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ATTENBOROUGH: The natural world
is full of extraordinary animals

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with amazing life histories.

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Yet, certain stories
are more intriguing than most.

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The mysteries
of a butterfly's life-cycle,

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or the strange biology
of the emperor penguin.

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some of these creatures were surrounded
by myths and misunderstandings

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for a very long time.

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And some have only recently
revealed their secrets.

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These are the animals
that stand out from the crowd.

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The curiosities 1 find
most fascinating of all.

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some animals have mastered
the art of deception.

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The cuckoo tricks other birds
into raising its young,

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while the death's-head hawkmoth
infiltrates the nests of bees

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to steal their precious honey.

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They're cheats and imposters.

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(CUCKOO WARBLING)

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The call of the cuckoo has long been
regarded as a sign of spring,

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but, in fact, it's the call of a killer
and a cheat.

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The cuckoo lays its egg in the nests
of other birds

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and somehow persuades them to treat it
and its chick as if it were their own.

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How does it get away with it?

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It's a question that has puzzled
people for centuries.

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1n Britain, the cuckoo
arrives at the time

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when most birds
are nesting and laying eggs.

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Early egg collectors notice
that the nests of some birds

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had a slightly odd-looking egg in them.

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These are the eggs laid by a number
of different birds.

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Marsh warbler, spotted flycatcher,
linnet and the whitethroat.

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And amongst each of those clutches,
there is a fraudster.

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A cuckoo egg, which mimics
that of its host.

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Although cuckoos are long known to lay
their eggs in the nests of other birds,

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no one had actually
described it happening.

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And then, in the 1 8th century,
an English country doctor,

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with an interest in natural history
decided to investigate.

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Edward jenner lived here in
Berkeley, Gloucestershire

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and is best known for his work
on the smallpox vaccine.

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In fact, he's said to be the father
of vaccination and that

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his work has saved more human lives
than that of any other man.

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What is less known is that he first
achieved scientific distinction

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by his observations
on the behaviour of the cuckoo.

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At the time, it was believed
that a cuckoo removes

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all of the eggs in a nest
and then lays its own.

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By doing so, it would ensure its own
chick gets all the food brought in

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by the unwitting nest owners.

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But Edward Jenner's detailed
observations were to reveal

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a rather darker tale.

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jenner's work on cuckoos
was published in 1 788

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here in the Philosophical Transactions
of the Royal society,

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the world's first scientific society.

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It was entitled simply

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Observations on the Natural history
of the Cuckoo by Mr Edward jenner.

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In it, he reported that it was not
the parent cuckoo,

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but the newly-hatched chick,

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which pushes the eggs and nestlings
of the foster parents out of the nest.

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As soon as it hatches,
the cuckoo chick's instinct

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is to kill anything else in the nest.

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1t's still blind and naked, but it has a
cup-shaped depression on its back,

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into which an egg fits perfectly.

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But, sometimes,
the other eggs hatch earlier.

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And Jenner's observations of how the
cuckoo chick deals with its nest mates

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were quite shocking.

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He writes, ''The mode of accomplishing
this was very curious.

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''The little animal with the assistance
of its rump and wings

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''contrived to get the bird on its back

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''and making a lodgement of the burden
by elevating its elbows,

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''clambered backwards with it
up the side of the nest,

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''until it reached the top, where,
resting for a moment,

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''it threw off its load with a jerk
and quite disengaged it from the nest.''

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The real villain had been uncovered.

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jenner's views were met
with incredulity and some disbelief,

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but, nonetheless, they earned him
the fellowship of the Royal Society.

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It was the greatest honour that could
be given to a scientist at the time.

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Jenner's observations
had revealed the true nature

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of the cuckoo's deception.

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But it still wasn't clear why the cuckoo
should opt for this strange way

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of raising its young.

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1t wasn't until 1 00 years later
that Charles Darwin

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finally provided an explanation
with his theory of evolution.

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The cuckoo's behaviour has evolved
to increase its own breeding success.

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By avoiding the task of raising chicks,

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the cuckoo can lay more eggs
than any other bird,

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as many as 25 in a season.

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While it makes evolutionary sense
for the cuckoo to lay its eggs

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in the nests of others,
what about its victims?

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Why do they put up with this trickery?

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1t seems that they sometimes don't.

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And this was revealed in
an early natural history film in 1 920.

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The Cuckoo's Secret was made by
Edgar Chance and Oliver Pike,

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an egg collector
and a wildlife filmmaker.

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Chance was fascinated by cuckoos

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and spent a great deal of time
following them.

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He was the first person known
to see a cuckoo lay its egg.

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The deception involved
stealth and speed.

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The female waits until a nest
is unattended and then she strikes,

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but, if she's spotted,
the owners fight back.

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1f she's successful, the whole deception
takes less than 1 0 seconds.

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she removes and eats just one egg
and replaces it with her own.

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The Chance and Pike film solved one
mystery, but there were still others.

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How does the cuckoo choose its victim?

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And why don't the nest owners
reject the alien egg?

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Green warblers are one
of the cuckoos main targets,

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and the pair has a nest just in here.

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The female warbler has laid
four speckled eggs

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and, using a model egg,
I can illustrate the cuckoo's trickery.

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This is the sort of egg that the cuckoo
would lay in the reed warbler's nest.

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It matches the reed warbler's actual
egg very closely in colour.

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Experiments with model eggs have shown

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that reed warblers have become very good
at recognising an alien egg,

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and either throw it out
or desert their nest to start afresh.

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so the cuckoo has to make sure
that it produces an egg

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that is a very good match.

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The cuckoo and its victims
are evolving competitively.

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(WARBLING)

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With each generation,
cuckoos improve their mimicry,

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while the nest owners become better
at spotting a foreign egg.

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While many birds are very good at
detecting a strange egg in their nest,

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they seem incapable of recognising the
monstrous cuckoo chick as an imposter.

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But the deception is not complete.

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The young cuckoo is much larger
than a reed warbler chick,

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so it also needs a lot more food.

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How does it get enough?

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The cuckoo has a solution.

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1t now uses vocal deception,

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to trick its foster parents
into providing more food.

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This is a sonogram of the sound waves
produced by a single reed warbler chick

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begging for food.

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And below it is the
call of a cuckoo chick.

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And as you can see,
it looks very different.

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In fact, it more closely
resembles the calls

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of a whole nestful
of reed warbler chicks.

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so, the cuckoo chick's call
is a super stimulus

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that sounds like
a whole nestful of chicks.

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And it appears to work.

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The adult birds rush back and forth
providing the imposter

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with the same amount of food as they
would for an entire brood of their own.

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At three weeks old, the cuckoo chick
has spilled out of the nest.

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1t's now almost eight times the size
of its foster parent.

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1t was over 200 years ago that
Edward Jenner first shocked us

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with his revelation of the cuckoo's
extraordinary lifestyle.

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Now we know that its unusual behaviour
is due to an extraordinary arms race

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that has resulted in one of the most
fascinating specialisations in nature.

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The cuckoo's success relies on deceiving
just two parent birds,

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but our second subject is a moth that is
able to deceive hundreds of bees.

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How does it infiltrate one of the most
heavily-guarded nests in nature?

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This wonderful creature was once one
of the most feared insects in Europe.

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It's a death's-head hawkmoth.

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And it's easy enough to see
how it got its name.

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It has this mark on its back
that looks just like a human skull.

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This gave it a bad reputation
that lasted for centuries,

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but now there are new ideas about
this moth's strange appearance

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that may help explain
its extraordinary ability to rob hives

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without being stung.

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Death's-head hawkmoths
are a rare sight in Britain,

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for they spend most of their lives
in Africa and Asia.

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But every summer, a small number
of migrants arrive in northern Europe,

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and, if the weather is warm enough,
they breed.

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Their caterpillars, unlike the drab
adult moths, are beautifully coloured.

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After feeding for several weeks,

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they can grow to a length
of 1 3 centimetres.

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Once ready to become adults,
they pupate in the soil,

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and emerge as the sinister,
strangely-patterned moths.

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In the early 1 9th century,
a region of northern France

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was hit by a terrible pestilence.

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And, at the same time, a large number
of hawkmoths were seen in the area.

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The local people linked the deaths
to these night-flying insects.

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But there was another even more
disturbing side to this moth.

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It could make an unusual noise.

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(SQUEAKING)

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There, a strange squeak, and that
only added to its chilling reputation.

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Moths don't usually squeak.

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Tiger moths sometimes produce
ultrasonic warning clicks

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that tell bats that they're poisonous
and not good to eat,

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but this is not a noise
we can generally hear.

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Perhaps the death's-head hawkmoth
squeaks to scare predators like birds.

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However, other large migratory moths
don't make such a sound.

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This makes the death's-head hawkmoth's
squeak all the more surprising.

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And it has intrigued people
for centuries.

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These moths are more than 200 years old.

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We know that because
the hand-written label there

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tells us they were collected in 1 801
by a Robert Darling Willis,

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the personal physician
to King George III.

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George III is well known

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as the king who suffered
from bouts of madness.

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And on a visit to see
the King during one of them,

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Dr Willis discovered these large moths
in the monarch's bed chamber.

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Unable to identify them,
the doctor sent them to his grandson,

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who was at that time superintendent at
the Museum of Zoology in Cambridge.

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He confirmed that they were
death's-head hawkmoths.

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And, unusually for an insect,
this moth produces a loud call

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that has been likened to the mournful
cry of a grief-stricken child.

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Did the disturbed king hear
the plaintive calls of a hawkmoth?

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That, we don't know.

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But, certainly, many of the ordinary
people of the 1 9th century

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were struck with a sense of terror
whenever this moth appeared.

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The moth's unusual appearance and
strange behaviour baffled people.

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But in nature, such traits
usually have a purpose.

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And it may be for the
death's-head hawkmoth,

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that they enable it to break into
beehives and steal their honey.

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These are the giant honeybees
of southeast Asia.

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And they form some of the
largest bee colonies in the world.

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1 once got up close to one
in order to demonstrate

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their response to a predator.

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1 had a model of a large hornet,
which produced a kind of Mexican wave

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and that makes it very difficult
for an aggressor to land.

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This covering of bees looks
impossible to penetrate.

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But at night, a thief can break
through their ranks.

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A death's-head hawkmoth
lands on the carpet of bees

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and pushes its way through
without being attacked.

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1n just a few seconds, it takes some
sips of honey and emerges unharmed.

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Getting past the guard bees
is quite a feat,

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but surviving inside
is even more astounding.

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Death's-head hawkmoths raid domestic
beehives too and can be quite a pest.

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somehow the moth slips past
the guards and, as if invisible,

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walks through the hive
heading straight for the honeycomb.

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1t then feeds unnoticed.

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How does it do this?

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One theory proposes
that its spooky appearance

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may help it avoid being attacked.

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Miriam Rothschild, a great entomologist
and expert on fleas and butterflies,

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suggested that the moth's skull pattern
looks like the head of a worker bee

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and that this could play a role
in the moth's deception.

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Well, this is a photograph
of a worker bee face

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taken through a microscope.

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Let's see how it looks
next to a close-up photo

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of the skull pattern of the moth.

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There.

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Well, I suppose there's
a slight resemblance,

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but given the fact that most moths raid
beehives and nests during the night,

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it's unlikely the bees could
see that much detail.

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The most likely answer lies
in the scent the moth gives off.

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1n America, in the 1 950s, a German
entomologist called Thomas Eisner

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studied chemical ecology, in particular,
the chemical defences of insects.

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Most famously, he illustrated how
bombardier beetles fire hot acid

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onto a predator.

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He also studied moths,

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and showed that the feathery projections
on their abdomens

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and their large antennae were used
to produce and pick up scent.

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1t seemed that many insects were
using scent in surprising ways.

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Tests on the chemical scents
produced by hawkmoths

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reveal a remarkable similarity to those
produced by the worker bees

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in the hives that they raid.

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Their scent is not identical,
but it contains several key chemicals

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that exactly match
those produced by bees.

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so, the death's-head hawkmoth's scent
acts as an invisibility cloak

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that makes it undetectable
to the worker bees in the nest.

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With thick scales on its body,
clawed feet that grip the honeycomb,

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and a short, pointed proboscis
to pierce the honey cells,

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the moth has evolved into
an effective hive robber.

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But there is another even
more impressive imposter

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that can also penetrate the protective
defences of an insect colony.

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1ts victims are not bees, but ants.

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The imposter that invades this ant nest
doesn't get in there by flying,

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nothing as blatant as that.

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Instead, the caterpillars of
some species of blue butterfly,

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like this one, wait for red ants
to collect them.

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Remarkably, passing ants
don't kill them.

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They pick them up and take
them back into their nest.

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The cuckoo caterpillar will stay inside
the nest for up to 1 0 months.

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just like the death's-head hawkmoth,
it produces a chemical scent

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that deceives the ants.

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This pink caterpillar, which belongs
to the Alcon blue butterfly,

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has been collected because, to them,
it smells just like the young

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of their own nest.

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They become controlled by the
imposter's intoxicating scent,

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and feed the butterfly larva even more
regularly than they do their own.

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There's another way this imposter
pulls off its deceptive trick,

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when it's inside the nest, the butterfly
larva makes a strange chattering noise.

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To our ears, it's very faint, but it's
clear enough to other insects.

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This is it.

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(LARVA CHATTERING)

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And this is the sound that's made
by a queen ant.

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(QUEEN ANT CHATTERING)

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To worker ants,
these calls are very similar.

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And they react
by treating the butterfly larva

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as if it's one of their own.

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Caterpillars of the blue butterfly
are impressive imposters.

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Not only do they mimic the scent of the
ants, but their queen's calls too.

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This seems to trump the death's-head
hawkmoth's ability as a nest invader.

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But the hawkmoth may also be using
sound to trick its victims.

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Remember the eerie squeak
that was thought to be so frightening?

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(SQUEAKING)

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There.

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The hawkmoth makes
this sound inside the beehive

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when it enters to steal honey.

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It's been suggested that this
might calm the bees

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because the squeak is thought
to sound like the piping call

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that the queen honeybee
makes to pacify her workers.

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We can't be sure if the call
and the strange skull marking

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evolved to deceive bees, but we can be
certain that the death's-head hawkmoth's

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life as an imposter is more curious

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than the superstitions that have
surrounded it for hundreds of years.

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The cuckoo and the hawkmoth
are both audacious imposters,

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but the cuckoo's ability to make
its victim raise its young

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is perhaps the most
accomplished deception of all.