0:00:02 > 0:00:06The natural world is full of extraordinary animals
0:00:06 > 0:00:08with 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 > 0:00:22or the strange biology of the emperor penguin.
0:00:23 > 0:00:25Some of these creatures
0:00:25 > 0:00:28were surrounded by myth and misunderstandings
0:00:28 > 0:00:29for a very long time...
0:00:30 > 0:00:33..and 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 > 0:00:43The curiosities I find most fascinating of all.
0:00:51 > 0:00:55Spiders spin intricate webs using their own silk
0:00:55 > 0:01:00and birds weave nests from strips of leaves.
0:01:00 > 0:01:04In this programme, I investigate the skill of these spinners and weavers
0:01:04 > 0:01:07and the way they use such materials
0:01:07 > 0:01:10to produce such truly complex structures.
0:01:18 > 0:01:21Birds build a variety of nests,
0:01:21 > 0:01:26each with a design that is characteristic of their species.
0:01:26 > 0:01:30The simplest nests are just sticks wedged into position,
0:01:30 > 0:01:32but some are more complicated.
0:01:32 > 0:01:36The long-tailed tit builds a delicate nest
0:01:36 > 0:01:39from plant material and spider silk,
0:01:39 > 0:01:43and weaverbirds do, literally, weave with leaves.
0:01:46 > 0:01:50But are such skills learned or instinctive?
0:01:53 > 0:01:56In 1905, Eugene Marais,
0:01:56 > 0:01:59a South African writer and scientist,
0:01:59 > 0:02:02was intrigued by the complexity of weaverbird nests.
0:02:02 > 0:02:06He wanted to understand more about their nest building skills
0:02:06 > 0:02:09and performed a rigorous, but simple, experiment
0:02:09 > 0:02:11to see if they learnt how to make nests
0:02:11 > 0:02:16or if they built them using what he called "cultural instinct".
0:02:16 > 0:02:20He took eggs from a pair of wild weaverbirds
0:02:20 > 0:02:24and put them into a canary's nest to hatch.
0:02:24 > 0:02:29Then he encouraged the next three generations of weaverbirds to breed,
0:02:29 > 0:02:31but gave them no nest material
0:02:31 > 0:02:34and hatched their eggs, once again, under canaries.
0:02:34 > 0:02:38When nesting time came for the fourth generation of weaverbirds,
0:02:38 > 0:02:40he gave them natural nest materials
0:02:40 > 0:02:42and, without hesitation,
0:02:42 > 0:02:46they vigorously set about constructing perfect wild nests.
0:02:49 > 0:02:53So nest-building is largely under genetic control,
0:02:53 > 0:02:58but it is influenced by experience and the environment.
0:02:58 > 0:03:02Nests of the same kind of weaverbird are not always exactly the same,
0:03:02 > 0:03:04and the birds, of necessity,
0:03:04 > 0:03:07must have some flexibility in how they build.
0:03:09 > 0:03:12Nests that hang are particularly difficult to make
0:03:12 > 0:03:17as the birds have to work against gravity with no support from below.
0:03:17 > 0:03:20Weaverbirds solve part of this problem
0:03:20 > 0:03:22with a skill none others have.
0:03:22 > 0:03:25They're the only birds that can tie knots.
0:03:26 > 0:03:29These knots vary and are worked on until the weaver succeeds
0:03:29 > 0:03:34in attaching several strands of grass to a suitable branch or stem.
0:03:37 > 0:03:40These first fastenings are crucial
0:03:40 > 0:03:43as the whole of the completed nest will hang from them.
0:03:48 > 0:03:51Once the birds have secured the foundation,
0:03:51 > 0:03:52they can start to weave.
0:03:58 > 0:04:03Weaving is just one way of binding leaves together.
0:04:03 > 0:04:05There are others.
0:04:08 > 0:04:11These are tailorbird nests.
0:04:11 > 0:04:15They consist of folded leaves stuffed with soft material
0:04:15 > 0:04:18and stitched together using spider silk.
0:04:18 > 0:04:21The tailorbird pierces the leaves with its sharp beak
0:04:21 > 0:04:26and then binds them together by pulling silk through the holes.
0:04:26 > 0:04:30The complete operation involves a number of different skills.
0:04:31 > 0:04:34Making the holes is like riveting.
0:04:34 > 0:04:36Two leaves are placed together
0:04:36 > 0:04:40and then pierced to create matching holes above and below.
0:04:42 > 0:04:46Then the edges are sewn up.
0:04:47 > 0:04:51The upper surface of the leaf is kept to the outside
0:04:51 > 0:04:53to help the nest look unobtrusive.
0:04:56 > 0:05:01The result is a secure pocket, which is then stuffed with a soft lining.
0:05:08 > 0:05:13The materials the birds choose to sew up their nest can vary.
0:05:13 > 0:05:14At the turn of the century,
0:05:14 > 0:05:17there was a report in The Common Birds Of Bombay
0:05:17 > 0:05:20of weaverbirds watching carpet makers and tailors
0:05:20 > 0:05:22as they worked on verandas.
0:05:22 > 0:05:24When the coast was clear,
0:05:24 > 0:05:27the birds flew down and stole tiny pieces of thread
0:05:27 > 0:05:30with which to sew up their nests.
0:05:32 > 0:05:34Birds search with a clear idea
0:05:34 > 0:05:37of what will be suitable nest material.
0:05:37 > 0:05:40Many use sticks and twigs.
0:05:43 > 0:05:47They will, however, occasionally use other material
0:05:47 > 0:05:48that does the same job...
0:05:49 > 0:05:52..and their choices are sometimes surprising.
0:05:54 > 0:05:59This nest was found in an aircraft hangar in the 1950s
0:05:59 > 0:06:02and it's made entirely of twisted wire.
0:06:03 > 0:06:07When it was discovered, it contained two blackbird eggs.
0:06:07 > 0:06:09It's an unusual nest for a blackbird,
0:06:09 > 0:06:13but similar nests have been found belonging to crows and pigeons.
0:06:17 > 0:06:20Weaverbirds work with natural material
0:06:20 > 0:06:22and, like the tailorbird,
0:06:22 > 0:06:26they have to solve the problem of joining leaves together.
0:06:26 > 0:06:29After making a knot to secure the basic framework,
0:06:29 > 0:06:31they begin their weaving.
0:06:33 > 0:06:35They construct the main egg chamber
0:06:35 > 0:06:37and then add a small entrance
0:06:37 > 0:06:41around the first securely knotted ring of leaves.
0:06:44 > 0:06:48The male, as he works, is under intense scrutiny.
0:06:49 > 0:06:51Females are looking for mates
0:06:51 > 0:06:55and males that build firm, well-positioned nests
0:06:55 > 0:06:57are favoured as fathers.
0:06:58 > 0:07:03When he finishes, a male advertises his handiwork by fluttering.
0:07:04 > 0:07:07But he may be forced to build several nests
0:07:07 > 0:07:11before a female finally chooses him as a partner.
0:07:13 > 0:07:16Weaverbirds' nests are very conspicuous.
0:07:17 > 0:07:21Other birds, however, go to some trouble to conceal them.
0:07:25 > 0:07:28We may not have tailorbirds or weaverbirds in Britain,
0:07:28 > 0:07:31but we do have long-tailed tits -
0:07:31 > 0:07:32delicate little birds
0:07:32 > 0:07:36that make intricate and finely constructed nests.
0:07:39 > 0:07:41With tiny, repetitive movements,
0:07:41 > 0:07:43they use loops of spider silk
0:07:43 > 0:07:47to felt together a mixture of wool and moss.
0:07:56 > 0:08:00Both male and female work on the construction.
0:08:01 > 0:08:03As the nest takes shape,
0:08:03 > 0:08:05they decorate the outside
0:08:05 > 0:08:09with several thousand tiny flakes of lichen.
0:08:19 > 0:08:22The nest is then lined with hundreds of feathers
0:08:22 > 0:08:25and provides a delicate but strong structure
0:08:25 > 0:08:27to house the growing chicks.
0:08:30 > 0:08:34And it's a nest that's particularly hard to find
0:08:34 > 0:08:36because of its covering of lichen.
0:08:39 > 0:08:42For years, it was believed that this acted as a sort of camouflage
0:08:42 > 0:08:45to help hide the nest.
0:08:45 > 0:08:48But the recent discovery of long-tailed tit nests
0:08:48 > 0:08:51covered with small flakes of paper and polystyrene
0:08:51 > 0:08:56have helped explain more clearly the reason for this decoration.
0:08:56 > 0:09:00Rather than helping to blend the nest with its background,
0:09:00 > 0:09:04these small flakes reflect light from it, making it almost invisible.
0:09:04 > 0:09:09And it seems paper and polystyrene do the job just as well as lichen.
0:09:12 > 0:09:17The largest and perhaps the most long-lasting nest of all
0:09:17 > 0:09:19is made by the social weaverbird.
0:09:23 > 0:09:26They live in the dry areas of southern Africa
0:09:26 > 0:09:27and work together
0:09:27 > 0:09:31to build what looks like a great haystack up in a tree.
0:09:34 > 0:09:36New nest chambers are continually added.
0:09:36 > 0:09:40As many as 100 pairs of birds may live together
0:09:40 > 0:09:42under the one roof, as you might say.
0:09:48 > 0:09:52The chambers provide shade during the day
0:09:52 > 0:09:54and keep out the chill at night...
0:10:00 > 0:10:04..and the whole construction is so robust
0:10:04 > 0:10:07that it may provide mass housing
0:10:07 > 0:10:09for generation after generation of birds.
0:10:20 > 0:10:24Recently, the biggest nest ever recorded was discovered
0:10:24 > 0:10:28attached to telegraph poles in the Kalahari Desert.
0:10:28 > 0:10:32It's more than seven metres across and three metres high.
0:10:32 > 0:10:36So weaverbirds make their nests in many different ways
0:10:36 > 0:10:40and it was once thought that they worked entirely by instinct,
0:10:40 > 0:10:43but this is not so.
0:10:43 > 0:10:47They are amongst the most expert nest-builders in the animal kingdom,
0:10:47 > 0:10:49and this array of nests
0:10:49 > 0:10:52shows the complex and elaborate designs
0:10:52 > 0:10:53that they can produce.
0:10:53 > 0:10:55Recent studies suggest
0:10:55 > 0:10:57that weaverbirds may be using mental skills
0:10:57 > 0:11:01that are not dissimilar to those required to make simple tools.
0:11:02 > 0:11:07For weaverbirds, a well-built nest is a ticket to successful breeding.
0:11:08 > 0:11:12Who would imagine that such complexity could be produced
0:11:12 > 0:11:15using just a foot and a beak.
0:11:18 > 0:11:21Weaverbirds make their elaborate nests
0:11:21 > 0:11:24from simple materials they find around them.
0:11:24 > 0:11:28Another of nature's extraordinary builders are the spiders.
0:11:28 > 0:11:30They make their complex webs
0:11:30 > 0:11:35from an incredible substance they produce themselves - silk.
0:11:38 > 0:11:40Spider silk is unique.
0:11:40 > 0:11:43It's very thin, very strong
0:11:43 > 0:11:46and has many exciting potential uses.
0:11:46 > 0:11:48Spiders spin it with ease,
0:11:48 > 0:11:51but scientists have been trying to copy it for many years.
0:11:51 > 0:11:54To do that, we need to understand two of the spider's secrets -
0:11:54 > 0:11:57the exact structure and nature of their silk,
0:11:57 > 0:12:01and the way they transform it from a fluid into a thread.
0:12:03 > 0:12:06Spider silk is a truly remarkable material.
0:12:06 > 0:12:08It can withstand impact
0:12:08 > 0:12:12and it can be strong, stretchy and sticky all at the same time.
0:12:14 > 0:12:17Spiders produce it from special glands inside their bodies
0:12:17 > 0:12:21and extrude it from tiny nipples called spinnerets
0:12:21 > 0:12:24at the back end of their abdomens.
0:12:24 > 0:12:27And what is more, they can produce up to seven different kinds,
0:12:27 > 0:12:29each with its own purpose.
0:12:31 > 0:12:35For centuries, it was the only silk known to man.
0:12:35 > 0:12:38The Ancient Greeks used cobwebs to stop bleeding
0:12:38 > 0:12:42and Australian Aborigines used it to catch small fish.
0:12:43 > 0:12:45Then, in the Far East,
0:12:45 > 0:12:49a different and mysterious new kind of silk started to appear,
0:12:49 > 0:12:51and in much larger quantities.
0:12:52 > 0:12:54According to Chinese legend,
0:12:54 > 0:12:58the first person to weave silk into a fabric
0:12:58 > 0:13:01was the Empress Leizu, back in the 27th century BC.
0:13:02 > 0:13:06She was having tea in her garden under a mulberry tree,
0:13:06 > 0:13:09when a cocoon fell from the branch above
0:13:09 > 0:13:11and dropped into her cup
0:13:11 > 0:13:13and started to unravel.
0:13:13 > 0:13:15Whether that's true or not,
0:13:15 > 0:13:19the Empress Leizu is now honoured as the goddess of silk,
0:13:19 > 0:13:22and silk-moth farming dates back
0:13:22 > 0:13:24to the beginning of Chinese civilisation.
0:13:24 > 0:13:29The silk was traded right across the Near East and into the Roman Empire.
0:13:29 > 0:13:32The Chinese traders were sworn to secrecy
0:13:32 > 0:13:36about how this marvellous material was made.
0:13:36 > 0:13:38But in the year 532,
0:13:38 > 0:13:42the Roman emperor Justinian managed to find out
0:13:42 > 0:13:46that it came not, as some suspected, from a spider's web,
0:13:46 > 0:13:48but from the cocoon of a moth.
0:13:51 > 0:13:54Silk moth caterpillars produce large quantities of silk
0:13:54 > 0:13:58and they make it in a very different way to spiders.
0:13:58 > 0:14:01The caterpillars feed voraciously on mulberry leaves,
0:14:01 > 0:14:05and then, when they're full-grown and ready to transform into a moth,
0:14:05 > 0:14:09they spin silken cocoons in which they will pupate.
0:14:09 > 0:14:13Unlike spiders, which have specialised spinning organs,
0:14:13 > 0:14:16silk moth caterpillars produce silk from their salivary glands.
0:14:18 > 0:14:22Each cocoon is made from a single, unbroken filament,
0:14:22 > 0:14:26that can be over 500 metres long.
0:14:26 > 0:14:30This silk is plentiful and easy to spin commercially,
0:14:30 > 0:14:33but it isn't as tough as spider silk.
0:14:36 > 0:14:41And spider silk also has more exciting potential uses.
0:14:44 > 0:14:46An orb web like this
0:14:46 > 0:14:50is constructed over a Y-shaped scaffold of silk threads,
0:14:50 > 0:14:53which are extremely strong.
0:14:53 > 0:14:57Unlike silkworms, the female spiders, which spin the webs,
0:14:57 > 0:14:59are very territorial and aggressive
0:14:59 > 0:15:03so farming and collecting spider silk is very difficult,
0:15:03 > 0:15:05but it has been done.
0:15:07 > 0:15:11In 1762, a Spanish missionary called Termeyer
0:15:11 > 0:15:14made a machine that held a single spider,
0:15:14 > 0:15:16from which he pulled a silken thread.
0:15:18 > 0:15:21In London, Daniel Rolt, a factory worker,
0:15:21 > 0:15:24attached spiders to a small steam machine
0:15:24 > 0:15:28and succeeded in reeling out 18 metres of silk a minute.
0:15:28 > 0:15:33That led to machines that were able to milk several spiders at a time.
0:15:37 > 0:15:40Experiments then stopped, until 2004,
0:15:40 > 0:15:43when two textile artists in Madagascar
0:15:43 > 0:15:46built a machine based on these early designs,
0:15:46 > 0:15:50with which they made something very special indeed.
0:15:51 > 0:15:55The golden colour of this stunningly beautiful spider silk shawl
0:15:55 > 0:15:58is completely natural.
0:15:58 > 0:16:00The silk from which it was made
0:16:00 > 0:16:04was produced by 1,063,000 spiders,
0:16:04 > 0:16:07like this one, over four years.
0:16:07 > 0:16:11Local people collected 3,000 spiders a day
0:16:11 > 0:16:14and trained handlers extracted silk
0:16:14 > 0:16:16from groups of 24 at a time.
0:16:16 > 0:16:21After being milked, the spiders were released back into the wild.
0:16:21 > 0:16:26The individual silk strands were then twisted into a thread which was
0:16:26 > 0:16:29woven into this intricately patterned fabric on looms.
0:16:33 > 0:16:35Now, this kind of silk fabric production
0:16:35 > 0:16:37couldn't work commercially.
0:16:37 > 0:16:40Apart from being hard work to make in quantity,
0:16:40 > 0:16:45spider silk isn't really a very suitable thread for fabric.
0:16:45 > 0:16:49As a cloth, it reacts badly to moisture and heat,
0:16:49 > 0:16:52but in its natural state, as a single thread,
0:16:52 > 0:16:54it has physical qualities
0:16:54 > 0:16:56that could be exploited medically.
0:16:57 > 0:16:59These special characteristics
0:16:59 > 0:17:04are a consequence of the molecular structure of spider silk.
0:17:04 > 0:17:08It consists of two large protein molecules.
0:17:08 > 0:17:10One is stretchy and spaghetti-like
0:17:10 > 0:17:13and the other has a harder, crystalline structure.
0:17:13 > 0:17:15Combined, these two proteins
0:17:15 > 0:17:20give silk unique qualities of strength and flexibility.
0:17:21 > 0:17:25Spiders store these proteins as a gel-like liquid in their bodies
0:17:25 > 0:17:26and when they need to make silk,
0:17:26 > 0:17:29they extrude it through the spinnerets,
0:17:29 > 0:17:32combining the molecules in a special way.
0:17:33 > 0:17:36If we hold down a spider without harming it
0:17:36 > 0:17:39we can see this process in more detail.
0:17:39 > 0:17:41Normally, the spider would attach
0:17:41 > 0:17:43the end of the silk filament
0:17:43 > 0:17:45to an object and then move away,
0:17:45 > 0:17:48so that the filament is pulled from the spinnerets.
0:17:48 > 0:17:51We can produce the same reaction,
0:17:51 > 0:17:54by gently pulling the end of the filament itself.
0:17:54 > 0:17:57Internally, the silk liquid is passing down a long duct
0:17:57 > 0:18:02in which stretchy elements within the protein molecules
0:18:02 > 0:18:04are lined with harder crystalline ones,
0:18:04 > 0:18:07to create an extremely strong and tough thread.
0:18:10 > 0:18:13Scanning electron microscopes
0:18:13 > 0:18:16reveal how the liquid emerges from the spinnerets.
0:18:16 > 0:18:20Incredibly, spiders can convert liquid proteins
0:18:20 > 0:18:23into a hardened thread at room temperature
0:18:23 > 0:18:25with very little energy.
0:18:25 > 0:18:28If we could understand and copy this process,
0:18:28 > 0:18:31it would be a major scientific breakthrough.
0:18:32 > 0:18:35Scientists have, in fact, spent many years
0:18:35 > 0:18:39trying to replicate the spider's liquid silk and the way it's spun.
0:18:39 > 0:18:43Recently, the genes of spider-silk proteins were cloned
0:18:43 > 0:18:45and put into goats
0:18:45 > 0:18:48to try and produce silk in their milk.
0:18:48 > 0:18:51It worked, and when the goats had kids,
0:18:51 > 0:18:55silk proteins were extracted from the mother's milk.
0:18:57 > 0:18:58But none of these processes
0:18:58 > 0:19:03have yet produced silk that is as tough as natural spider silk.
0:19:05 > 0:19:08This machine is called a tensile tester
0:19:08 > 0:19:12and it shows how strong and stretchy spider silk can be.
0:19:12 > 0:19:16This dragline silk is being pulled apart,
0:19:16 > 0:19:19and a graph shows the force the fibre is taking
0:19:19 > 0:19:21and at what point it breaks.
0:19:21 > 0:19:23A steel thread of similar diameter
0:19:23 > 0:19:25would have broken by now.
0:19:31 > 0:19:33There, it's broken.
0:19:33 > 0:19:38Spider silk is the toughest natural material known to man.
0:19:41 > 0:19:43A single thread of web silk,
0:19:43 > 0:19:45less than a millimetre thick,
0:19:45 > 0:19:48can absorb the impact of fast-moving prey
0:19:48 > 0:19:51and bring it to a halt without breaking.
0:19:51 > 0:19:54Complete webs can stretch enormously
0:19:54 > 0:19:57and then return to their original shape
0:19:57 > 0:19:59with a minimum of damage.
0:20:02 > 0:20:06Incredibly, spiders can make this complex material
0:20:06 > 0:20:09from just fresh air, flies and water.
0:20:10 > 0:20:13The best we can do in making a material like it
0:20:13 > 0:20:17requires oil, chemicals and a great deal of energy.
0:20:19 > 0:20:23Although we now better understand the structure of spider silk
0:20:23 > 0:20:25and the natural spinning process,
0:20:25 > 0:20:27we still can't perform the spider's magic
0:20:27 > 0:20:30and copy this extraordinary substance.
0:20:31 > 0:20:35But using small amounts of natural spider silk in clever ways
0:20:35 > 0:20:39has, nonetheless, a very exciting future.
0:20:40 > 0:20:42A sumptuous golden cloth
0:20:42 > 0:20:45is just one possible product.
0:20:46 > 0:20:50This is a dream that has become a reality,
0:20:50 > 0:20:53and shows just how lovely spider silk can be.
0:20:55 > 0:20:57But it also has the potential
0:20:57 > 0:20:59to make other dreams come true.
0:20:59 > 0:21:02It's a biodegradable material
0:21:02 > 0:21:05that we're now using to make artificial joints,
0:21:05 > 0:21:09and it may even help repair damaged spinal tissue.
0:21:11 > 0:21:16This curiosity of nature could eventually save lives.