Original subtitles

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.

With its precious cargo secured, the bee prepares for flight.

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.

Subtitles by Red Bee Media Ltd