0:00:02 > 0:00:06The natural world is full of extraordinary animals
0:00:06 > 0:00:09with amazing life histories.
0:00:09 > 0:00:13Yet certain stories are more intriguing than most.
0:00:15 > 0:00:19The mysteries of a butterfly's life cycle
0:00:19 > 0:00:23or the strange biology of the Emperor penguin.
0:00:23 > 0:00:26Some of these creatures were surrounded by myth
0:00:26 > 0:00:30and misunderstandings for a very long time
0:00:30 > 0:00:33and some have only recently revealed their secrets.
0:00:35 > 0:00:38These are the animals that stand out from the crowd.
0:00:38 > 0:00:42The curiosities I find most fascinating of all.
0:00:52 > 0:00:56Some animals have mastered the art of deception.
0:00:56 > 0:01:00The cuckoo tricks other birds into raising its young,
0:01:00 > 0:01:04while the death's-head hawkmoth infiltrates
0:01:04 > 0:01:07a nest of bees to steal their precious honey.
0:01:09 > 0:01:12They're cheats and impostors.
0:01:19 > 0:01:24CUCKOO CALLS
0:01:24 > 0:01:29The call of the cuckoo has long been regarded as a sign of spring,
0:01:29 > 0:01:33but in fact it's the call of a killer and a cheat.
0:01:33 > 0:01:37The cuckoo lays its egg in the nests of other birds and somehow
0:01:37 > 0:01:42persuades them to treat it and its chick as if it were their own.
0:01:42 > 0:01:44How does it get away with it?
0:01:44 > 0:01:48It's a question that has puzzled people for centuries.
0:01:49 > 0:01:52In Britain, the cuckoo arrives at a time
0:01:52 > 0:01:55when most birds are nesting and laying eggs.
0:01:55 > 0:02:00Early egg collectors noticed that the nests of some birds
0:02:00 > 0:02:03had a slightly odd-looking egg in them.
0:02:03 > 0:02:06These are the eggs laid by a number of different birds.
0:02:06 > 0:02:12A marsh warbler, spotted flycatcher, a linnet and a whitethroat.
0:02:12 > 0:02:17Amongst each of those clutches, there is a fraudster, a cuckoo egg,
0:02:17 > 0:02:19which mimics that of its host.
0:02:22 > 0:02:25Although cuckoos are long known to lay their eggs in the nests
0:02:25 > 0:02:29of other birds, no-one had actually described it happening.
0:02:30 > 0:02:34Then, in the 18th century, an English country doctor
0:02:34 > 0:02:38with an interest in natural history decided to investigate.
0:02:40 > 0:02:44Edward Jenner lived here in Berkeley, Gloucestershire,
0:02:44 > 0:02:49and is best known for his work on the smallpox vaccine.
0:02:49 > 0:02:52In fact, he is said to be the father of vaccination and that
0:02:52 > 0:02:57his work has saved more human lives than that of any other man.
0:02:57 > 0:03:02What is less known is that he first achieved scientific distinction
0:03:02 > 0:03:05by his observations on the behaviour of the cuckoo.
0:03:08 > 0:03:12At the time, it was believed that a cuckoo removes
0:03:12 > 0:03:15all of the eggs in a nest and then lays its own.
0:03:17 > 0:03:20By doing so, it would ensure its own chick gets all the food
0:03:20 > 0:03:23brought in by the unwitting nest owners.
0:03:25 > 0:03:29But Edward Jenner's detailed observations were to reveal
0:03:29 > 0:03:31a rather darker tale.
0:03:33 > 0:03:37Jenner's work on cuckoos was published in 1788
0:03:37 > 0:03:41here in the Philosophical Transactions of the Royal Society,
0:03:41 > 0:03:44the world's first scientific society.
0:03:44 > 0:03:45It was entitled simply...
0:03:45 > 0:03:49"Observations on the natural history of the cuckoo,
0:03:49 > 0:03:51"by Mr Edward Jenner."
0:03:51 > 0:03:54In it, he reported that it was not the parent cuckoo
0:03:54 > 0:03:57but the newly hatched chick which pushes the eggs
0:03:57 > 0:04:00and nestlings of the foster parents out of the nest.
0:04:01 > 0:04:03As soon as it hatches,
0:04:03 > 0:04:08the cuckoo chick's instinct is to kill anything else in the nest.
0:04:08 > 0:04:10It's still blind and naked
0:04:10 > 0:04:13but it has a cup-shaped depression on its back
0:04:13 > 0:04:15into which an egg fits perfectly.
0:04:17 > 0:04:22But sometimes the other eggs hatch earlier and Jenner's observations
0:04:22 > 0:04:25of how the cuckoo chick deals with its nest mates
0:04:25 > 0:04:27were quite shocking.
0:04:29 > 0:04:30He writes...
0:04:30 > 0:04:33"the mode of accomplishing this was very curious.
0:04:33 > 0:04:37"The little animal, with the assistance of its rump and wings,
0:04:37 > 0:04:39"contrived to get the bird on its back
0:04:39 > 0:04:43"and, making a lodgement of the burden by elevating its elbows,
0:04:43 > 0:04:46"clambered backwards with it up the side of the nest
0:04:46 > 0:04:49"until it reached the top, where, resting for a moment,
0:04:49 > 0:04:52"it threw off its load with a jerk
0:04:52 > 0:04:56"and quite disengaged it from the nest."
0:04:56 > 0:04:59The real villain had been uncovered.
0:04:59 > 0:05:03Jenner's views were met with incredulity and some disbelief,
0:05:03 > 0:05:07but nonetheless they earned him the Fellowship of the Royal Society.
0:05:07 > 0:05:09It was the greatest honour that could be given to
0:05:09 > 0:05:11a scientist at the time.
0:05:12 > 0:05:14Jenner's observations had revealed
0:05:14 > 0:05:18the true nature of the cuckoo's deception.
0:05:18 > 0:05:21But it still wasn't clear why the cuckoos should opt for this
0:05:21 > 0:05:24strange way of raising its young.
0:05:27 > 0:05:31It wasn't until 100 years later that Charles Darwin finally
0:05:31 > 0:05:35provided an explanation with his theory of evolution.
0:05:36 > 0:05:38The cuckoo's behaviour has evolved
0:05:38 > 0:05:41to increase its own breeding success.
0:05:41 > 0:05:43By avoiding the task of raising chicks,
0:05:43 > 0:05:47the cuckoo can lay more eggs than any other bird,
0:05:47 > 0:05:50as many as 25 in a season.
0:05:53 > 0:05:55While it makes evolutionary sense for the cuckoo
0:05:55 > 0:05:59to lay its eggs in the nests of others, what about its victims?
0:05:59 > 0:06:02Why do they put up with this trickery?
0:06:02 > 0:06:05It seems that they sometimes don't.
0:06:06 > 0:06:10This was revealed in an early natural history film in 1920.
0:06:12 > 0:06:16The Cuckoo's Secret was made by Edgar Chance and Oliver Pike,
0:06:16 > 0:06:20an egg collector and a wildlife film maker.
0:06:20 > 0:06:23Chance was fascinated by cuckoos
0:06:23 > 0:06:25and spent a great deal of time following them.
0:06:25 > 0:06:29He was the first person known to see a cuckoo lay its egg.
0:06:31 > 0:06:36The deception involves stealth and speed.
0:06:36 > 0:06:40The female waits until a nest is unattended and then she strikes.
0:06:40 > 0:06:43But if she is spotted, the owners fight back.
0:06:44 > 0:06:46If she is successful,
0:06:46 > 0:06:50the whole deception takes less than ten seconds.
0:06:50 > 0:06:54She removes and eats just one egg and replaces it with her own.
0:06:59 > 0:07:02The Chance and Pike film solved one mystery,
0:07:02 > 0:07:03but there were still others.
0:07:05 > 0:07:07How does the cuckoo choose its victim?
0:07:08 > 0:07:12And why don't the nest owners reject the alien egg?
0:07:21 > 0:07:24Reed warblers are one of the cuckoo's main targets
0:07:24 > 0:07:27and the pair has a nest just in here.
0:07:32 > 0:07:35The female warbler has laid four speckled eggs,
0:07:35 > 0:07:39and, using a model egg, I can illustrate the cuckoo's trickery.
0:07:41 > 0:07:44This is the sort of egg that a cuckoo would lay
0:07:44 > 0:07:46in the reed warbler's nest.
0:07:47 > 0:07:52It matches the reed warbler's actual egg very closely in colour.
0:07:54 > 0:07:58Experiments with model eggs have shown that reed warblers
0:07:58 > 0:08:01have become very good at recognising an alien egg
0:08:01 > 0:08:06and either throw it out or desert their nest to start afresh.
0:08:06 > 0:08:09So the cuckoo has to make sure that it produces an egg
0:08:09 > 0:08:11that is a very good match.
0:08:15 > 0:08:21The cuckoo and its victims are evolving competitively.
0:08:21 > 0:08:24With each generation, cuckoos improve their mimicry,
0:08:24 > 0:08:28while the nest owners become better at spotting a foreign egg.
0:08:30 > 0:08:31While many birds are very good
0:08:31 > 0:08:34at detecting a strange egg in their nest,
0:08:34 > 0:08:37they seem incapable of recognising
0:08:37 > 0:08:39the monstrous cuckoo chick as an impostor.
0:08:42 > 0:08:45But the deception is not complete.
0:08:45 > 0:08:48The young cuckoo is much larger than the reed warbler chick,
0:08:48 > 0:08:51so it also needs a lot more food.
0:08:51 > 0:08:53How does it get enough?
0:08:54 > 0:08:57The cuckoo has a solution.
0:08:57 > 0:09:01It now uses vocal deception to trick its foster parents
0:09:01 > 0:09:03into providing more food.
0:09:05 > 0:09:08This is a sonogram of the sound waves produced by a single
0:09:08 > 0:09:11reed warbler chick begging for food.
0:09:11 > 0:09:14Below it is the call of a cuckoo chick,
0:09:14 > 0:09:17and, as you can see, it looks very different.
0:09:17 > 0:09:21In fact, it more closely resembles
0:09:21 > 0:09:25the calls of a whole nestful of reed warbler chicks.
0:09:27 > 0:09:32So, the cuckoo chick's call is a super stimulus
0:09:32 > 0:09:36that sounds like a whole nestful of chicks.
0:09:36 > 0:09:38And it appears to work.
0:09:40 > 0:09:42The adult birds rush back and forth,
0:09:42 > 0:09:45providing the impostor with the same amount of food
0:09:45 > 0:09:48as they would for an entire brood of their own.
0:09:52 > 0:09:55At three weeks old, the cuckoo chick
0:09:55 > 0:09:57has spilled out of the nest.
0:09:57 > 0:10:01It's now almost eight times the size of its foster parent.
0:10:07 > 0:10:09It was over 200 years ago
0:10:09 > 0:10:11that Edward Jenner first shocked us
0:10:11 > 0:10:15with his revelation of the cuckoo's extraordinary lifestyle.
0:10:17 > 0:10:20Now we know that its unusual behaviour
0:10:20 > 0:10:22is due to an extraordinary arms race
0:10:22 > 0:10:25that has resulted in one of the most fascinating
0:10:25 > 0:10:27specialisations in nature.
0:10:33 > 0:10:38The cuckoo's success relies on deceiving just two parent birds.
0:10:40 > 0:10:42But our second subject is a moth
0:10:42 > 0:10:45that is able to deceive hundreds of bees.
0:10:45 > 0:10:47How does it infiltrate
0:10:47 > 0:10:50one of the most heavily guarded nests in nature?
0:10:53 > 0:10:56This wonderful creature was once
0:10:56 > 0:10:59one of the most feared insects in Europe.
0:10:59 > 0:11:01It's a death's-head hawkmoth,
0:11:01 > 0:11:04and it's easy enough to see how it got its name.
0:11:04 > 0:11:06It has this mark on its back
0:11:06 > 0:11:09that looks just like a human skull.
0:11:09 > 0:11:12This gave it a bad reputation that lasted for centuries,
0:11:12 > 0:11:16but now there are new ideas about this moth's strange appearance
0:11:16 > 0:11:19that may help explain its extraordinary ability
0:11:19 > 0:11:22to rob hives without being stung.
0:11:26 > 0:11:29Death's-head hawkmoths are a rare sight in Britain,
0:11:29 > 0:11:32for they spend most of their lives in Africa and Asia.
0:11:34 > 0:11:36But every summer, a small number of migrants
0:11:36 > 0:11:38arrive in northern Europe
0:11:38 > 0:11:41and if the weather is warm enough, they breed.
0:11:44 > 0:11:48Their caterpillars, unlike the drab adult moths,
0:11:48 > 0:11:49are beautifully coloured.
0:11:52 > 0:11:54After feeding for several weeks,
0:11:54 > 0:11:56they can grow to a length of 13 centimetres.
0:11:59 > 0:12:03Once ready to become adults, they pupate in the soil
0:12:03 > 0:12:07and emerge as the sinister, strangely patterned moths.
0:12:12 > 0:12:14In the early 19th century,
0:12:14 > 0:12:18a region of northern France was hit by a terrible pestilence
0:12:18 > 0:12:21and at the same time, a large number of hawkmoths
0:12:21 > 0:12:22were seen in the area.
0:12:22 > 0:12:27The local people linked the deaths to these night-flying insects.
0:12:27 > 0:12:31But there was another even more disturbing side to this moth.
0:12:31 > 0:12:34It could make an unusual noise.
0:12:35 > 0:12:36SQUEAKING
0:12:36 > 0:12:38There.
0:12:38 > 0:12:39A strange squeak.
0:12:39 > 0:12:42And that only added to its chilling reputation.
0:12:47 > 0:12:49Moths don't usually squeak.
0:12:51 > 0:12:55Tiger moths sometimes produce ultrasonic warning clicks
0:12:55 > 0:12:58that tell bats that they're poisonous and not good to eat,
0:12:58 > 0:13:01but this is not a noise we can generally hear.
0:13:03 > 0:13:05Perhaps the death's-head hawkmoth squeaks
0:13:05 > 0:13:07to scare predators like birds.
0:13:09 > 0:13:11However, other large migratory moths
0:13:11 > 0:13:13don't make such a sound.
0:13:15 > 0:13:17This makes the death's-head hawkmoth's squeak
0:13:17 > 0:13:19all the more surprising,
0:13:19 > 0:13:22and it has intrigued people for centuries.
0:13:24 > 0:13:27These moths are more than 200 years old.
0:13:27 > 0:13:31We know that because the handwritten label there tells us
0:13:31 > 0:13:36they were collected in 1801 by a Robert Darling Willis,
0:13:36 > 0:13:40the personal physician to King George III.
0:13:40 > 0:13:42George III is well-known as the king
0:13:42 > 0:13:44who suffered from bouts of madness
0:13:44 > 0:13:47and on a visit to see the king during one of them,
0:13:47 > 0:13:51Dr Willis discovered these large moths in the monarch's bedchamber.
0:13:52 > 0:13:56Unable to identify them, the doctor sent them to his grandson,
0:13:56 > 0:13:58who was at that time superintendent
0:13:58 > 0:14:00at the Museum of Zoology in Cambridge.
0:14:00 > 0:14:04He confirmed that they were death's-head hawkmoths
0:14:04 > 0:14:07and, unusually for an insect,
0:14:07 > 0:14:09this moth produces a loud call
0:14:09 > 0:14:12that has been likened to the mournful cry
0:14:12 > 0:14:14of a grief-stricken child.
0:14:15 > 0:14:19Did the disturbed king hear the plaintive calls of a hawkmoth?
0:14:19 > 0:14:21That we don't know.
0:14:21 > 0:14:24But certainly many of the ordinary people of the 19th century
0:14:24 > 0:14:28were struck with a sense of terror whenever this moth appeared.
0:14:30 > 0:14:34The moths' unusual appearance and strange behaviour baffled people.
0:14:36 > 0:14:39But in nature, such traits usually have a purpose.
0:14:40 > 0:14:43And it may be for the death's-head hawkmoth
0:14:43 > 0:14:47that they enable it to break into beehives and steal their honey.
0:14:49 > 0:14:52These are the giant honey bees of south-east Asia,
0:14:52 > 0:14:56and they form some of the largest bee colonies in the world.
0:14:58 > 0:15:01I once got up close to one in order to demonstrate
0:15:01 > 0:15:04their response to a predator.
0:15:04 > 0:15:06I had a model of a large hornet,
0:15:06 > 0:15:09which produced a kind of Mexican wave,
0:15:09 > 0:15:12and that makes it very difficult for an aggressor to land.
0:15:12 > 0:15:14BUZZING
0:15:14 > 0:15:17This covering of bees looks impossible to penetrate.
0:15:21 > 0:15:22But at night,
0:15:22 > 0:15:25a thief can break through their ranks.
0:15:25 > 0:15:28A death's-head hawkmoth lands on the carpet of bees
0:15:28 > 0:15:32and pushes its way through without being attacked.
0:15:33 > 0:15:36In just a few seconds, it takes some sips of honey
0:15:36 > 0:15:37and emerges unharmed.
0:15:39 > 0:15:41Getting past the guard bees is quite a feat,
0:15:41 > 0:15:45but surviving inside is even more astounding.
0:15:50 > 0:15:53Death's-head hawkmoths raid domestic beehives too,
0:15:53 > 0:15:55and can be quite a pest.
0:16:02 > 0:16:06Somehow, the moth slips past the guards and, as if invisible,
0:16:06 > 0:16:10walks through the hive, heading straight for the honeycomb.
0:16:12 > 0:16:14It then feeds unnoticed.
0:16:16 > 0:16:17How does it do this?
0:16:20 > 0:16:23One theory proposes that its spooky appearance
0:16:23 > 0:16:25may help it avoid being attacked.
0:16:25 > 0:16:28BUZZING
0:16:28 > 0:16:30Miriam Rothschild, a great entomologist
0:16:30 > 0:16:32and expert on fleas and butterflies,
0:16:32 > 0:16:35suggested that the moth's skull pattern looks like
0:16:35 > 0:16:37the head of a worker bee,
0:16:37 > 0:16:40and that this could play a role in the moth's deception.
0:16:40 > 0:16:43Well, this is a photograph
0:16:43 > 0:16:46of a worker bee face taken through a microscope.
0:16:46 > 0:16:50Let's see how it looks next to a close-up photo
0:16:50 > 0:16:52of the skull pattern of the moth.
0:16:55 > 0:16:56There.
0:16:56 > 0:16:59Well, I suppose there's a slight resemblance,
0:16:59 > 0:17:02but given the fact that most moths raid beehives and nests
0:17:02 > 0:17:05during the night, it's unlikely the bees
0:17:05 > 0:17:07could see that much detail.
0:17:07 > 0:17:11The most likely answer lies in the scent the moth gives off.
0:17:14 > 0:17:16In America in the 1950s,
0:17:16 > 0:17:19a German entomologist called Thomas Eisner
0:17:19 > 0:17:22studied chemical ecology - in particular,
0:17:22 > 0:17:24the chemical defences of insects.
0:17:27 > 0:17:31Most famously, he illustrated how bombardier beetles
0:17:31 > 0:17:33fire hot acid onto a predator.
0:17:37 > 0:17:39He also studied moths,
0:17:39 > 0:17:42and showed that the feathery projections on their abdomens
0:17:42 > 0:17:46and their large antennae were used to produce and pick up scent.
0:17:47 > 0:17:51It seemed that many insects were using scent in surprising ways.
0:17:53 > 0:17:56Tests on the chemical scents produced by hawkmoths
0:17:56 > 0:18:00reveal a remarkable similarity to those produced by the worker bees
0:18:00 > 0:18:02in the hives that they raid.
0:18:02 > 0:18:04Their scent is not identical,
0:18:04 > 0:18:06but it contains several key chemicals
0:18:06 > 0:18:08that exactly match those produced by bees.
0:18:11 > 0:18:14So the death's-head hawkmoth's scent
0:18:14 > 0:18:16acts as an invisibility cloak
0:18:16 > 0:18:20that makes it undetectable to the worker bees in the nest.
0:18:25 > 0:18:27With thick scales on its body,
0:18:27 > 0:18:29clawed feet that grip the honeycomb,
0:18:29 > 0:18:32and a short, pointed proboscis to pierce the honey cells,
0:18:32 > 0:18:36the moth has evolved into an effective hive robber.
0:18:39 > 0:18:42But there is another, even more impressive impostor
0:18:42 > 0:18:45that can also penetrate the protective defences
0:18:45 > 0:18:47of an insect colony.
0:18:47 > 0:18:50Its victims are not bees but ants.
0:18:52 > 0:18:55The impostor that invades this ant nest
0:18:55 > 0:18:57doesn't get in there by flying.
0:18:57 > 0:18:59Nothing as blatant as that.
0:18:59 > 0:19:03Instead, the caterpillars of some species of blue butterfly,
0:19:03 > 0:19:08like this one, wait for red ants to collect them.
0:19:08 > 0:19:11Remarkably, passing ants don't kill them.
0:19:11 > 0:19:14They pick them up and take them back into their nest.
0:19:14 > 0:19:18The cuckoo caterpillar will stay inside the nest
0:19:18 > 0:19:20for up to ten months.
0:19:20 > 0:19:22Just like the death's-head hawkmoths,
0:19:22 > 0:19:25it produces a chemical scent that deceives the ants.
0:19:27 > 0:19:32This pink caterpillar, which belongs to the alcon blue butterfly,
0:19:32 > 0:19:34has been collected because, to them,
0:19:34 > 0:19:38it smells just like the young of their own nest.
0:19:38 > 0:19:41They become controlled by the impostor's intoxicating scent,
0:19:41 > 0:19:44and feed the butterfly larva even more regularly
0:19:44 > 0:19:46than they do their own.
0:19:48 > 0:19:52There's another way this impostor pulls off its deceptive trick.
0:19:52 > 0:19:54When it's inside the nest,
0:19:54 > 0:19:58the butterfly larva makes a strange chattering noise.
0:19:58 > 0:19:59To our ears, it's very faint,
0:19:59 > 0:20:02but it's clear enough to other insects. This is it.
0:20:04 > 0:20:06CHATTERING NOISE
0:20:06 > 0:20:10And this is the sound that's made by a queen ant.
0:20:12 > 0:20:15SIMILAR CHATTERING NOISE
0:20:17 > 0:20:20To worker ants, these calls are very similar,
0:20:20 > 0:20:23and they react by treating the butterfly larva
0:20:23 > 0:20:25as if it's one of their own.
0:20:27 > 0:20:31Caterpillars of the blue butterfly are impressive impostors.
0:20:31 > 0:20:34Not only do they mimic the scent of the ants,
0:20:34 > 0:20:37but their queen's calls too.
0:20:37 > 0:20:40This seems to trump the death's-head hawkmoth's ability
0:20:40 > 0:20:42as a nest invader.
0:20:45 > 0:20:49But the hawkmoth may also be using sound to trick its victims.
0:20:52 > 0:20:55Remember the eerie squeak that was thought to be so frightening?
0:20:57 > 0:20:58SQUEAKING
0:20:58 > 0:21:00There.
0:21:00 > 0:21:03The hawkmoth makes this sound inside the beehive
0:21:03 > 0:21:05when it enters to steal honey.
0:21:05 > 0:21:09It's been suggested that this might calm the bees,
0:21:09 > 0:21:12because the squeak is thought to sound like the piping call
0:21:12 > 0:21:15that the queen honey bee makes to pacify her workers.
0:21:17 > 0:21:19We can't be sure if the call and the strange skull marking
0:21:19 > 0:21:23evolved to deceive bees, but we can be certain
0:21:23 > 0:21:26that the death's-head hawkmoth's life as an impostor
0:21:26 > 0:21:29is more curious than the superstitions
0:21:29 > 0:21:32that have surrounded it for hundreds of years.
0:21:34 > 0:21:38The cuckoo and the hawkmoth are both audacious impostors,
0:21:38 > 0:21:42but the cuckoo's ability to make its victim raise its young
0:21:42 > 0:21:45is perhaps the most accomplished deception of all.