You might think that the lights above my head are stars,
but they can't be because I'm in a cave.
Each one of those tiny lights
is produced by the larva of a small insect called a fungus gnat
as a way of attracting its prey.
The result is a display
that must surely rank as one of the most magical illuminations
in the whole of the natural world.
But shine a light sideways across the ceiling...
then you can see that each little blue lamp
is surrounded by a curtain of glistening, beaded filaments,
curtains that are invisible at other times.
They're lures, and they can be lethal.
Insects, hatching in the water below,
fly up towards these tiny lights.
And here, they are trapped by threads of this extraordinary material
that is the unique possession of the invertebrates.
This is silk.
This astonishing cave is near the small town of Waitomo in New Zealand.
Each light comes from the back end of a larva
as it lies in a transparent tube of mucus
slung from the ceiling by silken threads.
And it's produced by phosphorescent chemicals
in a special compartment opening from the side of its intestine.
The silk comes from glands at the other end,
inside the larva's mouth.
The larvae move around.
They fix a silk thread to the rock
and slowly inch their way over the ceiling along a network of threads.
Arriving in a new position, the larva produces more silk,
but this time it allows the thread to dangle downwards.
As each section emerges from its mouth,
the larva, with a gulp, adds a blob of glue.
Eventually, a single strand may be a metre long.
There can be several hundred larvae in a single square metre of cave roof
and they all work hard producing strand after strand.
The more they make, the greater their chances of catching something.
Below, mayfly are hatching from the stream that runs through the cave.
They've been carried in here by the current from outside as larvae.
Now, they must look for a mate.
But they find the blue lights above irresistible.
And they're caught.
The fungus gnat detects its victim's struggles
from lines that run between the threads.
Having made a capture, it turns off its light.
That saves energy.
Laboriously, it makes its way across to the thread from which the vibrations are coming.
It hauls it up and eats what's hanging on the end.
It also eats the filament.
That saves silk.
This wonderful hunting technique
is just one of an enormous number of varied ways in which animals use silk.
Silk really is an extraordinary material.
It's stronger than a steel thread of the same diameter
and, unlike steel, it's elastic.
It can stretch up to twice its length.
The inhabitants of the undergrowth
developed the ability to produce this marvellous material
very early in their evolutionary history,
over 300 million years ago.
At first, it seems they used it in a very simple way, as an adhesive.
And lacewings still do.
Though for them, it's an adhesive with a difference.
This is a female.
She is looking for a safe place to deposit her eggs.
Silk will provide it
but not exactly in the way you might think.
She will lay up to 300 eggs, almost twice her body weight.
However, there are plenty of other insects around that will eat those eggs
if they find them.
So she doesn't glue them directly on the plant stem.
First, she produces a little drop of sticky silk
and then, at the end of that, the egg.
It's suspended safely in midair.
The silk is produced by glands in her abdomen in liquid form.
It's the very act of pulling it out that changes it from liquid to solid.
And that is true for all invertebrate silk.
She will lay up to 30 eggs a day,
each on its own stalk.
That silken thread is so incredibly fine
that insect predators like these ants walk right by the eggs
without realising that there is a tasty meal within millimetres of them.
So, despite regular ant patrols in search of food,
the lacewing's eggs remain undiscovered.
After three days, they begin to hatch.
Now, at least, if danger threatens,
her offspring will be able to help themselves
by running away.
In the lush rainforest of Trinidad,
you can find sheets of silk wrapped around trees.
Here it's also used for protection
but by a quite different creature in a quite different way.
The manufacturers, a little-known group of insects called web spinners,
live beneath.
They graze on algae and lichens hidden by the sheets immediately above them.
They produce their silk not from their abdomens or their mouths,
but from glands in their forelegs.
Each leg has about 150 tiny silk ejectors
which, between them, create a thin silken tissue.
An ant in search of prey
strolls over the surface of the web spinners' marquee,
but the silk sheet, thin though it is, is impervious to smells
and as long as the web spinner doesn't move too much,
the ant will be unaware of it, a millimetre beneath its feet.
(THUNDER RUMBLING)
And the tent, like any decent tent, is waterproof.
In fact, the tent is so waterproof
that the web spinners beneath are in danger of not getting enough water.
So after the storm is over,
they bite holes in places where a little rain has accumulated
and drink the tiny puddle dry.
Of course, the hole has to be repaired after a drink,
but that's easy enough when you have an almost limitless supply of silk in your legs.
Of all the inhabitants of the undergrowth that have exploited silk,
none have done so with more variety and skill than the spiders.
And this is almost certainly the first way in which they used it.
Here on this bank in the Malaysian rainforest,
there are strands of silk radiating from this little patch in the middle.
Watch what happens if I touch one of them.
(EXCLAIMING)
I can't help jumping.
That was a trapdoor spider
and it was so swift that you hardly saw it.
Let's see if I can get it to do it again.
The spider, when hungry, sits close behind the trapdoor.
The strands outside are all connected to a silken collar
that surrounds the mouth of the hole.
Each of her feet is in contact with it.
The slightest twitch is enough to tell her that something's moving around outside.
A single twitch will produce no reaction.
That could be caused by a falling leaf or a drop of water,
but a repeated vibration, especially if it moves from one strand to another,
could mean prey.
Prey like this beetle.
Got it!
Now, it will kill it.
This is the most ancient of living spiders.
The fact that it has uniquely segmented plates on its back
shows that it's more closely related than any other
to those pioneer hunters, the scorpions.
And, like them, it has a powerful venom.
Once bitten, its victim has little chance.
Trip lines were one of the earliest of the spiders' hunting techniques,
but other, later spiders,
used silk to build much more sophisticated structures.
Orb webs are so familiar to us
that we tend to forget what complex structures they are.
A single one can contain up to 60 metres of silk of up to six different kinds
and involve 3,000 separate attachments.
And, what's more, some orb web spiders spin a different one every night.
The biggest and best webs are made, in most species, by the female.
She has to start by bridging the gap across which she's to hang her web.
The faintest breeze will catch a filament as she spins it
and carry it away into space.
With luck, it will catch on a suitable anchor point.
There!
She runs across the filament, trailing a line of much thicker, stronger silk
and ties it off.
Then she goes back to the middle of this line
and drops down another.
And she tightens it.
The junction at the top becomes the hub of the web
to which she will attach radiating spokes.
These must be particularly strong
for the shape of the whole structure depends on them.
Once they're complete, she adds a spiral,
working from the middle outwards.
This first spiral is quite widely spaced because it's only temporary.
It will serve as a scaffolding, along which she runs
to add a stronger, stickier and more closely spaced spiral.
That's this one.
As the filament for this emerges from her spinneret,
she coats it with glue from separate glands in her abdomen.
After completing one section, she eats the scaffolding line.
It has no further use and it saves valuable silk.
At first, this glue is evenly spread,
but each time she fixes a section, she twangs it with her leg
so that it breaks up and forms a line of droplets.
She can complete the whole intricate, elegantly symmetrical structure
in about an hour.
When an insect strikes the web,
the capture spiral stretches and then retracts to its former size
without distorting its shape and without such a severe recoil
that the insect might be catapulted off again.
The beads of glue are the key.
Tension on the surface of a droplet
hauls any slack into it.
When the insect hits, it pulls out the coils of thread in each droplet,
slowing the insect to a momentary standstill.
And then the surface tension pulls the silk back into each drop.
So the spiral thread doesn't break
and the web as a whole regains its symmetry.
The spider sits with her legs resting on the spokes.
Any vibration on them will travel up her leg
and be received by a small sense organ in the joint.
This is covered with microscopic slits, which are distorted by the slightest movement.
So the spider is immediately aware of the tiniest tremor.
Once alerted, she pulls on neighbouring spokes of the web
to assess exactly in what direction and how far away the signals originate.
The fly is on the verge of breaking loose.
Here she comes.
She isn't hindered by the glue she put on the capture spiral
because her feet are coated with a special oil.
Once her victim is in her grasp,
she produces yet another kind of silk.
It emerges as a sheet from a group of minute spigots.
This is a fuzzy silk that's used for wrapping
and, at moments like this, as a shroud.
The biggest and strongest webs are those made by Nephila,
the golden orb web spider of the tropics.
They may be several metres across
and they're strong enough to catch small birds.
This time, only a moth.
After a killing bite, she returns to the hub of her web to wrap it up.
But big webs bring problems.
It's not easy to control what happens on their outer regions.
This is Argyrodes.
She's only one-hundredth the weight of Nephila
so she can move across this huge web undetected.
And she's a thief.
A fly has arrived not far from her.
She has a chance to steal it.
But Nephila has also detected its arrival...
and claims it without much difficulty.
Another fly is caught in the web.
Argyrodes now stands a better chance
since Nephila is busy feeding.
She cuts the filaments between the fly and Nephila
so that vibrations made by its struggles won't reach her.
Nephila, sitting at the hub of the web,
seems quite unaware of what's going on at its outer margin.
The fly is now hanging from a single thread,
but it's five times the weight of Argyrodes and too heavy for her to carry.
She has to be clever.
She attaches a thread to it
and runs it up to a twig outside the web.
Nephila is still occupied with her meal.
Another line, just to make sure.
Now she can snip the last filaments of the web and haul it away.
Safely off Nephila's web at last,
Argyrodes can enjoy her stolen meal in safety.
(CHURCH BELLS TOLLING)
For all its complexity,
the orb web was one of the first kind of silken traps devised by spiders.
Subsequently, other species modified it in some quite extraordinary ways.
There's a web in this yew tree that's triangular.
A slice, as it were, from an orb.
It's made by Hyptiotes
and her body forms an essential link in its mooring cable.
To be effective, the web has to be very taut.
Hyptiotes ratchets up the tension
by hauling in the main cable and coiling it above her body.
Tighter.
And that's about as tight as it will go.
Now she has to wait.
Flies can sometimes disentangle themselves from a web
if the spider doesn't grab them quickly,
but a fly hitting this web won't get that chance.
A strike triggers an instant reaction.
In slow motion, you can see what happens.
Hyptiotes immediately lets go of the coil she was holding over her back.
That causes her web to collapse
and almost instantaneously entangle the prey.
Few flies that hit a Hyptiotes web manage to escape.
The gladiator spider makes her web
from a very special kind of multi-strand silk,
which she backcombs to make fuzzy.
She carefully attaches this to a framework of ordinary un-fuzzy filaments.
The fuzzy silk doesn't have glue on it,
but it will entangle hairy legs.
And it's also extremely elastic,
which is crucially important.
It's finished.
She reaches down with her forelegs to check how far away she is from the ground.
Then she snips most of the framework threads
and holds the fuzzy rectangle between her four front legs.
She's ready.
Her enormous eyes are so sensitive she can hunt in near-darkness.
A bush cricket would make a rich meal,
but it's very powerful and it could put up a good fight.
Now it must be parcelled up
and the fuzzy silk makes excellent wrapping,
just as it does for Hyptiotes.
In Australia, there's a species of spider
that has taken web construction a stage further still.
It builds not just in two dimensions but three.
It regularly takes up residence in people's backyards and on their verandas.
There's one under this plant holder.
It's the notorious and very venomous redback.
And what's brought it here is the extraordinary way in which it uses silk.
The female usually builds at night and constructs this very elaborate web.
Its not just wide, it's deep.
To make it, she needs two flat surfaces, one beneath the other,
and that's what she's found underneath the plant holder.
First, she drops down, pulling a thread behind her.
She sticks the end to the veranda floor.
Then she goes back up again, trailing a second line,
which she sticks to the first, so strengthening it.
Then she pulls the line tight.
That is a crucial element in the construction.
Down she goes again.
By the time she's finished,
she will have fixed several dozen of these sticky, taut, vertical lines.
An ant is approaching in the distance.
An orb web would never catch one of these.
It's a scout, leading an exploring party.
Searching beneath the plant holder,
it's almost bound to blunder into one of the redback's lines.
It struggles and so seals its fate.
And its followers go the same way.
The threads carry the vibrations back to the redback waiting above.
She has no need to hurry.
Her meals are suspended in midair. Escape is impossible.
She hauls them up in her own good time.
The redback's trap is certainly economical with silk,
but one North American spider hunts with just a single filament.
This may look like a bird dropping
but that's just a disguise to fool anything that might want to eat it.
In fact, it's a spider
and one with an even more extraordinary hunting technique.
It's a bolas spider.
Throughout the day, she remains motionless,
but when evening comes, she prepares for action.
She abandons her disguise and starts to move.
Slowly, she makes her way down to the underside of the leaf.
There she hangs from a horizontal thread.
Next, she starts to spin a single strong line,
pulling it out of her spinneret with her back legs.
And at the end, there is a sticky globule.
This is her bolas.
It's all she needs.
She climbs back up to her leaf
and takes up her position on the horizontal thread,
with her weighted filament dangling from one of her front legs.
A moth.
She whirls her bolas but misses.
But she has ways of enticing the moth back.
She can produce a pheromone, a chemical perfume,
that the moth finds irresistible.
What is more, she can change it
to suit the particular species of moth that happens to be around.
The moth comes back.
This time she's got it.
Now, she starts to wrap it.
But she's not finished yet.
Different moths and a different pheromone.
Silk can do other things as well.
It can totally change a spider's lifestyle
and turn a solitary killer
into a creature that hunts in great packs.
This enormous web above me contains thousands of spiders.
They're all tiny but because they work together,
they can kill prey many times their own size.
Any spider sitting on its web
might be expected to react aggressively towards another that approaches it,
but not these.
These tiny ant-size spiders seem totally relaxed in one another's presence.
More than that, they cooperate with one another,
working together to repair and extend their huge silken palace.
There are tens of thousands of them in this one
and they are constantly at work.
Their home can rise 15, 20 metres up towards the canopy.
It's so big, it's a major obstacle in the airways of the forest.
This cricket weighs several hundred times as much as one of these spiders.
However, the slightest attempt to free itself
only serves to attract lots of them from all over the giant web.
Soon it's surrounded by hundreds.
They squirt glue from their spinnerets,
immobilising the cricket limb by limb.
They sink their tiny jaws into its most vulnerable places,
its joints, and inject their venom.
Before long, the cricket is dead
and the horde of tiny victors share their vast meal.
On occasion, even a solitary spider must meet another spider.
Male, after all, must meet female.
This is a male Argiope and he's looking for a mate.
But she is huge, ten times bigger than he is.
He has to be very careful if he's not to be mistaken for prey and eaten.
Once he reaches her, he starts stroking her body,
nibbling her toes.
From their taste, he can tell whether the female is a virgin.
If she is, she will be less likely to eat him.
To confirm that her taste is encouraging, he wipes his feet across his mouth.
Apparently, he's reassured
for he starts to snip some of the strands of her web
to create an open space in it.
He runs a line across it, down towards her.
And now, he plucks it like a guitar string.
He's doing very well.
She's not attacked him, yet.
She spreads her eight legs. It's a clear invitation to mate.
He checks the taste on his legs again and decides to go further.
He pauses.
After mating he has, at best, a 50-50 chance of staying alive.
But nothing ventured, nothing gained.
He moves in and delivers his sperm.
But his luck runs out.
Virgin she may be
but, with mating completed, she grabs him and binds him in silk.
She will eat him later.
Some spiders don't spin webs of any kind,
but they still need silk to help them find a mate.
And there's one such just here.
It's a female wolf spider. A solitary, wandering hunter.
Like all spiders, she trails a dragline of silk behind her wherever she goes.
It's a safety line in case she falls
or is blown away or needs to drop out of sight in a hurry.
And here's a male.
He's noticed her dragline.
The taste of a silk line is very informative for him, too.
It tells him that it comes from a female,
so he follows.
His black palps are covered in hairs which are extremely sensitive.
Each hair contains a nerve which can detect even minute quantities
of female pheromone.
Now, he's within sight of her.
Being active hunters, wolf spiders have excellent eyesight,
so he uses his black palps to send visual signals to her.
This display is not slowed down.
This is how he does it.
It takes a lot of energy and, while he's performing,
his heartbeat triples.
She encourages him by tapping her legs.
He's now within striking distance.
The palps he's waving, like those of all male spiders,
are loaded with sperm.
He leans over, inserts one of them into her abdomen,
and pumps his sperm into her.
Then he does the same with the other.
And that's that, at any rate, as far as he is concerned.
Three weeks pass and the female's ovaries start to produce eggs.
The male's sperm that the female has been holding within her for all this time
is now released and fertilises them.
At last, she's ready to lay.
But she needs a safe place in which to do so.
And, once again, silk provides a solution to her problems.
She starts by spinning a silken sheet,
stretched between fragments of the leaf litter.
She uses that fuzzy silk that comes from multiple nozzles.
It will provide a soft padding to protect her eggs.
She expels a drop of liquid onto the sheet.
And into the liquid, she injects her fertilised eggs.
There may be several dozen of them.
She checks that the drop has dried.
She adds more fuzzy silk to protect it
and its vulnerable contents from knocks and bumps.
Then she changes silk
and starts to spin a tougher kind to cover the whole capsule.
She cuts the platform free from its attachments
and goes round it, pinching the cut edges firmly together.
Finally, she covers the whole parcel with a waterproof silken wrapping.
She now carries her precious package with her wherever she goes.
She seeks out patches of sunlight
so that she can warm it and speed the development of the eggs within.
It's a long process that may last several weeks.
And then, at last,
her babies are sufficiently developed to leave their nursery.
But, even now, she doesn't abandon them.
They climb up her legs and onto her back.
The egg capsule is now empty and can be discarded.
And away they go.
It's a somewhat rough ride but the babies, even at this early stage in their lives,
know how silk can keep them out of trouble.
They use it to tie themselves to their mother's back.
And then they use it for yet another purpose
and produce it in such abundance
that, in some seasons of the year, it covers great areas of the open countryside.
This wonderful shimmering carpet of gossamer,
strands of the finest silk,
is the creation of a million baby spiders.
It's autumn in England
and time for spiderlings to leave their mothers.
The youngsters climb up the threads they've spun
to reach the topmost twigs of the bushes.
They tip their abdomens into the air
and the gentle breeze catches the filaments as they issue from the spinnerets.
Some filaments drift down and become entangled in the bushes.
But when conditions are right, the threads rise vertically upwards.
And away the spiderlings go.
On a calm day, they may only travel a few metres,
but if there's a breeze, as there is now, they can be swept up high into the sky.
Spiderlings have been recorded
thousands of feet up and can travel for hundreds of miles.
So silk can be used for transport
as well as looking after the young, courtship
and, of course, catching prey.
In an area of heath like this around me,
it's been estimated that there's probably 14,000 miles of silk,
enough to stretch from here in England to Australia.
Ingenious though we are,
we've not yet been able to invent anything as strong,
as light or as elastic as silk.