0:01:21 > 0:01:28Twenty thousand years ago, this cave in Wales was home for human beings.
0:01:28 > 0:01:33We know because their bones have been found here.
0:01:33 > 0:01:38It's good. You're out of the wind and the rain. You can make a fire,
0:01:38 > 0:01:46and you've got a reasonable chance of defending yourself against your enemies, whether human or animal.
0:01:46 > 0:01:54In short, here, you've got some control over your surroundings and you can make yourself comfortable.
0:01:54 > 0:01:59Animals find homes for themselves for the same sort of reasons.
0:01:59 > 0:02:04Some use ready-made ones, like caves. Bats, for example.
0:02:04 > 0:02:11But others build ingenious and elaborate structures to shield themselves from a hostile world.
0:02:14 > 0:02:21A rocky coast is one of the most difficult of all places in which to live.
0:02:21 > 0:02:26Continuously pounded by waves, submerged twice every 24 hours
0:02:26 > 0:02:29and twice exposed to the air.
0:02:31 > 0:02:34To survive on the rocks,
0:02:34 > 0:02:38small molluscs secrete almost unbreakable shells.
0:02:38 > 0:02:42When they're gone their homes are sought-after.
0:02:50 > 0:02:54And in this pool, cut off by the falling tide,
0:02:54 > 0:03:01there's a large housing market, full of anxious tenants. This could be what they want.
0:03:13 > 0:03:21Hermit crabs have found the easiest of all solutions to the housing problem using somebody else's.
0:03:21 > 0:03:24There is, of course, a major difficulty.
0:03:24 > 0:03:30As a householder grows, he needs a bigger house. This might be one.
0:03:30 > 0:03:36Dimensions are carefully checked. Too big is as bad as too small.
0:03:36 > 0:03:39Enemies could pull an occupier out.
0:03:39 > 0:03:42It's just the thing!
0:03:42 > 0:03:47Now a slightly smaller home is on the market.
0:04:12 > 0:04:15And another one, smaller still.
0:04:15 > 0:04:19And another hopeful tenant.
0:04:24 > 0:04:28Nobody wants to vacate a perfect residence,
0:04:28 > 0:04:33but they can be forced to leave by strongarm tactics.
0:04:47 > 0:04:51Instead of stealing a hole for yourself,
0:04:51 > 0:04:53you could dig one.
0:04:53 > 0:04:58Rosy bee-eaters, like all their family, do just that.
0:05:09 > 0:05:17They're troubled, not with a shortage of houses, but of building sites.
0:05:17 > 0:05:24It's the dry season. This entire flock has chosen one sandbank in the middle of the Niger River.
0:05:24 > 0:05:30The site's desirable. Insects hatch from the river and provide food.
0:05:30 > 0:05:35Being surrounded by water, it's protected from land predators.
0:05:35 > 0:05:42Above all, its sand, recently exposed by the falling water, is free of vegetation, and loose.
0:05:42 > 0:05:50Much easier to dig in than the vertical river-banks and cliffs most other kinds of bee-eaters use.
0:05:55 > 0:06:00So rosy bee-eaters come from many miles around to nest here.
0:06:10 > 0:06:15That means there is great overcrowding.
0:06:21 > 0:06:24One benefit from such numbers
0:06:24 > 0:06:33is that those who haven't got their heads down digging can keep an eye out for danger.
0:06:44 > 0:06:47There are, inevitably, quarrels.
0:06:47 > 0:06:51A half-dug hole represents a lot of work,
0:06:51 > 0:06:56and a bird will steal another's if it can.
0:07:00 > 0:07:03They work in pairs.
0:07:03 > 0:07:10One does the digging, the other chases away strangers who might get in the way.
0:07:17 > 0:07:20It's hot work, too!
0:07:20 > 0:07:23But, with the river close by,
0:07:23 > 0:07:27it's easy to take a cool, refreshing dip.
0:07:33 > 0:07:40In a month, the breeding season will be over, the river will rise again and holes will be flooded.
0:07:40 > 0:07:48But by then, the young and their parents will have flown and won't need a home for another year.
0:07:48 > 0:07:51Some need a refuge throughout life.
0:07:51 > 0:07:57The open grasslands of the American west are exposed places to live.
0:07:57 > 0:08:01A small animal sitting around here is very vulnerable.
0:08:01 > 0:08:06So prairie-dogs dig for protection.
0:08:07 > 0:08:13And the prairie-dog community also has its alarm system.
0:08:13 > 0:08:16Below, there's a warm, safe refuge.
0:08:16 > 0:08:21The animals are so successful they can proliferate in huge numbers
0:08:21 > 0:08:27and form great settlements with hundreds of tunnels and entrances.
0:08:27 > 0:08:31I'm in the middle of one of these towns,
0:08:31 > 0:08:38and there are a couple of dozen burrows within a few yards of me.
0:08:38 > 0:08:44But why build so many elaborately shaped burrows when digging's hard?
0:08:44 > 0:08:51There's one way to get a clue. This candle produces a perfectly harmless smoke.
0:08:51 > 0:08:54If lit and placed in the burrow
0:08:54 > 0:08:58the smoke doesn't just blow away,
0:08:58 > 0:09:08but a wisp of it gets carried down along the tunnel, emerging at an entrance mound twenty yards away.
0:09:08 > 0:09:11So these two holes are connected.
0:09:11 > 0:09:18It's obviously useful to have an escape hole if you're pursued into your burrow by a wild ferret.
0:09:18 > 0:09:21But there's more to it than that.
0:09:21 > 0:09:28One problem about having a long burrow like this is that it can get very stuffy.
0:09:28 > 0:09:35The prairie-dog deals with that problem by building two differently-shaped entrances.
0:09:35 > 0:09:38One is low to the surface of the prairie
0:09:38 > 0:09:43and the other has this mud tower built around it.
0:09:43 > 0:09:48Wind blowing over the prairie moves faster a foot above ground
0:09:48 > 0:09:50than it does at ground level.
0:09:50 > 0:09:55So a breeze moving across here sucks stale air from the burrow.
0:09:55 > 0:09:58It's a home with air-conditioning.
0:09:58 > 0:10:03No matter how long the prairie-dog remains underground,
0:10:03 > 0:10:06the air of its home remains fresh.
0:10:09 > 0:10:14This refuge was not dug, it was woven.
0:10:14 > 0:10:17From silk.
0:10:23 > 0:10:28Only spiders and insects have the ability to produce silk,
0:10:28 > 0:10:32and this strange insect a web-spinner
0:10:32 > 0:10:37has spinnerets on the end of its forelegs, like boxing-gloves.
0:11:02 > 0:11:08Caterpillars have spinnerets just inside the mouth.
0:11:08 > 0:11:12The silk comes out in one continuous filament
0:11:12 > 0:11:17and a single moth caterpillar can produce a thread 3,000 ft long.
0:11:17 > 0:11:23This substance provides us with one of the most luxurious fabrics.
0:11:23 > 0:11:28The caterpillar uses it to build the protected cocoon
0:11:28 > 0:11:34within which it will transform itself into an adult winged moth.
0:11:44 > 0:11:49Tent caterpillars build co-operatively.
0:11:49 > 0:11:54Their mother laid a batch of three hundred or so eggs
0:11:54 > 0:11:59and now all the hatchlings are erecting a communal shelter.
0:12:05 > 0:12:09As the caterpillars grow in size, they need more space
0:12:09 > 0:12:14and they continually add new floors to their dwelling.
0:12:18 > 0:12:23Each tent acts rather like a greenhouse.
0:12:23 > 0:12:27The air trapped inside is quickly warmed by the sun
0:12:27 > 0:12:35so that early in the morning, the caterpillars are ready to set out to look for leaves
0:12:35 > 0:12:42just that little bit earlier than other species that might be competing with them.
0:12:56 > 0:13:03Silk is such a useful building material that others who can't make it steal it.
0:13:03 > 0:13:12A hermit humming-bird uses sticky spider silk to bind her nest to the edge of a leaf.
0:13:30 > 0:13:35Flying round and round, as only a humming-bird can,
0:13:35 > 0:13:38with a strand in her beak,
0:13:38 > 0:13:45she creates a suspended nest, sheltered from the rain beneath the roof of the leaf
0:13:45 > 0:13:50and more difficult for predators to reach than one on a branch.
0:13:50 > 0:13:55The Indian tailor-bird also uses silk,
0:13:55 > 0:13:58not to bind, but to stitch.
0:14:14 > 0:14:20She searches all the bushes around for her silk threads.
0:14:40 > 0:14:46With this spectacular feat of craftsmanship,
0:14:46 > 0:14:51she converts two floppy leaves into a single, firm cup.
0:15:01 > 0:15:03It may not LOOK strong,
0:15:03 > 0:15:09but it's quite secure enough to hold a lining of fibre and hair
0:15:09 > 0:15:15and mother and chicks sitting on top.
0:15:22 > 0:15:27Leaves form excellent protection from the rain.
0:15:27 > 0:15:32You need it nowhere more than here in a tropical rain forest.
0:15:32 > 0:15:36Many animals living here feed on fruit.
0:15:36 > 0:15:41If their shelters are permanent, like a cave or a hollow tree,
0:15:41 > 0:15:49they may have to travel long distances back and forth every day in order to find a fruiting tree.
0:15:49 > 0:15:51Temporary encampments are helpful.
0:15:51 > 0:15:57The creatures living under this leaf use it elegantly to this end.
0:15:57 > 0:16:06They cut through these side ribs so the leaf flops down to form a watertight tent. There they are!
0:16:06 > 0:16:12Tent-making bats, the size of golf-balls, and pure white,
0:16:12 > 0:16:17though the light filtering through the leaf makes them look green.
0:16:17 > 0:16:25They'll only use this shelter for a few nights, then off to another leaf near another fruiting tree.
0:16:25 > 0:16:31But you can use leaves in a more radical way to build a home.
0:16:31 > 0:16:35Weaver-birds are the great experts. It's the males who do the building.
0:16:35 > 0:16:41The first step is to tie a leaf strip onto a twig.
0:16:41 > 0:16:46It's not easy, for the fibre is very springy.
0:16:55 > 0:16:59The trick is to keep a firm hold on it with one foot,
0:16:59 > 0:17:04then you can tie the knot with your beak.
0:17:10 > 0:17:14It's a simple half-hitch, but a firm one,
0:17:14 > 0:17:19and all subsequent work will literally depend on it.
0:17:20 > 0:17:27Knotting takes practice, and this young bird is having some trouble.
0:17:29 > 0:17:32The next step is to weave a ring.
0:17:37 > 0:17:43But you can't do that until you've got the first knot right.
0:17:58 > 0:18:03The ring has got to be big enough to allow its maker to slip through.
0:18:03 > 0:18:08But not SO big that it will allow larger animals to do so.
0:18:08 > 0:18:14But it certainly mustn't be too small!
0:18:17 > 0:18:25The strips have to be fresh and supple, and the birds get supplies from a patch of grass nearby.
0:18:25 > 0:18:33They tear off strips by gripping the side of the grass blade close to the ground and then flying up.
0:18:35 > 0:18:41Over a thousand of these strips are needed for a single nest.
0:18:41 > 0:18:44Once the ring is complete and firm,
0:18:44 > 0:18:46work starts on the roof.
0:18:56 > 0:18:59The novice still has his problems.
0:19:04 > 0:19:10Their technique, in essence, is like that used by human weavers.
0:19:10 > 0:19:17A strip is threaded alternately above and below a series of strips that run at right angles to it.
0:19:17 > 0:19:25In the beak of a master craftsman this produces neat and beautiful results.
0:19:30 > 0:19:33In less skilful beaks,
0:19:33 > 0:19:38well...not so good, but he's learning.
0:19:49 > 0:19:54Very critical eyes are watching progress.
0:19:54 > 0:20:00A female selects her mate largely on his ability as a weaver.
0:20:00 > 0:20:06And he calls attention to it with his fluttering wings.
0:20:07 > 0:20:11But others have the same idea.
0:20:20 > 0:20:22She flies over to have a look.
0:20:25 > 0:20:30The novice is clearly being a little optimistic.
0:20:30 > 0:20:33No-one is taking any notice.
0:20:34 > 0:20:37Eventually, she makes her choice.
0:20:44 > 0:20:50This looks neat enough, but it's not yet won him a mate.
0:20:53 > 0:20:57But this bird, luckier or more skilful, has.
0:20:57 > 0:21:02And now he can get on with finishing the job.
0:21:08 > 0:21:13Th whole construction is completed by adding, with a looser weave,
0:21:13 > 0:21:16a long, downward-pointing entrance.
0:21:17 > 0:21:21This will deter unwelcome visitors.
0:21:25 > 0:21:30If, after a few days, the weaver hasn't attracted a mate,
0:21:30 > 0:21:32then all his work is wasted.
0:21:32 > 0:21:39For a female never chooses a nest that is so old it's turned brown.
0:21:39 > 0:21:41There's only one thing to be done.
0:21:41 > 0:21:47He'll have to start all over again, dismantling his first attempt.
0:21:47 > 0:21:49This is the only place he can build
0:21:49 > 0:21:54because all the rest of the sites are occupied,
0:21:54 > 0:21:59and dismantling it is almost as hard work as weaving it.
0:22:06 > 0:22:10On rocky cliffs like this,
0:22:10 > 0:22:17the problem is not so much shortage of sites for the nest, but of material with which to build it.
0:22:17 > 0:22:24Shags like to have something to cushion their eggs and stop them rolling about.
0:22:24 > 0:22:32But there's not much around, except for what the sea washes up. That's a very mixed bag indeed.
0:22:53 > 0:23:01Of course, there's an easier way of getting stuff than carrying it all the way from the seashore.
0:23:24 > 0:23:28But if you're caught redhanded there's big trouble!
0:23:49 > 0:23:54When material is in such short supply, almost anything will do.
0:24:02 > 0:24:10Even the beak and bones of another bird, a tern, or the dried corpse of a rabbit.
0:24:17 > 0:24:22There's no shortage of building material here.
0:24:28 > 0:24:32Particularly if you build in wood,
0:24:32 > 0:24:37which is the life-long preoccupation of this animal.
0:24:37 > 0:24:39It's a beaver.
0:25:17 > 0:25:22This is one of the most massive of all animal constructions.
0:25:22 > 0:25:29It's a dam that's blocked this valley and built up behind it a sizable lake.
0:25:29 > 0:25:37Its foundations are sticks that have been rammed vertically into the bed of the stream.
0:25:37 > 0:25:45Horizontal poles have been laid across those and then boulders dumped on to give the thing weight.
0:25:45 > 0:25:52The downstream side slopes gently, buttressed with poles. Upstream is more vertical, faced with mud.
0:25:52 > 0:25:57It was designed, built, maintained by a beaver family over decades.
0:25:57 > 0:26:01Passed from one generation to another.
0:26:01 > 0:26:07Such large properties need constant care and attention.
0:26:07 > 0:26:13Dams need a spillway to carry away the continual flow of the stream.
0:26:13 > 0:26:20After heavy rains, it has to be enlarged to allow rising water to escape before it bursts the dam.
0:26:20 > 0:26:26And when the flood subsides, the dam has to be built up again.
0:26:40 > 0:26:48The beavers have very clear ideas about the exact position for any one piece,
0:26:48 > 0:26:53and labour away until they get it just right.
0:26:53 > 0:26:58Large beams are needed for structural strength.
0:27:09 > 0:27:14Small twigs, leaves and mud are essential to plug the gaps.
0:27:28 > 0:27:32The purpose of all this labour is to create a lake.
0:27:32 > 0:27:36During the summer, they sink branches in it.
0:27:36 > 0:27:41In winter when the lake is frozen over,
0:27:41 > 0:27:48they will dive beneath the ice to retrieve the still-green leaves from cold storage.
0:27:48 > 0:27:53It has another purpose. It makes their home virtually impregnable.
0:28:01 > 0:28:07This is the lodge the family residence.
0:28:07 > 0:28:11There seems to be no way into it.
0:28:11 > 0:28:16That's because the entrance, in fact, is underwater, about here.
0:28:16 > 0:28:24So you have to be a skilled swimmer and an underwater diver to get into the residence.
0:28:24 > 0:28:28It's a pretty well burglar-proof home.
0:28:28 > 0:28:35Ingenious though the beavers are, they do little more than cut wood up into convenient lengths.
0:28:35 > 0:28:44Some animals have discovered how to process wood and turn it into an altogether more malleable material.
0:28:46 > 0:28:49Wasps chew up wood,
0:28:49 > 0:28:57mix it with their saliva, make it into a fine paste that dries into a light, strong material PAPER.
0:28:57 > 0:29:03The common European wasp produces a very high-quality paper,
0:29:03 > 0:29:07and, with it, builds nests of great perfection.
0:29:07 > 0:29:13Within these identical hexagonal cells, a huge workforce is raised
0:29:13 > 0:29:18to serve the queen and maintain the nest.
0:29:20 > 0:29:27This tiny Malaysian hover-wasp is one of the least ambitious wasp builders.
0:29:27 > 0:29:32Her nest of rather crumbly paper is just a few open cells on a stem.
0:29:32 > 0:29:37These are clearly vulnerable to the elements and predators,
0:29:37 > 0:29:43but she protects them from their main enemies ants
0:29:43 > 0:29:50by smearing the egg in each cell and ringing the stem with a sticky repellent that blocks access.
0:29:51 > 0:29:58This nest is suspended from the ceiling of a cave by a narrow paper stalk.
0:29:58 > 0:30:01It's well-protected from weather
0:30:01 > 0:30:08but the females guarding the open cells must be ever-watchful for raiders.
0:30:17 > 0:30:24Other species protect their young by building a paper wall around the cells.
0:30:24 > 0:30:31They often pattern it by using different coloured materials to give some degree of camouflage.
0:30:31 > 0:30:37With only a single entrance, the nest is readily defendable.
0:30:37 > 0:30:40But some predators are unstoppable.
0:30:40 > 0:30:45This nest has been wrecked and its young stolen by a giant hornet.
0:30:45 > 0:30:50It's a merciless eater of larvae of other species. Few nests are safe.
0:30:50 > 0:30:57Bees construct their defences with a substance no other animal produces wax.
0:30:57 > 0:31:03Workers secrete it from abdominal glands. It is honey, combined with fat.
0:31:03 > 0:31:11Tropical stingless bees mix it with resin and build entrance tubes to their nest within the tree-trunk.
0:31:11 > 0:31:15These tubes often take bizarre shapes.
0:31:15 > 0:31:21All have a narrow entrance, often flared into a landing platform,
0:31:21 > 0:31:26which is heavily guarded by platoons of sentries
0:31:26 > 0:31:29who vet every arrival.
0:31:31 > 0:31:33Inside, the workers labour,
0:31:33 > 0:31:40building a maze of interconnecting struts and plates to support the brood cones.
0:31:47 > 0:31:52The resin stiffens the waxy structures
0:31:52 > 0:31:55and antibiotic chemicals within it
0:31:55 > 0:31:57reduce the risks of infection.
0:32:01 > 0:32:05Those cells that will contain young
0:32:05 > 0:32:10are first three-quarters filled with pollen.
0:32:10 > 0:32:14Then the huge queen comes over to inspect them.
0:32:18 > 0:32:26As soon as the cell's provisioning is complete, the queen drops an egg into it.
0:32:26 > 0:32:31Immediately, one of the workers seals off the top with wax.
0:32:50 > 0:32:57In a separate part of the nest, there are special pots for storing honey.
0:32:57 > 0:33:00This is why they must use wax.
0:33:00 > 0:33:03Paper cells couldn't hold liquid.
0:33:03 > 0:33:06They will be filled to the brim,
0:33:06 > 0:33:13for their contents are the reserves for the times when there's little or no food to be found outside.
0:33:13 > 0:33:19Wax IS a superb building material, but very expensive to produce.
0:33:19 > 0:33:23MUD is much cheaper!
0:33:35 > 0:33:41These pea-sized vessels are the work of another kind of wasp.
0:33:41 > 0:33:43A potter wasp.
0:33:50 > 0:33:55Once again, saliva is an important ingredient.
0:33:55 > 0:34:00It prevents the mud from crumbling when it dries.
0:34:00 > 0:34:07With jaws scissoring away on the inside, to keep the mud properly mixed and fluid,
0:34:07 > 0:34:12and front legs checking the thickness of the wall on the other,
0:34:12 > 0:34:18she lays the mud round in a strip, using a technique potters call coiling.
0:34:18 > 0:34:26When the main body of the pot is finished, this greatly-accomplished potter brings another ball of mud
0:34:26 > 0:34:32and adds a final and most elegant flourish.
0:35:13 > 0:35:15In goes an egg.
0:35:19 > 0:35:22Now the cells must be provisioned.
0:35:22 > 0:35:27A potter wasp doesn't feed her larvae on chewed bodies,
0:35:27 > 0:35:30nor does she supply honey.
0:35:30 > 0:35:36She gives it living food a caterpillar, paralysed by her sting.
0:35:36 > 0:35:42The lip, built so carefully around the entrance, helps to guide it in.
0:35:47 > 0:35:53The pot mouth is then sealed with a clay pellet, and the lip removed.
0:35:53 > 0:35:58The larva, having eaten its caterpillar, and become an adult,
0:35:58 > 0:36:04emerges by breaking through the pot's side. The pots survive for several years.
0:36:07 > 0:36:09These much bigger mud constructions
0:36:09 > 0:36:15were built by cliff swallows in the American Midwest.
0:36:15 > 0:36:21Protected from winter rain, they too may last for several years.
0:36:21 > 0:36:25Each spring, the birds fly up from Argentina.
0:36:25 > 0:36:33They arrive in a flock and, as a flock, inspect the old tenements they occupied last year.
0:36:46 > 0:36:51Their favourite building sites are beneath natural overhangs.
0:36:51 > 0:36:56The trouble is, there are not many of them,
0:36:56 > 0:37:02so they readily take advantage of a man-made one, if they can find it.
0:37:02 > 0:37:05Old buildings have disadvantages.
0:37:05 > 0:37:13They can be infested with vermin, optimistically waiting to parasitise the new occupants.
0:37:13 > 0:37:17The flock as a whole decide whether to reoccupy a particular site.
0:37:17 > 0:37:20Once they've decided, each pair claims a nest and smartens it up.
0:37:54 > 0:37:56To get the mud as it wants it,
0:37:56 > 0:38:02a bird may have to gather some wet material from the water's edge
0:38:02 > 0:38:07and then mix it in its mouth with drier mud from farther back.
0:38:48 > 0:38:53The consistency of the mud is crucial.
0:38:53 > 0:38:55If it's too dry, it won't stick.
0:38:55 > 0:38:59If too sloppy, it's hard to handle.
0:38:59 > 0:39:04And working upside-down with it can be a real problem!
0:39:17 > 0:39:24When the chicks hatch, the price of using old buildings may have to be paid.
0:39:24 > 0:39:30These, whose parents chose their home wisely, are fit enough.
0:39:30 > 0:39:37But in other nests the parasites have had a feast and are proliferating.
0:39:37 > 0:39:41These young swallows will probably not survive.
0:39:47 > 0:39:52But most do. Their parents succeeded in raising them,
0:39:52 > 0:40:00while, at the same time, spending the minimum of their energy and time on the labour of building.
0:40:01 > 0:40:08The most impressive of all animal homes are built by the smallest of all labourers.
0:40:08 > 0:40:11Termites.
0:40:11 > 0:40:16They have, to perfection, ALL the qualities you'd want from a home.
0:40:16 > 0:40:24Security, heating, air-conditioning and self-contained nurseries, gardens and sanitation systems.
0:40:24 > 0:40:31Termites of many different species build their fortresses all over the Tropics.
0:40:31 > 0:40:36This kind, in northern Australia, builds a particularly strange one.
0:40:36 > 0:40:44It has a broad flank, a narrow edge and is placed so the flank catches the full strength of morning sun,
0:40:44 > 0:40:46so it's almost painful to touch.
0:40:46 > 0:40:49But, on the other side, it's cool.
0:40:49 > 0:40:54What is more, all the hills here are placed in this way,
0:40:54 > 0:40:59with their narrow edges pointing north and south,
0:40:59 > 0:41:03which is why they're called magnetic termites.
0:41:03 > 0:41:08This orientation has nothing to do with magnetism,
0:41:08 > 0:41:10and everything to do with heat.
0:41:10 > 0:41:15Termites don't like the cold and are easily overheated.
0:41:15 > 0:41:18Here, they avoid both disasters.
0:41:18 > 0:41:24Morning finds them on the eastern side, warmed by the rising sun.
0:41:24 > 0:41:28By midday, the danger is overheating.
0:41:28 > 0:41:34But now, only the knife edge along the top catches the sun.
0:41:36 > 0:41:44Most termites deal with temperature extremes by retreating below ground where conditions are very stable.
0:41:44 > 0:41:50But these termites live in places that are flooded each year
0:41:50 > 0:41:57and unless they build homes of this particular shape they'd overheat, be chilled or drown.
0:41:57 > 0:42:05But it's to West Africa that you must go if you want to see the ultimate in termite architecture.
0:42:05 > 0:42:12The biggest, the most complex and the most subtly sophisticated of all their buildings.
0:42:12 > 0:42:17This immense fortress, towering fifteen feet above me,
0:42:17 > 0:42:20is the work of a Nigerian termite.
0:42:20 > 0:42:23But what could be in those towers?
0:42:23 > 0:42:28They sound...hollow. There's an easy way to find out.
0:42:32 > 0:42:34Very little.
0:42:34 > 0:42:39This long chimney is virtually empty.
0:42:39 > 0:42:47To find the inhabitants, you have to penetrate much further into the nest.
0:43:10 > 0:43:14The workers are continually building,
0:43:14 > 0:43:19constructing magnificent arches, vaults and corridors.
0:43:27 > 0:43:30Among them are the bigger soldiers,
0:43:30 > 0:43:37their huge heads filled with the muscles needed to power their great jaws.
0:43:39 > 0:43:45Each worker positions a mud pellet as demanded by a master plan,
0:43:45 > 0:43:50though how they are able to do so we don't begin to understand.
0:43:50 > 0:43:57They store their food, dead wood, in special chambers throughout the nest.
0:43:57 > 0:44:03Wood is very hard to digest but they extract the most from it by first eating it
0:44:03 > 0:44:10and then cultivating a fungus on their dung which extracts more of the nutrient.
0:44:10 > 0:44:18They then eat the fungus. It grows only inside termite hills, where the temperature is exactly right.
0:44:18 > 0:44:22In the very heart of the fortress,
0:44:22 > 0:44:24lives the queen.
0:44:30 > 0:44:33She produces a thousand eggs a day
0:44:33 > 0:44:38to provide fresh recruits for the teams of gardeners and masons
0:44:38 > 0:44:41and the ranks of the army.
0:44:45 > 0:44:48She resides in a special chamber
0:44:48 > 0:44:55which the workers renovate and adapt to accommodate her growing bulk.
0:44:55 > 0:45:03After a year or two, she is, in effect, a prisoner as she is too big to squeeze through corridors.
0:45:03 > 0:45:05But that is of no consequence.
0:45:05 > 0:45:13She's so bloated with egg-producing machinery that she couldn't move, even if she wanted to.
0:45:13 > 0:45:21Her eggs, as she produces them, are carried away to nurseries by the attentive, indefatigable workers.
0:45:21 > 0:45:25There are 1.5 million insects in this one colony.
0:45:25 > 0:45:33They and their gardens generate a lot of heat. Within this enclosed building the air could become foul.
0:45:33 > 0:45:40The fungus and colony will die if the temperature varies by over 2 degrees from 31 degrees Centigrade.
0:45:40 > 0:45:45But the colony has a solution, and it's an architectural one.
0:45:48 > 0:45:53This, six feet beneath the surface of the earth,
0:45:53 > 0:45:56is the cellar of the colony.
0:45:56 > 0:46:02Its floor is studded with shafts that go down 12, 14 feet,
0:46:02 > 0:46:09down to the water table, where the worker termites can gather moist mud to carry on their building.
0:46:09 > 0:46:17And its ceiling is a great plate which carries the entire weight of the colony.
0:46:17 > 0:46:24But on its underside is what I think is the most remarkable animal structure I've ever seen.
0:46:24 > 0:46:27Lines of concentric veins.
0:46:27 > 0:46:32They are made of mud and absorb moisture from the colony above.
0:46:32 > 0:46:38As it evaporates, it leaves this incrustation of white salts.
0:46:38 > 0:46:43But, more important than that, as it evaporates, it cools
0:46:43 > 0:46:48so that this, the cellar, is much the coolest part of the colony.
0:46:48 > 0:46:54And it's this that drives the air-conditioning.
0:46:54 > 0:47:01The air, continuously heated by all the activity in the middle of the building,
0:47:01 > 0:47:04rises into the upper storeys.
0:47:04 > 0:47:12This basement, many degrees colder, draws down the stale, warm air from the colony above,
0:47:12 > 0:47:17down long chimneys which go right round the edge of the cellar.
0:47:17 > 0:47:24As it does so, there's a seepage of gas through porous dimples in the walls.
0:47:24 > 0:47:28Oxygen flows in, carbon dioxide out.
0:47:28 > 0:47:36So these spires and turrets are key elements in an air-conditioning system of a near-perfect mansion
0:47:36 > 0:47:44that has stout walls to protect its inhabitants from the elements and their enemies,
0:47:44 > 0:47:51deep dungeons where they can gather moisture, space inside for barns where they can store their food,
0:47:51 > 0:47:54gardens where they can grow crops.
0:47:54 > 0:48:02And yet all this was built by tiny insects with minute brains, working in total co-operation, in darkness.
0:48:02 > 0:48:09We might like to think that we are the most accomplished architects that the world has ever seen,
0:48:09 > 0:48:14but built in human terms, with each worker termite the size of me, this would stand a mile high.
0:48:14 > 0:48:17And we haven't done that yet.
0:49:01 > 0:49:05Subtitles by Red Bee Media Ltd