1
00:01:14,480 --> 00:01:17,920
On the 25th December 1643,

2
00:01:17,920 --> 00:01:22,400
the Captain of a ship,
homeward bound from the East Indies,

3
00:01:22,400 --> 00:01:25,480
sighted land just south of Java.

4
00:01:25,480 --> 00:01:30,040
He had found the coral-encrusted tip
of an extinct volcano,

5
00:01:30,040 --> 00:01:33,120
which he called Christmas Island.

6
00:01:33,120 --> 00:01:38,200
Had he landed, he would have found
no ordinary tropical paradise.

7
00:01:38,200 --> 00:01:45,360
Because this island, now Australian,
is ruled by crabs...
hundreds of millions of them.

8
00:01:51,440 --> 00:01:56,720
The sea SHORE is the place
where you would expect to find crabs.

9
00:01:58,920 --> 00:02:04,400
Crabs are crustaceans,
and basically sea creatures,

10
00:02:04,400 --> 00:02:07,520
like this amphibious Grapsus.

11
00:02:07,520 --> 00:02:14,520
But here, crabs are not confined
to the coast, for Christmas Island
is unique for its LAND crabs.

12
00:02:21,760 --> 00:02:26,800
The Indian Ocean brings
year-round warmth and high humidity,

13
00:02:26,800 --> 00:02:31,440
which have fostered
a lush covering of forest.

14
00:02:32,960 --> 00:02:37,480
This jungle is ideal
for land crustaceans -

15
00:02:37,480 --> 00:02:40,440
like these blue crabs.

16
00:02:43,760 --> 00:02:50,440
It's their hard, mineralised shell
that has enabled these creatures
to explore life on land.

17
00:02:54,080 --> 00:03:00,680
It's strong enough to support them,
and impermeable enough
to stop them drying out.

18
00:03:00,680 --> 00:03:07,160
Covered with sensitive bristles,
it is jointed like a suit
of medieval armour.

19
00:03:07,160 --> 00:03:12,080
The first of five pairs of legs
are armed with powerful claws,

20
00:03:12,080 --> 00:03:17,080
and the shell around the body
encloses the crab's gill chambers.

21
00:03:17,080 --> 00:03:21,040
They have to be kept
fully charged with water.

22
00:03:27,200 --> 00:03:31,240
Although the claws
are packed with muscle,

23
00:03:31,240 --> 00:03:36,200
they're still capable of being used
with all the delicacy of forceps.

24
00:03:38,400 --> 00:03:44,920
Crabs even have built-in cutlery
to manipulate food into the mouth.

25
00:03:44,920 --> 00:03:48,480
The armour makes crabs look fierce.

26
00:03:48,480 --> 00:03:55,560
But their eyes betray the fact
that inside the armour
are creatures of some sensitivity.

27
00:03:55,560 --> 00:04:03,960
Out of water they might find it hard
to keep their eyes clean,
for they have no eyelids like us.

28
00:04:03,960 --> 00:04:07,960
Instead they have special brushes.

29
00:04:11,640 --> 00:04:18,760
Blue land crabs need water
to breathe, and so can only live
near pools and streams.

30
00:04:18,760 --> 00:04:22,720
Other kinds are not so restricted.

31
00:04:28,480 --> 00:04:31,520
These are red crabs.

32
00:04:31,520 --> 00:04:36,560
There are 130 million of them,
and they dominate the forest.

33
00:04:39,640 --> 00:04:47,560
When it's dry,
they take refuge in moist burrows,
from which they emerge to feed.

34
00:04:53,800 --> 00:05:01,280
Touching and tasting with the legs,
the red crabs are the gardeners
of the forest.

35
00:05:01,280 --> 00:05:07,680
It's they who decide
which seeds survive,
and which don't.

36
00:05:07,680 --> 00:05:10,760
They also chew the leaf litter.

37
00:05:10,760 --> 00:05:17,280
Elsewhere in the world,
fallen vegetation is broken down
by a range of organisms.

38
00:05:17,280 --> 00:05:20,600
But here it is chiefly crabs.

39
00:05:20,600 --> 00:05:25,600
Their droppings are fertiliser,
returning nutrients to the plants,

40
00:05:25,600 --> 00:05:29,560
and, as they burrow,
they till the soil.

41
00:05:31,440 --> 00:05:34,520
With over 4,000 crabs to the acre,

42
00:05:34,520 --> 00:05:40,880
the forest floor
is kept clear of vegetation,
leaving little for others...

43
00:05:40,880 --> 00:05:44,880
..except these
Christmas Island thrushes.

44
00:05:53,600 --> 00:05:56,640
Even forest crabs enjoy a drink.

45
00:05:56,640 --> 00:06:00,680
But they do so less often
than the blue crabs.

46
00:06:00,680 --> 00:06:03,760
Their gill chambers are like lungs,

47
00:06:03,760 --> 00:06:11,960
which need to be kept moist,
but do not have to be constantly
recharged with water.

48
00:06:11,960 --> 00:06:16,920
Red crabs have a simpler way
of keeping their vision clear.

49
00:06:18,920 --> 00:06:25,840
The built-in eye cups are filled,
drop by drop,
to make effective eye washes.

50
00:06:36,840 --> 00:06:42,160
16 kinds of land crabs
live on Christmas Island,

51
00:06:42,160 --> 00:06:45,240
including this large hermit.

52
00:06:45,240 --> 00:06:52,160
It collects a shell from the shore,
then lumbers inland with it
as portable protection.

53
00:06:52,160 --> 00:06:56,600
But, in the forest,
are the biggest of all land crabs.

54
00:07:05,200 --> 00:07:10,160
These mighty robber crabs
have prodigious strength.

55
00:07:30,000 --> 00:07:33,040
They've got claws like wire cutters,

56
00:07:33,040 --> 00:07:37,560
and they make light work of tearing
this frigate bird to pieces.

57
00:07:44,640 --> 00:07:48,680
The robber crab's ancestors
were marine hermits.

58
00:07:48,680 --> 00:07:53,000
Today they no longer pick up
discarded mollusc shells,

59
00:07:53,000 --> 00:07:57,040
but have themselves
become massively armoured,

60
00:07:57,040 --> 00:08:01,080
and are the most terrestrial
of all crabs.

61
00:08:09,200 --> 00:08:13,240
Guided by an astonishing
sense of smell,

62
00:08:13,240 --> 00:08:18,200
they scuttle long distances
to scavenge fruit and carcases.

63
00:08:25,400 --> 00:08:29,360
Robbers are the hyenas
of the crab world.

64
00:08:29,760 --> 00:08:33,800
THUNDER

65
00:08:43,840 --> 00:08:49,440
The November monsoons bring
torrential rain to Christmas Island,

66
00:08:49,440 --> 00:08:54,960
and this triggers one
of Nature's most spectacular events.

67
00:09:12,680 --> 00:09:16,720
All over the island,
red crabs are on the move.

68
00:09:16,720 --> 00:09:24,600
They appear from everywhere,
and they seem to know
where they're going.

69
00:09:32,640 --> 00:09:35,680
They pour out from the forest,

70
00:09:35,680 --> 00:09:40,320
channelled by gullies
and other natural pathways.

71
00:09:40,320 --> 00:09:47,080
They're heading
for the nearest shore...
to spawn.

72
00:09:58,440 --> 00:10:04,480
It's an exhausting business,
especially if there's
little to drink,

73
00:10:04,480 --> 00:10:11,480
So the legions march,
mostly while it's cool,
in the early morning and evening.

74
00:10:11,480 --> 00:10:14,560
For them, the journey is essential.

75
00:10:14,560 --> 00:10:22,520
Unable to raise their young on land,
they MUST trek several kilometres
each year to their ancestral home...

76
00:10:22,520 --> 00:10:25,480
..the sea.

77
00:11:18,720 --> 00:11:21,800
The journey is a perilous one,

78
00:11:21,800 --> 00:11:29,880
for the exodus from the forest
along the traditional routes
brings them into an alien world.

79
00:11:34,880 --> 00:11:39,720
TRAIN HOOTS

80
00:11:45,200 --> 00:11:49,280
Phosphate used to be mined
on the island,

81
00:11:49,280 --> 00:11:57,080
and a million crabs are crushed
by the rail and road traffic
each year.

82
00:12:02,280 --> 00:12:06,400
The carnage accounts
for only one per cent,

83
00:12:06,400 --> 00:12:11,080
and the dead are quickly scavenged.

84
00:12:11,080 --> 00:12:17,960
Occasionally the crabs hit back,
as their powerful claws
puncture the tyres that kill them.

85
00:12:22,600 --> 00:12:30,280
By early December, the residents
of Christmas Island wake up
to find crabs on their doorsteps.

86
00:12:30,280 --> 00:12:37,560
To some it may seem like
a nightmare, but most people here
carry on regardless,

87
00:12:37,560 --> 00:12:44,760
and work round the crustaceans
which you can't even eat.

88
00:12:51,320 --> 00:12:55,360
The migrating creatures
turn up everywhere,

89
00:12:55,360 --> 00:13:00,040
and they certainly have
no regard for fair play.

90
00:13:00,040 --> 00:13:02,960
This golf course has special rules

91
00:13:02,960 --> 00:13:05,920
for when crabs get in on the game!

92
00:13:18,440 --> 00:13:23,480
The large males are first
to reach their destination.

93
00:13:23,480 --> 00:13:29,000
After two weeks,
the travel-weary crabs
quench their thirst,

94
00:13:29,000 --> 00:13:35,880
and allow the waves
to cleanse their bodies
of dirt and grime.

95
00:13:35,880 --> 00:13:42,880
But, like human bathers,
these air-breathing land crabs
must be cautious when taking a dip.

96
00:13:42,880 --> 00:13:46,840
They're hopeless swimmers
and easily drown.

97
00:14:06,040 --> 00:14:11,120
Perhaps the taste of the salt
and the feel of the waves

98
00:14:11,120 --> 00:14:17,520
reassures them that they have,
at last, reached the right place
to spawn.

99
00:14:21,320 --> 00:14:26,360
Like people, they can suffer
from heat stroke, which CAN be fatal.

100
00:14:26,360 --> 00:14:33,280
The full force of the tropical sun
sends them scuttling back
into the shade.

101
00:14:38,760 --> 00:14:45,760
Once they've freshened up,
the males retire to the terraces
above the shore

102
00:14:45,760 --> 00:14:50,840
to prepare for the arrival
of the females.

103
00:14:50,840 --> 00:14:58,200
This is where
the business of breeding
begins in earnest.

104
00:14:58,200 --> 00:15:05,560
To start with,
the males excavate burrows
to accommodate their mates.

105
00:15:07,960 --> 00:15:12,320
Now, these otherwise peaceful crabs

106
00:15:12,320 --> 00:15:17,360
become fiercely territorial -
especially in defence of burrows.

107
00:15:46,160 --> 00:15:50,240
Most arguments are mainly
bravado and bluff.

108
00:15:50,240 --> 00:15:57,640
Certainly the full force
of the claws is rarely
brought to bear on an opponent.

109
00:16:16,360 --> 00:16:22,320
The female often
takes the initiative
by stepping into the male's burrow.

110
00:16:22,320 --> 00:16:27,280
The mating then proceeds
amidst a confusing tangle of legs.

111
00:16:35,680 --> 00:16:40,760
The male then takes over,
manoeuvring his mate into position.

112
00:16:40,760 --> 00:16:45,720
He soothes her by tapping
a gentle tattoo on her back.

113
00:16:52,240 --> 00:16:56,240
If she's in the mood to mate,
she'll go limp.

114
00:16:56,240 --> 00:17:01,240
If she continues to struggle,
the male will reject her.

115
00:17:04,600 --> 00:17:08,640
This is the prelude
to proper coupling.

116
00:17:08,640 --> 00:17:16,600
The males have specially
modified legs, with which the sperm
is introduced into the female.

117
00:17:19,040 --> 00:17:26,840
After the sexual embrace,
the male abandons her to team up
with others returning to the forest.

118
00:17:26,840 --> 00:17:30,400
His mate has the burrow to herself.

119
00:17:30,400 --> 00:17:38,960
Soon she lays 100,000 eggs
into a pouch formed by her lowered
abdomen and tiny, special limbs.

120
00:17:38,960 --> 00:17:43,480
Here she'll wait for about 12 days,
while the embryos develop,

121
00:17:43,480 --> 00:17:48,000
before making HER rendezvous
with the sea.

122
00:17:48,000 --> 00:17:53,760
MATING CALL

123
00:17:53,760 --> 00:17:56,800
Meanwhile, the birds start to breed.

124
00:17:56,800 --> 00:18:01,200
Christmas Island is renowned
for its seabirds.

125
00:18:01,200 --> 00:18:05,440
Several, like this frigate,
are unique to the island.

126
00:18:30,240 --> 00:18:33,280
As Christmas Day approaches,

127
00:18:33,280 --> 00:18:38,240
the calls of our egg-laden female
signal that she's ready to spawn.

128
00:18:40,000 --> 00:18:44,920
CLICKING CALL

129
00:18:45,040 --> 00:18:49,960
She's joined by millions of others,
each bearing bunches of ripe eggs.

130
00:18:54,400 --> 00:18:57,440
Beaches are few and far between,

131
00:18:57,440 --> 00:19:02,480
so these crabs have to use
a treacherous stretch of coast,

132
00:19:02,480 --> 00:19:07,160
the remnants of an ancient
coral reef.

133
00:19:07,160 --> 00:19:14,560
Here, the corrosive effects
of rain and sea have created
these limestone pinnacles,

134
00:19:14,560 --> 00:19:18,880
which are razor-sharp
and deeply honeycombed.

135
00:19:26,400 --> 00:19:31,480
Once the crabs have negotiated
the labyrinth of rock,

136
00:19:31,480 --> 00:19:37,120
they find themselves
in a magical setting
for the spawning.

137
00:19:45,320 --> 00:19:52,760
After days underground,
the females must surely relish
the cool salt spray.

138
00:20:32,240 --> 00:20:37,200
The spawning crabs are governed
by the lunar cycle.

139
00:20:37,200 --> 00:20:44,560
Their arrival MUST coincide with
the last quarter of the waning moon,
at high tide just before dawn.

140
00:20:48,600 --> 00:20:53,560
Nightfall - and the females await
the very peak of the tide,

141
00:20:53,680 --> 00:20:57,600
into which they will release
their eggs.

142
00:21:07,760 --> 00:21:14,560
Spawning is not without its dangers,
for those that lose their grip
will either drown,

143
00:21:14,560 --> 00:21:18,240
or be dashed on the rocks below.

144
00:21:28,120 --> 00:21:32,600
Meanwhile, in the relative safety
of a nearby beach,

145
00:21:32,600 --> 00:21:37,240
other crabs are congregating,
each bearing 100,000 eggs,

146
00:21:37,240 --> 00:21:42,280
and all waiting for the tide
to reach its highest point.

147
00:21:42,280 --> 00:21:45,240
This is the climax of the migration.

148
00:21:55,840 --> 00:21:59,560
Suddenly, as if by some command,

149
00:21:59,560 --> 00:22:04,600
they throw caution to the wind
and scramble for the surf.

150
00:22:04,600 --> 00:22:08,600
This is where they'll consign
their eggs to the sea.

151
00:22:29,680 --> 00:22:32,760
The scene is not without poignancy.

152
00:22:32,760 --> 00:22:39,760
Although the ocean will give
life to the mother-crab's offspring,
SHE may be drowned.

153
00:22:39,760 --> 00:22:44,800
Claws held high to shake free
her eggs, it's a dangerous moment,

154
00:22:44,800 --> 00:22:48,840
as she's likely to be knocked over
and swept away.

155
00:22:48,840 --> 00:22:53,360
As the females spawn,
the water runs brown with eggs.

156
00:23:44,800 --> 00:23:50,920
By dawn most females
are heading home.
Only a few remain.

157
00:23:50,920 --> 00:23:57,840
Bundles of eggs which fell onto
the sand provide easy pickings
for loitering crabs.

158
00:24:02,840 --> 00:24:07,440
Some arrived too late to spawn,
and must wait for the next night.

159
00:24:10,720 --> 00:24:14,680
The odd one
decides to go ahead anyway.

160
00:24:16,640 --> 00:24:24,360
Some females may have taken part
in this spectacular spawning
for as many as 10 consecutive years.

161
00:24:24,360 --> 00:24:27,320
For others, it's their last.

162
00:24:31,440 --> 00:24:35,400
But the sea holds the promise
of new life.

163
00:24:39,720 --> 00:24:45,760
These tiny planktonic crab larvae
are called zoea.

164
00:24:45,760 --> 00:24:51,040
The odds are greatly stacked
against their survival.

165
00:24:51,040 --> 00:24:57,480
As the tide sweeps them out,
they run the gauntlet
of many voracious fish.

166
00:24:57,480 --> 00:25:04,960
Those that manage to cross
the fringing reef are then
at the mercy of the ocean currents.

167
00:25:04,960 --> 00:25:08,040
Where they go, is a mystery.

168
00:25:08,040 --> 00:25:16,760
Most years they completely vanish,
presumably swept far
from their island home.

169
00:25:16,760 --> 00:25:25,360
But in about one year in six,
the ocean currents bring back
a crop of young crabs.

170
00:25:25,360 --> 00:25:33,160
After a month at sea,
the larvae are still swimming,
using their tiny tails like shrimps.

171
00:25:34,680 --> 00:25:42,200
But now they are creatures
of TWO worlds,
anxious to clamber ashore.

172
00:25:42,200 --> 00:25:46,080
In a January dawn,

173
00:25:46,080 --> 00:25:51,040
the water's edge teems with millions
of the little creatures.

174
00:25:54,960 --> 00:26:01,960
Shortly, they'll moult,
casting off for ever
their ability to live in the sea,

175
00:26:01,960 --> 00:26:04,920
and turn into miniature crabs.

176
00:26:30,760 --> 00:26:37,160
In exceptional years,
a seething carpet of crablets
overwhelms the coastal terraces

177
00:26:37,160 --> 00:26:40,120
and the visiting beachcombers.

178
00:26:51,640 --> 00:26:59,680
For local children,
the sudden influx of young crabs
provides them with new playthings.

179
00:26:59,680 --> 00:27:04,680
But the fresh arrivals can expect
no quarter from hungry adult crabs.

180
00:27:04,680 --> 00:27:10,920
Their parental concern stopped
when their eggs were consigned
to the sea.

181
00:27:20,080 --> 00:27:24,040
In a few days,
the moment to moult arrives.

182
00:27:25,880 --> 00:27:33,760
Each becomes transformed
into a miniature land crab -
the size of an ant.

183
00:27:36,240 --> 00:27:41,200
With the energy of new life,
they scamper into the forest.

184
00:27:45,800 --> 00:27:50,360
The tiny crabs retrace the journey
made by their parents.

185
00:27:51,800 --> 00:27:56,080
Then they mysteriously disappear
for 12 months or so.

186
00:27:59,960 --> 00:28:06,440
In three or four years' time,
the survivors will emerge
from the forest

187
00:28:06,440 --> 00:28:12,160
to join the great spawning migration
of the crabs of Christmas Island.

188
00:28:42,440 --> 00:28:45,640
Subtitles by Janet Waters.
1988