Our planet is the greatest living puzzle in the universe.
A collection of worlds
within worlds.
Each one a network of relationships
and connections
between all their living parts
leading to the diverse and complex world we live in.
And at the heart of many of these worlds
is a very special group of animals.
The insects and their close relatives,
the arachnids and crustaceans,
classed together as the arthropods.
Together, they account for 80% of all animal species on our planet.
In these three specials,
we're going to explore the connections and relationships
that they have with us, our planet
and with each other.
Ultimately to understand how this group
hold the key to life itself
inside nature's microworlds.
Humans evolved around 200,000 years ago
into a world that was dominated by the arthropods.
In that time, we've learnt to live alongside each other,
taking the benefits and putting up with some of the annoyances.
But do we understand what life would be like
without this group of animals?
How many of us really know
how intricately linked our lives have become
that, without the arthropods, life as we know it would not exist?
Some even question
if survival of the human race would be possible at all.
But how can this be?
What have the arthropods ever done for us?
The ways they affect human life are diverse and far reaching
and to really understand the importance of this influence,
we need to unpick the relationships,
both good and bad,
that we have with the arthropods.
One of the most intriguing ways they influence us
occurs in the forests of Kenya.
These driver ants are searching for food.
They're efficient hunters
moving through the forest like a tidal wave.
They'll eat any living animal in their path.
Colonies can number up to 22 million
and it's said that even elephants will turn and flee
when they see them coming.
These lethal predators are actually totally blind.
They rely on touch, smell and chemical signals to find their way.
The soldiers flank the raiding columns of workers
with immense jaws raised.
Anything that can't outrun them
risks becoming their prey.
This is perhaps how most of us view arthropods -
creepy crawlies that are nothing more than a problem.
But their presence is actually
a real asset for these villagers.
The ants can capture up to 100,000 insects in a single raid,
providing invaluable pest control for the farmers.
Pests inside homes and in surrounding fields are removed,
dismembered and devoured.
In fact, the whole place is given a five-star ant clean-up.
Thanks to their highly effective cleaning raids,
these ants play a key role
in the lives of the locals.
But arthropods can provide us
with something even more important than a service.
They can provide us with one of the essential elements of life.
900 miles south of Kenya
lies Lake Malawi.
Beneath the water, something's stirring.
Trillions and trillions of lake fly larvae are getting ready to emerge.
After many months buried in the sediment on the lake floor,
they'll take to the air to mate.
Towers of mating flies stretch hundreds of metres into the air.
Like smoke, they rise
from the surface of the lake.
The towers of flies are swept by the wind towards the shore
and towards human habitation.
Here, they cloak vegetation
and engulf whole forests and villages in their path.
This may seem like an annoyance,
but, actually, these flies present great opportunity.
Villagers sweep baskets through the air to catch the flies.
The biomass of these flies is equivalent to huge herds of game
that roam the surrounding plains,
but they're far easier to catch.
The flies are then made into patties
and fried in hot oil.
Each patty contains half a million flies
and has seven times more protein than the average beef burger.
For people who have little protein in their diet,
this can be a lifesaver.
It may feel a long way from our idea of a perfect meal,
but the importance of eating arthropods
shouldn't be underestimated.
Over 11 million tonnes of crustaceans
are consumed by humans every year.
In Botswana, the mopane worm collection industry
is worth millions of pounds each year.
For 2.5 billion people worldwide,
insects are a vital source of food.
More than a thousand insect species
form a regular part of the human diet.
Rich in vitamins, protein and minerals.
It's mainly in the West
that people are uncomfortable with the idea of eating insects.
But the United Nations believe
that eating insects instead of mammal meat
may provide a solution to stamping out famine
and reducing climate change.
The raising of livestock such as cows, pigs and sheep
occupies two thirds of the world's farmland
and generates 20% of all greenhouse gases.
With the human population projected to reach nine billion
in just 40 years' time,
the consumption of arthropods
could provide a healthy Earth-saving measure.
So, in the future, arthropods have the potential
to address our global food crisis.
That's no small claim.
But they've also played an enormous role in shaping our past
to such an extent that human life, as we know it,
would not exist if it weren't for this next arthropod product.
It all started with a cocoon
and a beautiful piece of cloth.
China - home to a billion people
and a very special arthropod.
This is a silk worm caterpillar.
They eat only mulberry leaves.
And, after 50 days of feeding,
they'll be 10,000 times heavier and ready to transform.
25% of their body mass is made up of silk glands.
They spin a cocoon using a single thread
which can be over 900 metres in length.
And it's this silk that forms the basis of an industry
that's shaped our history
and today, has a commercial value
of up to £300 million.
The cocoons are boiled and precious silken threads begin to unwind.
But this arthropod product is not only responsible for human clothing.
It's shaped our culture for over a thousand years.
The transport of silk from Asia towards Europe
led to the establishment of the famed Silk Road around 200 BC.
This 4,000-mile trade route
forged relationships between different and diverse cultures.
And was pivotal in the development of the civilisations
in China, India, Europe and Arabia.
So silk has shaped human culture and distribution,
but there's another arthropod product that's valued so highly
humans will risk their life trying to collect it.
The Himalayas, in Nepal.
These men are climbing 400 metres up sheer cliffs
to steal from giant honey bees.
They're the largest honey bee in the world
and their stings are notoriously painful.
So what could make men risk their lives in this way?
Honey!
These bees, like honey bees the world over,
take nectar from the surrounding flowers
and spit it into the cells in the comb.
Enzymes in their saliva break down the sugars
and water evaporates until the condensed honey remains.
This honey will be the colonies' sole source of food
during the colder winter months
and they'll give up their lives to protect it.
So the honey gatherers will not only have to deal with perilous heights,
but also with angry bees.
When the men finally reach the comb,
they must manoeuvre sticks
to work free a section of honey.
With little protection against the stings,
they must work quickly before being overcome by the bees venom.
The honeycomb is dropped into a suspended basket
and then lowered to the ground.
They leave a large section of the comb intact
so the colony can rebuild its honey supplies.
Job complete, the men can descend to enjoy their hard-won prize.
Honey's made up of 80% natural sugars
and so, provides a vital energy-rich food source
for these mountain dwellers.
So prized is this product
that the farming of arthropods for their honey has now gone global.
Around 1.2 million tonnes of honey is produced worldwide each year.
When you think that one little bee in its entire lifetime
produces only about a spoonful of honey,
that's a humbling amount of work
from our arthropod friends.
But honey isn't the only product that bees provide us with.
Bees and their relatives
have a much more far reaching and significant effect on us humans.
Without which, it's questionable if humans would survive at all.
And to see what this is,
we must examine a wonderful process happening all around us
and responsible for shaping the world we live in.
The coastal cliffs of Sardinia,
in the Mediterranean,
are home to an unusual plant.
The dead horse arum.
It looks like a dead rotting animal
and has a smell to match.
This canny flower even raises its temperature
by as much as 20 degrees above the surrounding vegetation
to complete its disguise.
The smell is taken by the wind
and it's not long before the arum is noticed.
These flies are hoping they've found a carcass
on which to lay their eggs,
but, instead, they become trapped.
Inside the flower,
they brush against the female stigma
releasing any pollen they're already carrying.
This flower is now pollinated.
Spines prevent the flies' escape and they're trapped.
Overnight, when the flies are inactive,
the spines wither and the male pollen above them ripens
ensuring that, in the morning,
each exiting fly is coated with pollen to take to the next flower.
This flower has invested everything
in the process of cross-pollination.
It's modified its appearance,
its smell, its temperature
and its internal barriers,
all to ensure the transfer of pollen grains
from one plant to another.
And it's this process of pollination
that's the next key
to why the arthropods are pivotal to human success
and to our very own food chain.
As much as 35% of all human food
is dependent on pollination by arthropods.
Across the world, the value of crops pollinated by insects
is over £120 billion a year.
Without them, we wouldn't have apples, almonds, cherries, oranges,
tomatoes or squash on our supermarket shelves.
84% of crop species grown in Europe
still depend on insect pollination.
Without insects, our crops would flounder,
supermarket stocks would plummet
and life on Earth would irreversibly suffer.
But to really understand our relationship with the arthropods,
we need to examine their negative effects as well as the positive.
The deserts of West Africa.
Moisture in the soil and increased temperatures
provide the triggers for a mass hatching.
Eggs that may have lain dormant for 20 years hatch
and flightless locusts, called hoppers emerge.
These hoppers follow the smell of freshly sprouting grass.
After about 20 days of feasting,
they transform into winged adults and form a swarm.
A swarm can cover an area of 1,000 square miles
and can literally blot out the sun.
They eat their own body weight in food each day.
En masse, they can get through 200,000 tonnes of crops,
enough to feed half a billion people.
Many arthropods have the potential to reach biblical proportions.
Their ability to reproduce quickly and prolifically
means their numbers, left unregulated,
can snowball out of control.
For us humans, that can present a real problem.
And there's a parasite that's utilised this breeding success
and today, it's the biggest cause of human fatality on our planet.
It kills 3,000 people every day
and without arthropods, it wouldn't exist.
Throughout history,
this relentless killer has claimed more victims than any other disease.
It's killed more people than both the world wars put together
and at least 40% of the world's population are at risk.
The disease is carried by the Anopheles mosquito
and it's called malaria.
But, really, this mosquito
is just a pawn in a parasite's game.
The parasite lives by eating the red blood cells
of the victim it attacks.
When a mosquito bites an infected person,
it sucks up the blood containing the parasite into its gut.
The parasite multiplies...
..then, burrows into the mosquito's saliva gland...
..where it's squirted into the blood
of the mosquito's next victim.
And so, the cycle continues.
But can we really blame the mosquito?
It gains nothing from carrying the parasite.
And, ironically, mosquitoes,
along with other arthropods,
might be the ultimate solution to this deadly disease
in their ability to regulate each other.
An example of this is played out
in a field in the South Downs.
These aphids are doing what aphids do best -
multiplying.
They're breeding machines
and, by the end of a season,
a single aphid can have produced over a billion descendants.
Each aphid uses their specialised mouth parts
to suck out the plants' juices.
Left uncontrolled, they can devastate a whole field of crops.
Luckily for farmers and gardeners,
there's a crack team of predators on standby.
Firstly, the colourful but ferocious ladybird.
One ladybird can eat over 5,000 aphids in a lifetime.
But working alone, they'd have their work cut out
to keep up with the prolific breeding of the aphids.
Luckily, they've got backup.
Money spiders parachute in from surrounding fences and hedgerows.
The spiders spin delicate but lethal orb webs
and wait for their prey to arrive.
When the bumbling ladybird has had her fill,
her movements dislodge further aphids
that drop into the silken traps below.
This natural balance of predators and prey
may seem only relevant to gardeners and farmers,
but the global importance of this natural biological control
is not to be underestimated.
Pest control services provided by insects were valued
at over 60 billion dollars a year, in the USA alone.
This is a service we really can't afford to lose.
And the arthropod regulators could potentially provide some hope
against the worst disease the human race has ever faced.
There are plans for a non-malaria-carrying mosquito
to be released to outcompete the deadly malaria-carrying ones.
So we've seen how arthropods provide us with food and products.
How they've shaped our distribution and culture.
We've seen how pivotal they are to our own food chain
and how their presence can regulate pests and even fatal diseases.
But there's one final key to how they influence our lives...
..one final offering from the arthropods
that could shape the way we exist and operate in years to come.
In this vast colony,
every army ant appears to be following a master plan,
like tiny cogs in a huge machine.
They allocate resources depending on environmental conditions.
If a rich food source is found,
workers will appear to deal with the bounty.
They build organised highways with no congestion.
They construct shelter and a place to rear their young
using their own bodies.
They stage foraging raids
and vacate an area of forest when food sources dwindle.
They're efficient, responsive and smart.
Everything our human organisations strive to be.
But this colony doesn't function
like any organisation we humans are familiar with.
There's no central control, no figure of authority.
The queen ant may have her lofty title,
but plays no role in coordination.
And we're just starting to learn how such efficiency is achieved.
Haulage companies and airports are learning to operate like ants.
Abandoning pre-determined master plans
and instead focusing on smaller,
smarter decisions.
And it's not just the ants that we're learning from.
Bees are teaching us how to build honeycomb-style structures
providing maximum strength while using minimal materials.
Spiders are helping us design crawling robots
for inspecting ship hulls
and nuclear reactors.
Butterflies hold the key in their wings
to harnessing the sun's energy more efficiently than ever before.
And termites, with their unpowered air conditioning towers,
are inspiring architects.
It seems that arthropods really do have a lot to teach us.
Arthropods have been pivotal in shaping our culture
and distribution.
Without them, our food chains would collapse
and pests would multiply beyond control.
We humans would do well to remember
that arthropods could survive perfectly well without us.
But life as we know it could not continue without them.
Our planet is the greatest living puzzle in the universe.
A collection of worlds within worlds.
Each one a network of relationships and connections
between all their living parts,
leading to the diverse and complex world we live in.
And at the heart of many of these worlds
is a very special group of animals...
..the insects and their close relatives, the arachnids
and crustaceans - classed together as the arthropods.
Together they account for 80% of all animal species on our planet.
In these three specials, we're going to explore the connections
and relationships that they have with us,
our planet...
..and with each other.
Ultimately to understand how this group
hold the key to life itself inside nature's microworlds.
At least one species of Arthropod
can be found in every microworld on Earth.
From baking deserts and lush rainforests...
..to open oceans...
..and dark caves.
And although seemingly insignificant in size...
..the influence they have on our planet is immense.
But to understand how arthropods have come to play such a vital role,
we must explore a wide variety of ecosystems.
And we'll investigate the arthropods'
greatest influence of all.
Could they be responsible for the richness and diversity
of nature's many microworlds?
There's one microworld
where the impact of a single species of arthropod is evident -
the Argentinean Pampas Grassland.
A landscape that's been created almost solely by one tiny creature.
Grass cutter ants.
These insects are only one-and-a-half centimetres long
and yet they achieve something few animals are capable of.
Through their activities,
they have completely altered their own environment.
Grass cutter ants are the farmers of these grasslands
and like farmers, they shape the vegetation.
Each year, a single colony will harvest
over half a tonne of grass cuttings.
Surprisingly, these ants don't actually eat grass,
but they have found a way to cultivate their crops
and this happens underground.
Their nests dominate the subterranean environment
with tunnels extending over seven metres deep.
Here they share their chambers
with a special fungus that's found nowhere else on Earth.
And this fungus can digest grass.
The ants feed their grass harvest to the fungus
and in return the fungus produces edible gardens.
These fungus gardens are prolific enough
to feed the whole colony of ants.
All 5 million of them!
But their impact does not end there.
They also alter the landscape.
The fungus releases carbon dioxide -
lethal in large concentrations.
But the ants have a clever way of combating its build up.
They construct massive towers that help draw fresh air in
and suck stale air out,
effectively acting like air conditioners.
These grass cutter ants,
with their incredible building and farming skills,
have completely shaped this microworld.
An ecosystem which, without the ants, would not even exist.
The arthropods' domination of an environment
is not always so complete
but it can have just as big an impact.
In the most expansive ecosystem on our planet,
an arthropod plays such a key role that, without it,
the largest animal that has EVER lived could not exist.
Life within the ocean evolved 3 billion years prior to life on land.
And today it's the home of 230,000 marine animal species.
Arguably the most important of these,
the ones that are the key
to this whole interconnected oceanic ecosystem are...
..the krill.
Found across the world's oceans, from the tropics to the poles,
these arthropods fuel the ocean's food chain.
The reason they're so vital to sustaining life in the oceans
is their ability to consume phytoplankton on a massive scale.
Phytoplankton are microscopic organisms -
the sea's equivalent of grass.
So vast in number, their blooms can be seen from space.
And krill are the ocean's biggest consumer of phytoplankton.
Just one species, the Antarctic Krill,
has a combined mass of 379 million tonnes.
That's over 90 million tonnes heavier
than the biomass of the whole human race.
Few large animals can feed on the ocean's phytoplankton
but they can feed on krill.
So these tiny arthropods are a critical link
at the bottom of the ocean's food chain.
The krill feed the fish, which feed bigger fish,
which feed the birds and seals,
and so the food chain continues.
But sometimes the number of links in the chain is remarkably small.
The blue whale.
The biggest animal that's ever lived on the planet
has short-circuited the ocean's food chain
and gone straight for the krill.
Rather than teeth, these ocean giants are equipped
with a fine mesh of bristles, called baleen,
which allow each whale to filter out up to 40 million krill a day.
Without these tiny arthropods, the blue whale may never have evolved.
Arthropods play a pivotal role in the underwater web of life
but their influence isn't just confined to the sea.
On dry land, arthropods are also the key food source
for a whole host of other animals.
Birds...
reptiles...
amphibians...
and mammals.
Like the blue whales, there are also land-based animals
that have special adaptations for feeding on arthropods,
like the pangolin with its powerful digging claws.
And the giant anteater that has a 60cm long tongue,
perfect for reaching into ant and termite mounds.
But there's an even more surprising group of predators
that rely on arthropods for their food.
And they don't even belong to the animal kingdom.
One species can be found in the boglands of Scotland.
The soil here is waterlogged and lacking in vital nutrients,
especially nitrogen.
Under such conditions few plants can grow
but thanks to the presence of arthropods,
one species has found a way.
This strange-looking plant is the sundew -
so named because of the dew-like droplets on its leaves -
but they're also extremely sticky.
Their sweet smell attracts many insects.
As mosquitoes emerge from the boggy water,
they're drawn straight into a sticky trap.
Sensitive to touch, the tentacles quickly wrap around the prey.
Eventually, the insect dies in the sticky fluid.
With the help of enzymes, its body is absorbed by the sundew.
Without insects, this plant would not survive.
And without arthropods, many of our planet's food chains would collapse.
While the arthropods' role as a food source
is crucial to the survival of millions of animals
and even some plants,
it's only a part of the giant jigsaw
that makes our planet's ecosystems tick.
Nutrients form the building blocks of life.
So, for a microworld to maintain its balance,
it's vital that these nutrients aren't wasted.
This is where our next team of arthropods
play a critical role as the recyclers.
Within the rainforests of Borneo,
a giant cave is home to a staggering 3 million wrinkle-lipped bats.
With over 37 tonnes of insects consumed every night,
a huge mound of bat droppings builds up.
But this waste isn't wasted.
Reaching up to 100 metres in height,
this nutrient-rich mound fuels a seething mass of cockroaches.
One of the densest concentrations of cockroaches in the world.
Working with bacteria and fungi, they break down the faeces.
This is how they keep this giant mound under control
and keep the nutrients moving around this tightly connected microworld.
It's the recyclers that hold the key to this cave's ecosystem.
But their influence is perhaps even greater 5,000 miles away,
on the plains of Africa.
This is the Serengeti...
..home to the big five...
..and the dung beetles.
Using their remarkable sense of smell, they hone in on their target.
True to their name, dung beetles are the masters of recycling dung.
They don't need to eat or drink anything else,
as dung provides all the moisture and nutrients they need.
As the beetles roll off and bury their own food balls,
the dung patch quickly vanishes.
But for these beetles, dung isn't just a good source of food.
This male is building a giant brood ball, to help him entice a female.
Mission accomplished!
And now the female has the perfect place to lay her eggs.
While the beetles' circle of life is centred around dung,
the grasslands' entire ecosystem is centred around the dung beetles.
Without these amazingly efficient recyclers,
the daily dose of 5,000 tonnes of dung
would soon swamp the African plains.
Thanks to the cleaning up operations of dung beetles,
the grasslands are nurtured,
allowing the grazers to be fed,
which in turn sustain the predators.
And it's in death where another team of arthropod recyclers
come into their own.
Blow flies can smell a dead body from up to a mile away.
As soon as they arrive, there's a frenzy of egg laying
as each female deposits up to 300 eggs on the carcass.
In just under 24 hours the eggs hatch,
allowing the voracious maggots to get to work on the flesh.
Using special enzymes and their claw-like mouthparts,
they can break down proteins in next to no time.
In less than a week, they'll have moulted twice,
consumed 60% of the carcass
and increased tenfold in size.
With feeding over, the maggot begins its next stage of life.
Within a few days, a fly emerges.
This will go on to mate and produce the next generation of recyclers.
So efficient are these recyclers that, despite their size,
arthropods process more flesh
than all the large carnivores put together.
By cleaning up dead animals,
the waste disposal teams of the arthropod world
limit the spread of disease
and ensure the return of nutrients back into the food chain.
This is all part of keeping nature's microworlds in balance
but there is a twist in this tale.
The arthropods' efficiency and ability to reproduce quickly
means that their populations could easily spiral out of control.
So who keeps the arthropods in check?
The answer is the arthropods themselves.
The woodlands of England.
Spiders mostly prey on insects and other spiders
and they use a range of strategies to capture their prey.
The best-known is this - the sticky web.
An orb web can contain up to 60 metres of silk
and involve 3,000 different attachments.
It takes about an hour to build and then it's just a waiting game.
She sits at the centre with her legs resting on the spokes.
Ready to pick up the tiniest vibration.
As soon as a tremor spreads down the web, she pulls on different spokes.
In this way, she can work out exactly where her prey has landed.
With her feet coated in a special oil,
she can move freely across her web
to secure and then devour her victim.
While this capture has gone perfectly to plan,
it's not always the case.
About half the potential prey manage to escape.
But there's another web that's a more effective trap
and it's designed by the aptly-named triangle spider.
Its web may not look as impressive as the classic orb web
but it is far more deadly.
The spider's body forms an essential link in her trap.
But to be effective, she has to ratchet up the tension.
Tighter...
and tighter.
On this web, flies don't get a second chance.
Their impact triggers the spider's release,
causing the web to fire and entangle the prey.
Few flies manage to escape.
Which is pretty good for an individual's web
but when spiders team together,
the results are even more impressive.
In the rainforests of South America,
a section of the canopy is enveloped in a massive tangle of webs.
This tree-top death trap
is the work of tens of thousands of tiny spiders.
Spanning three metres across, it can capture a whole host of prey.
Including this cricket,
which is several hundred times larger than the spiders.
But that doesn't put these spiders off.
Working together, they can kill prey many times their own size.
They squirt glue from their spinnerets,
immobilising the cricket,
and then they inject their venom.
Before long, their victim is dead
and now they begin their communal feast.
Numbering over 40,000 species,
spiders are found across the globe and exist in nearly every habitat.
Thanks to their silken traps and venom,
these predators play a pivotal role
in keeping the planet's many microworlds in balance.
The controllers of the arthropod world are a key piece of the puzzle
that keeps our planet ticking over
but they're not the most important.
To find out what is, we need to explore
a far more harmonious relationship,
one that began in prehistoric times.
140 million years ago, the world was a very different place.
The plant kingdom was dominated by a few species of conifers and ferns.
For these plants, sexual reproduction relies upon either the wind or water.
With millions of tiny pollen grains
dispersed in the hope that some are intercepted
by individuals of the same species.
Rich in oils and proteins,
pollen grains are expensive to produce and the majority are wasted.
But then an incredible relationship began,
which would change the colour and diversity of our planet
and ultimately create the richest ecosystem of all.
The presence of insects allowed a new kind of plant to evolve.
The flowering plants.
To reduce the squandering of pollen,
these plants no longer relied on wind or water for pollination,
instead they recruited insects to pollinate them
with nectar-loaded flowers.
Tailoring their advertisements to match insect senses,
a burst of colour and smell quickly spread across the planet.
In the fields of southern France,
sunflowers grow to face the rising sun.
One after another,
hundreds of individual florets produce pollen-covered stamens.
As these bees busily feed on nectar,
they brush against the stamens collecting pollen
and then carry it from flower to flower.
The sunflower's fertilised and the bee is fed -
it's a win-win situation.
Over the generations, this mutually beneficial relationship
has created some incredibly specialised partnerships
between arthropods and the flowers they pollinate.
One of which can be found in the grasslands of England.
The pyramidal orchid keeps its nectar rewards
at the end of long tubes formed by the petals,
so that a long tongue is needed to get it out.
The burnet moth has one such tongue.
As it feeds, a horseshoe-shaped package of pollen
clips onto its long proboscis.
The only way the moth can remove the pollen
is by visiting other pyramidal orchids.
This time, as its tongue reaches for a nectar drink,
the pollen sacks come into contact
with the flower's sticky female surface
and a speck of pollen is transferred across.
The flower is pollinated.
But an even more elaborate partnership
has evolved in the rainforests of Central America.
This strange-looking flower is a bucket orchid.
Instead of nectar, it has another offering for its arthropod partner.
The euglossine bee is attracted to special fragrant oils
on the orchid's petals.
It gathers these oils into pouches on its legs
and will later use this perfume to attract female bees.
Other creatures are attracted to this flower
but after slipping into the flower's fluid-filled buckets, few survive.
While the bee depends on the orchid for its reproduction,
the orchid likewise depends on the bee.
Unlike other insects,
falling into the orchid's trap is not fatal for this bee.
The bucket orchid has an escape route
specifically designed for its partner.
Most of the flower is covered in a slippery fluid
but tiny knobs, which the bee can grab onto, guide it to an exit.
And, as it squeezes through the gap,
just big enough for the bee,
the flower's pollen is glued onto its back.
On its next visit to a bucket orchid,
the bee fulfils its part of the deal.
While gathering more aromatic oils, it's lured into the flower again.
And this time, as it leaves,
the pollen packets are deposited onto the new flower.
The orchid is fertilised.
And it's through this process, pollination,
that arthropods have exerted their greatest influence of all.
For over 100 million years,
the pollinators and their flowering partners have evolved,
diversified...
..and spread across the planet.
With their success came an explosion of life,
as they created new opportunities,
new habitats
and new ecosystems.
Today there are over a quarter of a million species
of arthropod pollinators.
80% of all plant species on Earth depend on them
and without them some of the richest ecosystems on our planet,
including the tropical rainforests,
would not even exist.
From the harvesters and providers
to the recyclers and controllers...
..each group of arthropods has a truly astonishing influence
on the workings of our planet.
But it's ultimately the pollinators
that have the greatest influence of all.
Our planet is the greatest
living puzzle in the universe.
A collection of worlds
within worlds,
each one a network
of relationships and connections
between all their living parts,
leading to the diverse
and complex world we live in.
And at the heart of many of these worlds
is a very special group of animals -
the insects, and their close relatives -
the arachnids and crustaceans,
classed together as the arthropods.
Together, they account for 80% of
all animal species on our planet.
In these three specials,
we're going to explore the connections and relationships
that they have with us,
our planet...
..and with each other,
ultimately, to understand how this group
hold the key to life itself inside nature's microworlds.
Arthropods are the most abundant
and diverse
group of animals in the world.
They inhabit
every continent and every ocean...
..from the harsh climate
of Antarctica...
..to the driest of deserts around the equator.
From the lushest jungles
to the highest mountain peaks.
There are an estimated ten million species.
More than all the other animal groups combined.
But what is the secret of their success?
What is the single key to their global domination?
To understand this, we need to unpick, one by one,
the factors that influence the lives of arthropods.
First, we need to understand what arthropods are
and where they came from.
And to do that,
we must travel to Delaware Bay,
on the east coast of America.
400 million years ago,
the first land animals
pulled themselves out of the sea.
They were the ancestors of the arthropods
who dominate our planet today.
And each spring, on the highest tides of the full and new moons,
a similar spectacle still occurs.
These are horseshoe crabs -
some of the most primitive arthropods alive today.
They're here to breed.
The males are two-thirds the size of their mates
and cluster along the water's edge as the females arrive.
Clinging to the female's shell,
he's pulled up the beach,
fertilising her eggs as she lays.
For these crabs,
breeding on land is only possible
because of the arthropod blueprint.
Their basic body plan
is the same as all arthropods -
a hard exoskeleton,
segmented body,
and jointed legs.
A body plan that's persisted unchanged for 400 million years.
A body plan as adaptable as it is simple.
The key design feature is no doubt the exoskeleton.
A hard external skeleton,
largely made of chitin, that provides protection,
support for muscles,
but most importantly, prevents water loss from the body.
The ability of the exoskeleton to retain water
is the factor that allows these crabs
to lay their eggs on land
and ultimately allowed arthropods
to be the first animals to colonise the land.
But even this master of design,
the exoskeleton, has a weakness.
How do you grow inside a suit of armour?
To see that,
we must travel 400 miles south
to a freshwater microworld in South Carolina.
This crayfish is getting ready to transform -
something all arthropods must do
to increase their size.
In preparation, he withdraws calcium from his shell
and stores it in little white tablets on the side of his head.
His hard exoskeleton then splits,
and the larger soft-bodied crayfish emerges.
It can take up to a few days for
the new exoskeleton to fully harden,
and before this occurs,
the crayfish is vulnerable.
This queen snake is on a hunt for a meal.
The hardened armour of the crayfish is too much for her,
but she can detect the chemicals
given off by the soft body
of a freshly moulted crayfish
and knows this is her chance.
As soft as a doughnut,
this crayfish provides a hearty meal.
So the exoskeleton,
vital to their success,
also leaves them vulnerable.
And it has another significant defining effect on all arthropods.
It restricts their size.
This is the largest terrestrial arthropod - the coconut crab.
This crab will moult each year,
and can live until he's 60,
yet is still no larger than a newborn baby.
If you must transform
every time you need to grow,
then there's a limit to how big you can get.
But this apparent size disadvantage
can be seen as an asset.
It opens up a whole new world for the arthropods.
And to see how,
we must travel to
the Flow Country, in Scotland.
This is the fairy wasp,
a quarter of a millimetre long.
They spend nearly all their lives underwater.
She is one of the smallest known arthropods alive on the planet
and almost invisible to the naked eye.
She makes a tiny water flea
look like a giant.
This female is looking for
a very specific place to lay her eggs.
She positions
her microscopic ovipositor
to pierce into the stem of a plant,
where the eggs of a water beetle have been laid.
She deposits up to 100 eggs
inside a single beetle egg.
When the young hatch, they have a ready source of food -
the water beetle's undeveloped young.
It's only the size of this wasp
that opens up this niche for her to exploit.
In fact, the arthropods' diminutive size
gives them a real trump card in the game of life.
It allows them to exploit microhabitats.
Be it an egg,
a gall on an oak tree,
or a single leaf.
The wealth of habitats and niches
available to them is virtually infinite.
But being small also makes them vulnerable.
Their size and abundance
makes them an ideal food source
for a whole host of other animals...
..including the biggest animal to have ever lived.
The blue whale.
So if size is not the ultimate key to their success,
we must look elsewhere and examine
why the diversity of arthropods
has evolved so much faster than in all other animal groups.
How do the arthropods speed up their evolution?
To find out, we must travel to a microworld
in our very own back gardens.
This is a female cabbage aphid.
In spring, she produces
100 offspring in just a week.
Her offspring already have babies inside them,
so this mother aphid
is nurturing her granddaughters
even before they're born.
If all her descendants survived and bred,
by the end of the summer,
there'd be 1,560 billion trillion aphids!
She is the ultimate breeding machine.
This ability to reproduce prolifically
is a real trait of the arthropods.
Having lots of offspring and a quick life cycle
increases the chances of genetic mutations occurring.
And it's these mutations,
however bizarre they seem,
that increase the diversity of the gene pool.
They can provide novel solutions
to life's challenges...
..and ultimately lead to
the evolution of new species.
This means that arthropods have the ability to respond to opportunities
and potentially fill niches faster than any other group of animals.
This does gives them a winning hand
and provides another vital piece in our jigsaw.
But it's not the whole story.
We've seen how arthropods have been around for over 400 million years,
how their winning body plan
has stood them in good stead for all this time.
We've seen how their size enables them to exploit microhabitats,
and rapid reproduction has accelerated their evolution.
All factors that have enabled them to fly,
squelch, crawl,
and scuttle
into the myriad of forms we see today.
But there's a twist in the tale.
For the real key to their global success and diversity,
we must look much closer to home.
To really understand
the diversity of the arthropods,
we must examine how the presence
of other arthropods affects them.
Firstly, let's look at what can be achieved
when arthropods work together.
This colony of 40,000 bees
is focused on a single task -
the production of honey.
They have a single queen,
who is the only bee to lay eggs.
She can lay up to 2,000
in a single day.
Each bee is roughly a centimetre and a half in length.
Their exoskeleton prevents them from growing any further
in this adult form.
But there's an animal over a million times its weight on the prowl...
..and he's after their honey.
To lose their honey now would be fatal for their colony.
It'll be their only source of food
during the cold winter months.
But this super society won't give up
its hard-won prize without a fight.
They attack and sting en masse.
The first stinger releases an alarm pheromone
that tells other bees to join in.
The stings are barbed
and hook into the skin of the bear.
Each sting has its own nervous system
and pumps venom into the attacker.
Worker bees can only sting once...
..and then they die.
It's the ultimate sacrifice for their colony.
But the bees are victorious.
The bear is repelled.
Teamwork enables these bees
to defend their precious honey
against an intruder many thousands of times their own size.
So working together can offer great advantages for defence.
But it's one thing if your attacker is an animal like a black bear
and quite another if it's the environment itself.
So how does working as a team allow you to live in
one of the toughest environments in the world?
To find out, we must travel 9,000 miles
to the mangroves of Australia.
They may look like a benign place to live,
but they're actually packed with
potentially deadly natural forces.
Hot tropical sun, salty water,
and the risk of drowning with every high tide.
But in the mangrove mud is where these ants
have chosen to build their nest.
And teamwork has turned the tide to their advantage.
Each high tide brings a fresh bounty of food
that the ants can harvest.
But this tide also brings the threat of drowning
and the precious ant larvae being swept away.
The ants have a cunning strategy.
Every tide, these ants combine their forces
and move the entire nest, larvae and all,
into bell-shaped chambers they've built,
which trap the air, keeping them safely above the waterline.
Here, they'll remain for several hours, until the tide retreats.
So cooperation between arthropods of the same species
offers great advantages.
But we must look elsewhere
for the ultimate key to the success of the arthropods.
We must examine the idea
that diversity stems not only from cooperation,
but also exploitation.
A female bolas spider.
She's hunting for food...
..and she's got a pretty unique way of doing it.
She spins a single thread of silk,
thinner than a human hair,
with a sticky globule on the end.
And from special glands on her abdomen,
she produces a pheromone to attract her prey.
She waits.
An approaching moth,
but she hasn't quite got her eye in.
She doesn't miss twice.
So arthropods affect their own diversity
by providing a food source.
And necessity being the mother of all invention,
they've evolved some diverse and ingenious ways
of catching each other.
But the exploitative relationships between them don't end there.
The Mojave desert in California.
This is a female blister beetle.
She lays her eggs in the scorching sand of the desert,
a few centimetres below the surface.
The perfect temperature for incubation.
When the larvae hatch,
they need to find food - and fast.
En masse, they climb the nearest stem of grass
and form a cluster.
They release a pheromone
identical to that produced by a female digger bee,
and it isn't long before they're noticed.
This is a male digger bee and he's come to mate,
but instead of an amorous reception,
he's boarded by hundreds of larvae.
Temporarily stunned,
he falls to the floor,
but quickly regains his composure...
..and heads off in search of another female.
While he's mating,
his stowaways jump ship.
The female then returns to her burrow,
where she's secreted pollen
for her unhatched young.
The blister beetle's larvae have reached safety
and a ready supply of food,
and when the pollen is finished,
they'll consume the young of the digger bee.
So we know that predation
and exploitation lead to diversity.
But there's one final factor
that affects the success of the arthropods.
One final vital key that unlocks a greater understanding
of their world, and without which,
the array of life we see today
would not be present,
and it's diversity itself.
Diversity breeds diversity.
Arthropods are part of a constant arms race
to outmanoeuvre and exploit each other,
a process called coevolution.
To see coevolution at work,
we must head to a meadow
in the Swiss Alps.
This is a female Alcon Blue butterfly.
She lays her eggs on the gentian plant,
and when they've hatched into caterpillars
and eaten their fill, they drop onto the ground.
Surrounded by foraging ants,
you'd think they'd be at risk,
but the ants dutifully collect them
and transport them back to their nest,
where they're cleaned and fed.
The Alcon Blue caterpillars have bewitched the ants.
They emit chemicals that convince the ants
they're one of their own larvae,
even producing noises
similar to those made by the queen ant,
to ensure the royal treatment.
They've checked in to a five-star ant hotel.
But the ingenuity of this butterfly species
presents an opportunity to any other species canny enough to exploit it.
This is an ichneumon wasp.
Out of hundreds of ants' nests,
she's able to detect the one
that contains an Alcon butterfly caterpillar.
The ants' response to any invader is to attack...
..but she releases a pheromone
that deranges the ants.
They begin to attack each other...
..and this buys her the time she needs.
The wasp makes a beeline for
the butterfly larvae,
where she will lay her eggs.
Job complete, she leaves the nest.
The ants' nest, released from the wasp's spell,
returns to normal.
The caterpillars remain in the nest
until the following summer,
when they transform into a pupa,
and after about a month,
the adult butterflies emerge.
But not every pupa contains
an Alcon Blue adult.
A young ichneumon wasp.
The exploiter has become the exploited.
Diversity has presented opportunity.
The wasp has evolved to exploit the butterfly...
..who exploits the ants.
Their lives are intricately linked.
They have coevolved.
And this is the final vital key
to the abundance
and diversity of the arthropods.
The process of coevolution.
All over the world,
the opportunities presented by other arthropods
are creating the pressure to innovate and evolve.
No doubt this diversity wouldn't exist
if it weren't for that winning body plan,
small size,
ability to reproduce,
work cooperatively,
and finally, predate and exploit each other.
But it's this snowballing effect
of diversity itself
that raises arthropods onto
a whole new level.
The arthropods have lived,
survived and thrived on Earth
for 400 million years...
THUNDER BREAKS
..through extreme climate change,
volcanic events,
ice ages,
and the extinction of the dinosaurs.
In fact, arthropods have survived and thrived
when 99.9% of all species
that ever lived have become extinct.
They are the most successful
and diverse group of animals to have ever lived.