, nutritious yolk flows into the snake's gut.

Then, what's left of the shell is regurgitated.

But that, of course, was a small meal.

Some snakes can tackle much bigger meals than that.

An African rock python - one of the biggest of all snakes,

that can grow over seven metres, 20 feet long.

And it is eating an antelope.

It too has an elastic ligament connecting its jaws.

It killed the antelope not with venom,

but by squeezing it so tightly that it was unable to breathe.

A python's teeth can't cut or rip.

It has to swallow its prey whole, or not at all.

And that may take a day or more.

Without limbs, the python can't push the antelope down its throat.

Instead, it hitches its jaws diagonally back and forth

so that they, as it were, walk over the prey.

Its tube-like body has to stretch so extremely

to accommodate such a gigantic meal

that its flanks have torn, but such injuries heal very quickly.

The last of the antelope, its hooves, are about to disappear.

Gone.

The python will now hide itself away

and begin the long process of digestion.

Everything will be dissolved - skin, hair, hooves, even horns.

This python will not need to eat again for a year or more.

Wherever it's warm and there are animals of some kind,

there will be snakes to hunt them,

no matter how difficult the conditions

and how awkward the mouthful.

Crabs are in plentiful supply in this mangrove swamp.

There must be 50 on any one of these trees around me.

They're all up there waiting for the tide to go out

so that they can feed in the mud below.

So, there is a meal for a snake here, but crabs are not easy to tackle.

They're strong, armour-plated and covered in spines.

For a snake to tackle one of these

would be like me trying to eat a lobster twice the size of my head

with my hands tied behind my back.

But there is a snake that knows how to do so.

The crabs cling to the arching struts of the mangroves

to keep out of the way of predatory fish,

but as the tide retreats, it becomes safe for them to climb down

and start looking for such edible bits

as the tide has left behind on the mud.

For the moment they're safe, but soon the sun will set.

Then the snakes will come out of their burrows.

They hunt in the darkness,

but we'll be able to follow them with our infra-red cameras.

It's now very dark indeed

and the snake has to find its way around entirely by touch and smell.

Finding crabs is not difficult.

They swarm all over the mud

and the snake is almost bound to encounter one

sooner rather than later.

The snake is armed with venom,

and has short, strong fangs which can pierce a crab's shell and stun it.

But that's only half the problem.

It's what it does after it's caught its crab

that sets it apart from all other snakes.

It has it.

Now what?

The crab is so large that the snake can't swallow it whole.

Slowly and deliberately, the snake dismembers the crab.

Each leg contains nutritious muscle.

But the crab's armoured body is simply discarded.

Too difficult.

There are hard-shelled creatures in fresh waters, as well as in salt.

Not nearly as many,

but sufficient number for some snakes to specialise in eating them.

And in the eastern United States, many rivers contain crayfish.

Like crabs, they have a hard protective shell,

and they have particularly powerful pincers as well.

The queen snake, however, eats crayfish and nothing else.

But not just any crayfish.

It's very selective.

Crayfish, as they grow, shed their armour.

Every three to four weeks, a split appears across the back of its shell.

The old shell hinges away

and the crayfish hauls itself out and expands its body, which is soft.

It's now that the snake has its chance.

A newly moulted crayfish looks much the same,

but it gives off different chemicals

that the snake can detect in the water with its tongue,

and from some distance away.

It can swallow this crayfish because, since it's newly moulted,

it's as soft as a boiled egg.

On occasion, snakes have to grapple not only with their prey

but with one another, in disputes over mates and territory.

This is one of the most formidable, the king cobra.

Highly venomous and about four metres, 14 feet long.

Disputes between rival male king cobras

are potentially very dangerous indeed, for this species specialises

in eating other kinds of snakes.

So they observe strict rules in their fights,

which prohibit the use of their lethal bite.

Slowed down, it's a performance full of grace, as each contestant strives

not to kill his opponent but simply to slam him to the ground.

The defeated male leaves the arena and no harm has been done.

Snakes must also find a way

of preventing their courtship from becoming lethal.

This is a Californian king snake, a male.

He has detected the scent of a female ready to mate.

Like all snakes, his eyesight is not good

but he can tell from the taste of the air that she's close by.

In fact, she is within inches.

For some time, the two follow one another, nose to tail.

The male begins to caress her,

sensually jerking and rocking his body as he holds her close.

He has a pair of sexual organs,

one of which can project to the left and the other to the right.

So, no matter which side of him she happens to lie, he can reach her.

At last, union is achieved.

They may remain together for several hours.

In a few weeks' time, the female will lay a clutch of eggs.

It may take six or seven weeks for them to hatch,

but the regions where most snakes live are warm enough

for them to develop without any help from the parents.

Cobras lay them on the ground in the leaf litter.

Their soft, parchment-like shell is easily split when pushed from within.

The front end of a cobra hatchling is quite capable of giving a bite,

even while the back end is still within the shell.

Their fangs may be small,

but since it only takes a tiny drop of cobra venom to kill an animal,

these youngsters can be as lethal as their parents.

They already have that characteristic warning signal, the hood.

Not all snakes lay their eggs.

In some species, the female retains them within her body

until they're ready to hatch, so she gives birth to live young.

The marshes of Northern Argentina...

home to one of the largest of live-bearing snakes, the anaconda.

This is a female and she's heavily pregnant.

It's morning, and she's chilly,

so she moves out of the water

and on to the swamp to warm herself in the sun.

Slowly, the day begins to warm up.

Now it's getting a little too hot for her, so she moves back

to the water to cool off.

In this way, she manages to keep her body close to 29 degrees C,

perfect for the babies developing within her.

But she won't give birth here and now.

There are caiman around.

At last, she finds the quiet pool that she needs,

and her contractions start.

The first of her babies has arrived.

Up it goes to the surface to take its first breath of air.

But there are more babies to come.

Eventually, she produces 15.

In fact, that's quite modest for an anaconda.

They can produce up to 40.

Right from the beginning of their lives they're totally independent,

and get no care or protection from their mother.

The anaconda spends so much of its time in water, and is such

a powerful swimmer, that it can be properly considered aquatic.

Snakes have become adapted to almost every environment,

including even the sea, as this one has.

It doesn't often bite, but it does have an extremely powerful venom

so I'm not going to handle it.

But I will help it a little with this stick.

As you can see, it has a very flattened...

paddle at the end of its tail,

but on land, it's pretty helpless.

However, if I assist it...

in getting into the sea...

And now it's in its element.

Sea snakes have had to modify many of the features

that enabled their far distant ancestors to colonise the land.

They still have a lung with which to breathe air like other snakes,

but they can also absorb oxygen from sea water through their skin.

Salt inevitably gets into a sea snake's body, but the snake manages

to get rid of that by excreting it from a gland under its tongue.

It also needs to drink fresh water, so in calm seas,

it waits at the surface for rain.

Sea snakes really are truly marine creatures.

They can live out here in the open ocean,

and the only clue you have to their link with the land is that

they have to come up every quarter of an hour or so for a gulp of air.

Most sea snakes, like this bar-bellied species, hunt fish.

They have one of the most lethal venoms known,

which kills almost instantaneously.

And that is a very important quality

if you hunt fast-swimming ocean-going prey.

But paradoxically, the most highly specialised sea snake of all

has abandoned venom altogether.

It has a beak like a turtle and a wholly different way of feeding.

Reef fish don't like to have it around.

They mob it.

It doesn't even retaliate.

It's not interested in them.

It's after their eggs.

These, the fish have stuck to the stony branches of the coral.

The snake's hardened, turtle-like top lip enables it to scrape them off.

It's such a slow-moving browser

that algae and other small organisms grow on its skin,

as they do on the bottom of a boat.

The loss of limbs could seem to be a handicap,

and certainly makes a snake seem alien creatures to us.

But it is that very loss

that has enabled the snakes to colonise every environment,

from below to the ground to above the ground,

from bushes to trees, to the air and even to the sea.

And it is that absence of limbs, too,

which has enabled them to do it with such elegance and grace.

Filming venomous snakes

presented a lot of special problems to the Life In Cold Blood team.

But the toughest was trying to film the rattlesnake hunting in the wild.

A rattlesnake making a kill has rarely even been seen,

and never before filmed, and for several reasons.

For one thing, rattlesnakes are so well camouflaged

they're very difficult to find.

We enlisted the help of snake expert Harry Greene and his team.

They've been studying a group of timber rattlesnakes

using radio telemetry, which enables them to find their rattlesnakes

at any time of day or night.

Most of us would never find them. And they're superbly camouflaged.

Exactly,

but that's one of the wonderful things about radio telemetry,

we can have an animal that we can dial up.

To have any chance of success,

the crew had to be able to find the rattlesnakes on their own.

So producer James Brickell had to take a course

in telemetry techniques himself.

Point it a little bit more over this way.

Each snake has been implanted with a tiny transmitter.

If you dial its frequency, you can pick up a beeping sound,

and that gets louder the nearer you get to the snake.

RHYTHMIC BEEPING

It's just like trying to find your favourite rock'n'roll station,

but now we're going to find our favourite rattlesnake.

So you just punch in its number and it's on the air.

It sounds simple in theory, but there's a snag.

It's here somewhere.

Just be really careful, guys.

In a forest, the signal can bounce off trees

and give you a false reading,

so that it can seem that the snake is everywhere,

and you don't want to think a reading is false

and then tread on your snake by mistake.

...And you'll find he's up there somewhere.

Let's find him.

James, it's starting to get dark.

He's in there. I reckon he's hunting.

James, be careful where you're going.

And it isn't just the one snake you're tracking.

There are dozens of others in the area that aren't tagged.

Follow my hand, there he is.

About 20 feet.

Six metres.

And so at last, the crew meet a very special snake called Hank.

Hank is in a perfect position for his ambush.

To film the action without disturbing him or his prey,

cameraman Mark MacEwen has fitted his camera with motion detectors,

from a burglar alarm.

They will turn on the camera without anyone having to be there.

So, for the first time, they set up their gear in front of a live snake.

They can now leave Hank and track another of Harry's snakes.

So that means you know individual snakes over a long period of time.

Do they differ very much?

Absolutely, absolutely.

Now there are species differences,

so certain rattlesnakes species are more nasty-tempered than others,

but even among a...within a population you'll have one

that just never gets riled up

and one you know you just can't get too close to

without it getting upset.

With one camera set up on Hank, James decides to track another snake,

and to do so in the dark, which is when most rattlesnakes hunt.

But in the pitch blackness, there was a distinct possibility that

James would accidentally get so close to the snake he was looking for,

he would step within striking distance.

Quite unnerving if you haven't done it before.

It's actually pretty dangerous

walking around in the middle of the night

trying to find a rattlesnake in these conditions.

It's really close. It's stronger here, over near these logs.

I think the snake's about probably five, 10 metres away.

It would be easier to find a needle in a haystack,

than to find a reptile that looks

like a load of dead leaves in a huge pile of dead leaves.

Have you found him, fellas?

Negative, Mark, we've got to a huge pile of logs and wood.

The team decide to abandon tracking the second snake

and instead check on the camera they'd left on Hank in the afternoon.

I think it's too dangerous to go poking around in there,

and you wouldn't get the lights and the camera in,

so we're going to come back.

We've seen things on your videos we've never seen before,

which is kind of surprising.

I mean, we've watched snakes a lot, all the rattlesnake biologists,

and we've seen things on your videos we haven't seen before.

So its actually kind of exciting to think about how this kind of

collaboration might really be a feedback

between the media and the public and science and so forth.

And something very surprising had happened.

At our very first attempt and in broad daylight,

a chipmunk had tripped the motion detectors and Hank makes a kill

right in front of the cameras.

We've got a strike already, we've got it.

-I thought you were winding me up.

-I said, "James, something's happened."

I thought, "That's a classic wind-up." First night, to get that.

We hadn't got the eating shot, but it's a start.

And then the camera is set off again

by a second chipmunk behaving very strangely.

We showed the recording to Harry, and he was fascinated.

Now what was that chipmunk doing?

Was it perceiving something that the other chipmunk left

as some kind of alarm odour or something?

Was it perceiving the odour of the rattlesnake,

or was it something I can't even imagine yet?

But something was going on there that I didn't know to expect anyway,

and it's in your film.

Hank could clearly be the star of the show,

so the crew decide to concentrate all their efforts on him

and to track him for two weeks around the clock.

They quickly learn that

despite his ability to hurt one of them very seriously,

he seems pretty unconcerned.

In fact, he never even rattles a warning at them.

The more they get to know him,

the more they think they've got a good chance of filming another hunt.

But then there is a serious problem.

It's just been raining here non-stop for the past three days,

and they say that Tuesday afternoon's hard rain storm was...

Just as things are looking so promising, New York State has its

worst floods for a decade and all filming comes to a standstill.

As you can see, the weather's awful.

Won't affect the rattlesnake at all, he's perfectly happy.

He'll be sat down in here just waiting.

But it does affect the mammals.

The chipmunks and the mice, they'll just be hunkered down somewhere,

not doing anything very much, and it affects us, but he'll be fine.

We can't film anything, so it's just a matter of waiting now.

After tracking him in the rain for ten days,

there's a break in the weather and Hank starts hunting again.

He chooses a position for an ambush in a very accessible spot.

The team has another chance to use their remote cameras,

this time operating in night vision.

James, just be careful where you come in. Don't go that way.

I think that's the direction he's headed in.

You've got something, have you?

We've got him hitting a mouse in the middle of frame and swallowing it.

This time they get more than the strike.

This time, Hank decides to eat his dinner, very obligingly,

right in front of the camera.

Mate, that is the most incredible piece of behaviour

you have ever seen.

So, after two weeks and a lot of effort, they succeed in capturing

a crucial and intimate moment in the life of this very special snake.

People don't automatically love snakes, most of them don't.

And yet, if you can show them things about the lives of these animals

that impress them with the fact these are animals

with complex daily activities.

These aren't waiting around for an opportunity to kill people.

When you tell people things like that, they get drawn in.

And hopefully when we show them your films, they'll be drawn in.

-Well, you've drawn me in. Thank you very much.

-Pleasure.

And when I get to see the footage, it's fair to say

that I'm just as knocked sideways as the crew had been.

There's the mouse.

Oh, my goodness!

Yes.

That's a dead mouse all right.

Next week, join me for the story of the armoured giants -

the tortoises, turtles and crocodiles.

Subtitles by Red Bee Media Ltd