1
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There's an insect in this garden

2
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that all gardeners loathe...

3
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aphids.

4
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They've made enemies of gardeners,

5
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but in the undergrowth they have friends...

6
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ants.

7
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Ants herd aphids
to the best possible feeding places

8
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just as human shepherds will herd their sheep
to the best pastures.

9
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And just as shepherds protect
their flocks against wolves

10
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so ants protect the aphids
against their insect enemies.

11
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Ladybirds are among the most dangerous.
They, after all, eat aphids.

12
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So the ants must get rid of them.

13
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That's not easy. It's quite hard to get a grip
on the polished shell of a ladybird.

14
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But eventually, success.

15
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Aphids excrete a liquid that ants relish, honeydew.

16
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That's why ants protect them.

17
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Such close relationships
are frequent among insects,

18
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perhaps because they've had so long
to develop them.

19
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They appeared on land, after all,

20
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about a hundred million years
before any backboned animal.

21
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And they can also evolve much faster

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because they can produce several generations
within a single year.

23
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So, perhaps it's not surprising

24
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that they have developed relationships
between one another

25
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of a complexity that blows the mind.

26
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These associations extend
not only to other insects but to plants.

27
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They were established at a very early period.

28
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Plants are the basis of all life.

29
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For only they can combine
minerals in the ground with gases from the air

30
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and produce something worth eating.

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Insects, however, not only eat them

32
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they also exploit them
in much more devious ways.

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Tropical rain forests are famous
for being thick, tangled masses of vegetation.

34
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But in this one, in Peru,

35
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there are mysterious clearings

36
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where only one
or, at the most, two kinds of trees will grow.

37
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The local people call such places as this
Devil's Gardens

38
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and believe that spirits kill other kinds of trees.

39
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And the real killers of those trees?

40
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Well, they've only just been discovered.

41
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The leaves of the surviving trees

42
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all have these swellings on their stems.

43
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And going in and out are armies

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of tiny, tiny ants.

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The swellings are their homes.

46
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Specially developed for them by the tree.

47
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And in them, safe from predators,
the ants keep their eggs and larvae.

48
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They even keep domestic livestock,

49
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white scale insects, which, like aphids,
supply the ants with drinks of honeydew.

50
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Producing this accommodation
also benefits the tree,

51
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for the ants provide their landlord
with a valuable service.

52
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They guard it against its enemies.

53
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All kinds of insects will eat a plant's leaves
given the chance.

54
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But they don't get a chance, not on this tree.

55
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So the caterpillar goes elsewhere.

56
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This is a more formidable leaf muncher,

57
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a kind of giant grasshopper,

58
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several thousand times bigger
than any individual ant.

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That's not so easy to shift.

60
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But it does have a weak spot.

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If you can say that any insect has a heel,

62
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then this one has an Achilles heel.

63
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And the ants seem to know it.

64
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Enough is enough.

65
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The ants not only repel
their host's animal enemies,

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they also, perhaps more remarkably,
keep competing plants at bay.

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A squad of them leaves the barracks

68
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and sets out on one of their regular patrols
of the neighbourhood.

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They've found a newly-sprouted sapling.

70
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Perhaps it's grown from one of their landlord's
seeds. In which case, all well and good.

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But this one hasn't, it's an intruder.

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They go into action, biting its stems.

73
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Reinforcements arrive.

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Hundreds of tiny jaws cut into its stems.

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The sapling begins to wilt.

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But bites alone are not enough
for the ants to achieve their ends.

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They lift their abdomens and inject formic acid
into the crippled plant's wounds.

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The poison spreads through the plant's tissues
hastening its death.

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And within a few days
of being comprehensively stung,

80
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all these plants are dead.

81
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And the ants, or the "devils",

82
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have extended their garden still further.

83
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But the benefit of this drastic gardening,
of course, is not restricted to the plants.

84
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The ants also profit.

85
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They have ensured that their plant landlord

86
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can extend its territory without competition.

87
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And that provides them with more homes,
so they too can increase their numbers.

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It's one thing to provide food and shelter
in return for protection,

89
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but it's quite another thing
to be compelled to provide a home

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where before there was none.

91
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But some insects have the ability
to force a plant to do just that.

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They're called gall-makers
and this oak tree is infested with them.

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This odd wrinkled object at the base of an acorn,
is known as a knopper gall.

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Inside there is the tiny grub of a minute wasp.

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To understand how it got there
we have to go back to last spring.

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This tiny insect, scarcely bigger than a mosquito,

97
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is one of these gall wasps.

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There are lots of them
flying around the oak flowers.

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Most of the flowers by now have been pollinated
and are about to develop into acorns.

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The gall wasps too have mated

101
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and this female is looking for a place
to lay her eggs.

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She thrusts her ovipositor
into the base of the fertilised flower,

103
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and injects an egg.

104
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And that triggers a profound genetic change
in the growing oak bud.

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It develops, not into an acorn
but into something very different, a gall.

106
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Within, the tiny larva
whose secretions have caused the change

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feeds on the oak tree's tissues.

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As summer proceeds,
the galls become increasingly hard and woody.

109
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Autumn comes
and the oak tree starts to shed its leaves.

110
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It's shutting down for the winter.

111
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And with its leaves go both acorns and galls.

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Plant and insect life is suspended.

113
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But unseen changes are nevertheless taking place.

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Spring comes at last.

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Inside the gall something starts moving.

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The larva has turned into an adult wasp.

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It has spent nine months
within the oak tree's tissues.

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It has only a few weeks of its life left.

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Now as an adult
it must look for another oak to inject with eggs.

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A single oak tree may be afflicted by
70 different kinds of gall,

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each produced by a different species of wasp,

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and each with its own particular contorted shape.

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These hard shells may seem to be effective
defences for the little grub inside them,

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but not necessarily so.

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This is another kind of gall wasp

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and she's not a genetic engineer, she's a burglar.

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Behind her she trails her equipment
for breaking and entering, a drill.

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She carefully selects a site for her operations
and takes aim.

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She flicks away the drill's sheath and starts work.

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Her aim has to be very accurate
if she's to strike her target,

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the larva at the gall centre.

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The tip of her drill has a sharp cutting edge
of metallic zinc

133
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which pierces the gall tissues with ease.

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When she detects that she's reached
the central chamber,

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a microscopic egg travels down
the centre of the drill and into the larva.

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The operation is over.

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Her offspring will now hatch in the gall's centre,

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consume the flesh of the resident larva
and take over the gall.

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Galls are worldwide.

140
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California, for example,
has other species of oak tree

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and other kinds of gall.

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These particular ones are relatively tiny,
the size of peppercorns.

143
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You'd hardly notice them except for one thing.

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They jump.

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And not only do they jump,
they jump for three days.

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The tiny larvae within flip themselves about
inside their minute chambers.

147
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Why they should do so is not clear.

148
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Perhaps it's a way of moving their homes
into cracks and crevices

149
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where they're out of the reach
of predators and parasites

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and shaded from the hot Californian sun.

151
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Another gall in Hungary
protects itself in a more complex fashion.

152
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It recruits insect guardians.

153
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This gall is producing nectar.

154
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It's sweet.

155
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And it's producing it,
not for the benefit of the oak tree,

156
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but for the benefit of the tiny grub
that lies within the gall.

157
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Because the nectar attracts ants

158
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and ants serve as defenders
against any other intruders.

159
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And if you want to see how valuable they are,
let me remove some.

160
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Within a few minutes
a different kind of gall wasp appears.

161
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It's another of those burglars
looking for an existing gall

162
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into which it can inject its egg.

163
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But the ants have now returned
and they attack the intruder.

164
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Away it goes.

165
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The ants, having driven off the wasp,

166
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take their reward of nectar.

167
00:14:31,727 --> 00:14:35,515
In the normal course of events,
oak trees don't produce nectar,

168
00:14:35,607 --> 00:14:37,723
but many plants certainly do.

169
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It's a way of attracting insects

170
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that will transport their pollen
from one plant to another.

171
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And the colourful flowers are advertisements
proclaiming that nectar is there for the taking.

172
00:14:53,647 --> 00:14:57,117
But the plants must also ensure
that visiting insects

173
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collect the pollen as well as nectar

174
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and that leads to all kinds of complexities.

175
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Like many plants, the pyramidal orchid
has a way of ensuring that they do.

176
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The burnet moth
probes into the orchid's nectar store

177
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and, as it does so,
a horseshoe-shaped mass of pollen

178
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clips on to its long proboscis.

179
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Inconvenient it may be but the moth can't shift it.

180
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Away it goes to another flower,
taking the pollen with it.

181
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And this time as it probes for a drink,

182
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a speck of pollen is transferred
to the female part of the flower.

183
00:15:48,167 --> 00:15:49,486
The job is done.

184
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The traffic of insect pollinators
to and from flowers is so heavy

185
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and, in particular, so predictable,

186
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that it's not surprising
that some invertebrates have learnt to exploit it.

187
00:16:05,847 --> 00:16:12,116
A white crab spider sits almost invisible
on a white flower, waiting in ambush.

188
00:16:13,487 --> 00:16:15,318
And it catches a bee.

189
00:16:20,367 --> 00:16:24,565
The spider is clearly taking advantage
of the flower's advertising.

190
00:16:25,527 --> 00:16:28,246
It looks superbly camouflaged to our eyes,

191
00:16:28,327 --> 00:16:30,477
but insect eyes are different to ours

192
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and see parts of the light spectrum invisible to us.

193
00:16:34,767 --> 00:16:38,885
Under ultraviolet light we can get a better
idea of how they see things,

194
00:16:39,247 --> 00:16:44,162
and most surprisingly the spider looks
more obvious to them than it does to us.

195
00:16:44,887 --> 00:16:46,320
Why should that be?

196
00:16:46,927 --> 00:16:50,522
Perhaps it's because ultraviolet markings
on some flowers

197
00:16:50,607 --> 00:16:53,041
serve to guide insects to nectar.

198
00:16:53,367 --> 00:16:58,316
So maybe the spider's colour
is a positive attraction for bees.

199
00:17:01,527 --> 00:17:04,803
Certainly, honeybees seem more likely
to visit flowers

200
00:17:04,887 --> 00:17:07,447
with crab spiders on them than those without,

201
00:17:07,527 --> 00:17:09,916
often with fatal consequences.

202
00:17:16,647 --> 00:17:19,844
The relationships between the animals
that live in the undergrowth

203
00:17:19,927 --> 00:17:22,964
are full of such deceits and impostures.

204
00:17:23,207 --> 00:17:26,085
Here in Australia there's an intriguing example

205
00:17:26,207 --> 00:17:28,323
that has only just been discovered.

206
00:17:29,647 --> 00:17:30,636
This...

207
00:17:33,447 --> 00:17:36,120
is a feather-legged bug.

208
00:17:38,007 --> 00:17:41,556
It too manages to persuade prey to come close.

209
00:17:41,847 --> 00:17:45,840
But its invitations are aimed not at bees, but ants

210
00:17:45,927 --> 00:17:50,398
and what the ants get is a very nasty surprise.

211
00:17:52,367 --> 00:17:54,483
Like all members of the bug family,

212
00:17:54,567 --> 00:17:57,445
this one has a long tube for a mouth.

213
00:17:57,887 --> 00:18:01,038
Most stick it into plants to suck sap.

214
00:18:01,407 --> 00:18:04,524
Using it to eat an ant is more difficult.

215
00:18:05,887 --> 00:18:09,596
The bug starts by waving to passing ants.

216
00:18:10,167 --> 00:18:14,843
The feathery flanges on its legs are so large
they can be seen from quite a distance.

217
00:18:20,847 --> 00:18:23,361
The ants are visibly intrigued,

218
00:18:23,447 --> 00:18:26,280
but they're not yet close enough
for the bug to attack.

219
00:18:26,367 --> 00:18:29,040
So it reinforces its gestures

220
00:18:29,127 --> 00:18:33,359
by producing a chemical perfume
that the ants find irresistible.

221
00:18:34,367 --> 00:18:36,005
They come closer still.

222
00:18:39,327 --> 00:18:40,806
They climb all over the bug,

223
00:18:40,887 --> 00:18:44,436
trying to find the source
of this strange compulsive smell,

224
00:18:44,927 --> 00:18:47,521
and the bug does nothing to stop them.

225
00:18:59,007 --> 00:19:01,521
Where does that smell come from?

226
00:19:01,607 --> 00:19:03,404
Is it on the bug's legs?

227
00:19:14,327 --> 00:19:17,558
The bug now answers the ants' questions.

228
00:19:17,647 --> 00:19:21,925
It lifts itself up
and reveals a gland on its underside.

229
00:19:22,007 --> 00:19:24,237
That's what's producing the smell.

230
00:19:27,807 --> 00:19:30,879
The ant presses its head against the bug's chest

231
00:19:30,967 --> 00:19:32,764
to actually taste the gland.

232
00:19:32,847 --> 00:19:36,237
It's the perfect position for its own execution.

233
00:19:38,567 --> 00:19:42,003
The bug stabs its mouth into the back
of the ant's head.

234
00:19:48,047 --> 00:19:52,245
So a tube can be used
to suck nourishment from an insect,

235
00:19:52,327 --> 00:19:54,079
as well as from a plant.

236
00:19:54,967 --> 00:19:58,403
This is the rogue of the bug family, a killer.

237
00:20:03,767 --> 00:20:06,679
Ants are among the most numerous, widespread

238
00:20:06,767 --> 00:20:09,884
and frequently exploited members
of the undergrowth.

239
00:20:11,007 --> 00:20:15,319
These, in Australia,
collect seeds and store them underground.

240
00:20:16,167 --> 00:20:18,158
Plants encourage them to do so

241
00:20:18,247 --> 00:20:21,045
by adding a tasty capsule to their seeds.

242
00:20:21,607 --> 00:20:26,123
That may seem odd,
but these ants don't eat all the seeds they store.

243
00:20:26,207 --> 00:20:30,405
In fact, seeds are more likely to germinate
below ground than above.

244
00:20:31,287 --> 00:20:35,246
But not everything on this forest floor
is what it seems.

245
00:20:36,607 --> 00:20:40,646
When it comes to putting your eggs
in a suitable place,

246
00:20:41,127 --> 00:20:45,996
some insects persuade other insects
to do the job for them.

247
00:20:46,687 --> 00:20:49,565
This little object looks like a seed,

248
00:20:49,647 --> 00:20:52,286
and certainly, it's fallen from above,

249
00:20:52,367 --> 00:20:55,564
and that ant seems to think it's worth eating.

250
00:20:55,647 --> 00:21:00,926
But actually, it hasn't come from a plant,
it's come from another insect.

251
00:21:03,247 --> 00:21:05,044
And this is it.

252
00:21:05,127 --> 00:21:10,440
It's rather difficult to see
because it looks exactly like a dried leaf,

253
00:21:10,527 --> 00:21:12,563
but it's a stick insect.

254
00:21:12,647 --> 00:21:18,324
There's its head, antennae,
and that's the tip of its abdomen.

255
00:21:19,287 --> 00:21:24,315
As an adult, like this, it spends all its time
up in the trees eating leaves.

256
00:21:24,607 --> 00:21:28,566
And when the time comes to lay,
and this one is doing so,

257
00:21:28,647 --> 00:21:33,721
all she does is simply to flick away the egg,
and let it fall to the ground.

258
00:21:34,407 --> 00:21:37,956
But that's not quite as risky as you might think.

259
00:21:41,367 --> 00:21:46,964
Wherever you are, you can be pretty sure
that some ants will turn up looking for food.

260
00:21:47,327 --> 00:21:50,717
And that is exactly
what the stick insect's eggs look like.

261
00:21:50,807 --> 00:21:54,800
A nutritious seed,
complete with that fatty capsule at the tip.

262
00:21:56,967 --> 00:21:59,925
So the ants start to haul them away.

263
00:22:16,407 --> 00:22:20,446
Although the ants certainly eat
a great number of the seeds they store,

264
00:22:20,527 --> 00:22:23,803
stick insect eggs
don't seem to be quite as tempting.

265
00:22:23,887 --> 00:22:26,355
At any rate, the ants, after all their labour,

266
00:22:26,447 --> 00:22:29,723
usually leave the stick insect eggs untouched.

267
00:22:34,287 --> 00:22:37,404
While the seasons pass, the eggs lie underground,

268
00:22:37,487 --> 00:22:40,877
hidden from birds and any other predators
that might eat them.

269
00:22:40,967 --> 00:22:44,357
They may remain there, safe,
for up to three years,

270
00:22:44,847 --> 00:22:47,042
but eventually they hatch.

271
00:22:53,007 --> 00:22:55,680
It's only at this early stage of its life

272
00:22:55,767 --> 00:22:58,406
that a stick insect actually runs.

273
00:23:01,007 --> 00:23:04,966
The youngsters positively scamper
up into the tree branches.

274
00:23:11,007 --> 00:23:13,919
There they will take up their adult life of leisure,

275
00:23:14,007 --> 00:23:17,283
well-camouflaged, stolidly chewing leaves.

276
00:23:19,327 --> 00:23:22,876
Giving your offspring a good start in life
can take a lot of effort.

277
00:23:22,967 --> 00:23:26,721
So some insects have evolved
highly complex strategies

278
00:23:26,807 --> 00:23:31,085
to induce other species
to become nursemaids on their behalf.

279
00:23:33,727 --> 00:23:38,755
This Californian desert hardly seems to be
the best place to find nursemaids.

280
00:23:39,247 --> 00:23:43,399
But blister beetles
have an amazing way of discovering them.

281
00:23:46,447 --> 00:23:49,757
It starts simply enough with the female beetle.

282
00:23:50,127 --> 00:23:53,563
She has dug a hole
and is now laying her eggs in it.

283
00:23:58,407 --> 00:24:01,046
That done, she abandons them.

284
00:24:03,887 --> 00:24:08,244
A few centimetres below the surface of the sand
conditions are good for eggs.

285
00:24:08,327 --> 00:24:12,115
Not too cold, neither too hot,
even in the heat of the day.

286
00:24:14,847 --> 00:24:17,122
Six weeks later, they hatch.

287
00:24:18,127 --> 00:24:21,517
But these sands are very barren and scorching hot.

288
00:24:21,607 --> 00:24:25,077
Somehow the tiny larvae have got to find food

289
00:24:25,167 --> 00:24:27,362
and they won't find it here.

290
00:24:31,007 --> 00:24:34,079
Their survival depends on teamwork.

291
00:24:37,887 --> 00:24:41,243
Together, as a closely coordinated group,

292
00:24:41,327 --> 00:24:44,524
they climb up a stem of withered grass.

293
00:24:54,607 --> 00:24:57,963
When they get to the top,
there's nowhere else to go.

294
00:24:58,047 --> 00:25:02,199
They look dangerously exposed
to the sun and to other predators,

295
00:25:02,287 --> 00:25:05,882
but there they stay, in a tight squirming mass.

296
00:25:09,687 --> 00:25:11,678
For those that can get there,

297
00:25:11,767 --> 00:25:16,477
the top of this stem has become a stage
for a remarkable piece of deception.

298
00:25:17,167 --> 00:25:20,921
What these larvae want is a lift, a ride.

299
00:25:21,007 --> 00:25:26,286
And they want it so badly that sometimes
they'll even try and get it from a human finger.

300
00:25:27,567 --> 00:25:31,162
But what they're really searching for
is not a human finger.

301
00:25:31,247 --> 00:25:33,886
They're searching for another insect.

302
00:25:35,527 --> 00:25:38,280
Here it comes. A female digger bee

303
00:25:38,367 --> 00:25:41,837
leaving a tunnel
that she's just dug for her own young.

304
00:25:43,447 --> 00:25:45,517
She's off to gather pollen.

305
00:25:51,807 --> 00:25:55,083
She packs it into baskets on her back legs

306
00:25:55,167 --> 00:25:57,601
and takes it back to her burrow.

307
00:25:59,127 --> 00:26:03,803
It'll provide valuable food for her young
when they eventually hatch.

308
00:26:08,367 --> 00:26:12,519
And here comes a male.
He's on the lookout for a female.

309
00:26:17,647 --> 00:26:22,926
To him, the cluster not only looks like a female,
it smells like a female.

310
00:26:23,007 --> 00:26:26,283
For the beetle larvae are producing a perfume,
a pheromone,

311
00:26:26,367 --> 00:26:29,837
that is exactly like that emitted by a female bee.

312
00:26:30,687 --> 00:26:35,124
He alights in order to mate,
and in seconds is covered by the larvae

313
00:26:35,207 --> 00:26:37,198
that swarm all over him.

314
00:26:39,527 --> 00:26:44,078
At first, he seems stunned
by the shock of his sudden increase in weight.

315
00:26:45,687 --> 00:26:47,678
But then he's off again.

316
00:26:49,647 --> 00:26:53,640
Now his luck improves. This really is a female.

317
00:26:55,847 --> 00:26:59,442
And while he mates, his passengers jump ship.

318
00:27:17,807 --> 00:27:21,083
Now they're all on board a female bee.

319
00:27:28,007 --> 00:27:32,364
She, having mated, goes back to her nest to lay,

320
00:27:32,447 --> 00:27:34,597
taking the larvae with her.

321
00:27:37,167 --> 00:27:42,161
At last, the young beetle larvae
have reached safety and food,

322
00:27:42,247 --> 00:27:46,320
the store of pollen that the female digger bee
worked so hard to collect

323
00:27:46,407 --> 00:27:48,159
for her own young.

324
00:27:48,887 --> 00:27:52,038
So they hop off and tuck in.

325
00:27:57,887 --> 00:28:00,526
Not only do they consume the pollen,

326
00:28:00,607 --> 00:28:04,282
when that runs out,
they'll eat the young bee larvae, too.

327
00:28:06,807 --> 00:28:11,961
Blister beetles are not alone in using couriers
to take their offspring to food.

328
00:28:12,887 --> 00:28:15,879
The young of this botfly, here in Brazil,

329
00:28:15,967 --> 00:28:19,243
feed on the blood and tissues of living cows.

330
00:28:19,327 --> 00:28:21,921
But how is a female to get them there?

331
00:28:22,007 --> 00:28:26,956
She is a big insect. So big
that cows would notice if she landed on them,

332
00:28:27,047 --> 00:28:29,277
and would probably flick her off.

333
00:28:29,367 --> 00:28:31,722
She needs a lightweight courier.

334
00:28:33,287 --> 00:28:37,360
A housefly, a fraction of her weight.
That will do nicely.

335
00:28:39,087 --> 00:28:41,317
She drops down to stalk it.

336
00:28:47,567 --> 00:28:48,920
She's got it.

337
00:28:49,647 --> 00:28:53,526
She manipulates the housefly
into the right position.

338
00:28:54,087 --> 00:28:59,241
And now, one by one, she glues her eggs
onto the housefly's abdomen.

339
00:29:03,527 --> 00:29:05,085
Within a few seconds,

340
00:29:05,167 --> 00:29:09,319
the housefly has been coated
by about 30 cream-coloured eggs.

341
00:29:11,967 --> 00:29:14,800
The botfly releases its hapless messenger.

342
00:29:17,007 --> 00:29:20,761
The housefly seems well aware
that it's carrying an extra load

343
00:29:20,967 --> 00:29:22,719
but it can't get rid of it.

344
00:29:32,087 --> 00:29:35,124
So, it goes back to its normal business

345
00:29:35,447 --> 00:29:38,598
which includes visiting cows to drink their sweat.

346
00:29:41,647 --> 00:29:46,596
A small fly, unlike the lumbering botfly,
is no real irritation

347
00:29:46,687 --> 00:29:49,042
and is able to feed largely unhindered.

348
00:29:54,807 --> 00:29:58,561
The fly mops up the sweat
with its pad-shaped mouth parts.

349
00:29:58,767 --> 00:30:00,280
But as it feeds,

350
00:30:00,367 --> 00:30:04,963
so the warmth of the cow's body
causes the botfly's eggs to hatch.

351
00:30:11,327 --> 00:30:14,444
The larvae are armed with tiny hooks

352
00:30:14,527 --> 00:30:18,520
which help them get a grip on a cow's skin
and bore into it.

353
00:30:24,927 --> 00:30:29,842
So in a few minutes,
a cow can acquire a dozen botfly larvae,

354
00:30:29,927 --> 00:30:32,361
feeding away beneath its skin.

355
00:30:33,127 --> 00:30:35,960
Licking won't get rid of them now.

356
00:30:37,687 --> 00:30:41,999
A couple of months later, the full-grown larvae
emerge and drop to the ground.

357
00:30:44,487 --> 00:30:49,356
There they will burrow into the soil,
pupate and turn into adults.

358
00:30:52,687 --> 00:30:55,599
All kinds of creatures, great and small,

359
00:30:55,687 --> 00:30:58,804
are exploited by insect parents in this kind of way.

360
00:30:59,247 --> 00:31:01,283
This is Costa Rica.

361
00:31:01,367 --> 00:31:04,279
And here lives a species of orchard spider.

362
00:31:04,927 --> 00:31:07,999
They construct horizontal orb-webs

363
00:31:08,087 --> 00:31:10,647
as lovely as those made by any spider.

364
00:31:11,887 --> 00:31:15,197
But one individual has a hanger-on.

365
00:31:15,767 --> 00:31:19,806
An anonymous looking grub
is clinging to her abdomen.

366
00:31:25,807 --> 00:31:29,083
She seems little affected by having a passenger.

367
00:31:29,167 --> 00:31:33,922
And every day, as usual,
she builds a new and perfect web.

368
00:31:36,487 --> 00:31:39,126
She is just as efficient a hunter as ever

369
00:31:39,207 --> 00:31:43,598
but every catch she makes,
she shares, in effect, with her passenger.

370
00:31:44,207 --> 00:31:46,960
For the grub is sucking her juices.

371
00:32:00,247 --> 00:32:03,796
Her passenger stays with her for some two weeks,

372
00:32:03,887 --> 00:32:07,766
slowly growing in size, at her expense.

373
00:32:08,807 --> 00:32:12,402
And still, daily, she constructs a new web.

374
00:32:14,327 --> 00:32:17,683
Then, one evening when, as usual,
as she starts to spin,

375
00:32:17,767 --> 00:32:20,679
something seems to have gone
dramatically wrong.

376
00:32:26,567 --> 00:32:30,276
She seems incapable
of making her normal, beautiful orb.

377
00:32:30,367 --> 00:32:35,487
What she produces has no shape,
no radiating spokes, no sticky spiral.

378
00:32:35,567 --> 00:32:37,922
It's just an untidy tangle.

379
00:32:38,807 --> 00:32:40,604
The grub is responsible.

380
00:32:40,847 --> 00:32:43,122
It has injected her with a hormone

381
00:32:43,247 --> 00:32:46,876
that has spread to her brain and deranged her.

382
00:32:50,927 --> 00:32:53,395
She has only an hour or so to live.

383
00:32:53,487 --> 00:32:55,796
This is her last act.

384
00:32:56,207 --> 00:32:59,005
Small claspers inflate on the grub's back.

385
00:32:59,087 --> 00:33:01,999
With these it grasps the wreckage of the web

386
00:33:02,087 --> 00:33:05,477
so that it will not fall
as the dying spider loses her grip.

387
00:33:09,847 --> 00:33:13,044
It sucks the remaining fluid
from the spider's body.

388
00:33:18,247 --> 00:33:21,045
Slowly the liquid is withdrawn.

389
00:33:25,527 --> 00:33:28,200
Even the spider's legs are emptied

390
00:33:28,327 --> 00:33:31,000
until the corpse is no more than a husk.

391
00:33:34,407 --> 00:33:36,967
The grub has no further use for it.

392
00:33:39,327 --> 00:33:43,320
And now the grub,
clinging to the spider's last tangled web,

393
00:33:43,407 --> 00:33:45,762
starts to spin for itself.

394
00:33:52,927 --> 00:33:56,636
It needs a shelter in which to reorganise its body.

395
00:33:57,047 --> 00:33:58,560
A cocoon.

396
00:34:02,367 --> 00:34:06,804
Inside the lacy walls its body is breaking down,

397
00:34:06,887 --> 00:34:10,357
for it has to be reassembled
in a very different form.

398
00:34:15,927 --> 00:34:20,921
At last the killer is about to reveal
its true identity.

399
00:34:32,167 --> 00:34:33,441
It's a wasp.

400
00:34:34,927 --> 00:34:37,521
Now it must fly off to find a mate,

401
00:34:37,687 --> 00:34:42,681
so that another wasp egg
may be attached to another orchard spider.

402
00:34:51,247 --> 00:34:55,445
The opportunity to find creatures
to parasitize in the undergrowth

403
00:34:55,527 --> 00:34:57,597
seem almost endless

404
00:34:57,687 --> 00:35:00,759
and yet, surprisingly,
there are some parasitic wasps

405
00:35:00,847 --> 00:35:03,361
that find their victims in water,

406
00:35:03,447 --> 00:35:06,166
in lakes and ponds like this one.

407
00:35:06,567 --> 00:35:10,003
They're extremely small,
about a quarter of a millimetre long,

408
00:35:10,087 --> 00:35:13,159
in fact, one of the smallest of all insects.

409
00:35:13,247 --> 00:35:15,715
And I've got some in this test tube.

410
00:35:16,007 --> 00:35:18,999
And to give you an idea of just how small they are,

411
00:35:19,087 --> 00:35:24,286
I'll drop this pin in alongside them
to give a sense of scale.

412
00:35:25,487 --> 00:35:31,278
Yet, these tiny specks
have eyes, legs, feelers just like any other insect.

413
00:35:40,647 --> 00:35:42,842
They're known as fairy wasps,

414
00:35:42,927 --> 00:35:45,725
and spend nearly all their lives underwater.

415
00:35:46,247 --> 00:35:50,718
They make a tiny water flea,
itself only the size of a grain of sand,

416
00:35:50,807 --> 00:35:52,445
look like a giant.

417
00:35:52,847 --> 00:35:54,326
They're so minute

418
00:35:54,407 --> 00:35:57,922
they can lay their eggs
inside the eggs of other insects.

419
00:35:58,207 --> 00:36:01,244
And they choose those laid by water beetles.

420
00:36:04,767 --> 00:36:08,885
Water beetles lay their eggs inside plant stems.

421
00:36:10,127 --> 00:36:13,199
A female fairy wasp, having located one,

422
00:36:13,607 --> 00:36:19,842
uses its microscopically-thin ovipositor
to inject up to 100 or so eggs

423
00:36:19,927 --> 00:36:21,963
into just one of the beetle's.

424
00:36:30,447 --> 00:36:32,403
And here they hatch.

425
00:36:36,167 --> 00:36:39,125
The young wasps feed and grow,

426
00:36:39,207 --> 00:36:42,199
consuming the water beetle's undeveloped young.

427
00:36:45,727 --> 00:36:48,685
Not only that, they mate here.

428
00:36:57,527 --> 00:37:02,123
Then, at last,
they leave the shell of the beetle's egg.

429
00:37:12,887 --> 00:37:14,878
The females must now lay.

430
00:37:14,967 --> 00:37:18,039
And some will be able to do so in other ponds,

431
00:37:18,127 --> 00:37:21,722
because, in spite of everything,
they still have wings.

432
00:37:24,567 --> 00:37:28,879
Other bigger parasitic wasps
have totally lost their wings.

433
00:37:29,367 --> 00:37:32,040
You can find them on many a British heath.

434
00:37:33,167 --> 00:37:36,443
This one, Methoca, looks rather like an ant,

435
00:37:37,007 --> 00:37:40,522
and insects that live by hunting ants
easily mistake it for one.

436
00:37:41,927 --> 00:37:45,078
The tiger beetle is a very active ant hunter.

437
00:37:45,407 --> 00:37:47,477
It chases them and runs them down.

438
00:37:56,607 --> 00:37:58,882
And very successful it is.

439
00:38:02,127 --> 00:38:07,247
Earlier in its life, of course, as a larva
a tiger beetle can't run around.

440
00:38:07,647 --> 00:38:11,276
Instead the larva catches ants
by waiting in ambush.

441
00:38:12,847 --> 00:38:17,238
It plugs the entrance to its burrow
with its armoured, plate-like head.

442
00:38:17,487 --> 00:38:20,797
If an ant touches that, it's as good as dead.

443
00:38:32,807 --> 00:38:34,479
It works every time.

444
00:38:46,087 --> 00:38:50,000
Methoca, however, is a more awkward customer.

445
00:38:57,327 --> 00:39:00,364
The beetle larva is waiting with jaws agape.

446
00:39:06,567 --> 00:39:09,923
But Methoca is more agile than the usual ant

447
00:39:10,007 --> 00:39:13,920
and it manages to slip out
between the beetle larva's jaws.

448
00:39:17,487 --> 00:39:21,958
It grabs the larva's soft body and pulls.

449
00:39:27,367 --> 00:39:29,358
And now it stings it.

450
00:39:32,407 --> 00:39:37,003
Methoca climbs out of the tunnel
waiting for the poison to take effect.

451
00:39:43,207 --> 00:39:46,085
The sting has only paralysed the larva

452
00:39:46,167 --> 00:39:50,479
and the wasp drags the helpless creature
farther down its burrow.

453
00:39:52,647 --> 00:39:55,559
Now she lays her egg onto it.

454
00:40:03,207 --> 00:40:07,041
To prevent anything interfering
with her grub while it stays underground

455
00:40:07,167 --> 00:40:09,556
feeding on the paralysed beetle larva,

456
00:40:09,647 --> 00:40:11,399
she blocks up the entrance.

457
00:40:28,207 --> 00:40:33,201
This is the longest and most laborious part
of her motherly duties.

458
00:40:33,287 --> 00:40:36,006
But now, without any more work from her,

459
00:40:36,087 --> 00:40:40,285
her young will have all the food it needs
to develop into an adult.

460
00:40:45,567 --> 00:40:50,766
Underground nests are certainly
among the best protected of all insect nurseries

461
00:40:50,847 --> 00:40:54,806
and, indeed, they are very difficult
for parasites to break into.

462
00:40:56,727 --> 00:41:02,518
Ants defend their colonies against intruders
with great ferocity.

463
00:41:03,247 --> 00:41:06,284
And yet, here in this meadow in central Europe,

464
00:41:06,367 --> 00:41:10,519
there are ants' nests
where intruders live undetected.

465
00:41:10,607 --> 00:41:12,518
And there's one right here.

466
00:41:20,807 --> 00:41:23,879
This is the caterpillar...

467
00:41:24,967 --> 00:41:26,719
of the blue butterfly

468
00:41:27,127 --> 00:41:30,915
and it's lived in this nest undetected

469
00:41:31,007 --> 00:41:35,956
and protected by the ants
and fed by them for the last two years.

470
00:41:36,287 --> 00:41:40,439
Indeed, it's been so thoroughly accepted
by the ants

471
00:41:40,527 --> 00:41:45,601
that they will try and rescue it
in preference to the young of their own queen.

472
00:41:45,687 --> 00:41:48,121
As in fact they are doing right now.

473
00:41:52,847 --> 00:41:57,284
But how do these caterpillars get into
the ants' nest in the first place?

474
00:42:04,207 --> 00:42:08,997
Alcon blue butterflies
begin their courtship in June and July.

475
00:42:09,327 --> 00:42:12,876
They are surely one of the loveliest sights
of a European summer

476
00:42:12,967 --> 00:42:16,403
as they flutter and flirt
among the flowers of the meadow.

477
00:42:26,607 --> 00:42:28,916
Male and female meet...

478
00:42:29,007 --> 00:42:30,122
and join.

479
00:42:35,087 --> 00:42:36,645
Once they have mated

480
00:42:36,727 --> 00:42:41,164
the female Alcon blue must find a gentian plant.

481
00:42:48,807 --> 00:42:51,321
Here she lays her eggs.

482
00:43:04,447 --> 00:43:09,965
The caterpillars, when they hatch,
stay feeding on the gentian for a couple of weeks.

483
00:43:11,327 --> 00:43:13,795
But eventually they fall to the ground.

484
00:43:16,247 --> 00:43:20,160
There are ants everywhere in
a meadow like this, and they soon find it.

485
00:43:23,007 --> 00:43:25,521
It smells just like one of their own larvae

486
00:43:25,607 --> 00:43:29,725
and they start to haul it back
to where one of their larvae should be,

487
00:43:29,807 --> 00:43:31,160
in their nest.

488
00:43:32,487 --> 00:43:36,036
Other foragers from the same nest
have found another.

489
00:43:38,807 --> 00:43:43,403
During the next few weeks, as many as
half a dozen may be taken back to the nest.

490
00:43:49,447 --> 00:43:52,837
Here they are hauled down
to the nursery chambers

491
00:43:52,927 --> 00:43:55,521
and put with the ants' other eggs and larvae.

492
00:43:57,647 --> 00:44:00,798
And because the caterpillars continue
to produce a pheromone

493
00:44:00,887 --> 00:44:04,323
exactly like that produced by
the young ants themselves,

494
00:44:04,407 --> 00:44:06,841
they are treated as if they were young ants.

495
00:44:06,927 --> 00:44:09,316
Even though they are bigger
and a different colour.

496
00:44:11,567 --> 00:44:15,003
The caterpillars even mimic
the sound the ants make

497
00:44:15,087 --> 00:44:16,645
when they beg for food,

498
00:44:16,727 --> 00:44:19,844
so the workers dutifully feed and clean them.

499
00:44:25,647 --> 00:44:29,481
You might think that this caterpillar
has protected itself very well

500
00:44:29,567 --> 00:44:31,717
by deceiving these ants.

501
00:44:31,807 --> 00:44:35,322
But life in the undergrowth is full of surprises.

502
00:44:39,007 --> 00:44:40,963
An ichneumon wasp.

503
00:44:41,047 --> 00:44:43,322
It too, like the blue butterfly,

504
00:44:43,447 --> 00:44:46,086
wants to get its young into an ants' nest.

505
00:44:46,167 --> 00:44:47,964
But not merely as lodgers.

506
00:44:48,047 --> 00:44:50,766
It has a more sinister intention.

507
00:44:51,647 --> 00:44:54,844
Somehow or other, in a meadow full of ants' nests,

508
00:44:54,927 --> 00:44:58,283
it can detect which one harbours
a butterfly caterpillar,

509
00:44:58,367 --> 00:45:01,165
and this, it decides, is one of those.

510
00:45:02,487 --> 00:45:06,116
Once inside, the ants start to attack it,
as you might expect.

511
00:45:06,207 --> 00:45:10,359
But then, the ants' behaviour changes.
There is pandemonium.

512
00:45:10,447 --> 00:45:14,884
The wasp has released a pheromone
that makes the ants attack one another.

513
00:45:23,207 --> 00:45:28,918
With the defenders fighting among themselves,
the wasp is able to go deeper into the nest.

514
00:45:30,327 --> 00:45:33,763
It's reached the nursery
and here lie the caterpillars.

515
00:45:33,847 --> 00:45:35,963
Now they are defenceless.

516
00:45:42,767 --> 00:45:46,919
The wasp sets about injecting
each of them with an egg.

517
00:45:49,487 --> 00:45:52,604
A few ants do their best to prevent this.

518
00:45:52,687 --> 00:45:54,757
But there is no real opposition.

519
00:46:03,727 --> 00:46:06,764
While most of the ants continue
to fight among themselves,

520
00:46:06,847 --> 00:46:09,441
the wasp finds a second caterpillar.

521
00:46:12,887 --> 00:46:14,878
Another egg is laid.

522
00:46:26,287 --> 00:46:28,005
The wasp leaves.

523
00:46:31,167 --> 00:46:35,365
With the wasp gone,
the ant colony slowly returns to normal.

524
00:46:35,887 --> 00:46:39,402
The caterpillars are still there,
alive and apparently well,

525
00:46:39,487 --> 00:46:41,717
and the ants continue to care for them.

526
00:46:43,047 --> 00:46:45,356
Once the caterpillars are fully grown,

527
00:46:45,447 --> 00:46:48,086
each starts to construct a chrysalis,

528
00:46:48,287 --> 00:46:52,997
which all butterflies need as a protection
while they turn themselves into adults.

529
00:46:56,287 --> 00:46:59,882
Each chrysalis is cleaned and protected
by the ants

530
00:46:59,967 --> 00:47:02,117
as if it were one of their own pupae.

531
00:47:05,607 --> 00:47:07,723
One begins to hatch.

532
00:47:19,207 --> 00:47:22,040
Out of it comes, yes...

533
00:47:22,127 --> 00:47:23,685
a blue butterfly.

534
00:47:27,287 --> 00:47:29,118
It leaves its foster home.

535
00:47:32,647 --> 00:47:36,640
Out in the open its limp wings can expand.

536
00:47:39,207 --> 00:47:44,327
And now it's ready to flutter and flirt
just as its parents did.

537
00:47:45,727 --> 00:47:49,640
And the ants are still bewitched by
the traces of pheromone

538
00:47:49,727 --> 00:47:53,003
clinging to the empty shell
the butterfly leaves behind.

539
00:47:54,847 --> 00:47:58,601
But there are still others in the nest
as yet unhatched.

540
00:48:05,967 --> 00:48:09,323
And out of this one comes, not a butterfly,

541
00:48:10,167 --> 00:48:11,646
but a wasp.

542
00:48:21,007 --> 00:48:25,444
Hardwired into the microscopic brain
of this ordinary-looking insect

543
00:48:25,527 --> 00:48:29,884
are a whole series of skills,
sensitivities and reactions

544
00:48:29,967 --> 00:48:32,117
that will enable it, in its turn,

545
00:48:32,247 --> 00:48:35,045
to give its own offspring a special start in life.

546
00:48:35,607 --> 00:48:39,520
It can detect
what the ants themselves find undetectable.

547
00:48:40,167 --> 00:48:45,719
It can tell the difference
between an ant larva and the butterfly larva.

548
00:48:46,007 --> 00:48:49,283
What is more, in a meadow of 100 ants' nests,

549
00:48:49,367 --> 00:48:54,236
it will be able to find the one
that contains the butterfly caterpillar.

550
00:48:54,327 --> 00:48:57,046
How it does it, we have no idea.

551
00:48:57,127 --> 00:49:01,439
So it seems that among
the animals of the undergrowth

552
00:49:01,527 --> 00:49:03,995
there are many beneficial partnerships.

553
00:49:04,327 --> 00:49:09,082
But exploitation and deception
can work just as well.

