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The natural world is full of extraordinary animals with | 0:00:03 | 0:00:06 | |
amazing life histories. | 0:00:06 | 0:00:09 | |
Yet certain stories are more intriguing than most. | 0:00:09 | 0:00:13 | |
The mysteries of a butterfly's life cycle, | 0:00:16 | 0:00:19 | |
or the strange biology of the emperor penguin. | 0:00:19 | 0:00:23 | |
Some of these creatures were surrounded by myth | 0:00:23 | 0:00:26 | |
and misunderstandings for a very long time. | 0:00:26 | 0:00:29 | |
And some have only recently revealed their secrets. | 0:00:30 | 0:00:33 | |
These are the animals that stand out from the crowd, | 0:00:35 | 0:00:38 | |
the curiosities I find most fascinating of all. | 0:00:38 | 0:00:42 | |
Some of our most familiar animals puzzled scientific | 0:00:51 | 0:00:54 | |
minds for a surprisingly long time. | 0:00:54 | 0:00:58 | |
The mysterious comings | 0:00:58 | 0:00:59 | |
and goings of barn swallows led to some far-fetched ideas. | 0:00:59 | 0:01:03 | |
While the life cycle of the painted lady butterfly took centuries | 0:01:05 | 0:01:09 | |
to unravel. | 0:01:09 | 0:01:10 | |
But the abilities of some plants | 0:01:12 | 0:01:14 | |
and animals are so remarkable that they seem to be almost supernatural. | 0:01:14 | 0:01:19 | |
In this programme, I investigate the shocking power of a fish that | 0:01:19 | 0:01:24 | |
advanced our understanding of electricity, | 0:01:24 | 0:01:27 | |
and plants with senses that are surprising modern science. | 0:01:27 | 0:01:31 | |
How do these extraordinary powers help the organisms that | 0:01:33 | 0:01:37 | |
produced them? | 0:01:37 | 0:01:38 | |
The freshwater eel is surrounded by legends. | 0:01:45 | 0:01:49 | |
The first Europeans to explore the New World heard amazing | 0:01:49 | 0:01:53 | |
stories about it. | 0:01:53 | 0:01:55 | |
And when, in the 18th century, specimens of this strange fish | 0:01:55 | 0:01:58 | |
reached Europe, they created a sensation. | 0:01:58 | 0:02:01 | |
In 1776, Captain George Baker, | 0:02:03 | 0:02:07 | |
an American mariner and whaler, | 0:02:07 | 0:02:09 | |
made the long and difficult journey from South America across a | 0:02:09 | 0:02:12 | |
raging Atlantic Ocean to bring five live electric eels to London. | 0:02:12 | 0:02:18 | |
These are two of his actual eels. | 0:02:18 | 0:02:21 | |
Captain Baker and his five electric eels, or gymnotas as they were known, | 0:02:22 | 0:02:26 | |
set up shop in the Haymarket and offered two shillings | 0:02:26 | 0:02:30 | |
and sixpence for a shock, or five shillings for a spark. | 0:02:30 | 0:02:34 | |
Baker's eels had come all the way from the lower | 0:02:36 | 0:02:39 | |
reaches of the Amazon and Orinoco rivers, | 0:02:39 | 0:02:42 | |
where he had heard tales from the locals about their astonishing powers. | 0:02:42 | 0:02:47 | |
They called these fish "trembladores". | 0:02:47 | 0:02:51 | |
Humboldt, the famous naturalist and explorer, had described how he | 0:02:51 | 0:02:55 | |
had witnessed horses being killed by the repeated shocks from these fish. | 0:02:55 | 0:02:59 | |
And he himself accidentally stepped on one | 0:03:01 | 0:03:03 | |
and vividly described the effect. | 0:03:03 | 0:03:05 | |
"With each stroke, you feel an internal vibration that lasts | 0:03:06 | 0:03:10 | |
"two or three seconds, followed by a painful numbness. | 0:03:10 | 0:03:14 | |
"All day I felt strong pain in my knees and in all my joints." | 0:03:14 | 0:03:18 | |
I encountered this remarkable fish in its natural environment | 0:03:21 | 0:03:25 | |
when I filmed at the same rivers that Humboldt explored. | 0:03:25 | 0:03:29 | |
There was talk of me swimming with the eel, | 0:03:29 | 0:03:31 | |
but thankfully we had some technical difficulties with the diving | 0:03:31 | 0:03:35 | |
equipment that I was supposed to wear, | 0:03:35 | 0:03:37 | |
and so I stayed safely in a canoe and was able to demonstrate | 0:03:37 | 0:03:41 | |
another subtler, but equally remarkable, side to this fish. | 0:03:41 | 0:03:44 | |
The eels were constantly producing electric discharges. | 0:03:47 | 0:03:52 | |
Somehow they were generating a small, nonstop flowing current. | 0:03:52 | 0:03:56 | |
ELECTRIC DRONE | 0:03:56 | 0:03:58 | |
They were also able to sense electricity and were | 0:03:58 | 0:04:01 | |
attracted to electrical pulses emitted from my underwater detector, | 0:04:01 | 0:04:06 | |
suggesting that electricity plays a key role in their lives. | 0:04:06 | 0:04:11 | |
But at the time of their discovery, | 0:04:12 | 0:04:14 | |
no-one knew the full functions of their extraordinary abilities. | 0:04:14 | 0:04:18 | |
We now know that the shock was caused by electricity, | 0:04:20 | 0:04:24 | |
and I can demonstrate it by touching the animal with an electrode. | 0:04:24 | 0:04:29 | |
Watch. | 0:04:29 | 0:04:31 | |
There. You see? | 0:04:31 | 0:04:33 | |
The scope and the lights are flashing up and down. | 0:04:33 | 0:04:36 | |
Extraordinary. | 0:04:36 | 0:04:38 | |
But this is only a small indication of the real power of this fish. | 0:04:38 | 0:04:42 | |
If I were to try and pick it up, I could get | 0:04:42 | 0:04:44 | |
a jolt of an astonishing 600 volts, which is quite enough to kill me. | 0:04:44 | 0:04:49 | |
This 1960s educational film illustrated the shock, | 0:04:57 | 0:05:01 | |
even though the equipment used prevented | 0:05:01 | 0:05:04 | |
the volunteers from getting its full power. | 0:05:04 | 0:05:07 | |
They were to join hands and then connected to a live eel. | 0:05:07 | 0:05:10 | |
WOMAN SCREAMS | 0:05:12 | 0:05:15 | |
Firm believers in electric eels. Thank you very much. | 0:05:16 | 0:05:20 | |
You can imagine how startling Baker's electric eels | 0:05:21 | 0:05:24 | |
were 200 years ago. | 0:05:24 | 0:05:26 | |
In the 18th century, | 0:05:29 | 0:05:30 | |
electricity was becoming one of the most fashionable areas | 0:05:30 | 0:05:33 | |
of scientific investigation, but it was still very poorly understood. | 0:05:33 | 0:05:38 | |
Very few advances had been made since its discovery 150 years | 0:05:38 | 0:05:41 | |
earlier by Elizabeth I's personal physician, William Gilbert. | 0:05:41 | 0:05:45 | |
Gilbert repeated a trick that had been known about since Greek times. | 0:05:45 | 0:05:50 | |
Rubbing a piece of amber with cat fur, that allowed the amber | 0:05:50 | 0:05:54 | |
to attract a small object like a feather. Let's give it a try. | 0:05:54 | 0:05:58 | |
Here is a bit of amber. | 0:05:58 | 0:05:59 | |
There. | 0:06:03 | 0:06:04 | |
It had always been assumed that this amber effect was caused | 0:06:04 | 0:06:07 | |
by magnetism but Gilbert showed that it was something different. | 0:06:07 | 0:06:11 | |
He named this new force after the Greek word for amber, | 0:06:11 | 0:06:15 | |
electron, and so electricity was born. | 0:06:15 | 0:06:20 | |
Londoners of the time developed a fascination for this magical force. | 0:06:21 | 0:06:26 | |
Showmen staged bizarre spectacles to demonstrate its properties. | 0:06:26 | 0:06:31 | |
In one, a young boy attached to a friction generator | 0:06:31 | 0:06:35 | |
attracted small pieces of paper to his hands. | 0:06:35 | 0:06:37 | |
In another, a gentleman kissed a lady and was repulsed | 0:06:37 | 0:06:42 | |
by the charge carried through her whalebone corset. | 0:06:42 | 0:06:45 | |
No-one knew what to do with electricity | 0:06:46 | 0:06:49 | |
but a better understanding of its nature was slowly emerging. | 0:06:49 | 0:06:53 | |
More and more ingenious ways were developed | 0:06:54 | 0:06:56 | |
to create what we now call static electricity. | 0:06:56 | 0:07:00 | |
And soon it became something more than just a quirk of rubbing amber, | 0:07:00 | 0:07:04 | |
it became visible as a spark. | 0:07:04 | 0:07:06 | |
The ability to produce this characteristic blue spark | 0:07:11 | 0:07:14 | |
along with its invigorating smell became the signature | 0:07:14 | 0:07:17 | |
of this new force and it prompted scientists to make | 0:07:17 | 0:07:21 | |
obvious comparisons with other natural phenomena. | 0:07:21 | 0:07:24 | |
THUNDER | 0:07:24 | 0:07:26 | |
In the American colonies, Benjamin Franklin bravely, | 0:07:28 | 0:07:32 | |
or perhaps foolishly, flew kites into thunderstorms and proved that | 0:07:32 | 0:07:36 | |
lightning and the electric spark were one and the same. | 0:07:36 | 0:07:40 | |
But there's another common property of lightning and static electricity. | 0:07:41 | 0:07:45 | |
That is the ability to shock. | 0:07:45 | 0:07:47 | |
It wasn't long before a comparison was made between the shock from | 0:07:47 | 0:07:51 | |
the early generators and the shock that could be delivered by a fish. | 0:07:51 | 0:07:55 | |
The electric eel wasn't the only kind of fish | 0:07:58 | 0:08:00 | |
known to give humans a powerful jolt. | 0:08:00 | 0:08:03 | |
The ancient Egyptians knew that the electric catfish could also | 0:08:03 | 0:08:07 | |
give shocks and they called it the "Thunderer of the Nile". | 0:08:07 | 0:08:11 | |
And in the nearby Mediterranean lives the torpedo ray. | 0:08:12 | 0:08:17 | |
Its muscle batteries make it so bulky | 0:08:17 | 0:08:19 | |
it can't undulate its body like other rays | 0:08:19 | 0:08:22 | |
but has to propel itself by waving its tail. | 0:08:22 | 0:08:26 | |
Like the electric eel, | 0:08:26 | 0:08:28 | |
it uses its discharge to stun the other fish on which it prays. | 0:08:28 | 0:08:32 | |
Sadly, the pressure of celebrity and having to produce shocks | 0:08:34 | 0:08:38 | |
and sparks to order exhausted Baker's long-suffering eels | 0:08:38 | 0:08:42 | |
and they didn't last the winter. | 0:08:42 | 0:08:44 | |
But two were preserved and expertly dissected by John Hunter, | 0:08:44 | 0:08:49 | |
a very distinguished Scottish surgeon of the time | 0:08:49 | 0:08:52 | |
and he found a great number of striped muscular layers | 0:08:52 | 0:08:56 | |
that proved to be where the electricity was generated. | 0:08:56 | 0:08:59 | |
They are now referred to as Hunter's organs. | 0:08:59 | 0:09:03 | |
He found these muscles along the tail and sides of the eels | 0:09:04 | 0:09:08 | |
arranged in stacks. | 0:09:08 | 0:09:10 | |
One scientist called Galvani believed that animals | 0:09:12 | 0:09:15 | |
had their own natural electricity even without these electric organs | 0:09:15 | 0:09:20 | |
and he tried to prove this by connecting wires to frogs' legs | 0:09:20 | 0:09:25 | |
and making them twitch. | 0:09:25 | 0:09:27 | |
He called this phenomenon animal electricity. | 0:09:27 | 0:09:31 | |
But another scientist called Volta had other ideas. | 0:09:32 | 0:09:36 | |
He proved that the frog was merely a conductor for electricity | 0:09:36 | 0:09:40 | |
with a simple experiment. | 0:09:40 | 0:09:42 | |
Volta replaced Galvani's frog with discs of cloth | 0:09:43 | 0:09:48 | |
soaked in saltwater or acid | 0:09:48 | 0:09:50 | |
and sandwiched them between two different metals. | 0:09:50 | 0:09:53 | |
I can do the same thing with filter paper, | 0:09:53 | 0:09:56 | |
copper two pence pieces and these simple galvanised zinc washers. | 0:09:56 | 0:10:01 | |
Watch. | 0:10:01 | 0:10:02 | |
Tuppenny piece. | 0:10:04 | 0:10:06 | |
Filter. | 0:10:07 | 0:10:08 | |
And washer. | 0:10:08 | 0:10:10 | |
There, nearly 0.6 of a volt. | 0:10:14 | 0:10:16 | |
But the amount of electricity generated was tiny. | 0:10:17 | 0:10:21 | |
Certainly not enough to make the sparks seen from eels. | 0:10:21 | 0:10:25 | |
Unlike Galvani, Volta saw no distinction | 0:10:25 | 0:10:28 | |
between animal electricity and his new electricity from metals | 0:10:28 | 0:10:32 | |
so he now looked at animals to see how he might amplify his new device. | 0:10:32 | 0:10:37 | |
Was it significant that the muscles | 0:10:40 | 0:10:43 | |
producing the electric power in the eels were arranged in stacks? | 0:10:43 | 0:10:47 | |
Volta decided to add more stacks to his electric pile. | 0:10:49 | 0:10:54 | |
We call this way of connecting electric cells together | 0:10:54 | 0:10:57 | |
"in series", and we now know that it increases the voltage. | 0:10:57 | 0:11:01 | |
But Volta was about to find this out for the first time. | 0:11:01 | 0:11:04 | |
He piled up his tiny cells like the bands of muscle | 0:11:04 | 0:11:07 | |
in an electric fish. | 0:11:07 | 0:11:08 | |
Here I've got ten pairs. | 0:11:08 | 0:11:11 | |
And just watch. | 0:11:11 | 0:11:12 | |
Nearly six volts. | 0:11:15 | 0:11:16 | |
Wonderful. | 0:11:16 | 0:11:18 | |
Volta could now produce heat, shocks and even sparks | 0:11:18 | 0:11:22 | |
from electricity in a continuous never-ending stream. | 0:11:22 | 0:11:27 | |
He had made the first battery, partly inspired by the electric eel. | 0:11:28 | 0:11:33 | |
The pieces of the puzzle had come together and the eel's example | 0:11:34 | 0:11:38 | |
had helped to advance our understanding of electricity. | 0:11:38 | 0:11:41 | |
Eels, in fact, contain natural batteries. | 0:11:42 | 0:11:45 | |
Stacks of special muscles. | 0:11:45 | 0:11:48 | |
It's amazing to think when electricity is so much | 0:11:49 | 0:11:52 | |
a part of our lives today that before Volta | 0:11:52 | 0:11:55 | |
the only source of electricity was lightning, | 0:11:55 | 0:11:59 | |
a few static generators | 0:11:59 | 0:12:01 | |
and fish like this incredible electric eel. | 0:12:01 | 0:12:04 | |
Understanding how electric eels managed to find their way around | 0:12:09 | 0:12:13 | |
revealed a hitherto unknown animal sense. | 0:12:13 | 0:12:16 | |
But it's not just animals that have surprised us. | 0:12:18 | 0:12:21 | |
We're now discovering that plants too | 0:12:22 | 0:12:25 | |
have intriguing abilities that are still mysterious. | 0:12:25 | 0:12:29 | |
We think of plants as passive, still and silent. | 0:12:32 | 0:12:35 | |
But they may have more in common with animals than you might think. | 0:12:35 | 0:12:39 | |
New research suggests that they have surprising abilities. | 0:12:44 | 0:12:48 | |
It depends on how you look at them. | 0:12:48 | 0:12:51 | |
I first started seeing plants in a different light | 0:12:53 | 0:12:57 | |
when making a series called The Private Life of Plants. | 0:12:57 | 0:13:00 | |
We used time-lapse photography to reveal the way they move. | 0:13:01 | 0:13:06 | |
The bramble spreads aggressively - seemingly unstoppable. | 0:13:07 | 0:13:10 | |
Other plants pulsed to the rhythms of day and night. | 0:13:11 | 0:13:15 | |
And flower buds explode like fireworks. | 0:13:15 | 0:13:18 | |
So, with speeded up film, we had been able to translate | 0:13:21 | 0:13:25 | |
their time into ours | 0:13:25 | 0:13:27 | |
and to realise that they're constantly on the move. | 0:13:27 | 0:13:30 | |
200 years ago, one plant that moved very quickly indeed | 0:13:37 | 0:13:41 | |
attracted the attention of a great scientific mind. | 0:13:41 | 0:13:45 | |
It appeared to behave like an animal | 0:13:45 | 0:13:48 | |
and could move fast enough to catch its own food. | 0:13:48 | 0:13:51 | |
Charles Darwin was fascinated by the Venus flytrap. | 0:13:52 | 0:13:56 | |
He called it one of the most wonderful plants in the world. | 0:13:56 | 0:14:00 | |
He recognised that it could move in a very different way | 0:14:00 | 0:14:04 | |
to that of plant growth. | 0:14:04 | 0:14:06 | |
This movement was not only fast but also repeatable. | 0:14:06 | 0:14:10 | |
Darwin experimented and found that the traps | 0:14:10 | 0:14:12 | |
are not triggered by raindrops | 0:14:12 | 0:14:14 | |
but only by a very particular stimulation of the leaf hairs, | 0:14:14 | 0:14:18 | |
such as an insect might make. | 0:14:18 | 0:14:20 | |
But what intrigued him most was the speed of the reaction. | 0:14:20 | 0:14:25 | |
He sent one of these flytraps to a friend, Dr Burdon-Sanderson, | 0:14:25 | 0:14:29 | |
who was performing groundbreaking work on muscles and electricity. | 0:14:29 | 0:14:33 | |
His tests confirmed that the tiny electrical discharge | 0:14:33 | 0:14:37 | |
caused by an animal muscle cell contracting was almost identical | 0:14:37 | 0:14:41 | |
to those signals obtained by attaching electrodes to the flytrap | 0:14:41 | 0:14:45 | |
when it was shutting. | 0:14:45 | 0:14:47 | |
Although plants have no muscles, | 0:14:48 | 0:14:50 | |
electrical stimulation enables them to move in a similar way to animals. | 0:14:50 | 0:14:55 | |
Electrical signals cause cells to change the pressure of sap | 0:14:57 | 0:15:01 | |
in their leaves, so creating movement. | 0:15:01 | 0:15:04 | |
As a result, some plants, like animals, | 0:15:05 | 0:15:08 | |
can actively catch their prey. | 0:15:08 | 0:15:10 | |
Recently it's been discovered that other plants use electricity too | 0:15:13 | 0:15:18 | |
but for a very different purpose. | 0:15:18 | 0:15:20 | |
Plants are rooted to the ground and have a small negative charge. | 0:15:22 | 0:15:27 | |
The higher up the plant you go, the greater the electric charge. | 0:15:27 | 0:15:31 | |
This creates an electric field around the flower. | 0:15:31 | 0:15:34 | |
We can't see it but these electrodes are picking up the energy | 0:15:34 | 0:15:39 | |
of this tiny field and converting it into the sound that we can hear. | 0:15:39 | 0:15:43 | |
Bees, on the other hand, have a positive charge. | 0:15:44 | 0:15:48 | |
Friction whilst flying causes them | 0:15:48 | 0:15:50 | |
to lose electrons, leaving them electrically charged. | 0:15:50 | 0:15:54 | |
As a bee approaches a flower, the charge fields around the flower | 0:15:54 | 0:15:58 | |
and the bee interact, and the sound changes... | 0:15:58 | 0:16:01 | |
FALTERING ELECTRONIC BUZZ | 0:16:01 | 0:16:02 | |
..there. | 0:16:02 | 0:16:04 | |
And when it lands, the positive | 0:16:04 | 0:16:06 | |
and negative fields immediately cancel each other out. | 0:16:06 | 0:16:10 | |
As this happens, there are two very surprising consequences. | 0:16:10 | 0:16:13 | |
Firstly, the plant's negatively charged pollen actually | 0:16:13 | 0:16:18 | |
jumps across onto the positively charged bee. | 0:16:18 | 0:16:22 | |
Secondly, the plant has a changed electrical field | 0:16:22 | 0:16:26 | |
and when another bee comes along, it detects this altered | 0:16:26 | 0:16:30 | |
electrical signature and avoids the flower. | 0:16:30 | 0:16:33 | |
The plant is, in effect, telling the bee that it has no nectar | 0:16:33 | 0:16:37 | |
and to come back later. | 0:16:37 | 0:16:39 | |
When the flower has refilled its stores of nectar, it creates | 0:16:40 | 0:16:44 | |
a new electric charge which attracts another passing bee. | 0:16:44 | 0:16:49 | |
This simple on/off signal benefits both the bee and the flower, | 0:16:49 | 0:16:54 | |
but it does have its limitations. | 0:16:54 | 0:16:57 | |
The electrical field is tiny, | 0:16:58 | 0:17:00 | |
so insects can only detect it at close quarters. | 0:17:00 | 0:17:03 | |
But flowers can also draw attention to themselves over much | 0:17:04 | 0:17:08 | |
greater distances and they do this by floating messages in the air. | 0:17:08 | 0:17:13 | |
The perfume of a flower is not just a pleasant smell, | 0:17:15 | 0:17:18 | |
it's also the primary way in which plants communicate with insects. | 0:17:18 | 0:17:23 | |
A rose can contain over 400 chemical compounds and a bee | 0:17:23 | 0:17:27 | |
can recognise a particular combination from over a mile away. | 0:17:27 | 0:17:32 | |
The very latest research has discovered | 0:17:32 | 0:17:35 | |
that 90% of the chemicals made by plants, are also | 0:17:35 | 0:17:39 | |
produced by insects and that is no coincidence. | 0:17:39 | 0:17:42 | |
Most flowers produce scent to persuade insects to visit them, | 0:17:45 | 0:17:50 | |
but others use it in a more sophisticated way... | 0:17:51 | 0:17:55 | |
for protection. | 0:17:55 | 0:17:56 | |
Cabbages communicate with each other using smell. | 0:17:57 | 0:18:01 | |
When the leaves of one plant are being attacked by caterpillars, | 0:18:03 | 0:18:06 | |
it releases a scent which warns its neighbours. | 0:18:06 | 0:18:10 | |
They then produce chemicals in their leaves that caterpillars | 0:18:10 | 0:18:14 | |
don't like and so they avoid being eaten. | 0:18:14 | 0:18:16 | |
And scent also serves to call in the cavalry. | 0:18:18 | 0:18:21 | |
Leaves that are under attack give off a chemical alarm signal that | 0:18:22 | 0:18:26 | |
attracts wasps which obligingly pick off the caterpillar attackers. | 0:18:26 | 0:18:31 | |
So, vegetables, fruits, leaves and flowers are constantly | 0:18:35 | 0:18:39 | |
communicating with each other using touch, vision and smell. | 0:18:39 | 0:18:45 | |
They seem to exploit all the senses, apart, that is, from hearing. | 0:18:45 | 0:18:49 | |
But there are old stories that one particular plant is able to | 0:18:51 | 0:18:55 | |
produce a very strange sound. | 0:18:55 | 0:18:57 | |
Hundreds of years ago, a plant with a root that was thought to | 0:18:59 | 0:19:03 | |
resemble a human body was said to emit a sound that could kill. | 0:19:03 | 0:19:08 | |
The root was known to have strong anaesthetic | 0:19:08 | 0:19:10 | |
and hallucinogenic properties. And in the first century AD, | 0:19:10 | 0:19:14 | |
it was called a mandragora or mandrake as it's now known. | 0:19:14 | 0:19:19 | |
It was associated with magic and the supernatural | 0:19:19 | 0:19:23 | |
and was thought to derive power from a demon that emitted a dreadful | 0:19:23 | 0:19:27 | |
and fatal shriek if the plant was uprooted. | 0:19:27 | 0:19:30 | |
Fortunately, there were creative ways of avoiding | 0:19:31 | 0:19:34 | |
death from the killer sound. | 0:19:34 | 0:19:36 | |
One account advised plugging one's ears | 0:19:36 | 0:19:39 | |
and then tying a starving dog to the mandrake plant. | 0:19:39 | 0:19:43 | |
And then, as the dog lunged for food, the plant would be uprooted. | 0:19:43 | 0:19:48 | |
The dog would tragically die from the mandrake's shriek | 0:19:48 | 0:19:51 | |
but the man would survive. | 0:19:51 | 0:19:53 | |
This particular story may have arisen because drinks made with | 0:19:56 | 0:20:00 | |
the mandrake root can produce hallucinations. | 0:20:00 | 0:20:03 | |
But we're just beginning to realise that the sensory abilities | 0:20:07 | 0:20:11 | |
of a root could be as sophisticated as the rest of the plant. | 0:20:11 | 0:20:15 | |
Latest research suggests that roots are communicating underground. | 0:20:20 | 0:20:24 | |
And we now have the technology to eavesdrop on the roots' world. | 0:20:27 | 0:20:31 | |
Believe it or not, the roots of these corn seedlings can make | 0:20:34 | 0:20:39 | |
and sense sound. | 0:20:39 | 0:20:41 | |
The noise is very quiet but we can hear it with this equipment, | 0:20:41 | 0:20:46 | |
if I place a corn seedling in front of a laser beam Like this. | 0:20:46 | 0:20:50 | |
Now the sound vibration can be detected | 0:20:55 | 0:20:59 | |
and we can hear it through a speaker... | 0:20:59 | 0:21:01 | |
CRACKLING | 0:21:02 | 0:21:03 | |
..there. | 0:21:03 | 0:21:05 | |
That strange crackling is the sound of corn roots growing. | 0:21:05 | 0:21:10 | |
It can be seen as pulses on the screen. | 0:21:10 | 0:21:13 | |
It's been shown, too, that the corn roots respond to the sound | 0:21:13 | 0:21:16 | |
when it's played back to them. | 0:21:16 | 0:21:19 | |
Time-lapse footage shot over just a few hours clearly shows | 0:21:19 | 0:21:22 | |
the roots growing towards the tiny speakers that emit the sound. | 0:21:22 | 0:21:26 | |
There is much speculation | 0:21:27 | 0:21:29 | |
about the purpose of this curious phenomenon. | 0:21:29 | 0:21:32 | |
Perhaps it helps roots avoid growing into hard objects or being too | 0:21:32 | 0:21:36 | |
close to competing plants. | 0:21:36 | 0:21:39 | |
It could act like simple echolocation, | 0:21:39 | 0:21:42 | |
we just don't know but it's the first clear evidence that | 0:21:42 | 0:21:46 | |
plants have a rudimentary form of hearing | 0:21:46 | 0:21:49 | |
and might even be communicating underground using sound. | 0:21:49 | 0:21:53 | |
Sensitive equipment is creating a new window into the plant world | 0:21:53 | 0:21:57 | |
and it seems that, like animals, they have a sophisticated | 0:21:57 | 0:22:00 | |
sense of their environment and possess abilities that not | 0:22:00 | 0:22:04 | |
so long ago, we would have thought of as supernatural. | 0:22:04 | 0:22:08 | |
BIRDSONG | 0:22:16 | 0:22:22 | |
Swallows have successfully nested | 0:22:27 | 0:22:29 | |
and raised their young in this barn for several years. | 0:22:29 | 0:22:33 | |
These chicks will soon leave the nest and make their first | 0:22:33 | 0:22:36 | |
exploratory flights around the farm | 0:22:36 | 0:22:38 | |
but in a few weeks' time they will suddenly vanish. | 0:22:38 | 0:22:42 | |
Where do they go to? | 0:22:42 | 0:22:44 | |
In the past, that gave rise to some extraordinary speculations. | 0:22:44 | 0:22:48 | |
In fact, in the 18th century, it became a very long-running | 0:22:48 | 0:22:52 | |
debate, headed by some well-known Church figures. | 0:22:52 | 0:22:55 | |
And swallows are not the only birds that appear | 0:22:57 | 0:23:00 | |
and disappear with the changing seasons. | 0:23:00 | 0:23:03 | |
For centuries, people speculated about where such birds go. | 0:23:03 | 0:23:07 | |
One explanation was that some birds changed into others by growing | 0:23:07 | 0:23:12 | |
different adult plumage. | 0:23:12 | 0:23:15 | |
Perhaps the redstart turned into a robin... | 0:23:15 | 0:23:18 | |
..or the garden warbler into a blackcap. | 0:23:20 | 0:23:23 | |
Since these species where seldom present at the same time | 0:23:24 | 0:23:28 | |
the explanation seemed entirely plausible. | 0:23:28 | 0:23:30 | |
The barnacle goose was another mystery. | 0:23:35 | 0:23:37 | |
Each winter, huge, noisy flocks of them | 0:23:39 | 0:23:42 | |
appear on European shores, apparently from out of nowhere. | 0:23:42 | 0:23:45 | |
No-one had ever seen them build a nest or raise young. | 0:23:47 | 0:23:51 | |
The barnacle goose gave rise to some extraordinary folklore as this | 0:23:56 | 0:24:01 | |
mediaeval illustration shows. | 0:24:01 | 0:24:04 | |
It was thought that the geese grew on underwater trees, | 0:24:04 | 0:24:08 | |
starting life as small marine creatures called goose barnacles. | 0:24:08 | 0:24:13 | |
Goose barnacles do, of course, exist, they're small | 0:24:13 | 0:24:16 | |
shelled marine organisms with what looks like the head, | 0:24:16 | 0:24:20 | |
which is in fact enclosed by a shell, attached by a stalk, which | 0:24:20 | 0:24:25 | |
was thought to resemble the neck of a bird, to a bit of wood or a rock. | 0:24:25 | 0:24:30 | |
The confusion about the nature of the barnacle goose was put to | 0:24:33 | 0:24:37 | |
good use by some. | 0:24:37 | 0:24:39 | |
Since it was unclear whether it was a bird, | 0:24:39 | 0:24:41 | |
a fish or some other creature, you could surely be | 0:24:41 | 0:24:44 | |
allowed to eat it on days when meat was forbidden by the church. | 0:24:44 | 0:24:48 | |
But the most commonly held belief was that birds | 0:24:50 | 0:24:53 | |
disappear in winter because they hibernated. | 0:24:53 | 0:24:56 | |
Swallows and their close relatives, the swifts and martins, | 0:24:58 | 0:25:01 | |
were thought to do so in mud at the bottom of ponds and rivers | 0:25:01 | 0:25:06 | |
and it's easy to see how this idea originated | 0:25:06 | 0:25:09 | |
because the birds spent much of their time near water, skimming low | 0:25:09 | 0:25:13 | |
over the surface, hunting for insects or taking a drink. | 0:25:13 | 0:25:16 | |
It wasn't until the Middle Ages that another theory was proposed that | 0:25:18 | 0:25:22 | |
some birds may migrate | 0:25:22 | 0:25:25 | |
and one of its strongest proponents was an influential religious leader. | 0:25:25 | 0:25:30 | |
Frederick the second of Hohenstaufen was a powerful holy | 0:25:32 | 0:25:37 | |
Roman Emperor and known for his unorthodox views. | 0:25:37 | 0:25:40 | |
He ignored the philosophy of the Church | 0:25:40 | 0:25:43 | |
and based his knowledge of natural history on direct observation | 0:25:43 | 0:25:47 | |
rather than what was ordained. | 0:25:47 | 0:25:50 | |
Frederick was also a keen falconer and he wrote this book, | 0:25:50 | 0:25:54 | |
The Art Of Falconry, | 0:25:54 | 0:25:56 | |
and in it, surprisingly, | 0:25:56 | 0:25:58 | |
there are entire chapters on the migration of birds. | 0:25:58 | 0:26:02 | |
His confidence came from the fact that, | 0:26:02 | 0:26:04 | |
unlike his contemporaries and those before him, | 0:26:04 | 0:26:07 | |
he had actually observed birds in the field for himself. | 0:26:07 | 0:26:11 | |
He had no doubt about the migration and so, | 0:26:11 | 0:26:13 | |
little patience for the myths surrounding the barnacle goose. | 0:26:13 | 0:26:17 | |
He considered the story to be quite ridiculous | 0:26:17 | 0:26:20 | |
and argued that the birds simply breed in distant lands. | 0:26:20 | 0:26:24 | |
His views started a debate that split people into two camps, | 0:26:26 | 0:26:31 | |
those believing in the old hibernation theory | 0:26:31 | 0:26:34 | |
and those who supported the idea that birds migrate. | 0:26:34 | 0:26:37 | |
This was the start of a new era which was to sweep away myths | 0:26:38 | 0:26:43 | |
and focus instead on facts and careful observation. | 0:26:43 | 0:26:47 | |
Across Europe, the evidence for bird migration started to accumulate. | 0:26:47 | 0:26:52 | |
In Germany, a 12th century monk is said to have taken | 0:26:54 | 0:26:58 | |
a swallow from its nest and attached a parchment note to its leg | 0:26:58 | 0:27:02 | |
that read, "Oh, swallow, where do you live in winter?" | 0:27:02 | 0:27:05 | |
The following spring the bird returned with a note saying, | 0:27:07 | 0:27:10 | |
"In Asia, in the home of Petrus, that is Israel." | 0:27:10 | 0:27:14 | |
The story may not have been true, but it certainly gave the right hint. | 0:27:16 | 0:27:20 | |
In the early 16th century, a Bishop from Sweden called | 0:27:24 | 0:27:29 | |
Olaus Magnus reignited the debate about swallows with this picture. | 0:27:29 | 0:27:35 | |
He claimed that in winter, fishermen often drew up | 0:27:35 | 0:27:38 | |
swallows in their nets, hanging together in a mass. | 0:27:38 | 0:27:42 | |
This astonishing assertion provided ample fuel | 0:27:42 | 0:27:45 | |
for the anti-migration lobby and, unlikely as it was, | 0:27:45 | 0:27:49 | |
the view that swallows spent their winter underwater | 0:27:49 | 0:27:52 | |
became increasingly entrenched. | 0:27:52 | 0:27:54 | |
By the 18th century, the debate about migration versus hibernation | 0:27:58 | 0:28:02 | |
had come to a head and across the continent opinions were divided. | 0:28:02 | 0:28:08 | |
But new evidence was about to come from an unusual source. | 0:28:11 | 0:28:15 | |
Edward Jenner was an English country doctor who also had a deep | 0:28:16 | 0:28:20 | |
interest in natural history. | 0:28:20 | 0:28:23 | |
He noted that although swallows often splash in water | 0:28:23 | 0:28:27 | |
as they skim across it, they never immerse themselves. | 0:28:27 | 0:28:31 | |
Were they to do so, he suggested, their wings would become | 0:28:31 | 0:28:34 | |
so wet that they would be unable to fly. | 0:28:34 | 0:28:37 | |
To test his idea, Jenner reportedly held a swift | 0:28:38 | 0:28:41 | |
underwater for two minutes. | 0:28:41 | 0:28:44 | |
Not surprisingly, it died. | 0:28:44 | 0:28:46 | |
Jenner went on to devise another experiment to | 0:28:48 | 0:28:51 | |
discover where the birds go. | 0:28:51 | 0:28:53 | |
He took 12 swifts from their nests and marked them | 0:28:53 | 0:28:57 | |
by taking off two of their claws. | 0:28:57 | 0:28:59 | |
The following year, some of the birds he'd marked were caught | 0:28:59 | 0:29:02 | |
again in exactly the same spot. | 0:29:02 | 0:29:04 | |
Although Jenner could not discover where his swifts had been | 0:29:04 | 0:29:08 | |
over the winter, he was the first to show that they returned to use | 0:29:08 | 0:29:11 | |
the same breeding sites in the following years. | 0:29:11 | 0:29:15 | |
And we now know that this is true for swallows as well. | 0:29:15 | 0:29:18 | |
About the same time, across the Channel, a German bird enthusiast | 0:29:20 | 0:29:24 | |
had come up with a similar idea. | 0:29:24 | 0:29:26 | |
Johann Frisch caught several birds near his house and attached | 0:29:28 | 0:29:32 | |
to their legs woollen threads like this which he'd dipped | 0:29:32 | 0:29:36 | |
in red watercolour. | 0:29:36 | 0:29:38 | |
He predicted that if swallows really did spend | 0:29:38 | 0:29:40 | |
the winter at the bottom of lakes, the red colour would be washed off. | 0:29:40 | 0:29:45 | |
The following spring, Frisch's swallows returned | 0:29:45 | 0:29:48 | |
and the threads where unchanged. | 0:29:48 | 0:29:51 | |
It was a very simple but very effective experiment. | 0:29:51 | 0:29:55 | |
Evidence against the hibernation theory continued to mount | 0:29:55 | 0:29:59 | |
and eventually a new technique put the final nail in its coffin... | 0:29:59 | 0:30:04 | |
systematic bird ringing. | 0:30:04 | 0:30:06 | |
This bird has just been fitted with its own individual marker. | 0:30:09 | 0:30:13 | |
A small metal ring on its leg with a unique code of numbers. | 0:30:13 | 0:30:18 | |
It's part of a national scheme that's been running for over 100 | 0:30:18 | 0:30:21 | |
years and provides scientists with invaluable data on bird movements. | 0:30:21 | 0:30:26 | |
Early in the 20th century, the study of migration really took off. | 0:30:27 | 0:30:31 | |
Birds were recovered on their breeding and wintering grounds | 0:30:31 | 0:30:34 | |
and often en route, too. | 0:30:34 | 0:30:37 | |
600 years after Frederick von Hohenstaufen had first started | 0:30:37 | 0:30:41 | |
the debate, real evidence was beginning to accumulate. | 0:30:41 | 0:30:45 | |
In the summer of 1911, a metal ring just like this one, | 0:30:47 | 0:30:51 | |
was clipped onto the leg of a young swallow in Staffordshire. | 0:30:51 | 0:30:55 | |
The number on the ring was B830. | 0:30:55 | 0:30:59 | |
18 months later, the same bird was caught by a farmer in South Africa. | 0:30:59 | 0:31:04 | |
Here, at last, was the indisputable proof that swallows migrate | 0:31:04 | 0:31:09 | |
and spend the winter thousands of miles away. | 0:31:09 | 0:31:11 | |
Off you go. There we are. | 0:31:13 | 0:31:16 | |
Today, of course, we know that the swallows' migration is | 0:31:19 | 0:31:23 | |
one of the most impressive in all the animal kingdom. | 0:31:23 | 0:31:26 | |
It takes it across the largest desert in the world, the Sahara, | 0:31:26 | 0:31:31 | |
it's a gruelling and dangerous journey | 0:31:31 | 0:31:33 | |
and many die on the way from exhaustion or starvation. | 0:31:33 | 0:31:38 | |
They travel for nearly four months, covering nearly 10,000km | 0:31:38 | 0:31:43 | |
and eventually reach southern Africa. | 0:31:43 | 0:31:46 | |
And bird ringing also helped to dispel the myth of | 0:31:52 | 0:31:56 | |
the barnacle goose. | 0:31:56 | 0:31:58 | |
In the 1960s, a Norwegian expedition, ringed geese nesting | 0:31:58 | 0:32:02 | |
on the Arctic island of Spitsbergen. That autumn, some of the same | 0:32:02 | 0:32:07 | |
birds were sited on the west coast of Scotland, some 2,000km away. | 0:32:07 | 0:32:11 | |
Frederick von Hohenstaufen had been proved to be absolutely correct. | 0:32:13 | 0:32:18 | |
It took centuries to discover the truth behind the swallows' | 0:32:21 | 0:32:26 | |
seasonal movements. | 0:32:26 | 0:32:27 | |
But in their time, they baffled the minds of many great naturalists and | 0:32:27 | 0:32:32 | |
started one of the longest-running of all scientific debates. | 0:32:32 | 0:32:36 | |
But in the end, the true story proved to be even more extraordinary | 0:32:36 | 0:32:41 | |
than the fantastic myths that where invented to explain it. | 0:32:41 | 0:32:46 | |
Just like the swallow, | 0:32:48 | 0:32:50 | |
the painted lady butterfly seems to appear magically out of nowhere | 0:32:50 | 0:32:54 | |
and that started some extraordinary ideas and controversies. | 0:32:54 | 0:32:57 | |
The painted lady is one of our largest butterflies | 0:32:58 | 0:33:02 | |
and a familiar summer visitor to our gardens. | 0:33:02 | 0:33:05 | |
And yet, its appearance | 0:33:05 | 0:33:06 | |
and disappearance each year, has puzzled us for centuries. | 0:33:06 | 0:33:10 | |
It's only now that we're beginning to understand this extraordinary | 0:33:10 | 0:33:13 | |
life cycle and discover where it vanishes each year. | 0:33:13 | 0:33:16 | |
Early naturalists were confused by the sudden | 0:33:18 | 0:33:20 | |
appearance of painted ladies each spring because they were | 0:33:20 | 0:33:23 | |
unaware of the connection between butterflies and caterpillars. | 0:33:23 | 0:33:28 | |
For a very long time it was widely believed that butterflies | 0:33:28 | 0:33:32 | |
arise from rotting material by what was called spontaneous generation. | 0:33:32 | 0:33:37 | |
In the 1830s, a German scientist named Renous was arrested for heresy | 0:33:40 | 0:33:46 | |
for claiming that he could change caterpillars into butterflies. | 0:33:46 | 0:33:50 | |
Arresting someone for something now known to be common knowledge | 0:33:50 | 0:33:53 | |
may seem rather extreme, but at the time, many still believed that | 0:33:53 | 0:33:57 | |
caterpillars and butterflies were completely different creatures, | 0:33:57 | 0:34:00 | |
created by the hand of God. | 0:34:00 | 0:34:02 | |
Needless to say, people had been well aware of the existence of | 0:34:04 | 0:34:08 | |
both butterflies and caterpillars since the earliest times. | 0:34:08 | 0:34:12 | |
But the thought that any two were related, | 0:34:14 | 0:34:17 | |
let alone the same species, seemed impossible... | 0:34:17 | 0:34:21 | |
and it's easy to see why. | 0:34:21 | 0:34:23 | |
Not only do caterpillars and butterflies look like very | 0:34:26 | 0:34:30 | |
different types of animals, but the colours and patterns | 0:34:30 | 0:34:33 | |
of a caterpillar don't match up with those of its adult form. | 0:34:33 | 0:34:38 | |
The only way to know which lava and which butterfly go together | 0:34:38 | 0:34:42 | |
is to keep caterpillars and watch them turn into butterflies. | 0:34:42 | 0:34:46 | |
But it wasn't until the 17th century that anyone left | 0:34:46 | 0:34:50 | |
a record of doing that. | 0:34:50 | 0:34:51 | |
One of the first was a remarkable woman named Maria Sibylla Merian. | 0:34:52 | 0:34:57 | |
Merian was born in Germany at a time | 0:34:58 | 0:35:01 | |
when women still had little formal education | 0:35:01 | 0:35:04 | |
and no role in the scientific world, but she was an accomplished | 0:35:04 | 0:35:08 | |
artist and painted plants and insects she saw around her. | 0:35:08 | 0:35:12 | |
To do that, she kept caterpillars, fed them on leaves | 0:35:12 | 0:35:17 | |
and watched them turn into butterflies. | 0:35:17 | 0:35:19 | |
Merian produced hundreds of beautiful paintings of butterflies | 0:35:21 | 0:35:24 | |
and their stages of development | 0:35:24 | 0:35:26 | |
along with the plants on which they feed. | 0:35:26 | 0:35:29 | |
Her drawings are so exquisite | 0:35:29 | 0:35:30 | |
and detailed that they still rank among the best in the world. | 0:35:30 | 0:35:34 | |
Among the things she observed with great care, were things like this. | 0:35:37 | 0:35:41 | |
A curious, yet strangely beautiful object, it's a chrysalis, | 0:35:42 | 0:35:48 | |
the intermediate stage between a caterpillar and a butterfly. | 0:35:48 | 0:35:52 | |
She was one of the first to record the remarkable change | 0:35:55 | 0:35:59 | |
that takes place in the chrysalis. | 0:35:59 | 0:36:01 | |
It's one of nature's most extraordinary transformations. | 0:36:02 | 0:36:06 | |
At the age of 52, she sailed from Europe to South America on a | 0:36:11 | 0:36:15 | |
two-year expedition to study insects in the tropical jungles of Surinam. | 0:36:15 | 0:36:20 | |
It was an exceptional journey for any naturalist | 0:36:20 | 0:36:23 | |
at the time and particularly for a woman. | 0:36:23 | 0:36:26 | |
When she returned, she produced this beautiful book. | 0:36:26 | 0:36:29 | |
It turned out to be popular | 0:36:32 | 0:36:34 | |
because it was one of the few to be published | 0:36:34 | 0:36:36 | |
not in the scientific language of Latin but in Dutch. | 0:36:36 | 0:36:40 | |
Because of this, | 0:36:40 | 0:36:41 | |
her work was largely dismissed by scientists of the time | 0:36:41 | 0:36:45 | |
but Merian was one of the first naturalists to correctly | 0:36:45 | 0:36:48 | |
connect the caterpillar with its pupa and the adult form. | 0:36:48 | 0:36:52 | |
Today, Merian's book is widely | 0:36:54 | 0:36:56 | |
recognised as a pioneering work of scientific observation | 0:36:56 | 0:37:01 | |
and it put an end to the idea of spontaneous generation. | 0:37:01 | 0:37:06 | |
Around the same time, further evidence for the connection | 0:37:08 | 0:37:12 | |
between butterflies and caterpillars came from a different source. | 0:37:12 | 0:37:16 | |
In 1669, a Dutch scientist by the name of Jan Swammerdam published | 0:37:18 | 0:37:23 | |
the results of experiments which would finally prove that the | 0:37:23 | 0:37:27 | |
caterpillar and butterfly are one and the same animal. | 0:37:27 | 0:37:30 | |
Swammerdam was a master of the miniature and dissected the | 0:37:30 | 0:37:33 | |
caterpillars and pupae of butterflies and moths | 0:37:33 | 0:37:36 | |
under a microscope. With a steady hand and endless patience, | 0:37:36 | 0:37:40 | |
he carefully cut into the layers of skin with tiny scissors | 0:37:40 | 0:37:44 | |
and what he discovered was truly astonishing. | 0:37:44 | 0:37:47 | |
He found some of the body parts of a butterfly. | 0:37:49 | 0:37:54 | |
The structures were fragile and not complete but Swammerdam had proved | 0:37:54 | 0:37:58 | |
that caterpillar and butterfly are, indeed, one and the same animal. | 0:37:58 | 0:38:03 | |
We now know that without the caterpillar, there can be no butterfly. | 0:38:07 | 0:38:12 | |
Yet, for a very long time, | 0:38:12 | 0:38:13 | |
the painted lady seemed to be an exception. | 0:38:13 | 0:38:16 | |
Every spring, the adult butterflies would appear across Britain | 0:38:16 | 0:38:19 | |
without any sightings of their caterpillars. | 0:38:19 | 0:38:22 | |
While some butterflies hibernate in Britain, there was no sign | 0:38:23 | 0:38:27 | |
of painted ladies doing so. | 0:38:27 | 0:38:28 | |
Some speculated that they flew to warmer climates as birds do. | 0:38:29 | 0:38:34 | |
But how could a tiny insect cross the English Channel? | 0:38:35 | 0:38:39 | |
In the 20th century, swarms of butterflies moving across Europe | 0:38:40 | 0:38:43 | |
finally provided evidence that painted ladies do, indeed, | 0:38:43 | 0:38:47 | |
cross the sea. | 0:38:47 | 0:38:49 | |
And they were found to fly all the way from North Africa to Britain. | 0:38:49 | 0:38:53 | |
But there were almost no records of painted ladies making | 0:38:55 | 0:38:58 | |
the reverse trip south. | 0:38:58 | 0:39:00 | |
So, for years, it was thought that Britain must be | 0:39:00 | 0:39:03 | |
a dead-end for the most northerly stragglers. | 0:39:03 | 0:39:06 | |
And then, in 2009, the public was asked to help solve the mystery. | 0:39:08 | 0:39:14 | |
Among 12,000 sightings there were reports of painted ladies | 0:39:14 | 0:39:18 | |
flying out to sea in the autumn. | 0:39:18 | 0:39:21 | |
And a radar station detected them flying south | 0:39:22 | 0:39:25 | |
at heights of 500 metres, way beyond the sight of human eyes. | 0:39:25 | 0:39:30 | |
We now know that the painted ladies migration is a round-trip | 0:39:32 | 0:39:36 | |
of over 12,000km. But it's not made by any one individual. | 0:39:36 | 0:39:42 | |
Each only flies part of the way, | 0:39:42 | 0:39:45 | |
passing on the migratory baton to the next generation. | 0:39:45 | 0:39:48 | |
It's like a relay race with up to six generations of butterflies involved. | 0:39:48 | 0:39:53 | |
The painted ladies epic journey from one continent to the next | 0:39:55 | 0:39:58 | |
would be a truly astonishing feature in any animal | 0:39:58 | 0:40:01 | |
but for a tiny creature like this, it seems really extraordinary. | 0:40:01 | 0:40:05 | |
How does it battle the wind | 0:40:05 | 0:40:07 | |
and the weather and navigate across vast bodies of water? | 0:40:07 | 0:40:10 | |
And with no single individual ever undertaking the whole migration, | 0:40:10 | 0:40:14 | |
how do they find the way? | 0:40:14 | 0:40:16 | |
It seems that painted ladies are pre-programmed to either fly | 0:40:18 | 0:40:23 | |
north or south and this is determined whilst | 0:40:23 | 0:40:26 | |
they are still caterpillars, possibly by temperature | 0:40:26 | 0:40:29 | |
and day length and also by the plants they feed on but how | 0:40:29 | 0:40:34 | |
does this information get passed on from caterpillar to butterfly? | 0:40:34 | 0:40:39 | |
The answer may be hidden within the chrysalis. | 0:40:39 | 0:40:42 | |
Recently CT scanners have allowed us to look inside a pupa. | 0:40:43 | 0:40:49 | |
They reveal that some organs remain intact during the transformation. | 0:40:49 | 0:40:54 | |
A one-day-old pupa clearly shows the gut and breathing tubes | 0:40:56 | 0:41:00 | |
which only change slightly as the chrysalis develops. | 0:41:00 | 0:41:03 | |
Could it be that the brain or nerves also remain intact | 0:41:07 | 0:41:12 | |
and that memories are passed on? | 0:41:12 | 0:41:14 | |
Recent experiments in the lab appear to support this idea. | 0:41:15 | 0:41:20 | |
Scientists taught caterpillars to avoid specific | 0:41:20 | 0:41:24 | |
smells by linking them with an unpleasant reaction. | 0:41:24 | 0:41:27 | |
Later on, as adults, the same individuals remembered these | 0:41:28 | 0:41:32 | |
smells and chose to keep away from them. | 0:41:32 | 0:41:35 | |
If the experiences of a caterpillar can be carried over | 0:41:35 | 0:41:38 | |
to the adult, then maybe cues for migration can also be passed on. | 0:41:38 | 0:41:43 | |
Although we've unravelled much of the painted lady's life-cycle, | 0:41:45 | 0:41:49 | |
many questions remain. How far does each individual travel? | 0:41:49 | 0:41:54 | |
And do offspring follow similar routes to their ancestors? | 0:41:54 | 0:41:59 | |
One day we may know the answers but, for now, | 0:41:59 | 0:42:02 | |
they remain some of the unsolved mysteries of nature. | 0:42:02 | 0:42:06 | |
The arrival each spring of our painted lady butterflies | 0:42:09 | 0:42:12 | |
and our swallows never ceases to delight us | 0:42:12 | 0:42:15 | |
but now we also understand the extraordinary journeys | 0:42:15 | 0:42:18 | |
they undertake when they disappear again at the end of summer. | 0:42:18 | 0:42:22 |