0:00:35 > 0:00:37Whatever your feelings about snakes,
0:00:37 > 0:00:42you can't deny that they have an extraordinary beauty.
0:00:46 > 0:00:53Their lack of limbs compels them to deal with life's problems in ways that are utterly different from ours.
0:01:01 > 0:01:04But nonetheless, the techniques they've developed
0:01:04 > 0:01:06are spectacularly successful.
0:01:21 > 0:01:23Snakes have one of the simplest of body shapes,
0:01:23 > 0:01:27essentially just a long, thin tube,
0:01:27 > 0:01:31but they have some remarkably effective ways of getting around.
0:01:33 > 0:01:38They can climb a tree simply by embracing its trunk.
0:01:42 > 0:01:45Some can flatten their bodies
0:01:45 > 0:01:50so that they catch the air beneath them and glide.
0:01:53 > 0:01:56By hitching up their undersides,
0:01:56 > 0:02:00they can inch themselves forward in a straight line.
0:02:01 > 0:02:05A sinuous wriggle enables them to skate across loose sand.
0:02:10 > 0:02:14And the same action works equally well in water.
0:02:16 > 0:02:20There, some swim close to the surface.
0:02:20 > 0:02:26Others explore the depths and can stay underwater for hours on end.
0:02:29 > 0:02:32One, believe it or not, can jump.
0:02:52 > 0:02:56So, leglessness hardly seems such a handicap,
0:02:56 > 0:02:59but how did snakes get that way?
0:02:59 > 0:03:02Well, their remote ancestors 100 million years ago,
0:03:02 > 0:03:06at the time of the dinosaurs, did have legs,
0:03:06 > 0:03:08rather like today's lizards.
0:03:14 > 0:03:18Doubtless they were very effective runners,
0:03:18 > 0:03:24but some also started to burrow in search of prey.
0:03:25 > 0:03:28Below ground, legs are a hindrance,
0:03:28 > 0:03:30and over generations, they became smaller.
0:03:31 > 0:03:34Today, burrowing lizards such as skinks
0:03:34 > 0:03:37seem to be going through the same process.
0:03:37 > 0:03:40Many have tiny but recognisable legs.
0:03:40 > 0:03:45In others, the limbs have become nothing more than functionless flaps.
0:03:48 > 0:03:52In this burrowing lizard, the process has gone even further.
0:03:52 > 0:03:55The animal still has the face of a lizard...
0:03:55 > 0:03:58but its legs have disappeared totally.
0:04:03 > 0:04:07It seems that the ancestral snakes went through just such a process
0:04:07 > 0:04:12way back in geological history, some 95 million years ago.
0:04:14 > 0:04:17So, what did these very first snakes look like?
0:04:17 > 0:04:20Well, the answer can be found in Asian jungles,
0:04:20 > 0:04:23in American woodlands and gardens,
0:04:23 > 0:04:26and even in flowerpots like this.
0:04:31 > 0:04:36It may look like an earthworm, but actually it's a flowerpot snake,
0:04:38 > 0:04:40and it's completely blind.
0:04:40 > 0:04:45It doesn't need to see because it spends all its life underground.
0:04:45 > 0:04:50I'll put it back in its flowerpot,
0:04:50 > 0:04:54put a flower on top and it will live perfectly happily there
0:04:54 > 0:04:57in this flowerpot, all by itself, providing it has enough food.
0:04:59 > 0:05:03And there's a surprising amount for a small snake to eat underground.
0:05:03 > 0:05:06Ant larvae, for example.
0:05:18 > 0:05:20These early legless reptiles
0:05:20 > 0:05:24flourished and remained underground for a long time.
0:05:24 > 0:05:30Then, around 50 million years ago, some of them returned to the surface.
0:05:35 > 0:05:38Why? Well, by this time the dinosaurs had disappeared
0:05:38 > 0:05:41and the early mammals had arrived.
0:05:41 > 0:05:44They were more nutritious than beetles and worms,
0:05:44 > 0:05:47so the snakes began to catch them instead,
0:05:47 > 0:05:50and became so good at doing so that today,
0:05:50 > 0:05:52they are among the most skilful hunters on earth.
0:05:54 > 0:05:57Here in North America, there's a snake
0:05:57 > 0:06:01that combines its great speed and extraordinary senses
0:06:01 > 0:06:03in a remarkable hunting strategy
0:06:03 > 0:06:06we are only just beginning to understand.
0:06:10 > 0:06:11A timber rattlesnake.
0:06:14 > 0:06:16The morning sun has warmed its body,
0:06:16 > 0:06:19giving it energy, and it starts to move.
0:06:29 > 0:06:33It's searching for a place where it can conceal itself,
0:06:33 > 0:06:35and wait for prey to come within striking distance.
0:06:40 > 0:06:42A little chipmunk. It's in no danger yet.
0:06:42 > 0:06:47The rattlesnake can't move fast enough to chase and catch it.
0:06:50 > 0:06:52But small mammals tend to use the same paths
0:06:52 > 0:06:54as they run over the forest floor,
0:06:54 > 0:06:58and they leave behind a faint trail of scent.
0:06:58 > 0:07:02The rattlesnake can detect that scent with its tongue.
0:07:10 > 0:07:15It can also locate the warm-blooded chipmunk if it's nearby,
0:07:15 > 0:07:19with heat detectors in a pair of pits beneath its eyes.
0:07:21 > 0:07:25As it moves, it carefully holds its rattle above the ground
0:07:25 > 0:07:27so it makes no noise.
0:07:33 > 0:07:38It's chosen the place to wait at the bottom of this tree stump.
0:07:38 > 0:07:41Its colouration matches the ground so closely
0:07:41 > 0:07:44it needs no further concealment.
0:07:44 > 0:07:47Now, it's just a matter of time.
0:07:48 > 0:07:52Seeing a rattlesnake actually catching its prey
0:07:52 > 0:07:55is a very, very difficult thing to observe.
0:07:55 > 0:07:58In fact, some scientists have watched rattlesnakes for years
0:07:58 > 0:08:02without seeing that particular crucial moment.
0:08:02 > 0:08:07But we have a chance, partly because rattlesnakes are ambush hunters
0:08:07 > 0:08:10so we know exactly where to put up our gear,
0:08:10 > 0:08:12and partly because in that gear,
0:08:12 > 0:08:17we've got the very latest in surveillance equipment.
0:08:17 > 0:08:21There are remotely controlled cameras,
0:08:21 > 0:08:23and infra-red lights on stands.
0:08:25 > 0:08:29And there are motion detectors
0:08:29 > 0:08:32that will switch on the cameras if anything moves.
0:08:32 > 0:08:34So I needn't wait alongside.
0:08:34 > 0:08:39If anything happens, the cameras will switch on automatically.
0:08:41 > 0:08:43Later, I check the replay.
0:08:51 > 0:08:52There's a mouse,
0:08:52 > 0:08:54just along that log.
0:09:05 > 0:09:07That obviously came to nothing,
0:09:07 > 0:09:09but the cameras have started recording again
0:09:09 > 0:09:10and the snake is moving.
0:09:10 > 0:09:13He's checking out the trail with his tongue.
0:09:18 > 0:09:21See, that's exactly where that mouse was running.
0:09:27 > 0:09:31It's pitch dark and the mouse clearly has no idea that the snake is there.
0:09:33 > 0:09:35But the snake is well aware of the mouse,
0:09:35 > 0:09:38thanks, no doubt, to those heat-detecting pits.
0:09:43 > 0:09:46The snake strikes by suddenly straightening the curve in its neck,
0:09:46 > 0:09:49but at the moment, the mouse is not within range.
0:10:01 > 0:10:04He's worked out that that is the path
0:10:04 > 0:10:07along which the mice run.
0:10:09 > 0:10:12And he's getting himself properly adjusted
0:10:12 > 0:10:16so he can strike when he next gets a chance.
0:10:29 > 0:10:32Now once again, waiting.
0:10:32 > 0:10:35That's what snakes are so good at.
0:10:58 > 0:11:00Oh, my goodness!
0:11:06 > 0:11:08That's a dead mouse, all right.
0:11:11 > 0:11:12Slow down that shot,
0:11:12 > 0:11:16and you can see that the snake stabs the mouse just once.
0:11:19 > 0:11:22After three convulsive kicks, the mouse is dead.
0:11:29 > 0:11:31Snake is moving again.
0:11:33 > 0:11:34He's going back now
0:11:34 > 0:11:40to look for the one that he knows is dead back there.
0:11:42 > 0:11:43Where is it?
0:11:46 > 0:11:49Ah, now it looks as though he's really got it.
0:11:54 > 0:11:55That's his dinner,
0:11:55 > 0:11:57and that can last him
0:11:57 > 0:12:01for...three weeks,
0:12:01 > 0:12:04four weeks if necessary.
0:12:12 > 0:12:16Rattlesnakes are among the least obtrusive inhabitants
0:12:16 > 0:12:18of the forests of North America,
0:12:18 > 0:12:22and they're probably far more numerous than many people realise.
0:12:24 > 0:12:29Like many other animals, snakes use their nostrils to detect smells,
0:12:29 > 0:12:32but the most sensitive and accurate information
0:12:32 > 0:12:33about the world around them
0:12:33 > 0:12:37comes from that constantly flickering tongue.
0:12:46 > 0:12:50With this, a snake gathers molecules from the air
0:12:50 > 0:12:53and carries them back for evaluation
0:12:53 > 0:12:58to a pair of extremely sensitive organs in the roof of its mouth.
0:12:58 > 0:13:01To see just how important scent can be to a snake,
0:13:01 > 0:13:06I've come here to Carnac Island, just off the coast of Western Australia.
0:13:06 > 0:13:13It's home to a large population of highly venomous tiger snakes.
0:13:15 > 0:13:18Snakes have been established here for many years,
0:13:18 > 0:13:22but there's something odd about this particular population.
0:13:23 > 0:13:28Many of them have damaged heads, and some of them are actually blind,
0:13:28 > 0:13:29like this one.
0:13:29 > 0:13:35And yet, puzzlingly, in spite of the fact that they're blind,
0:13:35 > 0:13:39they all appear to be very well fed.
0:13:39 > 0:13:41So how do their heads get damaged,
0:13:41 > 0:13:44and how, in that condition when they can't see anything,
0:13:44 > 0:13:47can they catch all the prey they need?
0:13:52 > 0:13:56The snakes, of course, are not the only inhabitants of the island.
0:13:56 > 0:14:00It's also home for a large colony of silver gulls.
0:14:02 > 0:14:05The gulls breed throughout the year,
0:14:05 > 0:14:10so their chicks are a source of food for the snakes that never ends.
0:14:13 > 0:14:16In fact, the snakes eat pretty well nothing else.
0:14:21 > 0:14:24But the snakes don't get it all their own way.
0:14:24 > 0:14:27The gulls are valiant defenders of their nests and their chicks.
0:14:33 > 0:14:35Their stabbing beaks are powerful,
0:14:35 > 0:14:41sharp and strong, and the gulls always go for the snake's head.
0:15:05 > 0:15:08One in ten of the snakes are totally blinded.
0:15:09 > 0:15:12Tiger snakes don't have those heat-sensitive pits
0:15:12 > 0:15:14that rattlesnakes have,
0:15:14 > 0:15:18so these blinded hunters are guided entirely by their forked tongue.
0:15:19 > 0:15:23It's a superb direction-finding device.
0:15:23 > 0:15:27The snake can measure the strength of the smell separately
0:15:27 > 0:15:30on each of the two forks of its tongue.
0:15:30 > 0:15:35And if it wishes to follow up a smell, then it simply detects the one
0:15:35 > 0:15:38which has the stronger smell, and goes in that direction.
0:15:42 > 0:15:46Gull chicks are an ideal prey for a blinded snake,
0:15:46 > 0:15:50because they are programmed to stay on their nests.
0:16:06 > 0:16:11Once a snake has located it, a chick is doomed.
0:16:17 > 0:16:20Snakes, it must be admitted, have had a bad reputation
0:16:20 > 0:16:23ever since one appeared in the Garden of Eden.
0:16:23 > 0:16:28But in reality, even the most aggressive venomous snake
0:16:28 > 0:16:31will avoid biting a human being if it can.
0:16:31 > 0:16:35Why waste venom and risk a violent retribution
0:16:35 > 0:16:37by biting something you're not going to eat?
0:16:39 > 0:16:40To prevent misunderstanding,
0:16:40 > 0:16:44most venomous snakes warn other animals, including human beings,
0:16:44 > 0:16:46to keep out of their way.
0:16:46 > 0:16:50RATTLING
0:16:50 > 0:16:52Some snakes do that with sound.
0:16:59 > 0:17:02HISS!
0:17:04 > 0:17:07Others, such as cobras, give a visual signal,
0:17:07 > 0:17:12by expanding the skin around their heads to form a conspicuous hood.
0:17:14 > 0:17:16The threat of a bite
0:17:16 > 0:17:20is far better defence for a snake than the bite itself.
0:17:22 > 0:17:25However, there are some snakes
0:17:25 > 0:17:28that not only use their venom to kill their prey,
0:17:28 > 0:17:33but have also found a way of using it
0:17:33 > 0:17:37to deter their enemies without even biting them.
0:17:39 > 0:17:44This Mozambique cobra has a very special way of doing that.
0:17:47 > 0:17:50To demonstrate this with some degree of safety,
0:17:50 > 0:17:53I'm going to wear this visor which has been coated with a substance
0:17:53 > 0:17:57that turns pink in contact with venom.
0:17:57 > 0:17:59See what happens.
0:18:02 > 0:18:07It's watching me, waiting to see if I get too close for its liking.
0:18:15 > 0:18:19Venom spurts from its fangs.
0:18:19 > 0:18:23As it spits, it turns its head from side to side
0:18:23 > 0:18:27so that the jets have the best chance of hitting my eyes.
0:18:33 > 0:18:36Well, I was well and truly sprayed.
0:18:36 > 0:18:40Every one of those pink dots is a bead of venom,
0:18:40 > 0:18:42and if any one of them had gone in my eye,
0:18:42 > 0:18:45I would be now blind and in extreme pain.
0:18:45 > 0:18:50So it's a fair warning from that snake to me not to get any closer,
0:18:50 > 0:18:52and I daresay if I did
0:18:52 > 0:18:57I would deserve what I would get, which would be a bite.
0:18:57 > 0:19:00I have no intention of doing that.
0:19:00 > 0:19:05On the other hand, some snakes which may appear to be venomous
0:19:05 > 0:19:08are in reality quite harmless.
0:19:10 > 0:19:16These two snakes look very, very similar, and they both occur here
0:19:16 > 0:19:18in the southern United States,
0:19:18 > 0:19:21so you are quite likely to meet one or the other here.
0:19:21 > 0:19:26One of them, however, is harmless. It's called a king snake.
0:19:26 > 0:19:29The other one is a coral snake and highly venomous.
0:19:29 > 0:19:32One bite, certain death.
0:19:32 > 0:19:35The question is, which is which?
0:19:35 > 0:19:40Well, the key lies in the order of the colour rings.
0:19:40 > 0:19:47People here have a local saying - "Red and black, venom lack.
0:19:47 > 0:19:51"Red and yellow can kill a fellow."
0:19:51 > 0:19:57This one has red and black,
0:19:57 > 0:20:02so I guess that's a king snake.
0:20:02 > 0:20:04We'll see.
0:20:09 > 0:20:11So far, so good.
0:20:11 > 0:20:13Yeah, this is a king snake.
0:20:13 > 0:20:18And what a beautiful snake it is.
0:20:21 > 0:20:22A really lovely reptile.
0:20:29 > 0:20:32The king snake pretends to be venomous when it's not,
0:20:32 > 0:20:38and there's another snake that pretends to be dead when it isn't.
0:20:42 > 0:20:47Snakes, being cold-blooded, seem to relish the warmth of sun-baked roads
0:20:47 > 0:20:52and often bask on them, and as a result, of course, many get run over.
0:20:57 > 0:21:00But things aren't always exactly what they seem.
0:21:05 > 0:21:08He looks fairly dead.
0:21:11 > 0:21:16But in fact, this hog-nosed snake is perfectly all right.
0:21:19 > 0:21:23He was just feigning death
0:21:23 > 0:21:26so that things that might have been
0:21:26 > 0:21:29interested in a living snake
0:21:29 > 0:21:31are not, and what's more,
0:21:31 > 0:21:35he's produced rather a remarkable smell.
0:21:35 > 0:21:38In fact the smell, as it were,
0:21:38 > 0:21:41of rotting flesh.
0:21:41 > 0:21:46Maybe he was pretending, too, that he was not only dead but decomposing.
0:21:46 > 0:21:50Very convincing. Off you go.
0:21:56 > 0:21:59The lack of limbs that might seem to us to be such a huge handicap
0:21:59 > 0:22:03has not stopped snakes from getting around in all kinds of ways,
0:22:03 > 0:22:07and neither does it prevent them from tackling all kinds of meals.
0:22:09 > 0:22:11This South African snake
0:22:11 > 0:22:15has become a specialist in swallowing a particularly awkward mouthful.
0:22:20 > 0:22:24It's as accomplished a tree-climber as you'll find among snakes.
0:22:37 > 0:22:38The trees it frequents
0:22:38 > 0:22:41also hold colonies of masked weaver birds,
0:22:41 > 0:22:45that suspend their nests from the very tip of the branches.
0:22:45 > 0:22:50But the snake is a skilled enough climber to reach them.
0:22:50 > 0:22:54The weaver birds know it well and recognise it as a threat.
0:23:00 > 0:23:02BIRDS TWITTER
0:23:05 > 0:23:07It's well accustomed to these attacks.
0:23:28 > 0:23:35These defenders, however, are just too determined, and it retreats.
0:23:38 > 0:23:42But it doesn't give up altogether.
0:23:56 > 0:24:00This nest is unguarded.
0:24:04 > 0:24:08And this is what the snake is after, the eggs.
0:24:08 > 0:24:11Each is several times bigger than the snake's head
0:24:11 > 0:24:16but its jaws are linked by ligaments that are amazingly elastic.
0:24:22 > 0:24:25Once the egg is engulfed by the snake's jaws,
0:24:25 > 0:24:28powerful throat muscles push it down its gullet.
0:24:35 > 0:24:40Moving X-rays enable us to see exactly what's happening.
0:24:43 > 0:24:46Soon, the egg reaches a part of the backbone
0:24:46 > 0:24:49that has downward-pointing spines on it.
0:24:51 > 0:24:55The snake arches its backbone and then squeezes.
0:24:59 > 0:25:04The shell cracks and the spines on the backbone slit the membrane.
0:25:08 > 0:25:09The shell is crushed
0:25:09 > 0:25:13and rich, nutritious yolk flows into the snake's gut.
0:25:27 > 0:25:31Then, what's left of the shell is regurgitated.
0:25:33 > 0:25:36But that, of course, was a small meal.
0:25:36 > 0:25:40Some snakes can tackle much bigger meals than that.
0:25:42 > 0:25:47An African rock python - one of the biggest of all snakes,
0:25:47 > 0:25:50that can grow over seven metres, 20 feet long.
0:25:50 > 0:25:54And it is eating an antelope.
0:25:54 > 0:25:58It too has an elastic ligament connecting its jaws.
0:26:01 > 0:26:04It killed the antelope not with venom,
0:26:04 > 0:26:08but by squeezing it so tightly that it was unable to breathe.
0:26:12 > 0:26:15A python's teeth can't cut or rip.
0:26:15 > 0:26:19It has to swallow its prey whole, or not at all.
0:26:19 > 0:26:23And that may take a day or more.
0:26:23 > 0:26:28Without limbs, the python can't push the antelope down its throat.
0:26:28 > 0:26:33Instead, it hitches its jaws diagonally back and forth
0:26:33 > 0:26:37so that they, as it were, walk over the prey.
0:26:37 > 0:26:41Its tube-like body has to stretch so extremely
0:26:41 > 0:26:44to accommodate such a gigantic meal
0:26:44 > 0:26:48that its flanks have torn, but such injuries heal very quickly.
0:26:53 > 0:26:57The last of the antelope, its hooves, are about to disappear.
0:27:06 > 0:27:08Gone.
0:27:13 > 0:27:16The python will now hide itself away
0:27:16 > 0:27:19and begin the long process of digestion.
0:27:19 > 0:27:25Everything will be dissolved - skin, hair, hooves, even horns.
0:27:33 > 0:27:38This python will not need to eat again for a year or more.
0:27:43 > 0:27:46Wherever it's warm and there are animals of some kind,
0:27:46 > 0:27:48there will be snakes to hunt them,
0:27:48 > 0:27:51no matter how difficult the conditions
0:27:51 > 0:27:52and how awkward the mouthful.
0:27:55 > 0:27:58Crabs are in plentiful supply in this mangrove swamp.
0:27:58 > 0:28:02There must be 50 on any one of these trees around me.
0:28:02 > 0:28:06They're all up there waiting for the tide to go out
0:28:06 > 0:28:08so that they can feed in the mud below.
0:28:08 > 0:28:14So, there is a meal for a snake here, but crabs are not easy to tackle.
0:28:14 > 0:28:19They're strong, armour-plated and covered in spines.
0:28:19 > 0:28:21For a snake to tackle one of these
0:28:21 > 0:28:26would be like me trying to eat a lobster twice the size of my head
0:28:26 > 0:28:29with my hands tied behind my back.
0:28:29 > 0:28:32But there is a snake that knows how to do so.
0:28:33 > 0:28:37The crabs cling to the arching struts of the mangroves
0:28:37 > 0:28:39to keep out of the way of predatory fish,
0:28:39 > 0:28:43but as the tide retreats, it becomes safe for them to climb down
0:28:43 > 0:28:46and start looking for such edible bits
0:28:46 > 0:28:48as the tide has left behind on the mud.
0:28:56 > 0:29:01For the moment they're safe, but soon the sun will set.
0:29:01 > 0:29:04Then the snakes will come out of their burrows.
0:29:04 > 0:29:06They hunt in the darkness,
0:29:06 > 0:29:10but we'll be able to follow them with our infra-red cameras.
0:29:19 > 0:29:21It's now very dark indeed
0:29:21 > 0:29:27and the snake has to find its way around entirely by touch and smell.
0:29:36 > 0:29:38Finding crabs is not difficult.
0:29:38 > 0:29:41They swarm all over the mud
0:29:41 > 0:29:44and the snake is almost bound to encounter one
0:29:44 > 0:29:46sooner rather than later.
0:29:54 > 0:29:56The snake is armed with venom,
0:29:56 > 0:30:00and has short, strong fangs which can pierce a crab's shell and stun it.
0:30:00 > 0:30:03But that's only half the problem.
0:30:03 > 0:30:06It's what it does after it's caught its crab
0:30:06 > 0:30:08that sets it apart from all other snakes.
0:30:34 > 0:30:36It has it.
0:30:36 > 0:30:38Now what?
0:30:38 > 0:30:43The crab is so large that the snake can't swallow it whole.
0:30:43 > 0:30:47Slowly and deliberately, the snake dismembers the crab.
0:30:51 > 0:30:55Each leg contains nutritious muscle.
0:31:03 > 0:31:08But the crab's armoured body is simply discarded.
0:31:08 > 0:31:10Too difficult.
0:31:13 > 0:31:18There are hard-shelled creatures in fresh waters, as well as in salt.
0:31:18 > 0:31:19Not nearly as many,
0:31:19 > 0:31:23but sufficient number for some snakes to specialise in eating them.
0:31:25 > 0:31:30And in the eastern United States, many rivers contain crayfish.
0:31:34 > 0:31:38Like crabs, they have a hard protective shell,
0:31:38 > 0:31:41and they have particularly powerful pincers as well.
0:31:48 > 0:31:54The queen snake, however, eats crayfish and nothing else.
0:32:13 > 0:32:16But not just any crayfish.
0:32:20 > 0:32:24It's very selective.
0:32:24 > 0:32:28Crayfish, as they grow, shed their armour.
0:32:31 > 0:32:36Every three to four weeks, a split appears across the back of its shell.
0:32:39 > 0:32:41The old shell hinges away
0:32:41 > 0:32:46and the crayfish hauls itself out and expands its body, which is soft.
0:32:48 > 0:32:51It's now that the snake has its chance.
0:33:02 > 0:33:06A newly moulted crayfish looks much the same,
0:33:06 > 0:33:08but it gives off different chemicals
0:33:08 > 0:33:12that the snake can detect in the water with its tongue,
0:33:12 > 0:33:14and from some distance away.
0:33:31 > 0:33:37It can swallow this crayfish because, since it's newly moulted,
0:33:37 > 0:33:39it's as soft as a boiled egg.
0:34:03 > 0:34:08On occasion, snakes have to grapple not only with their prey
0:34:08 > 0:34:12but with one another, in disputes over mates and territory.
0:34:14 > 0:34:17This is one of the most formidable, the king cobra.
0:34:17 > 0:34:23Highly venomous and about four metres, 14 feet long.
0:34:24 > 0:34:28Disputes between rival male king cobras
0:34:28 > 0:34:33are potentially very dangerous indeed, for this species specialises
0:34:33 > 0:34:35in eating other kinds of snakes.
0:34:37 > 0:34:40So they observe strict rules in their fights,
0:34:40 > 0:34:44which prohibit the use of their lethal bite.
0:34:47 > 0:34:53Slowed down, it's a performance full of grace, as each contestant strives
0:34:53 > 0:34:57not to kill his opponent but simply to slam him to the ground.
0:35:54 > 0:35:59The defeated male leaves the arena and no harm has been done.
0:36:07 > 0:36:09Snakes must also find a way
0:36:09 > 0:36:13of preventing their courtship from becoming lethal.
0:36:13 > 0:36:17This is a Californian king snake, a male.
0:36:21 > 0:36:24He has detected the scent of a female ready to mate.
0:36:28 > 0:36:32Like all snakes, his eyesight is not good
0:36:32 > 0:36:37but he can tell from the taste of the air that she's close by.
0:36:41 > 0:36:45In fact, she is within inches.
0:37:08 > 0:37:14For some time, the two follow one another, nose to tail.
0:37:19 > 0:37:21The male begins to caress her,
0:37:21 > 0:37:26sensually jerking and rocking his body as he holds her close.
0:37:31 > 0:37:33He has a pair of sexual organs,
0:37:33 > 0:37:38one of which can project to the left and the other to the right.
0:37:38 > 0:37:42So, no matter which side of him she happens to lie, he can reach her.
0:37:45 > 0:37:48At last, union is achieved.
0:38:06 > 0:38:09They may remain together for several hours.
0:38:26 > 0:38:31In a few weeks' time, the female will lay a clutch of eggs.
0:38:31 > 0:38:34It may take six or seven weeks for them to hatch,
0:38:34 > 0:38:37but the regions where most snakes live are warm enough
0:38:37 > 0:38:40for them to develop without any help from the parents.
0:38:43 > 0:38:48Cobras lay them on the ground in the leaf litter.
0:38:55 > 0:39:02Their soft, parchment-like shell is easily split when pushed from within.
0:39:09 > 0:39:14The front end of a cobra hatchling is quite capable of giving a bite,
0:39:14 > 0:39:17even while the back end is still within the shell.
0:39:33 > 0:39:35Their fangs may be small,
0:39:35 > 0:39:40but since it only takes a tiny drop of cobra venom to kill an animal,
0:39:40 > 0:39:44these youngsters can be as lethal as their parents.
0:40:08 > 0:40:13They already have that characteristic warning signal, the hood.
0:40:16 > 0:40:19Not all snakes lay their eggs.
0:40:19 > 0:40:23In some species, the female retains them within her body
0:40:23 > 0:40:28until they're ready to hatch, so she gives birth to live young.
0:40:31 > 0:40:33The marshes of Northern Argentina...
0:40:33 > 0:40:38home to one of the largest of live-bearing snakes, the anaconda.
0:40:44 > 0:40:49This is a female and she's heavily pregnant.
0:40:56 > 0:40:59It's morning, and she's chilly,
0:40:59 > 0:41:01so she moves out of the water
0:41:01 > 0:41:04and on to the swamp to warm herself in the sun.
0:41:18 > 0:41:22Slowly, the day begins to warm up.
0:41:33 > 0:41:39Now it's getting a little too hot for her, so she moves back
0:41:39 > 0:41:41to the water to cool off.
0:41:44 > 0:41:49In this way, she manages to keep her body close to 29 degrees C,
0:41:49 > 0:41:52perfect for the babies developing within her.
0:41:59 > 0:42:03But she won't give birth here and now.
0:42:03 > 0:42:04There are caiman around.
0:42:11 > 0:42:14At last, she finds the quiet pool that she needs,
0:42:16 > 0:42:19and her contractions start.
0:42:46 > 0:42:50The first of her babies has arrived.
0:42:54 > 0:42:57Up it goes to the surface to take its first breath of air.
0:43:06 > 0:43:08But there are more babies to come.
0:43:26 > 0:43:29Eventually, she produces 15.
0:43:29 > 0:43:32In fact, that's quite modest for an anaconda.
0:43:32 > 0:43:36They can produce up to 40.
0:43:36 > 0:43:40Right from the beginning of their lives they're totally independent,
0:43:40 > 0:43:43and get no care or protection from their mother.
0:43:46 > 0:43:49The anaconda spends so much of its time in water, and is such
0:43:49 > 0:43:53a powerful swimmer, that it can be properly considered aquatic.
0:43:58 > 0:44:03Snakes have become adapted to almost every environment,
0:44:03 > 0:44:07including even the sea, as this one has.
0:44:07 > 0:44:11It doesn't often bite, but it does have an extremely powerful venom
0:44:11 > 0:44:13so I'm not going to handle it.
0:44:13 > 0:44:17But I will help it a little with this stick.
0:44:17 > 0:44:20As you can see, it has a very flattened...
0:44:20 > 0:44:23paddle at the end of its tail,
0:44:23 > 0:44:26but on land, it's pretty helpless.
0:44:28 > 0:44:30However, if I assist it...
0:44:30 > 0:44:33in getting into the sea...
0:44:38 > 0:44:41And now it's in its element.
0:44:44 > 0:44:48Sea snakes have had to modify many of the features
0:44:48 > 0:44:52that enabled their far distant ancestors to colonise the land.
0:44:52 > 0:44:56They still have a lung with which to breathe air like other snakes,
0:44:56 > 0:45:01but they can also absorb oxygen from sea water through their skin.
0:45:08 > 0:45:13Salt inevitably gets into a sea snake's body, but the snake manages
0:45:13 > 0:45:18to get rid of that by excreting it from a gland under its tongue.
0:45:18 > 0:45:22It also needs to drink fresh water, so in calm seas,
0:45:22 > 0:45:25it waits at the surface for rain.
0:45:25 > 0:45:31Sea snakes really are truly marine creatures.
0:45:31 > 0:45:34They can live out here in the open ocean,
0:45:34 > 0:45:39and the only clue you have to their link with the land is that
0:45:39 > 0:45:43they have to come up every quarter of an hour or so for a gulp of air.
0:45:54 > 0:45:59Most sea snakes, like this bar-bellied species, hunt fish.
0:45:59 > 0:46:02They have one of the most lethal venoms known,
0:46:02 > 0:46:04which kills almost instantaneously.
0:46:04 > 0:46:07And that is a very important quality
0:46:07 > 0:46:11if you hunt fast-swimming ocean-going prey.
0:46:11 > 0:46:16But paradoxically, the most highly specialised sea snake of all
0:46:16 > 0:46:18has abandoned venom altogether.
0:46:20 > 0:46:25It has a beak like a turtle and a wholly different way of feeding.
0:46:40 > 0:46:42Reef fish don't like to have it around.
0:46:42 > 0:46:44They mob it.
0:46:55 > 0:46:57It doesn't even retaliate.
0:46:57 > 0:46:59It's not interested in them.
0:47:06 > 0:47:08It's after their eggs.
0:47:08 > 0:47:12These, the fish have stuck to the stony branches of the coral.
0:47:17 > 0:47:23The snake's hardened, turtle-like top lip enables it to scrape them off.
0:47:31 > 0:47:33It's such a slow-moving browser
0:47:33 > 0:47:38that algae and other small organisms grow on its skin,
0:47:38 > 0:47:41as they do on the bottom of a boat.
0:47:45 > 0:47:49The loss of limbs could seem to be a handicap,
0:47:49 > 0:47:54and certainly makes a snake seem alien creatures to us.
0:47:54 > 0:47:56But it is that very loss
0:47:56 > 0:48:01that has enabled the snakes to colonise every environment,
0:48:01 > 0:48:04from below to the ground to above the ground,
0:48:04 > 0:48:07from bushes to trees, to the air and even to the sea.
0:48:07 > 0:48:10And it is that absence of limbs, too,
0:48:10 > 0:48:16which has enabled them to do it with such elegance and grace.
0:48:25 > 0:48:27Filming venomous snakes
0:48:27 > 0:48:32presented a lot of special problems to the Life In Cold Blood team.
0:48:32 > 0:48:37But the toughest was trying to film the rattlesnake hunting in the wild.
0:48:37 > 0:48:41A rattlesnake making a kill has rarely even been seen,
0:48:41 > 0:48:44and never before filmed, and for several reasons.
0:48:44 > 0:48:47For one thing, rattlesnakes are so well camouflaged
0:48:47 > 0:48:49they're very difficult to find.
0:48:49 > 0:48:53We enlisted the help of snake expert Harry Greene and his team.
0:48:53 > 0:48:56They've been studying a group of timber rattlesnakes
0:48:56 > 0:49:01using radio telemetry, which enables them to find their rattlesnakes
0:49:01 > 0:49:03at any time of day or night.
0:49:03 > 0:49:07Most of us would never find them. And they're superbly camouflaged.
0:49:07 > 0:49:08Exactly,
0:49:08 > 0:49:12but that's one of the wonderful things about radio telemetry,
0:49:12 > 0:49:14we can have an animal that we can dial up.
0:49:14 > 0:49:16To have any chance of success,
0:49:16 > 0:49:19the crew had to be able to find the rattlesnakes on their own.
0:49:19 > 0:49:22So producer James Brickell had to take a course
0:49:22 > 0:49:24in telemetry techniques himself.
0:49:24 > 0:49:27Point it a little bit more over this way.
0:49:27 > 0:49:31Each snake has been implanted with a tiny transmitter.
0:49:31 > 0:49:34If you dial its frequency, you can pick up a beeping sound,
0:49:34 > 0:49:37and that gets louder the nearer you get to the snake.
0:49:38 > 0:49:41RHYTHMIC BEEPING
0:49:43 > 0:49:47It's just like trying to find your favourite rock'n'roll station,
0:49:47 > 0:49:50but now we're going to find our favourite rattlesnake.
0:49:50 > 0:49:52So you just punch in its number and it's on the air.
0:49:52 > 0:49:56It sounds simple in theory, but there's a snag.
0:49:59 > 0:50:02It's here somewhere.
0:50:02 > 0:50:04Just be really careful, guys.
0:50:04 > 0:50:07In a forest, the signal can bounce off trees
0:50:07 > 0:50:09and give you a false reading,
0:50:09 > 0:50:12so that it can seem that the snake is everywhere,
0:50:12 > 0:50:14and you don't want to think a reading is false
0:50:14 > 0:50:16and then tread on your snake by mistake.
0:50:16 > 0:50:19...And you'll find he's up there somewhere.
0:50:19 > 0:50:21Let's find him.
0:50:21 > 0:50:23James, it's starting to get dark.
0:50:23 > 0:50:25He's in there. I reckon he's hunting.
0:50:25 > 0:50:26James, be careful where you're going.
0:50:26 > 0:50:28And it isn't just the one snake you're tracking.
0:50:28 > 0:50:31There are dozens of others in the area that aren't tagged.
0:50:34 > 0:50:37Follow my hand, there he is.
0:50:37 > 0:50:38About 20 feet.
0:50:38 > 0:50:41Six metres.
0:50:41 > 0:50:46And so at last, the crew meet a very special snake called Hank.
0:50:50 > 0:50:53Hank is in a perfect position for his ambush.
0:50:53 > 0:50:58To film the action without disturbing him or his prey,
0:50:58 > 0:51:02cameraman Mark MacEwen has fitted his camera with motion detectors,
0:51:02 > 0:51:04from a burglar alarm.
0:51:04 > 0:51:07They will turn on the camera without anyone having to be there.
0:51:08 > 0:51:14So, for the first time, they set up their gear in front of a live snake.
0:51:14 > 0:51:20They can now leave Hank and track another of Harry's snakes.
0:51:20 > 0:51:23So that means you know individual snakes over a long period of time.
0:51:23 > 0:51:25Do they differ very much?
0:51:25 > 0:51:27Absolutely, absolutely.
0:51:27 > 0:51:29Now there are species differences,
0:51:29 > 0:51:33so certain rattlesnakes species are more nasty-tempered than others,
0:51:33 > 0:51:36but even among a...within a population you'll have one
0:51:36 > 0:51:37that just never gets riled up
0:51:37 > 0:51:40and one you know you just can't get too close to
0:51:40 > 0:51:42without it getting upset.
0:51:42 > 0:51:46With one camera set up on Hank, James decides to track another snake,
0:51:46 > 0:51:50and to do so in the dark, which is when most rattlesnakes hunt.
0:51:50 > 0:51:54But in the pitch blackness, there was a distinct possibility that
0:51:54 > 0:51:57James would accidentally get so close to the snake he was looking for,
0:51:57 > 0:52:00he would step within striking distance.
0:52:00 > 0:52:04Quite unnerving if you haven't done it before.
0:52:08 > 0:52:10It's actually pretty dangerous
0:52:10 > 0:52:11walking around in the middle of the night
0:52:11 > 0:52:14trying to find a rattlesnake in these conditions.
0:52:21 > 0:52:24It's really close. It's stronger here, over near these logs.
0:52:24 > 0:52:28I think the snake's about probably five, 10 metres away.
0:52:28 > 0:52:30It would be easier to find a needle in a haystack,
0:52:32 > 0:52:34than to find a reptile that looks
0:52:34 > 0:52:38like a load of dead leaves in a huge pile of dead leaves.
0:52:38 > 0:52:41Have you found him, fellas?
0:52:41 > 0:52:46Negative, Mark, we've got to a huge pile of logs and wood.
0:52:46 > 0:52:49The team decide to abandon tracking the second snake
0:52:49 > 0:52:54and instead check on the camera they'd left on Hank in the afternoon.
0:52:54 > 0:52:57I think it's too dangerous to go poking around in there,
0:52:57 > 0:53:00and you wouldn't get the lights and the camera in,
0:53:00 > 0:53:01so we're going to come back.
0:53:01 > 0:53:04We've seen things on your videos we've never seen before,
0:53:04 > 0:53:06which is kind of surprising.
0:53:06 > 0:53:10I mean, we've watched snakes a lot, all the rattlesnake biologists,
0:53:10 > 0:53:14and we've seen things on your videos we haven't seen before.
0:53:14 > 0:53:18So its actually kind of exciting to think about how this kind of
0:53:18 > 0:53:20collaboration might really be a feedback
0:53:20 > 0:53:23between the media and the public and science and so forth.
0:53:23 > 0:53:26And something very surprising had happened.
0:53:26 > 0:53:29At our very first attempt and in broad daylight,
0:53:29 > 0:53:34a chipmunk had tripped the motion detectors and Hank makes a kill
0:53:34 > 0:53:36right in front of the cameras.
0:53:43 > 0:53:46We've got a strike already, we've got it.
0:53:46 > 0:53:50- I thought you were winding me up.- I said, "James, something's happened."
0:53:50 > 0:53:55I thought, "That's a classic wind-up." First night, to get that.
0:53:55 > 0:53:58We hadn't got the eating shot, but it's a start.
0:53:58 > 0:54:00And then the camera is set off again
0:54:00 > 0:54:03by a second chipmunk behaving very strangely.
0:54:03 > 0:54:07We showed the recording to Harry, and he was fascinated.
0:54:07 > 0:54:09Now what was that chipmunk doing?
0:54:09 > 0:54:11Was it perceiving something that the other chipmunk left
0:54:11 > 0:54:14as some kind of alarm odour or something?
0:54:14 > 0:54:16Was it perceiving the odour of the rattlesnake,
0:54:16 > 0:54:19or was it something I can't even imagine yet?
0:54:19 > 0:54:23But something was going on there that I didn't know to expect anyway,
0:54:23 > 0:54:24and it's in your film.
0:54:24 > 0:54:27Hank could clearly be the star of the show,
0:54:27 > 0:54:30so the crew decide to concentrate all their efforts on him
0:54:30 > 0:54:33and to track him for two weeks around the clock.
0:54:33 > 0:54:35They quickly learn that
0:54:35 > 0:54:38despite his ability to hurt one of them very seriously,
0:54:38 > 0:54:40he seems pretty unconcerned.
0:54:40 > 0:54:43In fact, he never even rattles a warning at them.
0:54:43 > 0:54:46The more they get to know him,
0:54:46 > 0:54:49the more they think they've got a good chance of filming another hunt.
0:54:49 > 0:54:52But then there is a serious problem.
0:54:52 > 0:54:55It's just been raining here non-stop for the past three days,
0:54:55 > 0:54:59and they say that Tuesday afternoon's hard rain storm was...
0:54:59 > 0:55:04Just as things are looking so promising, New York State has its
0:55:04 > 0:55:08worst floods for a decade and all filming comes to a standstill.
0:55:10 > 0:55:12As you can see, the weather's awful.
0:55:12 > 0:55:15Won't affect the rattlesnake at all, he's perfectly happy.
0:55:15 > 0:55:17He'll be sat down in here just waiting.
0:55:17 > 0:55:19But it does affect the mammals.
0:55:19 > 0:55:22The chipmunks and the mice, they'll just be hunkered down somewhere,
0:55:22 > 0:55:26not doing anything very much, and it affects us, but he'll be fine.
0:55:26 > 0:55:31We can't film anything, so it's just a matter of waiting now.
0:55:31 > 0:55:34After tracking him in the rain for ten days,
0:55:34 > 0:55:39there's a break in the weather and Hank starts hunting again.
0:55:39 > 0:55:43He chooses a position for an ambush in a very accessible spot.
0:55:43 > 0:55:46The team has another chance to use their remote cameras,
0:55:46 > 0:55:49this time operating in night vision.
0:55:49 > 0:55:52James, just be careful where you come in. Don't go that way.
0:55:52 > 0:55:54I think that's the direction he's headed in.
0:55:54 > 0:55:57You've got something, have you?
0:55:57 > 0:56:02We've got him hitting a mouse in the middle of frame and swallowing it.
0:56:02 > 0:56:05This time they get more than the strike.
0:56:05 > 0:56:10This time, Hank decides to eat his dinner, very obligingly,
0:56:10 > 0:56:12right in front of the camera.
0:56:12 > 0:56:15Mate, that is the most incredible piece of behaviour
0:56:15 > 0:56:16you have ever seen.
0:56:16 > 0:56:22So, after two weeks and a lot of effort, they succeed in capturing
0:56:22 > 0:56:27a crucial and intimate moment in the life of this very special snake.
0:56:27 > 0:56:31People don't automatically love snakes, most of them don't.
0:56:31 > 0:56:34And yet, if you can show them things about the lives of these animals
0:56:34 > 0:56:37that impress them with the fact these are animals
0:56:37 > 0:56:39with complex daily activities.
0:56:39 > 0:56:41These aren't waiting around for an opportunity to kill people.
0:56:41 > 0:56:46When you tell people things like that, they get drawn in.
0:56:46 > 0:56:49And hopefully when we show them your films, they'll be drawn in.
0:56:49 > 0:56:53- Well, you've drawn me in. Thank you very much.- Pleasure.
0:56:53 > 0:56:57And when I get to see the footage, it's fair to say
0:56:57 > 0:57:01that I'm just as knocked sideways as the crew had been.
0:57:01 > 0:57:03There's the mouse.
0:57:05 > 0:57:08Oh, my goodness!
0:57:09 > 0:57:12Yes.
0:57:12 > 0:57:14That's a dead mouse all right.
0:57:16 > 0:57:20Next week, join me for the story of the armoured giants -
0:57:20 > 0:57:24the tortoises, turtles and crocodiles.
0:57:29 > 0:57:31Subtitles by Red Bee Media Ltd