1
00:00:02,525 --> 00:00:07,022
This is a programme
about the most successful of all predators.
2
00:00:07,082 --> 00:00:09,485
Watch and wonder.
3
00:00:47,201 --> 00:00:52,947
This giant snake could squeeze me
till I'm unconscious
4
00:00:52,996 --> 00:00:57,380
and then it could unhinge
its lower jaw and eat me.
5
00:00:57,826 --> 00:01:02,723
So it's not surprising
that I treat it with some respect
6
00:01:02,758 --> 00:01:06,358
and that people have
a proper fear of some snakes.
7
00:01:07,321 --> 00:01:11,544
But the fact is that snakes
are wonderful creatures,
8
00:01:11,789 --> 00:01:15,931
superbly adapted to their particular lives.
9
00:01:16,135 --> 00:01:18,423
And to appreciate that,
10
00:01:18,549 --> 00:01:21,879
you have to see the world
through the snake's eyes.
11
00:01:21,914 --> 00:01:25,210
That's what this programme
is going to try to do,
12
00:01:25,654 --> 00:01:30,039
to allow you to become,
in your imagination, a snake.
13
00:01:47,643 --> 00:01:52,542
To enter into their world, we've used
miniature cameras on many snakes,
14
00:01:52,577 --> 00:01:56,005
but, in particular, a giant African python.
15
00:02:14,278 --> 00:02:18,778
Snakes are far and away
the most successful of all predators.
16
00:02:18,813 --> 00:02:22,245
There are 2,700 species of snake in the world.
17
00:02:23,012 --> 00:02:26,264
They come in all colours and sizes.
18
00:02:29,454 --> 00:02:33,519
They live at ground level and in trees.
19
00:02:36,214 --> 00:02:38,905
They live underground.
20
00:02:39,153 --> 00:02:41,809
They even live in the sea.
21
00:02:43,018 --> 00:02:47,002
There are snakes that live
16,000 feet up in the Himalayas.
22
00:02:47,768 --> 00:02:52,428
And snakes that live
in scorching waterless deserts.
23
00:02:53,566 --> 00:02:57,184
Some live as far north as the Arctic Circle.
24
00:02:59,274 --> 00:03:02,330
But most inhabit tropical forests.
25
00:03:04,950 --> 00:03:07,962
There are few places that don't have snakes.
26
00:03:08,691 --> 00:03:11,862
Antarctica and Ireland are among them.
27
00:03:13,521 --> 00:03:18,262
There are few hiding places
for the animals that snakes feed on.
28
00:03:19,519 --> 00:03:24,135
Some snakes hunt by day.
And most of them have huge round pupils.
29
00:03:24,170 --> 00:03:28,751
Some snakes hunt at night.
They have vertical slit pupils.
30
00:03:30,230 --> 00:03:34,570
All snakes can kill
from the moment they are born.
31
00:03:34,739 --> 00:03:37,350
Snakes are masters of camouflage...
32
00:03:38,765 --> 00:03:40,608
... and ambush.
33
00:03:41,463 --> 00:03:43,431
They can climb.
34
00:03:44,470 --> 00:03:46,367
They can even fly.
35
00:03:46,402 --> 00:03:48,532
They're killing machines.
36
00:03:51,314 --> 00:03:53,603
But they are also truly beautiful,
37
00:03:53,729 --> 00:03:57,461
with a range of behaviours
that are intricate and fascinating,
38
00:03:57,915 --> 00:04:02,861
from the vast gatherings of garter snakes
newly emerged from hibernation
39
00:04:02,896 --> 00:04:05,258
to the coiling behaviour of sea snakes,
40
00:04:05,293 --> 00:04:09,438
which use the technique
for rubbing barnacles off their skins.
41
00:04:11,858 --> 00:04:14,836
The smallest snake in the world lives here,
42
00:04:14,871 --> 00:04:17,573
and here, and here.
43
00:04:17,938 --> 00:04:21,751
In fact, any town or city anywhere in the tropics.
44
00:04:21,924 --> 00:04:25,862
This snake is so small
it's been exported in the soil of tropical plants
45
00:04:25,897 --> 00:04:28,806
to garden centres all over the world.
46
00:04:30,338 --> 00:04:32,788
Like this one in Sao Paulo.
47
00:04:34,747 --> 00:04:36,644
It looks like a worm.
48
00:04:36,679 --> 00:04:41,421
In fact, it's difficult to see
which is its head and which its tail...
49
00:04:43,163 --> 00:04:45,131
... until it tongue-flicks.
50
00:04:46,867 --> 00:04:51,208
This is a typhlops, five or six centimetres long,
51
00:04:51,337 --> 00:04:56,174
practically blind,
and feeding on tiny invertebrates.
52
00:04:56,209 --> 00:05:02,722
So the world's smallest snake
is also the world's most widespread snake.
53
00:05:07,014 --> 00:05:10,793
At the other end of the scale,
possibly the world's largest snake -
54
00:05:11,362 --> 00:05:14,226
certainly the heaviest - is the anaconda.
55
00:05:14,261 --> 00:05:17,639
It can reach nearly nine metres in length...
56
00:05:21,025 --> 00:05:23,518
... have a bodily girth as big as a pig,
57
00:05:23,553 --> 00:05:26,011
and weigh as much as 200 kilograms.
58
00:05:29,186 --> 00:05:33,125
Animals without legs. They seem so ridiculous.
59
00:05:33,160 --> 00:05:36,029
So unversatile, so inefficient.
60
00:05:36,434 --> 00:05:38,816
Yet we know this isn't so.
61
00:05:38,851 --> 00:05:44,244
Otherwise snakes wouldn't be
the most successful predators on the planet.
62
00:05:48,152 --> 00:05:51,164
But if we go back in time a few million years,
63
00:05:51,494 --> 00:05:54,953
we discover that snakes then did,
in fact, have legs.
64
00:05:55,320 --> 00:06:02,043
The ancestor of modern snakes might have
looked like this, a kind of marine lizard.
65
00:06:02,246 --> 00:06:04,617
But when this animal came out of the water
66
00:06:04,903 --> 00:06:09,370
and tried to run beneath undergrowth
or chase its prey underground,
67
00:06:09,405 --> 00:06:12,505
it would have found its legs an encumbrance,
68
00:06:12,540 --> 00:06:14,553
so over generations it lost them.
69
00:06:14,640 --> 00:06:17,046
And that's the point about snakes.
70
00:06:17,780 --> 00:06:22,488
It was actually an advantage for them
to lose their limbs.
71
00:06:29,160 --> 00:06:31,932
Now snakes could move equally well
72
00:06:32,060 --> 00:06:37,215
on the ground, under the ground,
in undergrowth, in trees or in water.
73
00:06:37,376 --> 00:06:43,286
And different snakes solve the problem
of legless movement in different ways.
74
00:06:45,107 --> 00:06:49,175
Our giant python moves
by contracting and relaxing the muscles
75
00:06:49,417 --> 00:06:52,716
along the underside of its body.
76
00:06:55,260 --> 00:06:59,521
The muscular movement ripples
down the body in waves from nose to tail,
77
00:06:59,610 --> 00:07:04,353
the scales gripping the ground
and pushing the snake forward.
78
00:07:07,624 --> 00:07:11,325
So the python moves ahead in a straight line.
79
00:07:15,157 --> 00:07:18,537
This kind of snake movement
isn't particularly fast,
80
00:07:19,024 --> 00:07:23,154
but it uses very little energy -
just 20 calories a day.
81
00:07:23,189 --> 00:07:25,738
A python only eats occasionally
82
00:07:26,343 --> 00:07:30,570
and doesn't have that many enemies
it needs to escape from.
83
00:07:33,553 --> 00:07:36,837
But how does such a slow animal
ever catch anything?
84
00:07:36,872 --> 00:07:43,518
Well, we'll be returning to our giant python
to discover if its hunt is successful or not.
85
00:07:50,433 --> 00:07:55,544
Most snakes, like this Cape cobra,
move in a serpentine way.
86
00:08:01,594 --> 00:08:05,088
The snake pushes at the point
where its body bends,
87
00:08:05,123 --> 00:08:07,063
and that propels it sideways.
88
00:08:07,194 --> 00:08:10,367
But if two opposite coils push at the same time,
89
00:08:10,424 --> 00:08:15,696
the sideways forces cancel each other out
and the snake is propelled forwards.
90
00:08:17,678 --> 00:08:21,987
Some snakes can move really fast
using this method.
91
00:08:23,503 --> 00:08:25,910
From the marks the cobra leaves,
92
00:08:25,962 --> 00:08:30,626
it's clear that it's only pushing
at the points where its body bends.
93
00:08:36,589 --> 00:08:40,139
This sidewinder racing over the Sahara at night
94
00:08:40,174 --> 00:08:45,159
has perfected a way of moving that works well
on slippery and very hot surfaces.
95
00:08:51,736 --> 00:08:56,142
As its name implies, it goes sideways,
or, rather, diagonally.
96
00:08:56,177 --> 00:08:59,769
It doesn't slide.
Muscular waves move along its body,
97
00:08:59,980 --> 00:09:05,091
lifting and twisting sections and then
setting them down a short distance away.
98
00:09:05,542 --> 00:09:09,082
Thus the body sort of rolls along
from neck to tail,
99
00:09:09,409 --> 00:09:12,742
leaving a characteristic track
behind it in the sand
100
00:09:12,777 --> 00:09:14,965
which could only be from a sidewinder.
101
00:09:21,058 --> 00:09:26,295
But, at the end of the day,
snakes don't travel all that fast, do they?
102
00:09:26,330 --> 00:09:28,522
Well, that's where you're wrong.
103
00:09:39,927 --> 00:09:44,601
There is a snake in Africa that's been called
the most dangerous in the world
104
00:09:44,636 --> 00:09:47,265
because of its speed.
105
00:09:53,981 --> 00:09:59,861
0ver long distances, the black mamba
can travel at bursts of seven miles an hour.
106
00:09:59,896 --> 00:10:02,784
But over short sprints
it can move at 14 miles an hour.
107
00:10:02,819 --> 00:10:07,933
Some observers claim to have seen mambas
going at 18, even 20, miles an hour,
108
00:10:08,792 --> 00:10:11,915
faster than most people can sprint.
109
00:10:11,950 --> 00:10:16,855
It can even travel with a third of its body
raised off the ground.
110
00:10:19,109 --> 00:10:22,980
Certainly, the black mamba
is the most feared snake in Africa.
111
00:10:23,105 --> 00:10:27,168
It's highly strung, twitchy, aggressive.
112
00:10:28,861 --> 00:10:36,067
A black mamba can move fast in trees,
on open ground or in water.
113
00:10:40,636 --> 00:10:43,795
In thick undergrowth it would overtake you.
114
00:10:44,064 --> 00:10:46,283
Mambas can kill a human
with two drops of venom
115
00:10:46,822 --> 00:10:55,815
and they can inject formidable amounts of it.
116
00:10:55,850 --> 00:10:57,291
No wonder we fear them.
117
00:10:57,326 --> 00:11:03,504
More, it seems, than they fear us.
118
00:11:03,539 --> 00:11:08,844
But the snake's speed on land
can be transformed when it takes to water.
119
00:11:10,424 --> 00:11:14,116
In this medium, a cobra can triple its speed.
120
00:11:18,663 --> 00:11:23,037
All snakes are at home in water,
especially this anaconda.
121
00:11:25,817 --> 00:11:29,505
It makes them even more versatile,
adaptable hunters.
122
00:11:38,240 --> 00:11:39,931
In fact, so successful were snakes
123
00:11:39,996 --> 00:11:44,142
that four and a half million years ago
they spread into the sea.
124
00:11:44,177 --> 00:11:46,478
Now you can find 55 species of sea snake
125
00:11:48,401 --> 00:11:52,624
in the tropical waters
of the Indian and Pacific 0ceans.
126
00:11:52,864 --> 00:11:56,034
Sea snakes are all highly venomous.
127
00:12:00,913 --> 00:12:06,969
Having conquered the land and the sea,
snakes have even taken to the air.
128
00:12:08,667 --> 00:12:14,049
In the high jungles of Malaysia,
a lizard glides to safety from a pursuing snake -
129
00:12:14,702 --> 00:12:20,257
or so it thinks, because this is
a hunting snake that can follow it.
130
00:12:20,292 --> 00:12:24,593
It can contour its body to ride on the air
like the wing of an aeroplane.
131
00:12:24,632 --> 00:12:28,550
It can even steer itself
towards a particular landing spot.
132
00:12:35,885 --> 00:12:38,881
This time, however, the lizard escapes.
133
00:12:45,212 --> 00:12:46,330
All snakes kill.
134
00:12:47,007 --> 00:12:51,520
They do so in basically two different ways.
They either ambush or they hunt.
135
00:12:56,055 --> 00:13:00,633
In the deserts of the Kalahari,
the Cape cobra is a hunter par excellence.
136
00:13:00,568 --> 00:13:04,643
It's found its way towards a colony
of nesting weaver birds.
137
00:13:07,580 --> 00:13:10,830
As yet, they are still 100 metres away.
138
00:13:16,060 --> 00:13:19,858
The snake detects their presence
not simply with its inefficient sight,
139
00:13:20,033 --> 00:13:22,606
but by using its tongue.
140
00:13:24,956 --> 00:13:30,308
All kinds of particles drift around in the air -
odours, water droplets, pollen.
141
00:13:30,943 --> 00:13:35,960
In the little copse, trees, grass,
adult birds and chicks all give off scents.
142
00:13:40,395 --> 00:13:43,935
This kaleidoscope of particles
stream back to the snake
143
00:13:44,175 --> 00:13:47,359
which plucks them off the air with its tongue.
144
00:13:47,613 --> 00:13:51,590
The cobra's tongue retracts,
transferring the particles
145
00:13:51,725 --> 00:13:55,943
to a processing unit in the roof of its mouth,
its Jacobson's organ.
146
00:13:56,678 --> 00:13:59,649
All snakes have forked tongues. Why?
147
00:13:59,850 --> 00:14:01,850
They're tasting in stereo.
148
00:14:02,910 --> 00:14:04,678
establishing the direction
of the weaver bird chicks at long range.
149
00:14:32,974 --> 00:14:36,310
The Cape cobra is a superb tree climber.
150
00:14:36,713 --> 00:14:39,484
A miniature camera attached to its back
151
00:14:39,899 --> 00:14:46,820
gives a remarkable snake's-eye view
of its arboreal journey.
152
00:15:11,255 --> 00:15:16,609
The adult weaver birds escape
from their nests, streaming downwards.
153
00:15:24,326 --> 00:15:30,095
The nest entrances are underneath,
making them hard for predators to enter.
154
00:15:44,294 --> 00:15:49,280
The snake anchors itself by its tail,
letting its body hang free.
155
00:16:10,577 --> 00:16:15,786
Then it works its way systematically
from nest to nest.
156
00:16:24,431 --> 00:16:28,476
Eventually, the Cape cobra will strike lucky.
157
00:17:05,350 --> 00:17:08,540
Hunting snakes will go wherever there is prey.
158
00:17:08,626 --> 00:17:14,070
Climbing trees. Climbing rock faces.
159
00:17:14,105 --> 00:17:17,723
At the entrance to these caves
in Queensland, Australia,
160
00:17:17,901 --> 00:17:26,181
two species of python
have learned that the hunting is easy.
161
00:17:26,216 --> 00:17:28,439
Bats - millions of them.
162
00:17:32,624 --> 00:17:37,307
Revealed by night-vision cameras, the snakes
anchor themselves to the ceiling of the cave
163
00:17:37,655 --> 00:17:43,129
and try to pluck the bats out of the air.
164
00:17:55,164 --> 00:17:56,725
Pythons are not venomous.
165
00:17:56,760 --> 00:17:59,376
They squeeze their victims to death.
166
00:18:28,991 --> 00:18:35,017
Another snake hunter is found
on a tiny uninhabited island off Tasmania.
167
00:18:35,382 --> 00:18:40,007
Vast numbers of mutton birds
come to Chapel Island once a year
168
00:18:40,042 --> 00:18:42,777
to nest underground in burrows.
169
00:18:44,149 --> 00:18:46,235
They won't stay long.
170
00:18:46,557 --> 00:18:52,185
But it's now that tiger snakes
will get their annual feast.
171
00:18:53,263 --> 00:18:54,920
They're after the chicks.
172
00:18:55,184 --> 00:19:01,260
But to get at them, they'll first have to get past
the adult nesting bird.
173
00:19:12,595 --> 00:19:17,137
Unlike other killers at the top
of the food chain, such as big cats,
174
00:19:17,349 --> 00:19:23,667
snakes are comparatively small,
robust and adaptable.
175
00:19:30,502 --> 00:19:36,225
These tiger snakes can actually survive
for 11 months without food.
176
00:19:38,866 --> 00:19:45,053
In fact, not having to eat very often has been
one of the keys to the success of all snakes.
177
00:19:52,070 --> 00:19:56,711
Back in the African bush, our giant python
is making its way back to the hole
178
00:19:59,749 --> 00:20:02,377
This snake, too, hasn't had a meal for months,
179
00:20:02,412 --> 00:20:10,781
but, as we've seen,
that's no big deal for a large snake.
180
00:20:13,916 --> 00:20:19,151
Once underground,
its metabolism simply slows down.
181
00:20:19,465 --> 00:20:23,728
It's one of the great advantages
of being a cold-blooded predator.
182
00:20:24,140 --> 00:20:26,690
Snakes don't have to eat so often or so much,
183
00:20:26,725 --> 00:20:34,762
so they only need a 20th of the food
of a warm-blooded mammal of the same size.
184
00:20:36,997 --> 00:20:39,391
There's another way of catching prey.
185
00:20:39,642 --> 00:20:48,108
Instead of chasing after it, you can wait
for it to come to you. You can ambush it.
186
00:20:48,343 --> 00:20:51,722
South Africa. Table Mountain rises
out of a thin spit of land
187
00:20:51,903 --> 00:20:55,205
that bisects two mighty oceans.
188
00:20:55,536 --> 00:20:59,448
To the south is an area
strewn with rocky heathlands.
189
00:20:59,483 --> 00:21:01,667
This is the Fynbos.
190
00:21:05,862 --> 00:21:10,922
One of Africa's most notorious
and feared snakes, a puff adder,
191
00:21:11,281 --> 00:21:14,611
is warming up in the morning sun.
192
00:21:17,831 --> 00:21:21,608
Once the puff adder has reached
ideal operating temperature,
193
00:21:21,913 --> 00:21:26,072
it comes down off the rocks in search of food.
194
00:21:26,107 --> 00:21:30,453
Labelled ugly, bad-tempered,
fat, sluggish, vicious,
195
00:21:30,582 --> 00:21:34,159
in reality, the puff adder is simply efficient.
196
00:21:34,434 --> 00:21:42,517
It's a viper, and vipers are the most highly
evolved, sophisticated killers of all snakes.
197
00:21:42,726 --> 00:21:47,252
Today it's after striped mice.
198
00:21:51,834 --> 00:21:57,301
Like any professional assassin, the puff adder is
equipped with an arsenal of high-tech weaponry
199
00:21:57,502 --> 00:22:00,406
and extremely sensitive detection equipment.
200
00:22:00,675 --> 00:22:05,090
But it will not hunt. Its technique
is to wait for food to come to it.
201
00:22:05,125 --> 00:22:09,506
So the puff adder takes up
its ambush position near to a scent trail.
202
00:22:29,346 --> 00:22:33,847
Its eyes are particularly good
at detecting movement.
203
00:22:39,056 --> 00:22:43,301
But now the snake's other senses
come into play.
204
00:22:43,689 --> 00:22:45,149
It has special sound detectors.
205
00:22:45,884 --> 00:22:47,113
Rather than hearing sounds, like we do,
206
00:22:47,148 --> 00:22:52,226
it picks up vibrations
through the skin around its jaw bone.
207
00:22:53,061 --> 00:22:56,173
This doesn't work too well with airborne noises,
208
00:22:56,653 --> 00:23:02,740
but if the puff adder rests its jaw on the ground,
vibrations are amplified enormously.
209
00:23:02,775 --> 00:23:06,958
Even the miniscule impact
of this mouse's feet on sand
210
00:23:07,257 --> 00:23:09,920
can be detected by the snake.
211
00:23:11,213 --> 00:23:13,187
Now the snake tongue-flicks.
212
00:23:13,467 --> 00:23:21,204
It's targeting its prey
using its acute sense of taste and smell.
213
00:23:21,439 --> 00:23:25,182
But when the mouse moves
within 15 centimetres of the snake's head,
214
00:23:25,467 --> 00:23:31,451
cells in the adder's lips become stimulated
by the mouse's body heat
215
00:23:31,686 --> 00:23:36,335
and let the snake finally know
that it's within strike range.
216
00:23:36,370 --> 00:23:39,164
The information from sight,
217
00:23:39,486 --> 00:23:44,848
hearing, smell and taste and thermo-detection
218
00:23:44,883 --> 00:23:48,748
is processed by the snake's computer - its brain.
219
00:23:50,166 --> 00:23:53,101
The target is confirmed.
220
00:23:54,538 --> 00:23:58,768
The puff adder bites, venom is injected
deep into the mouse's tissues
221
00:24:00,785 --> 00:24:02,692
by its super-long fangs, and releases.
222
00:24:02,727 --> 00:24:06,436
It's anxious not to be hurt during the strike,
223
00:24:06,442 --> 00:24:11,583
so it uses its venom as a hunting aid
to immobilise or to slow down
224
00:24:11,618 --> 00:24:13,190
rather than to kill.
225
00:24:15,662 --> 00:24:19,017
The puff adder is now content
for its prey to escape.
226
00:24:19,052 --> 00:24:22,574
It probably won't go far
before the venom takes effect.
227
00:24:22,709 --> 00:24:26,979
The snake yawns to reset its jaw,
dislocated during the strike.
228
00:24:27,014 --> 00:24:29,448
It's in no hurry.
229
00:24:31,466 --> 00:24:34,567
The escaping mouse has left a trail behind it.
230
00:24:35,377 --> 00:24:38,776
Not a trail that you or I could detect,
but the snake can.
231
00:24:38,811 --> 00:24:43,132
The invisible paw prints of the mouse
release odour particles
232
00:24:43,167 --> 00:24:45,759
which waft towards the puff adder.
233
00:24:49,680 --> 00:24:53,867
It captures them with its forked tongue.
234
00:24:54,804 --> 00:24:59,313
The mouse has also left
invisible drops of urine behind it.
235
00:25:01,903 --> 00:25:07,189
The snake uses specialised cells on its retina
236
00:25:07,224 --> 00:25:11,363
to "see" ultraviolet reflectance
from this urine trail.
237
00:25:13,777 --> 00:25:18,584
As it sets out in pursuit, it also feels
the residual heat left on the ground
238
00:25:18,619 --> 00:25:21,003
by the paws of the unfortunate mouse.
239
00:25:27,587 --> 00:25:30,630
The puff adder follows this invisible trail
240
00:25:32,797 --> 00:25:33,202
back to its inevitable meal.
241
00:25:33,237 --> 00:25:39,180
Except that this time, it is not to be.
242
00:25:42,615 --> 00:25:45,286
Enter a secretary bird.
243
00:25:48,021 --> 00:25:53,016
A bird of prey that hunts
not on the wing, but on foot.
244
00:25:53,585 --> 00:25:56,271
And it uses its feet to kill.
245
00:25:57,193 --> 00:26:03,211
The secretary bird has a partiality for snakes.
246
00:26:04,475 --> 00:26:09,413
The puff adder has no chance.
Its strike is easily avoided by the secretary bird.
247
00:26:12,248 --> 00:26:13,791
(BIRD STAMPS)
248
00:26:17,304 --> 00:26:18,690
(THUD)
249
00:26:19,711 --> 00:26:23,703
And with two stamps of its foot,
the snake is dead.
250
00:26:27,389 --> 00:26:35,261
Africa's most feared ambusher
has itself been ambushed.
251
00:26:39,096 --> 00:26:43,134
Another technique used by ambushers
is camouflage.
252
00:26:44,055 --> 00:26:47,439
The ultimate camouflage expert
is the gaboon viper.
253
00:26:49,974 --> 00:26:53,223
Down there, on the forest floor,
is a gaboon viper.
254
00:26:53,258 --> 00:26:54,877
Can you see it?
255
00:26:57,336 --> 00:26:59,740
Let's go a bit closer.
256
00:26:59,951 --> 00:27:01,923
Got it yet?
257
00:27:02,370 --> 00:27:04,343
Now?
258
00:27:08,903 --> 00:27:12,251
Yes, that leaf there isn't a leaf at all.
259
00:27:12,286 --> 00:27:15,823
It's the back of the head of a gaboon viper.
260
00:27:29,746 --> 00:27:32,378
But you don't have to be camouflaged
261
00:27:33,575 --> 00:27:37,953
to deceive your prey
into thinking you're not there.
262
00:27:39,749 --> 00:27:42,599
Deep in the rainforests of Costa Rica,
263
00:27:42,646 --> 00:27:46,903
another ambusher, an eyelash viper,
has climbed a ginger flower
264
00:27:46,938 --> 00:27:49,724
and is waiting for its food to come to it.
265
00:27:49,759 --> 00:27:52,386
Humming birds.
266
00:27:55,339 --> 00:27:59,082
It's hardly camouflaged. We can see it easily.
267
00:27:59,398 --> 00:28:04,553
But its lack of movement
doesn't draw it to the humming bird's attention.
268
00:28:08,580 --> 00:28:11,440
To the bird, it's just another
brightly coloured bit of flower.
269
00:28:12,175 --> 00:28:15,014
The snake scents with its tongue.
270
00:28:16,055 --> 00:28:19,117
It'll have to be fast and accurate with its strike.
271
00:28:20,411 --> 00:28:22,629
The humming bird is possibly
the fastest of all small birds,
272
00:28:22,664 --> 00:28:30,893
so the snake uses a sense
which we sophisticated humans don't have.
273
00:28:31,128 --> 00:28:34,284
The eyelash viper can "see" heat.
274
00:28:38,028 --> 00:28:41,662
When the bird comes
to within 75 centimetres of the snake,
275
00:28:42,208 --> 00:28:48,000
the heat it gives off
fires up two sensors on the snake's face,
276
00:28:48,228 --> 00:28:53,873
small pits of supersensitive nerve endings.
277
00:28:55,908 --> 00:29:00,794
They're sensitive to changes of temperature
as small as 1,000th of a degree.
278
00:29:00,829 --> 00:29:04,209
They work in stereo,
giving the snake precise information
279
00:29:04,706 --> 00:29:09,050
on the range as well as the bearing
of the humming bird.
280
00:29:09,945 --> 00:29:14,627
The eyelash viper can even predict
where the bird will be
281
00:29:14,662 --> 00:29:16,396
in a split-second's time.
282
00:29:22,974 --> 00:29:26,341
The eyelash viper hits the bird in mid-air,
holding on to it.
283
00:29:27,869 --> 00:29:30,079
So fast-acting are the neurotoxins
in the venom
284
00:29:30,114 --> 00:29:38,511
that the bird is unconscious within seconds,
dead inside a minute.
285
00:29:41,746 --> 00:29:46,508
The strike of a poisonous snake
is a minor miracle of engineering.
286
00:29:48,543 --> 00:29:52,096
It first has to recoil and flex its body.
287
00:29:52,469 --> 00:29:56,165
Then it strikes, aiming phenomenally accurately.
288
00:29:56,714 --> 00:30:01,664
Then, using its mouth and fangs
like a hypodermic syringe with two needles,
289
00:30:01,899 --> 00:30:04,909
it has to inject its venom
without damaging its delicate fangs.
290
00:30:05,210 --> 00:30:07,984
Then it has to retreat out of harm's way.
291
00:30:08,790 --> 00:30:14,119
Just look at the fastest snake in the world
striking, the saw-scale viper.
292
00:30:18,654 --> 00:30:22,156
From coiled up to launching its strike
to unhinging its fangs,
293
00:30:22,191 --> 00:30:24,926
injecting venom, releasing its victim
and returning.
294
00:30:28,182 --> 00:30:29,732
Just look at it in real time.
295
00:30:32,867 --> 00:30:37,787
It all happens in one third of a second.
296
00:30:38,022 --> 00:30:43,127
But all that is nothing compared to
the complexity of the venom itself.
297
00:30:43,162 --> 00:30:45,813
Venom from the spitting cobra
is simply modified saliva.
298
00:30:46,048 --> 00:30:50,064
But it contains all kinds of toxic
chemical compounds.
299
00:30:51,272 --> 00:30:55,759
Its purpose is not to kill
but to immobilise the prey.
300
00:30:56,570 --> 00:30:59,219
And then to start digesting it.
301
00:30:59,935 --> 00:31:03,832
So the faster the victim,
the more potent the poison.
302
00:31:03,952 --> 00:31:07,633
The fastest acting of all venoms
are the neurotoxins
303
00:31:07,668 --> 00:31:14,755
which stop birds and fish in their tracks
before they can get away.
304
00:31:20,190 --> 00:31:25,770
Back in Africa, one of the largest
of ambush experts, our giant python.
305
00:31:25,805 --> 00:31:27,719
The same one that hasn't eaten for four months.
306
00:31:28,904 --> 00:31:31,773
But now it's desperate for food.
307
00:31:34,337 --> 00:31:39,666
It's detected the many scents of the animals
coming to drink at a waterhole.
308
00:31:40,115 --> 00:31:47,175
It takes up its ambush position underwater.
309
00:32:06,410 --> 00:32:08,693
For an animal so ponderous on land,
310
00:32:10,499 --> 00:32:14,646
it's transformed in water,
moving speedily with ease
311
00:32:14,681 --> 00:32:15,616
in this different medium.
312
00:32:37,065 --> 00:32:39,906
The snake selects its ambush position,
313
00:32:39,941 --> 00:32:46,808
sinks gently just below the surface and waits.
314
00:33:00,243 --> 00:33:04,618
We talk about the patience of a saint, but
it ought to be the patience of a python.
315
00:33:05,032 --> 00:33:08,408
The snake has to breathe - it has lungs -
316
00:33:08,692 --> 00:33:11,394
but the python can shut down its body at will.
317
00:33:11,595 --> 00:33:17,595
It only rises quietly to the surface to
take a breath every 15 minutes or so.
318
00:33:23,058 --> 00:33:25,684
The hours pass.
319
00:33:25,719 --> 00:33:28,869
Animals come and go to the waterhole.
320
00:33:43,510 --> 00:33:45,433
Night comes.
321
00:33:47,029 --> 00:33:51,822
Day comes. And still the python waits.
322
00:33:57,557 --> 00:33:58,591
Days pass.
323
00:33:59,192 --> 00:34:04,092
The vibrations of feet and the silhouettes
of animals are detected by the python.
324
00:34:04,704 --> 00:34:09,253
its senses working almost as well
beneath the water as above it.
325
00:34:09,535 --> 00:34:15,037
How long will it continue to wait? Well, we'll see.
326
00:34:18,072 --> 00:34:22,539
To any naturalist,
snakes are wonderful creatures.
327
00:34:23,380 --> 00:34:28,366
But there's no escaping the fact
that snakes kill a lot of people.
328
00:34:30,472 --> 00:34:34,796
A recent study revealed
that five million people worldwide
329
00:34:35,075 --> 00:34:38,252
are bitten each year by snakes.
330
00:34:43,470 --> 00:34:46,610
Of those, 40,000 die.
331
00:34:48,705 --> 00:34:52,505
In India alone
there are 12,000 deaths every year.
332
00:34:52,748 --> 00:34:54,740
The culprits? Cobras.
333
00:34:56,251 --> 00:34:57,858
And kraits.
334
00:35:00,158 --> 00:35:05,454
In South America, it's one of the fer-de-lances
that's most likely to kill you.
335
00:35:05,689 --> 00:35:08,135
In North America, rattlesnakes.
336
00:35:11,305 --> 00:35:17,877
Many is the snake that, in the search for water,
has found its way into a shower.
337
00:35:17,912 --> 00:35:20,304
This Egyptian cobra
needed a place of high humidity
338
00:35:20,611 --> 00:35:25,057
to soften its skin prior to sloughing it.
339
00:35:33,365 --> 00:35:35,748
There have even been authenticated stories
340
00:35:36,083 --> 00:35:41,344
of people waking up
to find snakes in bed with them.
341
00:35:47,306 --> 00:35:51,915
But our understandable fears
can turn into irrational paranoia.
342
00:35:51,950 --> 00:35:57,487
That's led to millions of snakes
being killed worldwide needlessly.
343
00:36:02,793 --> 00:36:07,099
The simple fact is that snakes
do not go out in search of people.
344
00:36:07,134 --> 00:36:11,405
They only bite defensively.
They only bite out of fear of us.
345
00:36:17,274 --> 00:36:20,655
The evil image of the snake is doubly unfair
346
00:36:20,953 --> 00:36:27,321
when you realise just how often
they're victims rather than aggressors.
347
00:36:27,356 --> 00:36:31,229
Even the most venomous of snakes
falls prey to other animals,
348
00:36:31,666 --> 00:36:34,924
like this white-bellied sea eagle
taking a sea snake,
349
00:36:34,959 --> 00:36:37,798
officially the most venomous snake in the world.
350
00:36:37,833 --> 00:36:43,266
The bird's rugged talons
are impervious to the snake's fangs.
351
00:37:09,664 --> 00:37:14,714
And snakes are routinely killed by other snakes.
352
00:37:19,945 --> 00:37:23,948
The much feared fer-de-lance
of Central and South America
353
00:37:23,983 --> 00:37:33,041
is merely a meal for the larger,
to us less frightening, mussurana.
354
00:37:44,476 --> 00:37:48,759
The fer-de-lance speeds off
like a bullet, but in vain.
355
00:37:50,785 --> 00:37:56,124
The mussurana kills it by constricting,
much like a boa or a python.
356
00:38:10,232 --> 00:38:14,665
This gold cobra in the Kalahari Desert
is also in dire peril.
357
00:38:14,700 --> 00:38:16,904
It's encountered a troupe of meerkats.
358
00:38:21,654 --> 00:38:25,402
The snake expands its hood
and strikes defensively,
359
00:38:25,992 --> 00:38:31,188
but the meerkats are too many and too quick.
360
00:38:31,398 --> 00:38:33,922
The evolutionary arms race
between snake and meerkat
361
00:38:33,957 --> 00:38:39,139
dictates that at this particular moment in history,
the snake will almost never win.
362
00:38:39,425 --> 00:38:46,436
The meerkats' reaction times
are a millisecond faster than the snake's.
363
00:38:48,171 --> 00:38:51,846
But an eagle going overhead
disturbs the meerkats
364
00:38:52,123 --> 00:38:58,017
and, in the confusion,
the snake manages to get away.
365
00:38:59,752 --> 00:39:04,275
It would seem that snakes
are hunted and reviled everywhere.
366
00:39:08,338 --> 00:39:12,913
But there is one wild haven
where they live in perfect safety.
367
00:39:15,263 --> 00:39:18,669
20 miles off the Atlantic coast of South America
368
00:39:18,757 --> 00:39:22,799
is a place where even snake lovers fear to tread.
369
00:39:26,821 --> 00:39:30,661
Ilha Queimada Grande is "Snake Island".
370
00:39:30,921 --> 00:39:35,986
It has the densest population of snakes on earth.
371
00:39:42,957 --> 00:39:48,683
It's paradise for snakes, but for man one
of the most dangerous places on the planet.
372
00:39:56,518 --> 00:40:01,282
No one, apart from scientists,
is allowed to land here.
373
00:40:03,846 --> 00:40:07,482
This lovely subtropical island has, in places,
374
00:40:07,534 --> 00:40:11,716
one snake for every pace you dare to walk.
375
00:40:14,343 --> 00:40:19,622
They're all one species, a type of fer-de-lance
called a golden lancehead.
376
00:40:27,658 --> 00:40:30,482
The snakes are on the ground,
377
00:40:30,483 --> 00:40:33,883
...they're in the trees,
378
00:40:33,944 --> 00:40:39,149
... they're at the summit of the island
and they're on the sea shore.
379
00:40:40,724 --> 00:40:46,474
They're even at home in the old lighthouse,
now long since abandoned.
380
00:40:47,782 --> 00:40:53,105
They're after millipedes and cockroaches
most of the year, and butterflies and lizards,
381
00:40:53,140 --> 00:40:57,970
but, come September,
they feast on migrating birds,
382
00:40:58,205 --> 00:41:00,092
taking them on the wing.
383
00:41:03,218 --> 00:41:05,974
The golden lancehead is highly venomous.
384
00:41:06,245 --> 00:41:11,643
Untreated, a person unlucky enough
to be bitten would almost certainly die.
385
00:41:11,843 --> 00:41:15,891
The story goes that of the last 11 fishermen
who chose to ignore the warnings
386
00:41:16,082 --> 00:41:22,126
and explore what seemed a paradise
all died within hours of landing.
387
00:41:30,986 --> 00:41:34,219
But what's a snake hell for us
is snake paradise for them.
388
00:41:34,254 --> 00:41:39,415
This is one of the few places on earth
where snakes are not persecuted.
389
00:41:39,622 --> 00:41:42,144
They're protected by the Brazilian government.
390
00:41:43,071 --> 00:41:49,259
They have plenty of food and there are
no other animals which predate on the snakes,
391
00:41:49,294 --> 00:41:51,299
so the snakes rule.
392
00:41:57,099 --> 00:42:00,214
The golden lanceheads, however, are nocturnal.
393
00:42:01,488 --> 00:42:04,333
What seems dangerous enough in the daylight
394
00:42:04,414 --> 00:42:07,372
gets far worse as the sun goes down.
395
00:42:09,713 --> 00:42:13,458
Then the snakes come out of the forests
and down from the trees
396
00:42:13,493 --> 00:42:16,166
to take possession of their kingdom.
397
00:42:27,937 --> 00:42:32,201
Back at the African waterhole,
after four long days,
398
00:42:32,236 --> 00:42:35,703
the giant python has selected its prey.
399
00:42:42,696 --> 00:42:49,608
Now it changes position in the water,
going into the reeds close to the bank.
400
00:42:55,043 --> 00:43:02,120
Its heat-sensitive pits tell it the exact range
and direction of a springbok.
401
00:43:21,949 --> 00:43:26,326
The snake's long, curved teeth anchor
into the springbok's flesh and hold fast.
402
00:43:26,361 --> 00:43:30,469
The springbok is pulled to the ground
by the python's weight.
403
00:43:30,654 --> 00:43:34,606
There's just time for the python
to throw a single coil over its prey.
404
00:43:34,815 --> 00:43:40,803
One coil becomes two coils
and the constriction begins.
405
00:43:42,238 --> 00:43:46,389
People imagine that a giant snake
kills by crushing its victim,
406
00:43:47,064 --> 00:43:48,796
breaking its bones.
407
00:43:49,024 --> 00:43:51,875
But that isn't true.
The python goes for the torso,
408
00:43:51,910 --> 00:43:57,084
wrapping its coils around the rib cage
that contains the lungs.
409
00:43:57,215 --> 00:44:03,787
It waits for the animal to breathe out,
and then tightens its grip a little.
410
00:44:03,822 --> 00:44:05,914
Here, inside the very coils of the python,
411
00:44:05,949 --> 00:44:09,058
the animal discovers
that every time it breathes out,
412
00:44:10,416 --> 00:44:13,798
the snake simply tightens its grip again.
413
00:44:14,805 --> 00:44:18,789
Eventually, the springbok can't expand
its lungs at all and it asphyxiates.
414
00:44:18,824 --> 00:44:23,685
But, also, senses on the python's underside
can detect the heartbeat of its victim
415
00:44:23,720 --> 00:44:31,194
and it may continue constricting
so long as it feels that heartbeat.
416
00:44:33,629 --> 00:44:38,617
Once its prey is dead or just unconscious,
the python releases its grip
417
00:44:38,652 --> 00:44:40,323
and, using the grain
of the animal's fur to guide it,
418
00:44:42,572 --> 00:44:47,025
moves round to the head
of the springbok to start eating.
419
00:45:00,513 --> 00:45:04,566
Everybody knows that the snake
can somehow unhinge its lower jaw.
420
00:45:04,767 --> 00:45:06,667
But that's only a part of the solution
421
00:45:06,871 --> 00:45:12,954
to eating an animal that is three times
the width of your head, with horns on top.
422
00:45:15,089 --> 00:45:20,165
The head of the snake
is divided into four main sections,
423
00:45:20,166 --> 00:45:22,166
the two halves of the lower jaw
424
00:45:22,167 --> 00:45:24,867
and the two halves of the upper jaw.
425
00:45:25,057 --> 00:45:28,155
All four sections
are connected by elastic ligaments
426
00:45:28,190 --> 00:45:31,254
that allow each to move independently
of the others.
427
00:45:36,551 --> 00:45:40,641
The python's brain
is sealed in a nice, little solid compartment
428
00:45:40,683 --> 00:45:42,977
on top of the skull behind the eyes.
429
00:45:43,110 --> 00:45:48,626
So, as the head splits into four,
the brain case rides over the top.
430
00:45:49,561 --> 00:45:54,209
In effect, the snake moves
over the top of the prey
431
00:45:54,434 --> 00:45:58,407
and the jaws just expand around it.
432
00:46:04,604 --> 00:46:06,960
But the prey is not necessarily dead.
433
00:46:06,995 --> 00:46:12,887
Horror of horrors, it might still be alive,
albeit unconscious.
434
00:46:20,374 --> 00:46:24,935
If you were swallowed by a giant snake,
this is what it might be like.
435
00:46:24,970 --> 00:46:29,821
The snake's peristaltic muscles,
used for swallowing,
436
00:46:30,065 --> 00:46:34,117
push you deeper and deeper into its throat.
437
00:46:34,152 --> 00:46:36,372
Your head is inside,
438
00:46:36,561 --> 00:46:41,727
but the rest of your body
is still outside the snake.
439
00:46:41,809 --> 00:46:44,318
The outside world disappears
440
00:46:44,388 --> 00:46:49,437
as the peristalsis relentlessly
pushes you deeper and deeper.
441
00:46:49,538 --> 00:46:54,838
Is it possible that the victim could actually
recover consciousness during this process?
442
00:46:54,930 --> 00:46:57,972
Who can tell?
443
00:47:09,357 --> 00:47:14,188
Eventually, the powerful acids
in the python's digestive juices do their job.
444
00:47:14,192 --> 00:47:17,023
They dissolve flesh and bone
445
00:47:17,582 --> 00:47:21,089
and convert the victim into nutrition.
446
00:47:26,125 --> 00:47:29,473
This python will not need to feed again this year.
447
00:47:38,938 --> 00:47:41,237
Snakes - animals that can go on the ground,
448
00:47:42,909 --> 00:47:46,624
under the ground, in the trees, or in water.
449
00:47:46,659 --> 00:47:49,723
Animals that can, at will, shut down their bodies,
450
00:47:49,771 --> 00:47:52,472
and then bring them up to speed again.
451
00:47:52,507 --> 00:48:00,685
Hunters equipped with a multitude of
detection devices and sophisticated weaponry.
452
00:48:00,720 --> 00:48:03,280
But hunters that can also
go for weeks between meals.
453
00:48:03,378 --> 00:48:07,758
Lightning fast in the strike,
snakes have conquered the planet.
454
00:48:07,793 --> 00:48:10,978
They are the most successful predators
on earth.