Original subtitles

20,000 years ago, this cave in Wales was home for human beings.

We know because their bones have been found here.

And it's a pretty good home, too.

Here you're out of the wind and the rain, you can make a fire to keep warm,

and you can defend yourself against enemies,

whether they're other human beings or wild animals like bears and wolves.

In short, here you've got some control over your surroundings,

and you can make yourself comfortable.

Animals, of course, find homes for themselves for very much the same sort of reasons.

Some use ready-made ones like this cave. Bats, for example.

0thers build the most ingenious and elaborate structures

to shield themselves from a world that can be so very hostile.

A rocky coast is one of the most difficult of all places in which to live.

Continuously pounded by waves, submerged twice every 24 hours,

and twice exposed to the air.

To survive, small molluscs secrete stout, almost unbreakable shells.

And when they're dead and gone, their vacated homes are much sought-after.

And in this pool, cut off by the falling tide,

there's a large housing market full of anxious tenants.

This could be just what they're waiting for.

Hermit crabs have found the easiest solution to the housing problem -

using somebody else's.

There is a major difficulty -

as a householder grows, he needs a bigger house. This might be one.

A check has to be made on the dimensions.

Too big is almost as bad as too small,

because then enemies could pull the occupier out.

It's just the thing.

Now a slightly smaller home is on the market.

And another one, smaller still.

And another hopeful tenant.

Nobody wants to vacate a perfect residence,

but they can be forced to leave by strong-arm tactics.

Instead of stealing a hole for yourself, you could dig one.

Rosy bee-eaters, like all their family, do just that.

They're troubled, not with a shortage of houses, but of building sites.

It's the dry season and this entire flock has chosen one sandbank

in the middle of the Niger river. It is, indeed, a very desirable site.

For one thing, insects hatching from the river provide a lot of food.

And, being surrounded by water, it's protected from land predators.

Most importantly, its sand, recently exposed by the fall in water,

So rosy bee-eaters come from many miles around to nest here.

That means there is great overcrowding.

0ne benefit from such numbers is that those who haven't got their heads down digging

can keep an eye out for danger.

There are, inevitably, quarrels.

A half-dug hole represents a lot of work and a bird will steal another's if it can.

They work in pairs - one does the digging,

the other chases away strangers who might get in the way.

It's hot work, too,

but with the river close by it's easy to take a cool, refreshing dip.

In a month or so, the breeding season will be over,

the river will rise again and the holes will be flooded,

but by then the birds will have flown and won't need a home for another year.

But some animals need a hole as a refuge throughout their lives.

The open grasslands of the American west are very exposed places to live.

A small animal sitting here is very vulnerable.

So prairie dogs dig for protection.

And the prairie dog community, like the bee-eater colony, has its alarm system.

(CHIRPING)

Below, there's a warm, safe refuge.

The animals are so successful that they can proliferate in huge numbers

and form great settlements with hundreds of tunnels and entrances.

I'm in the middle of one of these towns,

and there are a couple of dozen burrows within a few yards of me.

Why does the prairie dog build so many elaborate burrows, when digging is very hard work?

Well, there's one way to get a clue.

This is a candle which produces a perfectly harmless smoke.

If I light it...

..and put it in the burrow, we can see what happens.

The smoke doesn't all just blow away, but a wisp of it gets carried down along the tunnel

and eventually emerges at another entrance mound 20 yards away.

So these two holes are connected.

It's obviously useful to have an escape hole if you're pursued by, say, a wild ferret.

But there's more to it than that.

0ne of the problems about having a long burrow like this

is that it can get very stuffy.

The prairie dog deals with that problem

by building two differently-shaped entrances.

0ne is low to the surface of the prairie,

and the other has this mud tower built around it.

Wind blowing over the prairie moves faster a foot above ground

than it does at ground level.

So a breeze moving across this entrance will suck out the stale air from the burrow.

The prairie dog, in fact, has a home with air-conditioning!

So no matter how long the prairie dog remains underground,

the air of its home remains fresh.

This refuge was not dug.

It was woven from silk.

0nly spiders and insects have the ability to produce silk.

This strange insect, a web-spinner,

has spinnerets on the end of its forelegs like boxing gloves.

Caterpillars have spinnerets just inside the mouth.

The silk comes out in one continuous filament

and a single moth caterpillar can produce a thread 3,000 feet long.

This marvellous substance still provides human beings

with one of the most luxurious of all their fabrics. The caterpillar uses it

to build the protective cocoon within which it will transform itself

into an adult winged moth.

Tent caterpillars build co-operatively.

Their mother laid a batch of 300 or so eggs

and now all the hatchlings are erecting a communal shelter.

As the caterpillars grow in size, they need more space.

They continually add new floors to their dwelling.

Each tent acts rather like a greenhouse.

The air trapped inside is quickly warmed by the sun so that, early in the morning,

the caterpillars are ready to set out to look for leaves a little bit earlier

than other species that might be competing with them.

Silk is such a useful building material

that others who can't make it...steal it.

A hermit hummingbird uses sticky spider silk

to bind her nest to the edge of a leaf.

Flying round as only a hummingbird can, with a strand in her beak,

she creates a suspended nest, sheltered from the rain beneath the roof of the leaf

and far more difficult for predators to find

than one placed on a branch or on the ground.

The Indian tailor bird also uses silk,

not to bind but to stitch.

She searches all the bushes around for her silk threads.

With this spectacular feat of craftsmanship,

she converts two floppy leaves into a single firm cup.

It may not look strong,

but it's quite secure enough to hold a lining of fibre and hair,

and mother and chicks sitting on top.

Leaves form excellent protection from the rain.

There's nowhere you need it more than the tropical rainforest.

Many animals that live here feed on fruit.

If their shelters are permanent ones, like a cave or a hollow tree,

they may have to travel long distances every day in order to find a fruiting tree.

It's much more convenient to have temporary encampments,

and no creature uses leaves more elegantly for that purpose

than those living under this leaf.

They've cut through these side ribs so that the leaf flops down

and forms a perfect watertight tent.

And there they are.

Tent-making bats - the size of golf balls and pure white,

though the light filtering through the leaf makes them look green.

They'll only use this shelter for a few nights,

then they'll be off to another leaf near another fruiting tree.

But you can use leaves in a much more radical way than this to build a home.

Weaver birds are the great experts.

It's the males who do the building.

The first step is to tie a leaf strip onto a twig.

It's not easy, for the fibre is very springy.

The trick is to keep a firm hold on it with one foot.

Then you can tie the knot with your beak.

It's a simple half hitch but a firm one,

and all subsequent work will, literally, depend on it.

Knotting takes practice, and this young bird is having a little trouble.

The next step is to weave a ring.

But you can't do that until you've got the first knot right.

The ring has got to be big enough to allow its maker to slip through

and not so big that it will allow larger animals to do so.

But it certainly mustn't be too small.

The strips must be fresh and supple,

and the birds get supplies from a patch of grass nearby.

They tear off the strips by gripping the side of the grass blade close to the ground

and then simply flying straight up.

0ver a thousand of these strips are needed for a single nest.

0nce the ring is complete and firm, work starts on the roof.

The novice still has his problems.

Their technique, in essence, is the same as that of human weavers.

A strip is threaded alternately above and below other strips that run at right angles to it.

In the beak of a master craftsman, this produces neat and beautiful results.

In less skilful beaks...

Well, not so good. But he's learning.

Very critical eyes are watching progress.

A female selects her mate largely on his ability as a weaver,

and he calls attention to it with his fluttering wings.

But others have the same idea.

She flies over to have a look.

The novice is being a little optimistic.

No one is taking any notice.

And eventually she makes her choice.

This looks neat enough, but it's not yet won him a mate.

But this bird, luckier or more skilful, has,

and now he can get on with finishing the job.

The whole construction is completed by adding with a looser weave

a long, downward-pointing entrance tube.

This will deter unwelcome visitors.

If, after a few days, a weaver hasn't managed to attract a partner,

all his work is wasted.

For a female never chooses a nest that's so old it's turned brown.

There's only one thing to be done.

He'll have to start all over again.

That means dismantling his first attempt.

This is the only place he can build, as all the rest of the sites are occupied,

and dismantling it is almost as hard work as weaving it.

0n rocky cliffs like this, the problem is not so much shortage of sites for a nest

but of material with which to build it.

Shags like to cushion their breakable eggs to stop them rolling about.

But there's only what the sea washes up, and that's a very mixed bag indeed.

There's an easier way of getting stuff than carrying it all the way from the seashore.

But if you're caught red-handed, there's big trouble.

When material is in such short supply, almost anything will do.

Even the beak and bones of another bird, a tern,

or the dried corpse of a rabbit.

There's no shortage of building material here...

..particularly if you build in wood,

which is the lifelong preoccupation of this animal.

It's a beaver.

This is one of the most massive of all animal constructions.

It's a dam that's blocked this valley and built up behind it a sizeable lake.

Its foundations are sticks that have been rammed vertically into the bed of the stream.

Horizontal poles have been laid across those, then boulders are dumped on it to give weight.

The downstream side slopes gently and is buttressed with poles.

The upstream is more vertical and faced with mud.

It was designed, built and maintained by a family of beavers over decades,

and handed down through the generations.

If ever there was an ancestral pile, this is it!

Such large properties need constant care and attention.

Every dam has to have a spillway to carry away the flow of the stream.

After heavy rains, it has to be enlarged

to allow the rising water to escape before it bursts the dam.

When the flood subsides, the dam has to be built up again.

The beavers have very clear ideas about the exact position for any one piece

and labour away until they get it just right.

Large beams are needed for structural strength.

Small twigs, leaves and mud are essential to plug the gaps.

The purpose of all this labour is to create a lake.

In summer, they sink branches in it.

In winter, when the lake is frozen over, they dive beneath the ice

to retrieve the still green leaves from cold storage.

But it has another purpose, too: it makes their home virtually impregnable.

This...is the lodge,

the family residence.

There seems to be no way into it.

That's because the entrance, in fact, is underwater, just about here.

So you have to be a skilled swimmer and underwater diver to get into the residence.

In fact, it's a pretty well burglar-proof home.

Impressive though it is, and ingenious though the beavers are in utilising wood,

they do little more than cut it up into convenient lengths.

However, there are some animals that can process wood

and turn it into an altogether more malleable material.

Wasps chew up wood,

mix it with their saliva and make it into a fine paste,

which dries into a material that is both lightweight and strong - paper.

The common European wasp produces a very high-quality paper,

and with it builds nests of great perfection.

Within these identical hexagonal cells,

a huge workforce is raised to serve the queen and maintain the nest.

This tiny Malaysian hover wasp is one of the least ambitious wasp builders.

Her nest of rather crumbly paper is just a few open cells on a stem.

These are clearly vulnerable to the elements and predators,

but she protects them from their main enemies, ants, by smearing the egg in each cell

and ringing the stem with a sticky repellent that blocks access all round.

This nest is suspended from the ceiling of a cave by a narrow paper stalk.

It's well protected from the weather,

but the females guarding the open cells must be ever-watchful for raiders.

0ther species protect their young by building a paper wall around the cells.

They often pattern it by using different coloured materials for camouflage.

With only a single entrance, the nest is readily defendable.

But some predators are unstoppable.

This nest has been wrecked and its young stolen by another member of the wasp family,

a giant hornet. This bandit is a merciless eater of the larvae of other species

and few nests are safe from it.

Bees construct their defences with a substance no other animal produces - wax.

They secrete it from abdomen glands

and derive it from honey combined with fat.

Tropical stingless bees mix it with resin

and build entrance tubes to their nests within tree trunks.

These tubes often take bizarre shapes.

But they all have a narrow entrance, often flared into a landing platform,

which is heavily guarded by platoons of sentries who vet every arrival.

Inside, the workers labour, building a maze of interconnecting struts and plates

to support the brood combs.

The resin stiffens the waxy structures

and antibiotic chemicals within it reduce the risks of infection.

Those cells that will contain young are first three-quarters filled with pollen.

Then the huge queen comes over to inspect them.

As soon as a cell's provisioning is complete, the queen drops an egg into it.

Immediately, one of the workers seals off the top with wax.

In a separate part of the nest, there are special pots for storing honey.

This is why they must use wax. Paper cells couldn't hold liquid.

They will be filled to the brim, for they are the reserves for times

when there's little or no food to be found outside.

Wax is certainly a superb building material,

malleable, strong and capable of holding liquids,

but it's very expensive to produce.

Mud is much cheaper.

These pea-sized vessels are the work of another kind of wasp -

a potter wasp.

0nce again, saliva is an important ingredient.

It prevents the mud from crumbling when it dries.

With jaws scissoring away on the inside to keep the mud properly mixed and fluid,

and front legs checking the wall's thickness,

she lays the mud round and round in a strip,

using a technique human potters call coiling.

When the main body of the pot is finished,

this greatly accomplished potter brings another ball of mud

and adds a final and most elegant flourish.

In goes an egg.

Now the cells must be provisioned.

A potter wasp doesn't feed her larvae on chewed bodies or honey.

She gives it living food -

a caterpillar, paralysed by her sting.

The lip, built so carefully around the entrance, helps to guide it in.

The mouth of the pot will be sealed with a clay pellet and the lip removed.

The larva eats its caterpillar, turns into an adult,

and emerges by breaking through the side of the pot.

Although abandoned, the tough pots survive for several years.

These much bigger mud constructions were built by cliff swallows in the American mid-west.

Protected from winter rain, they too may last for several years.

Each spring, the birds fly up from Argentina.

They arrive in a flock and together, as a flock, inspect the old tenements

they occupied last year.

Their favoured building sites are beneath natural overhangs.

The trouble is, there's not many of them,

so they readily take advantage of a man-made one.

But, of course, old buildings do have their disadvantages.

They can be infested with vermin,

optimistically waiting to parasitize the new occupants.

The decision on whether to re-occupy a site is taken by the flock as a whole.

0nce they've made it, each pair claims a nest and starts smartening it up.

(CH0RUS 0F BIRD CALLS)

To get the mud as it wants it,

a bird may have to gather some really wet material from the water's edge

and then mix it in its mouth with drier mud from farther back.

The consistency of the mud is crucial.

If it's too dry, it won't stick, but if it's too sloppy, it's very difficult to handle.

And working upside down with it can be a real problem.

When the chicks hatch, the price of using old buildings may have to be paid.

These, whose parents chose their home wisely, are fit enough...

..but in other nests the parasites have had a feast and are proliferating.

These young swallows will probably not survive.

But most do. Their parents succeeded in raising them

while spending the minimum of their energy and time on the labour of building.

The most impressive of all animal homes are built by the smallest of all labourers.

Termites. They have, to perfection, all the qualities you could want from a home.

Security, heating, air conditioning and self-contained nurseries, gardens

and sanitation systems.

Termites of many different species build their fortresses all over the tropics,

but this kind in Northern Australia builds a particularly strange one.

It has a very broad flank, but a very narrow edge,

and it's so placed that the flank catches the full strength of the early morning sun

so that now it's almost painful to touch.

But...

..on the other side, in the shade, it's quite cool.

What is more, all the hills here are placed in this way,

with their narrow edges pointing north and south,

which is why they are called magnetic termites.

But, in fact, this orientation has got nothing to do with magnetism

and everything to do with heat.

Termites don't like the cold and are easily overheated.

And by building their hills in this way, they manage to avoid both those disasters.

In the morning, the termites move to the eastern side, which is warmed by the rising sun.

By midday, the danger is overheating,

but now only the knife edge along the top catches the sun.

(THUNDER)

Most termites deal with temperature extremes by retreating below ground

where conditions are very stable, but these ones live in places that are flooded each year

so they have to remain high in their mansions,

and unless they build homes of this particular shape, they would either overheat,

be chilled or drown.

But it's to West Africa you must go

if you want to see the ultimate in termite architecture,

the biggest, the most complex and most subtly sophisticated

of all their buildings.

This immense fortress, towering 15 feet above me,

is the work of a Nigerian termite.

But what could be in these towers? They sound hollow...

There's an easy way to find out.

Very little. This long chimney is virtually empty.

To find the inhabitants, you have to penetrate much further into the nest.

The workers are continually building, constructing magnificent arches,

vaults and corridors.

Among them are the bigger soldiers,

their huge heads filled with the muscles needed to power their great jaws.

Each worker places its pellet of mud in a position demanded by a master plan.

How they're able to do so, we don't begin to understand.

They store their food - dead wood - in special chambers throughout the nest.

Wood is very hard to digest, but they extract the most from it

by first eating it and then cultivating a fungus on their dung,

which extracts more of the nutriment.

They then eat the fungus.

This fungus grows nowhere else but inside termite hills,

where the temperature is exactly right for it.

In the very heart of the fortress lives the queen.

She produces a thousand eggs a day,

to provide fresh recruits for the teams of gardeners and masons

and the ranks of the army.

She resides in a special chamber which the workers renovate and adapt

to accommodate her growing bulk.

After a year or two she is, in effect, a prisoner,

for she's far too big to squeeze through the corridors of her residence.

But that is of no consequence.

She's so bloated with egg-producing that she couldn't move even if she wanted to.

And her eggs, as she produces them,

are carried away to the nurseries by the attentive, indefatigable workers.

There are a million and a half insects in this one colony.

They and their gardens generate a lot of heat.

Within this enclosed building the air could easily become foul and hot.

The fungus and therefore the colony itself would die

if the temperature varies more than two degrees from 31 degrees centigrade.

But the colony has a solution, and it's an architectural one.

This...six feet beneath the surface of the earth,

is the cellar of the colony.

Its floor is studded with shafts that go down 12-14 feet,

down to the water table, where worker termites can gather moist mud to carry on their building.

And its ceiling is a great plate

which carries the entire weight of the colony.

But on its underside is what I think is

really the most remarkable animal structure I've ever seen.

Lines of concentric veins.

They are made of mud and absorb moisture from the colony above,

and, as it evaporates, it leaves this encrustation of white salts on them.

But more important than that, as it evaporates, it cools,

so that this, the cellar, is much the coolest part of the colony.

And it's this that drives the air-conditioning.

The air, heated by all the activity in the middle of the building,

rises up into the upper storeys.

But this basement, thanks to these veins, is many degrees colder.

It draws down the stale warm air from the colony above,

down long chimneys which go right round the edge of the cellar.

As it does so, there's a seepage of gas

through porous dimples in the walls.

0xygen flows in and carbon dioxide out,

so that the mixture approximates to fresh air.

So these spires and turrets are key elements

in an air-conditioning system of a near-perfect mansion

that has stout walls to protect its inhabitants from the elements and from their enemies,

deep dungeons where they can gather moisture,

space inside for barns to store their food,

and gardens where they grow their crops.

And yet all this was built by tiny insects with minute brains,

working in total cooperation in the complete darkness.

We might like to think that we are the most accomplished architects in the world,

but if this was built in human terms with every worker termite the size of me,

then it would stand a mile high.

And we haven't done that yet!

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