0:00:03 > 0:00:05Planet Earth.
0:00:07 > 0:00:09Millions of different species.
0:00:11 > 0:00:14But a few are special.
0:00:16 > 0:00:19Born to thrive.
0:00:26 > 0:00:30The key to their success lies in their opportunism.
0:00:31 > 0:00:35For others it's down to their ability to collaborate.
0:00:38 > 0:00:42And for some, it's all about surviving, where others can't.
0:00:44 > 0:00:46So, what is their secret?
0:00:48 > 0:00:51By exploring the details deep beneath the skin,
0:00:51 > 0:00:56we'll discover the unique features that set some species apart.
0:00:59 > 0:01:00In this series, new behaviour
0:01:00 > 0:01:04and the very latest scientific discoveries
0:01:04 > 0:01:06will throw fresh insight
0:01:06 > 0:01:10into the wonder of animals.
0:01:24 > 0:01:29Whilst many species were striving to develop limbs,
0:01:29 > 0:01:32wings and fins,
0:01:32 > 0:01:38one group of animals opted for a completely different strategy.
0:01:40 > 0:01:42They lost their limbs.
0:01:43 > 0:01:46And yet, they've still become some of the most
0:01:46 > 0:01:49successful predators on earth.
0:01:56 > 0:01:58The snakes -
0:01:58 > 0:02:02now, I know you might think that they all look the same,
0:02:02 > 0:02:06but that simple body plan hides some remarkable adaptations.
0:02:06 > 0:02:11In this episode, we'll see how they move, sense
0:02:11 > 0:02:14and hunt in a huge variety of habitats
0:02:14 > 0:02:17all across the planet.
0:02:17 > 0:02:21Revealing how they rival their limbed counterparts at every turn -
0:02:21 > 0:02:24starting with movement.
0:02:24 > 0:02:27How do you get around without limbs?
0:02:34 > 0:02:39Without feet to lift its body, the entire weight
0:02:39 > 0:02:40of a snake rests on the ground.
0:02:43 > 0:02:45To spread the load evenly,
0:02:45 > 0:02:50a snake's internal organs are not clustered in one place like ours,
0:02:50 > 0:02:53but arranged throughout the body in a linear fashion.
0:02:56 > 0:02:59The liver and heart are elongated.
0:03:01 > 0:03:05Kidneys are not paired side by side
0:03:05 > 0:03:08but sit one behind the other.
0:03:10 > 0:03:16And a long, thin lung spans almost half the length of the body,
0:03:16 > 0:03:20accompanied by a tiny vestigial second lung.
0:03:23 > 0:03:26Protecting these delicate organs,
0:03:26 > 0:03:29a snake can have up to 400 pairs of ribs.
0:03:34 > 0:03:37And as many as 24 muscles are
0:03:37 > 0:03:40involved with the movement of each pair.
0:03:46 > 0:03:50It's this that gives snakes their unrivalled strength
0:03:50 > 0:03:53and flexibility.
0:03:57 > 0:04:01And they need it, to overcome the problem of resistance.
0:04:05 > 0:04:09To slide gracefully and effortlessly over rough ground, snakes have
0:04:09 > 0:04:13actually turned friction to their advantage.
0:04:18 > 0:04:22The puff adder can weigh 6kg.
0:04:28 > 0:04:33That's a big bulk to drag across the African grasslands.
0:04:34 > 0:04:38By contracting the muscles between its ribs and skin,
0:04:38 > 0:04:41it's able to pull itself forward in a straight line.
0:04:42 > 0:04:46And it has a helping hand...
0:04:46 > 0:04:48specialised scales.
0:04:51 > 0:04:54The belly scales of a puff adder are large and oblong.
0:04:56 > 0:05:01When laid flat, they're so smooth they offer very little friction.
0:05:01 > 0:05:05But when contracted, the bottom edges of the scales
0:05:05 > 0:05:08stick out and provide grip.
0:05:09 > 0:05:14This precise, crawling movement known as rectilinear motion,
0:05:14 > 0:05:17is common in large, heavy snakes,
0:05:17 > 0:05:20such as vipers, like the puff adder,
0:05:20 > 0:05:25boas and pythons.
0:05:27 > 0:05:31Allowing these stealth hunters to travel almost undetected.
0:05:38 > 0:05:42Other snakes can move much more rapidly
0:05:42 > 0:05:46and they do it using a completely different form of locomotion.
0:05:52 > 0:05:56The mamba is perhaps the fastest snake in the world.
0:05:56 > 0:06:02Now, this footage may look sped up but it's not, this is real-time.
0:06:07 > 0:06:11It's thought a black mamba can move at up to five metres a second.
0:06:18 > 0:06:22And it does this by using a unique method of locomotion that
0:06:22 > 0:06:25exploits the obstacles in its path.
0:06:35 > 0:06:39It may look like it's travelling roughly in a straight line.
0:06:40 > 0:06:44But slow down the footage and you can see
0:06:44 > 0:06:47it actually moves from side to side,
0:06:47 > 0:06:51pushing against the grasses and sticks that are in its way.
0:06:53 > 0:06:57This S-shaped movement, called lateral undulation
0:06:57 > 0:07:00is not only fast but efficient.
0:07:07 > 0:07:11The mamba may be quick,
0:07:11 > 0:07:15but it still has to push its body over the ground.
0:07:18 > 0:07:23One of the most efficient movers in the snake world is the sidewinder.
0:07:29 > 0:07:33The shifting, steep-sided terrain of the desert poses an even
0:07:33 > 0:07:36greater challenge to movement.
0:07:40 > 0:07:42But THEY have a solution.
0:07:44 > 0:07:47Instead of pulling themselves along,
0:07:47 > 0:07:50or pushing from one point to another,
0:07:50 > 0:07:53sidewinders place only two parts of their body on the
0:07:53 > 0:07:55ground at any time.
0:07:57 > 0:08:01The rest of the body lifts off the sand as it moves.
0:08:04 > 0:08:08Alternating these points of contact allows them to shift forwards.
0:08:13 > 0:08:17The acute angles formed as it winds are possible
0:08:17 > 0:08:21because sidewinders have fewer vertebrae than many snakes.
0:08:22 > 0:08:26In fact, only half of those found in a mamba.
0:08:31 > 0:08:36Having successfully overcome the challenge of moving on land...
0:08:38 > 0:08:40..snakes' versatility doesn't stop there.
0:08:43 > 0:08:46They can also climb.
0:08:48 > 0:08:50As on the ground,
0:08:50 > 0:08:53snakes use a combination of serpentine motion and
0:08:53 > 0:08:57specialised scales to master the vertical trunks of trees.
0:08:57 > 0:09:01Incredibly, some snakes can even
0:09:01 > 0:09:04adjust the angle of individual scales
0:09:04 > 0:09:09to fine-tune their grip and effectively defy gravity.
0:09:11 > 0:09:14But once up in the tree canopy, snakes are faced with the challenge
0:09:14 > 0:09:17of crossing from one branch to another.
0:09:19 > 0:09:24Again, their bodies provide a sophisticated solution.
0:09:25 > 0:09:30This Madagascan leaf-nosed snake mimics a vine as it
0:09:30 > 0:09:32lurks amongst the jungle foliage.
0:09:35 > 0:09:39Tree snakes are able to extend their body by more than a third
0:09:39 > 0:09:41to bridge gaps in the canopy.
0:09:44 > 0:09:49They maintain such poised cantilevers thanks to
0:09:49 > 0:09:52locking vertebrae that reinforce their spine.
0:09:55 > 0:09:59There are some gaps, however, which can't be bridged.
0:10:01 > 0:10:06Moving from one tree to another requires something rather special.
0:10:15 > 0:10:19For this, snakes have taken to the skies.
0:10:23 > 0:10:27With no wings to control their descent,
0:10:27 > 0:10:31flying snakes transform their whole body into an aerofoil.
0:10:35 > 0:10:41Splaying their ribs, their body flattens, doubling in width.
0:10:46 > 0:10:50They then arch this frame into a concave shape.
0:10:53 > 0:10:58This simple change creates aerodynamic forces
0:10:58 > 0:11:01comparable to a wing.
0:11:02 > 0:11:04The lift generated,
0:11:04 > 0:11:07combined with the snakes' characteristic sideways movement,
0:11:07 > 0:11:13allows them to glide for distances of up to 30 metres.
0:11:18 > 0:11:22So, with the land and skies colonised,
0:11:22 > 0:11:25there remains just one realm to master.
0:11:30 > 0:11:33All snakes can swim, to a degree.
0:11:34 > 0:11:38But one group has modified their already streamlined bodies
0:11:38 > 0:11:42to become high-performance swimmers.
0:11:46 > 0:11:51Most species of sea snake spend their entire lives in the ocean.
0:12:00 > 0:12:03They can swim to depths of more than 90 metres.
0:12:16 > 0:12:19To move in this marine environment,
0:12:19 > 0:12:22sea snakes have undergone a change in shape.
0:12:23 > 0:12:26Unlike the flying snakes,
0:12:26 > 0:12:29they've flattened their bodies in the opposite plane.
0:12:31 > 0:12:35Narrowing themselves vertically
0:12:35 > 0:12:38to become tall, thin blades.
0:12:42 > 0:12:46This adaptation, working in tandem with their paddle-like tails,
0:12:46 > 0:12:49increases their surface area...
0:12:52 > 0:12:57..enabling them to push against a larger volume of water,
0:12:57 > 0:13:00creating more thrust as they swim.
0:13:05 > 0:13:09Sea snakes have also developed an internal physiology that
0:13:09 > 0:13:12allows them to move more efficiently through water.
0:13:17 > 0:13:21Their lung extends almost the full length of their bodies.
0:13:24 > 0:13:28And whilst providing oxygen when the snake is submerged,
0:13:28 > 0:13:31in addition, it acts as a buoyancy control,
0:13:31 > 0:13:36helping the snake move up and down in the water column.
0:13:36 > 0:13:40Sea snakes are able to supplement their air supply
0:13:40 > 0:13:45by absorbing 25% of the oxygen they require through their skin.
0:13:46 > 0:13:50And this means they can remain underwater for up to
0:13:50 > 0:13:53two hours on a single breath.
0:13:58 > 0:14:01Having solved the problem of getting around,
0:14:01 > 0:14:05the next step is to find food and for this,
0:14:05 > 0:14:08snakes have an unrivalled collection of senses.
0:14:20 > 0:14:24Perhaps the snake's most familiar feature is its forked tongue,
0:14:24 > 0:14:26which it uses to smell.
0:14:28 > 0:14:30Its two tips or "tines"
0:14:30 > 0:14:34spread out as much as twice the width of its head...
0:14:39 > 0:14:42..significantly widening its field of detection.
0:14:46 > 0:14:48As the tongue swipes through the air,
0:14:48 > 0:14:52each tip simultaneously samples different points...
0:14:57 > 0:15:01..picking up scent particles as it goes.
0:15:12 > 0:15:16But a snake's tongue doesn't taste as ours does.
0:15:17 > 0:15:21It's merely a transport device,
0:15:21 > 0:15:23carrying odour molecules
0:15:23 > 0:15:26from the air or ground, back to the snake's
0:15:26 > 0:15:30olfactory centre, the Jacobson's Organ.
0:15:33 > 0:15:35Situated above the roof of the mouth,
0:15:35 > 0:15:38THIS is where the sample is analysed.
0:15:41 > 0:15:45The molecules from each tine are processed separately,
0:15:45 > 0:15:49allowing the snake to assess its surroundings in stereo.
0:15:55 > 0:15:58But a snake's tongue is capable of more than just
0:15:58 > 0:16:01sensing their environment.
0:16:10 > 0:16:15These garter snakes use them in a completely different way altogether.
0:16:18 > 0:16:20In North America,
0:16:20 > 0:16:24adult garter snakes hunt prey such as salamanders, frogs and toads.
0:16:26 > 0:16:29But juveniles need to start small.
0:16:31 > 0:16:34Having identified a good spot...
0:16:38 > 0:16:42..they then fully extend their tongues to delicately touch
0:16:42 > 0:16:44the surface of the water...
0:16:45 > 0:16:48..mimicking worms or insects...
0:16:50 > 0:16:52..to lure in their prey.
0:16:57 > 0:17:00It's the snake equivalent of fly fishing.
0:17:03 > 0:17:06Whilst garters use their tongues to smell and attract
0:17:06 > 0:17:10their food, snakes have another sense...
0:17:12 > 0:17:15..one that enables them to detect
0:17:15 > 0:17:18prey before they can even see it.
0:17:24 > 0:17:29Puff adders use their proximity to the ground to their advantage.
0:17:35 > 0:17:39By resting their lower jaw directly on the substrate,
0:17:39 > 0:17:43they can identify the slightest of movements...
0:17:46 > 0:17:49..from as much as a metre away.
0:17:53 > 0:17:58The footsteps of this striped mouse create tiny ground
0:17:58 > 0:18:00and surface vibrations.
0:18:02 > 0:18:05And when they reach the adder,
0:18:05 > 0:18:08they're transmitted through the jawbones to its inner ear.
0:18:08 > 0:18:12Whilst snakes don't have any external ear openings,
0:18:12 > 0:18:17the inner ear is extremely well developed to sense vibrations
0:18:17 > 0:18:20and low frequency sounds.
0:18:21 > 0:18:24In fact, the puff adder is even able
0:18:24 > 0:18:28to calculate the direction the mouse is travelling.
0:18:28 > 0:18:30You see, their jaws,
0:18:30 > 0:18:33like all snakes, are separated into two halves.
0:18:35 > 0:18:39By comparing the timing of vibrations that each jawbone receives
0:18:39 > 0:18:43the adder is able to detect the
0:18:43 > 0:18:45precise location of their prey.
0:18:48 > 0:18:51But what if there are no vibrations to detect?
0:18:52 > 0:18:55What if your prey isn't even on the ground?
0:19:01 > 0:19:06Some snakes have an additional sixth sense for hunting.
0:19:11 > 0:19:16Deep inside this cave in Borneo, bats are returning to roost.
0:19:20 > 0:19:23Flying fast and in the pitch darkness.
0:19:27 > 0:19:31When all we could sense is chaos and flapping...
0:19:33 > 0:19:35..a snake sees an opportunity.
0:19:44 > 0:19:47Its senses cut straight through the commotion
0:19:47 > 0:19:50to hone in on a victim.
0:19:53 > 0:19:56It can see heat.
0:20:00 > 0:20:03Pit vipers, boas and pythons
0:20:03 > 0:20:06all have specialised heat-sensitive pits.
0:20:09 > 0:20:12Located on the face, these organs are packed with
0:20:12 > 0:20:15exceptionally receptive nerve fibres.
0:20:20 > 0:20:22They can detect a temperature change
0:20:22 > 0:20:26of as little as one-thousandth of a degree.
0:20:28 > 0:20:32The nerves feed directly into the optic area of the snake's brain...
0:20:34 > 0:20:38..creating a combined thermal and visual map.
0:20:40 > 0:20:42With this unique ability,
0:20:42 > 0:20:47snakes can sense each individual bat as they fly past...
0:20:49 > 0:20:52..and select a precise target.
0:21:06 > 0:21:08With their super senses,
0:21:08 > 0:21:12snakes can see things that most animals can't.
0:21:12 > 0:21:16Combined with a remarkable body, they have risen to the challenge
0:21:16 > 0:21:19of locating and striking at prey.
0:21:20 > 0:21:23But next, they have to kill it.
0:21:24 > 0:21:27And, for this, our limbless serpents
0:21:27 > 0:21:30have come up with some ingenious solutions.
0:21:33 > 0:21:34SNAKE HISSES
0:21:34 > 0:21:38Snakes hunt a huge variety of prey.
0:21:45 > 0:21:47But the python takes on the largest.
0:21:51 > 0:21:54They use brute force to overpower animals
0:21:54 > 0:21:57often much larger than they are.
0:22:04 > 0:22:09Squeezing so tightly, they even cut off the blood flow
0:22:09 > 0:22:11to their own tissues.
0:22:17 > 0:22:21But for short periods, their muscles can survive without oxygen.
0:22:34 > 0:22:39To conserve energy, pythons only squeeze for as long as necessary.
0:22:46 > 0:22:49Each time its prey exhales,
0:22:49 > 0:22:53the python applies a burst of pressure.
0:22:55 > 0:22:58Only when they no longer sense a heartbeat
0:22:58 > 0:23:01do they stop squeezing.
0:23:06 > 0:23:11A python's next challenge is to swallow and then
0:23:11 > 0:23:14digest such a substantial kill.
0:23:21 > 0:23:24Connected by an elastic ligament, the two halves of a snake's
0:23:24 > 0:23:29lower jaw move independently and stretch around the prey.
0:23:33 > 0:23:39It then uses a series of powerful, concertina-like muscle contractions,
0:23:39 > 0:23:42to swallow the meal...whole.
0:23:45 > 0:23:48And the skin around the mouth can stretch by 20%
0:23:48 > 0:23:50to accommodate the load.
0:23:54 > 0:23:58But inside, the change is even greater.
0:24:06 > 0:24:09To fuel digestion, a python's organs
0:24:09 > 0:24:12dramatically increase in size.
0:24:14 > 0:24:19The heart, liver and intestines grow as much as 150%
0:24:19 > 0:24:22to take on the task.
0:24:26 > 0:24:30It can take weeks for a python to digest a kill of this size.
0:24:32 > 0:24:37But then, following such a feast, it won't need to feed for months.
0:24:37 > 0:24:40Possibly, as much as a year.
0:24:45 > 0:24:48But what about smaller species?
0:24:48 > 0:24:51They don't have as much muscle power.
0:24:52 > 0:24:56So how do they disable their prey before it fights back?
0:25:02 > 0:25:06Well, to hunt, these snakes have developed possibly
0:25:06 > 0:25:11the most deadly weapon in the animal kingdom.
0:25:15 > 0:25:17Venom.
0:25:18 > 0:25:20A highly-modified,
0:25:20 > 0:25:23sticky saliva containing a cocktail
0:25:23 > 0:25:26of powerful toxins and enzymes.
0:25:30 > 0:25:33It's administered in a split second through the snake's fangs.
0:25:37 > 0:25:41And these modified teeth can take on a number of forms.
0:25:43 > 0:25:47Recent research into their structure has revealed that most fangs
0:25:47 > 0:25:50are, in fact, solid and not hollow.
0:25:54 > 0:25:58The highly viscous venom lies in a groove on the front edge
0:25:58 > 0:26:02of the fang, until the snake strikes.
0:26:04 > 0:26:08It's then pulled from the groove into the prey's tissues,
0:26:08 > 0:26:10like liquid into blotting paper.
0:26:22 > 0:26:27However, the most effective delivery of venom is via hollow,
0:26:27 > 0:26:29needle-like fangs.
0:26:31 > 0:26:35The Pallas' viper has exactly such weaponry.
0:26:36 > 0:26:39And it uses them to full effect
0:26:39 > 0:26:42during the seasonal bird migration in China.
0:26:44 > 0:26:47A tenth of a second...
0:26:47 > 0:26:50is all it takes to strike.
0:27:06 > 0:27:10A viper's fangs can even rotate to manoeuvre around obstacles
0:27:10 > 0:27:14like bone and ensure that venom is
0:27:14 > 0:27:18injected deep into the tissues.
0:27:20 > 0:27:24It's not just one compound, it's a deadly concoction.
0:27:26 > 0:27:30In the Pallas' viper, the venom includes haemotoxins
0:27:30 > 0:27:33that attack the circulatory system, inducing massive
0:27:33 > 0:27:35internal bleeding.
0:27:38 > 0:27:41For other species it contains cytotoxins
0:27:41 > 0:27:43that break down cell walls
0:27:43 > 0:27:46and neurotoxins that disable the nervous system.
0:27:50 > 0:27:54And in some snakes venom is even thought to include enzymes
0:27:54 > 0:27:57which aid the digestive process.
0:28:03 > 0:28:07Snakes have the ability to use their body as
0:28:07 > 0:28:10no other animal can.
0:28:10 > 0:28:14With a unique means of movement, acute senses
0:28:14 > 0:28:18and remarkable hunting techniques,
0:28:18 > 0:28:20these adaptable predators have
0:28:20 > 0:28:24turned a lack of limbs to their ultimate advantage.
0:28:25 > 0:28:29And THAT is the wonder of snakes!