0:00:02 > 0:00:04'My name's Steve Backshall.'
0:00:04 > 0:00:05Wo-o-oo!
0:00:05 > 0:00:10'And this is my search for the Deadly 60.'
0:00:10 > 0:00:12That's not just animals that are deadly to me...
0:00:12 > 0:00:15but animals that are deadly in their own world.
0:00:17 > 0:00:19'My crew and I are travelling the planet.'
0:00:19 > 0:00:21Are you coming with me?!
0:00:21 > 0:00:23'Every step of the way.'
0:00:27 > 0:00:29'Deadly.'
0:00:31 > 0:00:33'Deadly is in paradise.
0:00:33 > 0:00:36'Mexico's Yucatan Peninsula.
0:00:36 > 0:00:39'It's a miraculous place, lying between the Caribbean Sea
0:00:39 > 0:00:41'and the Gulf of Mexico.
0:00:41 > 0:00:44'Home to pristine jungles...
0:00:44 > 0:00:50'seas alive with lethal fish you simply will not believe...
0:00:50 > 0:00:52'and it's peppered with cave systems,
0:00:52 > 0:00:57'some of which contain some spine-chilling predators.
0:00:57 > 0:00:59'We're going to be going underwater,
0:00:59 > 0:01:03'underground, and even doing both at once.
0:01:03 > 0:01:06'But first up, it's a high-octane marine mission,
0:01:06 > 0:01:09'and one of our toughest assignments yet.'
0:01:14 > 0:01:17On Deadly 60, we do love a challenge, and the next animal
0:01:17 > 0:01:20we're going looking for could be the most difficult,
0:01:20 > 0:01:22the most challenging, we've ever tried.
0:01:22 > 0:01:24Now, I know that might seem a little bit far-fetched
0:01:24 > 0:01:27when I'm walking down a paradise beach just after dawn,
0:01:27 > 0:01:29but this isn't where we're searching.
0:01:29 > 0:01:31We're heading out there into the open ocean.
0:01:31 > 0:01:35We're going in search of the fastest fish on Earth - the sailfish.
0:01:35 > 0:01:38'Growing up to 3m long,
0:01:38 > 0:01:41'with a distinctive spear-like upper jaw,
0:01:41 > 0:01:45'these imposing undersea snipers are the speedsters of the deep.
0:01:45 > 0:01:48'They feed on shoals of smaller fish,
0:01:48 > 0:01:51'but gather in tight formation and move as one,
0:01:51 > 0:01:53'in what's known as a baitball.
0:01:53 > 0:01:56'The idea is to confuse predators and work together
0:01:56 > 0:01:59'so that no single fish becomes an easy meal.
0:01:59 > 0:02:01'The sailfish chase and herd the baitball,
0:02:01 > 0:02:04'trying desperately to knock the fish off balance,
0:02:04 > 0:02:07'whilst the small fish are doing everything they can to survive.
0:02:09 > 0:02:12'So, to find the sailfish, first, we have to find a baitball.
0:02:12 > 0:02:15'But as sailfish can obliterate a sardine shoal in minutes,
0:02:15 > 0:02:17'we'll have to move fast.'
0:02:17 > 0:02:20We have tried to film sailfish before,
0:02:20 > 0:02:22in Mozambique in East Africa.
0:02:22 > 0:02:25We spent three days out at sea and saw nothing at all.
0:02:25 > 0:02:28This truly is one of the trickiest animals we could ever hope for,
0:02:28 > 0:02:31and the reason for that is that they're what as known as pelagic.
0:02:31 > 0:02:32It means that they're an open sea fish.
0:02:32 > 0:02:35So, finding them at all is really, really hard.
0:02:35 > 0:02:38All we've got to do is put in the hours.
0:02:49 > 0:02:51We're just over an hour away from shore
0:02:51 > 0:02:54and we're into prime sailfish-spotting habitat.
0:02:54 > 0:02:58Now, really, it's just a question of spending as much time as we can,
0:02:58 > 0:03:00just looking out and trying to spot these baitballs.
0:03:00 > 0:03:02They could be anywhere, and we've got quite a swell,
0:03:02 > 0:03:05making it really, really difficult to spot anything.
0:03:05 > 0:03:07These baitballs don't last very long.
0:03:07 > 0:03:10We're going to only have a few minutes to get into the water
0:03:10 > 0:03:12and stand any chance of spotting this incredible fish
0:03:12 > 0:03:15that we've come halfway round the world to find.
0:03:16 > 0:03:20'But the baitball itself is going to be submerged. So, out of sight.
0:03:22 > 0:03:27'Well, luckily, we're not the only ones in search of a sardine feast.
0:03:27 > 0:03:29'There are airborne huntsmen scouring the skies.
0:03:29 > 0:03:31'We just need to follow them.'
0:03:31 > 0:03:33BIRDS SQUAWK
0:03:33 > 0:03:36These classic, formidable silhouettes above me
0:03:36 > 0:03:39are frigate birds. They're, themselves, fabulous predators
0:03:39 > 0:03:42and really, really imposing animals,
0:03:42 > 0:03:44but these are the sign that we're looking out for,
0:03:44 > 0:03:48as they're going to be diving down, spotting the baitballs from above.
0:03:48 > 0:03:49They have far, far better eyes
0:03:49 > 0:03:52and a far broader range of vision than we could ever hope for.
0:03:52 > 0:03:55So, we're going to be watching the skies, watching these birds,
0:03:55 > 0:03:59and hopefully, they will find the baitballs and the sailfish for us.
0:04:00 > 0:04:02'What we need to look for
0:04:02 > 0:04:04'is a change in behaviour in the frigate birds,
0:04:04 > 0:04:08'as they dive to the surface in a frenzy of activity.
0:04:08 > 0:04:11'They'll be our early warning system.'
0:04:11 > 0:04:12Oh-h-h!
0:04:12 > 0:04:14'It wasn't long before we got our first glimpses,
0:04:14 > 0:04:18'and encountered some other people on the hunt for sailfish.'
0:04:19 > 0:04:22We're not the only people out here today looking for big fish.
0:04:22 > 0:04:24There's lots of game fishing boats out.
0:04:24 > 0:04:27There's one in front of us right now,
0:04:27 > 0:04:30and it looks like they might have snagged something of a good size.
0:04:30 > 0:04:32This is obviously a good sign for us.
0:04:32 > 0:04:35It means that there are sailfish out there,
0:04:35 > 0:04:38although personally I'd always rather hunt an animal with a camera
0:04:38 > 0:04:39than with a hook.
0:04:39 > 0:04:43'Sailfish can breach clear of the water when chasing prey,
0:04:43 > 0:04:46'seeking to remove parasites from their bodies,
0:04:46 > 0:04:48'or trying to evade a fisherman's hook.
0:04:48 > 0:04:52'It's a tantalising glimpse of their acrobatic abilities.
0:04:52 > 0:04:56'We'd been out on the choppy seas all day and about to head for home,
0:04:56 > 0:04:58'when something on the horizon caught my eye.'
0:04:58 > 0:05:02OK, we've just got exactly the sign that we've been looking out for.
0:05:02 > 0:05:04There are frigate birds.
0:05:04 > 0:05:08They're diving down, which looks like there could be a baitball.
0:05:08 > 0:05:11So, time is now absolutely critical. Things are really going to kick off.
0:05:11 > 0:05:15We've got to get over there and in the water as soon as possible.
0:05:15 > 0:05:16OK, guys, let's hit it!
0:05:16 > 0:05:19'The sardines are going to be frantically fleeing
0:05:19 > 0:05:22'from the birds and the predators beneath.
0:05:22 > 0:05:24'Keeping up with them is going to be near impossible.'
0:05:24 > 0:05:27This really is a once-in-a-lifetime opportunity.
0:05:27 > 0:05:31There's obviously an enormous shoal of fish there
0:05:31 > 0:05:34to have all of these birds active here.
0:05:34 > 0:05:36Just got to get in right, because they're so fast,
0:05:36 > 0:05:41once they decide to take off, you have no chance of following them.
0:05:41 > 0:05:42Right here. Right on the bottom.
0:05:42 > 0:05:45- Camera, camera, camera! - Go, go, go, right there!
0:05:45 > 0:05:46Right here, right in front of you!
0:05:49 > 0:05:53'I was hoping to see one sailfish, and at a distance.
0:05:53 > 0:05:58'Instead, there's a menacing shoal of dark shapes.
0:05:58 > 0:06:02'A pack of undersea wolves pursuing the sardines with murderous intent.
0:06:02 > 0:06:06'Their hydrodynamic shape makes them look like dark torpedoes,
0:06:06 > 0:06:08'and even casually cruising,
0:06:08 > 0:06:11'they disappear into the distance in seconds.'
0:06:14 > 0:06:16This is absolutely unbelievable.
0:06:16 > 0:06:21There must be 40 sailfish, maybe more.
0:06:21 > 0:06:24Just an enormous shoal of them with genuine intent.
0:06:24 > 0:06:28I haven't even actually seen the baitfish yet, and it was just
0:06:28 > 0:06:31the merest of glances before they disappeared off into the blue.
0:06:31 > 0:06:34If we can just get close enough, this is going to be unbelievable.
0:06:40 > 0:06:43- MUFFLED:- Over there, look over there! Can you see them?
0:06:43 > 0:06:45- Can you see them feeding?! - Go, go, go, go, go!
0:06:45 > 0:06:48'The sailfish have split the baitball,
0:06:48 > 0:06:50'isolating a smaller group.
0:06:50 > 0:06:53'This lot are as good as gone.'
0:06:56 > 0:06:58'The sailfish glide past like shadows.
0:06:58 > 0:07:01'They're deceptively big and can weigh more than me,
0:07:01 > 0:07:02'but their acceleration
0:07:02 > 0:07:05'would put any speedboat or sports car to shame.
0:07:05 > 0:07:08'Their sickle-shaped tails power them through the water.
0:07:08 > 0:07:11'They use their distinctive sail-like dorsal fins
0:07:11 > 0:07:13'to herd the small fish.
0:07:17 > 0:07:19'The sardines frantically flock together,
0:07:19 > 0:07:23'but they're battling the fastest force in the seas.
0:07:23 > 0:07:26'The sailfish lash around with their rapier upper mandible,
0:07:26 > 0:07:28'separating and stunning the sardines.
0:07:28 > 0:07:31'It's utterly remorseless.'
0:07:40 > 0:07:43I don't believe it. I just don't believe it.
0:07:43 > 0:07:48There was clouds of the fastest predator in the sea
0:07:48 > 0:07:51just circling around us, circling around us,
0:07:51 > 0:07:54coming up and hammering the small fish at the surface.
0:07:54 > 0:07:56We've got to get back in as quickly as we can.
0:07:56 > 0:08:00They're moving off in this direction.
0:08:02 > 0:08:06There are so many sailfish, you can see the dorsal fins
0:08:06 > 0:08:10actually cutting through the surface, almost like sharks.
0:08:10 > 0:08:15Look! Thrashing through the water. Definitely time to get in.
0:08:15 > 0:08:19There's the sardines! The sardines are here.
0:08:19 > 0:08:21'Under ceaseless attack,
0:08:21 > 0:08:24'the bait-ball is diminishing minute by minute.
0:08:24 > 0:08:28'The relentless onslaught continues from above,
0:08:28 > 0:08:30'with the swooping frigates.
0:08:30 > 0:08:34'Everywhere the hapless fish turn, they're torn to shreds.
0:08:38 > 0:08:41'The sardines may be more manoeuvrable,
0:08:41 > 0:08:46'but in explosive bursts of straight speed, the sailfish has no equal.
0:08:46 > 0:08:51'The bill slices side to side, disorientating the smaller fish,
0:08:51 > 0:08:54'leaving them as isolated, easy targets.
0:08:54 > 0:08:58'The sardines will take any shelter on offer - even me!
0:09:05 > 0:09:09'I'm in serious danger of getting skewered.
0:09:09 > 0:09:12'Once the bait-ball is diminished, the sailfish won't stop
0:09:12 > 0:09:16'until every last fish is gone.'
0:09:34 > 0:09:37'The sole memory of this dazzling display
0:09:37 > 0:09:40'are snowflakes of shimmering scales.'
0:09:42 > 0:09:45That was one of the most extraordinary things
0:09:45 > 0:09:49I've ever seen, in a lifetime looking at wildlife.
0:09:54 > 0:09:58I've just been absolutely surrounded by one of the most
0:09:58 > 0:10:02extraordinary predators on earth that is in its way,
0:10:02 > 0:10:04every bit as spectacular
0:10:04 > 0:10:08as seeing lions tear apart a gazelle in Africa.
0:10:08 > 0:10:12Within minutes, a huge shoal had been reduced to a few fish.
0:10:12 > 0:10:15There's no doubt in my mind that this is one of the most
0:10:15 > 0:10:18extraordinary animals that's ever been on the Deadly 60.
0:10:18 > 0:10:24The fastest fish in the sea - the sailfish. Definitely deadly.
0:10:26 > 0:10:29This swimming speedster can reach 68mph.
0:10:29 > 0:10:32A flick of their scimitar-shaped tail brings top speed
0:10:32 > 0:10:35in a millisecond. With their spear-like upper jaw,
0:10:35 > 0:10:38they stun their prey before gulping them down.
0:10:38 > 0:10:40It's a true Deadly icon.
0:10:40 > 0:10:42Scintillating sailfish...
0:10:42 > 0:10:44# Deadly! #
0:10:46 > 0:10:49We're journeying even further from the Yucatan Peninsular mainland
0:10:49 > 0:10:54to the island of Cozumel - not exactly Caribbean weather,
0:10:54 > 0:10:57but it's not going to be raining underwater and that's where
0:10:57 > 0:11:01we're heading, in search of some of the finest diving in Mexico.
0:11:03 > 0:11:06So below us now is a pristine coral reef
0:11:06 > 0:11:08at around about 20 metres of water.
0:11:08 > 0:11:10One thing about scuba-diving is that really,
0:11:10 > 0:11:12you have no idea what you'll find.
0:11:12 > 0:11:14You cannot predict it, but there's so many things
0:11:14 > 0:11:17that live on reefs that we could easily put onto our list.
0:11:17 > 0:11:21My hopes are fairly high - fingers crossed.
0:11:21 > 0:11:24So, after final preparations, with safety checks complete,
0:11:24 > 0:11:27we entered the underwater wonderland,
0:11:27 > 0:11:32in search of something deadly, but different, to add to the list.
0:11:35 > 0:11:38Well, this is really impressive.
0:11:38 > 0:11:40HE INHALES LOUDLY
0:11:40 > 0:11:45Exactly what you'd hope for from a Caribbean reef.
0:11:45 > 0:11:49The barrier reef that runs along the east coast of Mexico
0:11:49 > 0:11:54and down through Belize is the second-longest in the world
0:11:54 > 0:11:57after Australia's Great Barrier Reef.
0:11:57 > 0:11:59And it is truly magnificent.
0:12:00 > 0:12:05There is so much life here, so much biodiversity.
0:12:07 > 0:12:10And the colours are just exquisite.
0:12:14 > 0:12:17'And it wasn't long before we stumbled upon our first
0:12:17 > 0:12:20'killer candidate.'
0:12:21 > 0:12:29Just sleeping underneath this overhang here is a nurse shark.
0:12:29 > 0:12:32They're very unusual sharks, really.
0:12:32 > 0:12:36Quite often, people will say that a shark needs to be swimming,
0:12:36 > 0:12:39it needs to be up in the water column
0:12:39 > 0:12:43in order to drive water over its gills,
0:12:43 > 0:12:46but that's not always the case.
0:12:46 > 0:12:51These sharks have small holes behind their eyes called spiracles
0:12:51 > 0:12:53that they can breathe through,
0:12:53 > 0:12:57which enables them to lie like this, just chilling out in the daytime.
0:12:57 > 0:13:01At night though, they go out on the reef to hunt.
0:13:02 > 0:13:05Looking at the front of the nose,
0:13:05 > 0:13:09there are two sensory barbels that hang down.
0:13:09 > 0:13:11They use these to taste crustaceans
0:13:11 > 0:13:14and other animals that are down in the sand on the seabed.
0:13:14 > 0:13:17It uses those to sense its prey.
0:13:17 > 0:13:20They're really rather wonderful.
0:13:20 > 0:13:24I have a bit of a soft spot for nurse sharks.
0:13:24 > 0:13:28'Definitely a good start, but we've had lots of sharks on the list.
0:13:28 > 0:13:31'This time, I'd like to find something more unusual.'
0:13:33 > 0:13:38Some of the largest fish on the reef are groupers.
0:13:39 > 0:13:40This is a black grouper.
0:13:42 > 0:13:45Although it's actually changed colour quite dramatically
0:13:45 > 0:13:49from where it was originally - it's now gone much, much lighter.
0:13:49 > 0:13:52It has a huge lips,
0:13:52 > 0:13:54a big old mouth
0:13:54 > 0:13:56and they are predatory.
0:13:56 > 0:14:00This particular species feeds on smaller fish.
0:14:02 > 0:14:04Nice.
0:14:06 > 0:14:08'Another possible contender,
0:14:08 > 0:14:12'but I think we can find something with a bit more bite.'
0:14:12 > 0:14:14Oh, yes.
0:14:16 > 0:14:21Lurking underneath this crevice is truly a worthy contender
0:14:21 > 0:14:24for my Deadly 60 list.
0:14:24 > 0:14:26It's a green Moray eel.
0:14:27 > 0:14:32It's one of the largest species of Moray eel and this one here
0:14:32 > 0:14:37looks like he's probably as fat around as one of my legs.
0:14:37 > 0:14:40He's huge! Probably over two metres long
0:14:40 > 0:14:44and it's an animal that has quite a nasty reputation
0:14:44 > 0:14:49amongst divers and when you look inside their mouth, you can see why.
0:14:49 > 0:14:54They've got really quite an impressive set of teeth on them.
0:14:55 > 0:14:59During the daytime, they do tend to hide out in crevices like this.
0:14:59 > 0:15:03Occasionally, they will go out on the reef to hunt, but normally,
0:15:03 > 0:15:09they just sit here waiting in ambush for something to come by.
0:15:09 > 0:15:14One of the things though that actually sets Morays apart
0:15:14 > 0:15:16is their senses.
0:15:16 > 0:15:20The eyes are quite milky, not tremendously useful,
0:15:20 > 0:15:23but they have an incredible sense of smell.
0:15:23 > 0:15:26There are four nostrils.
0:15:26 > 0:15:29Two small, recessed ones just in front of the eyes
0:15:29 > 0:15:35and then at the end of the nose are two nostrils on tubes,
0:15:35 > 0:15:37and those are incredibly good
0:15:37 > 0:15:40at just plucking the tiniest scents out of the water.
0:15:40 > 0:15:43Then it will snap out and grab a hold of
0:15:43 > 0:15:48usually things like fish, sometimes crabs and other crustaceans as well.
0:15:50 > 0:15:54The green Moray - he's a menacing monster
0:15:54 > 0:15:57and I think has to go on my list.
0:15:59 > 0:16:01With huge, muscular bodies
0:16:01 > 0:16:03that can grow up to 2.5 metres long
0:16:03 > 0:16:07and gaping jaws that are rammed with rows of pointy teeth,
0:16:07 > 0:16:09these stealthy ambush predators
0:16:09 > 0:16:13sniff out their prey and snatch it as it passes.
0:16:13 > 0:16:15Moray eel...
0:16:15 > 0:16:16# Deadly! #
0:16:19 > 0:16:23'For the final leg of our Mexican mission, we're heading underground.
0:16:23 > 0:16:26'The Yucatan is peppered with caverns,
0:16:26 > 0:16:29'some of which are filled with sinister predators.
0:16:29 > 0:16:33'Others offer some of the most dramatic spectacles imaginable.
0:16:33 > 0:16:36'Sunken wonderlands filled with water so clear,
0:16:36 > 0:16:38'it feels like floating in air.
0:16:38 > 0:16:43'These caves were formed when sea and water levels were much lower,
0:16:43 > 0:16:46'but were later flooded with subterranean rivers.
0:16:46 > 0:16:47'They're called cenotes
0:16:47 > 0:16:51'and are one of the wonders of the natural world.'
0:16:52 > 0:16:56This is just unbelievable.
0:16:56 > 0:17:01All of these formations - they're like thrones and chandeliers.
0:17:01 > 0:17:06It's just some curious subterranean sunken kingdom,
0:17:06 > 0:17:08indescribably beautiful.
0:17:10 > 0:17:14'And amongst all this splendour, there is some wildlife.'
0:17:14 > 0:17:20Catfish are remarkably well adapted for living in these cave systems.
0:17:20 > 0:17:24Those long whiskers tapping around.
0:17:24 > 0:17:28They're called barbels and they're extremely sensitive.
0:17:30 > 0:17:34They're covered with receptors for tastes and smells
0:17:34 > 0:17:39and also thousands of very, very sensitive nerve endings.
0:17:40 > 0:17:45This animal is sensing its whole environment through those whiskers,
0:17:45 > 0:17:50so even in total darkness, it still knows what's going on.
0:17:50 > 0:17:54'Deeper in the cave, in a world that hasn't seen sunlight
0:17:54 > 0:17:58'in millions of years, it was as if we'd swum into a strange dream.'
0:17:58 > 0:18:03The water here has taken on a very, very curious consistency.
0:18:03 > 0:18:09It's because we've dropped from clear, freshwater into salty water.
0:18:11 > 0:18:16It's called a halocline - an area where salty water, which is heavy,
0:18:16 > 0:18:20sits underneath the lighter freshwater.
0:18:20 > 0:18:25Look at how the whole water has gone...all weird!
0:18:25 > 0:18:29Very, very curious.
0:18:31 > 0:18:34'In the next chamber, we found another animal hanging out.'
0:18:37 > 0:18:40Some of these caves are the perfect place
0:18:40 > 0:18:42for bats to make their day roosts.
0:18:42 > 0:18:46They're really safe from predators in here,
0:18:46 > 0:18:49but there's one cave system on the Yucatan Peninsula
0:18:49 > 0:18:52that I know of where the predators have learnt exactly
0:18:52 > 0:18:55where the bats live and they're nothing like so safe.
0:18:55 > 0:18:58That's where we're headed to next.
0:19:02 > 0:19:04This is our cave.
0:19:04 > 0:19:08Somewhere inside there is a massive colony of bats
0:19:08 > 0:19:11and the predators that are hunting for them...
0:19:11 > 0:19:14Well, for a clue, I've got my snake stick with me.
0:19:14 > 0:19:17This cave is home to dazzling,
0:19:17 > 0:19:21dangling hunters that have to be seen to be believed.
0:19:25 > 0:19:30The local people call this cave "La Cueva de las Serpientes Colgantes",
0:19:30 > 0:19:32or something like that - my Mexican isn't particularly good.
0:19:32 > 0:19:36But what it means is, "the cave of the hanging serpents".
0:19:36 > 0:19:38Which bodes well, I guess.
0:19:38 > 0:19:41For lots of people, that should be their living nightmare,
0:19:41 > 0:19:44but for me, it's a very exciting thought.
0:19:44 > 0:19:47'The snakes are here because they eat the bats,
0:19:47 > 0:19:50'but we're unlikely to see them hunting just yet.'
0:19:50 > 0:19:53One thing about cave that makes them
0:19:53 > 0:19:56really, really good for wildlife is that they're constant -
0:19:56 > 0:20:00they have constant temperature, the environment inside here tends
0:20:00 > 0:20:04to be very similar, day-in, day-out and the other thing is
0:20:04 > 0:20:08the animals that live here tend to be constant in their behaviour, too.
0:20:08 > 0:20:14Every single day, they'll be pouring out to the outside to feed.
0:20:14 > 0:20:17The fact that they do that like clockwork means that
0:20:17 > 0:20:20predators know exactly what they're going to do.
0:20:21 > 0:20:26Where I'm expecting to find the snakes is at areas
0:20:26 > 0:20:29that are natural bottlenecks, where the bats are going to have to
0:20:29 > 0:20:32pass through as they're heading out to feed.
0:20:34 > 0:20:37'The bats won't start properly emerging until nightfall,
0:20:37 > 0:20:38'so in the meantime,
0:20:38 > 0:20:42'I'd like to show you a snake before it's in full-on hunt mode.
0:20:43 > 0:20:47'And here's one, lazing around before the deluge begins.'
0:20:50 > 0:20:55So... This is the snake that we've come here to find.
0:20:56 > 0:20:58Isn't it beautiful?
0:20:58 > 0:21:01It's a Mexican night snake
0:21:01 > 0:21:05and gorgeous, gorgeous colours
0:21:05 > 0:21:09running down the length of its body.
0:21:09 > 0:21:11And it's chosen to live in this cave
0:21:11 > 0:21:15because of the amount of food that's around here.
0:21:15 > 0:21:20Now, it might seem incredible that a snake of this size could
0:21:20 > 0:21:22catch something as big as a bat.
0:21:22 > 0:21:25I mean, it only has a very tiny head,
0:21:25 > 0:21:29but it does have the ability to stretch its jaws
0:21:29 > 0:21:33and take in prey that's many, many times larger than its own head.
0:21:33 > 0:21:36Look at the size of the eyes.
0:21:36 > 0:21:40They're huge in comparison to most snakes of this size.
0:21:40 > 0:21:44So it's pretty good at seeing in near-total darkness.
0:21:44 > 0:21:48But it's also exceptional at striking out at animals
0:21:48 > 0:21:50and catching them on the wing.
0:21:50 > 0:21:56The underside of the body is concave - acts almost like one big,
0:21:56 > 0:22:00long suction cup and it also grips with these two portions
0:22:00 > 0:22:02of the underside of the body,
0:22:02 > 0:22:05plus those scales there give it extra grip.
0:22:05 > 0:22:10It makes them absolutely fantastic climbers - let's see it at work.
0:22:16 > 0:22:19'The first few bats are taking flight,
0:22:19 > 0:22:22'but soon these caverns will be thronged with flapping wings.
0:22:22 > 0:22:25'We need to find one of those bottlenecks
0:22:25 > 0:22:28'where the snakes are waiting to feed.'
0:22:28 > 0:22:32The main area that the bats are emerging from is a cave tunnel
0:22:32 > 0:22:35just here, to the side of where I'm standing now.
0:22:35 > 0:22:38If we go in there with all of our bright lights, then the snakes
0:22:38 > 0:22:42will simply call back into their holes, so the best thing for me
0:22:42 > 0:22:44to do is go in on my own,
0:22:44 > 0:22:48using this infrared camera with this light.
0:22:48 > 0:22:50Hopefully, the snakes won't pick that up
0:22:50 > 0:22:53and they'll be able to go about their business of hunting and
0:22:53 > 0:22:57I should stand at least a chance of seeing one catching a bat.
0:22:57 > 0:23:00So you guys wait out here, yeah? All right.
0:23:00 > 0:23:02See you soon!
0:23:08 > 0:23:12'Infrared light has a different wavelength to visible light,
0:23:12 > 0:23:14'which means that animals can't see it.
0:23:14 > 0:23:18'But I can't see it, either, so I'm crawling around in the pitch
0:23:18 > 0:23:21'darkness and my only view is through the camera.'
0:23:23 > 0:23:25OK,
0:23:25 > 0:23:28I've got a snake in front of me, in absolutely perfect position
0:23:28 > 0:23:32and posture, so I'm just going to hang out now
0:23:32 > 0:23:35and hope to catch it striking on camera.
0:23:40 > 0:23:44It's pulled itself back up into the rocks.
0:23:44 > 0:23:48It probably heard me and is feeling a bit intimidated.
0:23:48 > 0:23:52I might just have to push on a little bit further into the cave.
0:23:52 > 0:23:56'Every night, the bats have to run the gauntlet past these
0:23:56 > 0:24:00'hanging huntsmen to get out into the forests and feed.
0:24:00 > 0:24:02'There are tens of thousands of bats
0:24:02 > 0:24:06'and these must be some of the best-fed snakes on earth.'
0:24:10 > 0:24:12There's a snake. There's one right there.
0:24:12 > 0:24:16'The night snakes can get over a metre and a half in length
0:24:16 > 0:24:18'and this one doesn't look far off.'
0:24:18 > 0:24:21This is incredible. He's just hanging down,
0:24:21 > 0:24:22striking out into the air.
0:24:23 > 0:24:26And it seems like it's the vibrations
0:24:26 > 0:24:29that are caused by the bats as they fly past that he's centring on.
0:24:29 > 0:24:34It's not so much other cues, as just the pure movement of the bats.
0:24:36 > 0:24:39He's got one. It's got one right now.
0:24:40 > 0:24:43I didn't quite get the strike on camera, but it's so fast.
0:24:44 > 0:24:48It's wrapping coils of the body around the bat and now,
0:24:48 > 0:24:50what it's going to do is squeeze.
0:24:50 > 0:24:54Science shows that constricting snakes can actually sense
0:24:54 > 0:24:56the heartbeat of their prey, so they can tell
0:24:56 > 0:25:01if the animal is still alive, so as soon as this bat is completely dead,
0:25:01 > 0:25:04it will start to swallow it and that's when I can think about
0:25:04 > 0:25:07calling in the camera crew.
0:25:07 > 0:25:12It's a phenomenal sight. These bats are leaving in enormous numbers.
0:25:12 > 0:25:15There are tens of thousands of bats flying through here
0:25:15 > 0:25:17and they're travelling so quickly,
0:25:17 > 0:25:20but this snake, in total pitch darkness, still has
0:25:20 > 0:25:23the wherewithal, the speed, to strike out at
0:25:23 > 0:25:25and catch these bats in flight.
0:25:25 > 0:25:29It's just a remarkable feeding strategy.
0:25:31 > 0:25:33Johnny? Johnny!
0:25:35 > 0:25:38'Now the night snake is swallowing the bat,
0:25:38 > 0:25:41'it shouldn't be put off by our lights.'
0:25:51 > 0:25:54You can see it's manoeuvred the bat so that it's headfirst
0:25:54 > 0:25:58and it's starting to work it down its throat.
0:25:59 > 0:26:02It's an extraordinary achievement,
0:26:02 > 0:26:05just purely to get this bat down its throat.
0:26:09 > 0:26:12Look at that - it's pretty grotesque, really.
0:26:12 > 0:26:17It's eating a bat that's many times larger than its own head.
0:26:18 > 0:26:21You can see it's quite a fat-bodied snake.
0:26:21 > 0:26:25I mean, once it's got this one down into its stomach,
0:26:25 > 0:26:28it might easily feed again,
0:26:28 > 0:26:30possibly even twice more tonight.
0:26:30 > 0:26:34They are absolutely extraordinary snakes.
0:26:34 > 0:26:37I'm looking down into the tiny,
0:26:37 > 0:26:40needle-sharp, backwards-pointing teeth
0:26:40 > 0:26:43that are delivering that bat back into its gullet.
0:26:44 > 0:26:48You can see, it's having quite a struggle getting the animal down.
0:26:48 > 0:26:52You can see the exact shape of the bat running right down
0:26:52 > 0:26:54the back of its throat.
0:27:00 > 0:27:03The bat-munching Mexican night snake,
0:27:03 > 0:27:07quick enough in strike to catch the fastest-flying mammals
0:27:07 > 0:27:10on the wing. Definitely deadly!
0:27:13 > 0:27:15With superb climbing skills,
0:27:15 > 0:27:17they hang from the cave walls.
0:27:17 > 0:27:19Hunting in total darkness,
0:27:19 > 0:27:22they pick up tiny vibrations from their prey, catching bats
0:27:22 > 0:27:26that are much bigger than their heads and swallowing them whole.
0:27:26 > 0:27:29These splendid, stealthy serpents are going on my list.
0:27:29 > 0:27:31# Deadly! #
0:27:33 > 0:27:37'Join me next time as I continue my search for the Deadly 60.'
0:27:37 > 0:27:40This is one of the greatest spectacles I have ever witnessed.
0:27:55 > 0:27:59Subtitles by Red Bee Media Ltd
0:28:00 > 0:28:03# Deadly! #