The Swarming Hordes Life on Earth

Locusts. In the eyes of man, one of the greatest plagues on Earth.

But from a less human point of view,

they are dramatically successful members

of a group that itself is the most numerous and varied kind of animal in the world.

The insects.

Like all insects, the locust's body is divided into three parts.

A head, a middle section, and an abdomen that contains the digestive and reproductive organs.

The middle section is full of muscle and carries six legs

and usually a pair of wings.

Its skeleton is external, like a shell,

and it's made of chitin, a basically flexible material,

but one which can be hardened to make mouth parts tough enough to cut through leaves,

wood and even metal.

There may be as many as a million million individual locusts

in a single swarm like this.

And these locusts are only one species.

Science has so far described and labelled

nearly a million species of insects,

and there are probably two or three times as many still awaiting labels.

The very first insects evolved some 300 million years ago.

From the very beginning, many lived by eating plants,

but in one way at least the plants benefited from their presence.

They used them as messengers and recruited them with flowers.

Magnolias have flowers very like the first flowers developed by any plants.

They're relatively simple.

They contain both male and female cells.

The male cells come from these structures around here,

in the pollen,

and the female are buried

at the base of this structure in the centre.

Clearly, there's a strong chance this flower might fertilise itself,

but there's a real advantage to be gained if the pollen can come to

this female cell from another plant

because that way, there's a greater chance of variation in the offspring.

And variation is the raw material of evolution.

And it's here that the insects help the plants.

Beetles have probably fed on the spores of ferns and horsetails from early times.

So there can have been little difficulty in attracting them to the pollen in the first flowers.

Primitive moths also took to the habit very early.

Of course, if the insects ate all the pollen, that wouldn't help the plant,

but they're messy feeders, get grains all over them,

and these brush off onto other flowers and fertilise them.

So both plant and insect profit

and the habit of pollen munching began to spread.

The plants produced more pollen than they required for fertilisation,

and all kinds of insects visited flowers to feast on it.

The sexual reproduction of flowering plants ensures the variation in the offspring

on which natural selection depends for evolution to take place.

The greater the insect traffic from flower to flower and plant to plant,

the greater the potential for variety and evolution.

In time, the first flowers increased the prizes on offer.

They produced sweet tasting nectar,

and some insects turned their mouth parts into tubes

so that they could probe deep into the flowers and sip it.

But such delectable rewards had to be advertised.

Some flowers became brilliantly coloured so that they were conspicuous even from a distance.

Some also developed powerful perfumes to announce there was nectar on offer

and pollen to be transported.

The sheer beauty of flowers,

their elegance of shape, the exquisite colours and patterns,

are an endless source of delight to us.

But flowers appeared on Earth millions of years before man,

and they developed not to appeal to the human eye

but to the eyes of insects.

These designs are far from arbitrary.

They are signals indicating where pollen and nectar can be found.

These patterns of dots and lines

are as precise as instructions on an airfield,

showing the insect exactly where to land and which way to taxi.

Many insects can see parts of the spectrum that are invisible to us, such as ultraviolet.

So if we photograph a flower with film sensitive to ultraviolet light,

we can get an insect-eye view of it, which is sometimes very different.

This meadow cranesbill

seems to have faint lines on its petals,

but their ultraviolet markings are very distinct indeed.

Other plants have adopted a different tactic.

Instead of producing pollen in one place on a big flower,

they produce many tiny flowers in a showy bunch,

so that wherever visiting insects go, there is pollen and nectar to be gathered.

Some have taken this design so far,

that they have come to look like single flowers.

The yellow mass in the centre of this daisy is made up of several hundred small flowers,

each with its stamens and ovaries.

So it is to insects and their sensitive eyes

that we owe so much beauty.

But there are many drab flowers - the hazel, for example.

It's obvious these must rely on a quite different way of transporting pollen. The wind.

The male flowers have to be large

to produce the great quantities of pollen needed for such a haphazard method.

But the female flower, with no need to advertise,

is an inconspicuous little tuft.

Oak trees use a similar system

with separate male flowers that fill the atmosphere with pollen,

only a tiny proportion of which rains down onto the place where it serves its most proper purpose -

on the female flower.

Some flowers use wind in a different way, to summon insects with perfume.

The arum lily's intoxicating scent attracts them just as it pleases us.

But some insects have different tastes from ours.

The stapelia smells of rotting flesh,

disgusting to us, but extremely attractive to flies that feed on carrion.

And when they arrive,

they find flowers that tempt them still further,

for their petals actually resemble the wrinkled, decaying skin

of a dead animal.

The amorphophallus of the jungles of the Far East relies almost entirely on smell.

The overpowering stench that comes from this huge bloom,

as tall as a man, resembles that of rotting fish,

mixed perhaps with a little burnt sugar.

Its European relative, the modest wild arum or cuckoo pint of English hedgerows,

also produces a faint, unpleasant smell as well as warmth.

Having attracted numerous small flies, it then traps them.

The lower part of the scent-producing rod secretes little drops of oil.

Insect visitors lose their foothold and tumble past the slippery, downward-pointing hairs

into the lower chamber, where the flowers are.

The top ones are male, which are not yet mature.

There's nothing here for the insects.

Below the male flowers are the female flowers.

The small flies, which may have visited other arums the previous day,

now inadvertently spread pollen on them.

But the insects can't escape. The oily hairs keep them imprisoned

and they have to remain there all night.

The next morning, the hairs, the bars of their prison, have shrivelled.

The female flowers have closed their stigmas so they can no longer be fertilised,

and secreted a tiny drop of honey as a reward.

But the male flowers have opened and shed pollen over the flies,

which are now free to look for another arum in which they may, inadvertently, spend the night.

Pollen taken from one species of flower and deposited on a different species is wasted.

So there's been a tendency in the insect-flower alliance for particular partnerships to develop

and for one species of flower to become intimately involved with just one species of insect.

The nectar of some flowers is hidden away and reserved

for those insects with exactly the right mouth parts and feeding manners,

and which will assiduously visit all the blooms of that species

that they can manage during the flowering season.

The salvia blossom only opens its doors when an insect of the particular weight and shape of a bee

lands on its flight deck, triggering the stamens to stamp pollen on top of its abdomen.

The flowers go on producing nectar, and a few days later their ovaries become mature.

When a bee comes to visit them this time, it's the stigma projecting from the top of the ovary

that jerks downwards and collects the pollen.

This kind of relationship has led flowers away from the original circular designs like magnolias

to develop complicated constructions of triggers and levers,

delicately balanced platforms and slippery pits.

The bloom has now become a kind of obstacle course,

ensuring that the visitors are not able to collect their rewards

without completing the essential service of transporting the pollen.

The most complicated mechanisms of all are those produced by orchids.

Even now, there are some we don't understand.

This one, the flying duck orchid from Australia,

has the most extraordinary action as it opens,

but we don't know why it's shaped this way, why it moves like this

or on what insect it relies to carry its pollen.

This orchid attracts insects by sexual impersonation.

It gives off a perfume like that of a female ichneumon wasp.

When the male arrives, he finds something that not only smells like his female,

but looks remarkably like her.

At one end of the bloom, there's a mass of pollen stuck together into a horseshoe shape.

The ichneumon male copulates with the flower.

And the pollen mass is so placed that it fastens neatly onto his abdomen.

In fact, this orchid is totally dependent on one species of ichneumon wasp for pollination

and therefore reproduction.

The orchid can only survive as long as the ichneumon wasps do.

When the male insect copulates with the next flower,

he delivers the pollen from the last.

The yucca plant of Central America

has a relationship with its insect partner that is so close

that now both insect and plant are completely dependent on one another.

The yucca's creamy blossoms are visited by tiny moths.

During the day, the moths spend a lot of time moving from flower to flower and inspecting them.

All are not at the same stage of development.

The stamens become mature first and split open, and it's these that the moth is looking for.

In the late afternoon, the female moth, having already mated,

is collecting pollen from suitable flowers.

She's now gathered the pollen into a tight ball

which she holds under her head as she searches

for other flowers which are in a different state of development.

This time, she's more interested in the central part of the flower,

and takes up a position alongside one of the ovaries, which have a green-tipped stigma.

Here she will stay for about 20 minutes.

Her egg-laying tube is deep at the bottom of the flower's ovary,

and she's laying her own eggs there.

Having finished laying,

she separates some pollen grains from the ball she's collected

and smears them into the stigma with mouth parts specially developed for the purpose.

Now she will repeat the entire procedure

in other ovaries of the flower.

The egg-laying position again.

Again she will pollinate the flower.

First she removes a small amount of pollen from the ball she's holding.

By pollinating the flower,

she serves not only the yucca but her own offspring,

for she ensures the eggs in the ovary below will develop

so that her caterpillars when they hatch will have a rich source of food immediately to hand.

But the caterpillars won't eat all the seeds.

The moths don't lay as many eggs as that. So when the yucca comes into fruit,

there are plenty of undamaged seeds to ensure that new plants will appear.

But the balance is a very delicate one.

If it went wrong, it could be disastrous for both plants and insect.

Without the moth, the yucca would not be pollinated.

Nothing else has those specially modified mouth parts for pressing the pollen into the style.

And without the yucca, the moth's caterpillars would starve.

The seductive odours and beguiling shapes of flowers

are so attractive to the insects for whom they're designed

that they find them virtually irresistible.

Other insects turn that to their advantage in a different way.

This ginger flower has petals that move.

It's one of the most extravagant designs of any insect.

For this, with flaps on its legs that match the petals of the flower, is a mantis.

The butterfly comes to sip nectar.

There are many different kinds of mantis, all marvellously camouflaged,

all voracious hunters.

The flesh of an insect is succulent,

but to get at it the mantis has to deal with the external skeleton,

the shell of chitin.

Chitin is dead material. It won't expand.

It's one of the few limitations to the insect body that is otherwise so versatile.

In order to grow, all insects have to shed their skin at regular intervals,

and this bug is just about to do so.

A new, soft skin has formed underneath, and by sucking in air and inflating itself,

the bug is cracking its old skin.

Once free, the bug inflates itself still further,

stretching out the crinkles in its soft skin and expanding.

After an hour or so, its new skeleton has hardened.

A spiny leaf insect is just about to do the same trick.

Its old shell hangs from the branch above it

like the ghost of its former self.

But the more complicated an insect's body,

the more laborious and difficult this process of skin shedding becomes.

And some insects not only simplify it but exploit different food sources

by leading split lives.

This creature emerging from the egg will eventually become a butterfly.

But for the first part of its life, it will keep its body simple.

A caterpillar.

A caterpillar is little more than an eating machine.

This one starts its life as it means to go on by eating its own eggshell.

The caterpillar's existence is totally dedicated to food.

It won't breed, so it doesn't need sexual organs.

It has no cause to attract a mate,

so it need not send out any signals to one

or develop wings so it can fly off and look for one.

Its parents have gone to a great deal of trouble

to ensure it finds ample food immediately to hand,

so all it really needs is an efficient pair of jaws

and, behind them, a bag-like expandable body.

But if a caterpillar's body is to expand,

it can't have a hard, rigid external skeleton.

Just a thin, flexible skin that is easily shed and replaced.

And that could leave it vulnerable.

So caterpillars have to have other ways of protecting themselves.

Some do it by bluff,

developing markings that look like fearsome eyes.

Some rely on camouflage initially, and if that doesn't work,

they too try to startle.

The caterpillar of an Australian swallowtail

looks convincingly like a glistening bird dropping,

and if any predator thinks that's worth investigating,

then it suddenly, and unexpectedly, produces strange antennae.

Many caterpillars sprout long hairs tipped with poison

that can cause quite a rash on a human skin and certainly put off a lot of birds.

To make sure that would-be predators are in no doubt they're unpalatable,

the caterpillars advertise themselves with bright warning colours.

So, with the best protection they can muster,

the caterpillars industriously pack away their food,

slipping off their thin but often flamboyant skins when a bigger one is required

until they have grown as much as they need.

And then they prepare for the first of two highly dramatic transformations.

Many moths make the change in private behind a silken shroud.

Industriously, they spin and weave.

This one adds tiny pieces of bark to camouflage the cocoon.

Some of those that had poisonous bristles shed them in their final moult within their cocoons

and weave them into their wrappings

so that they will continue to protect them.

And now, all seems still.

Life, apparently, is suspended.

But inside, a profound revolution is taking place.

The caterpillar's body is breaking down into a kind of soup.

Clusters of cells that have remained dormant since the creature emerged from the egg

now become active, absorbing the soup, multiplying and reassembling a new body

from all the material that the caterpillar so industriously gathered.

Most butterfly caterpillars embark on this change unscreened by a cocoon.

Though usually inconspicuously close to a stem or under a leaf.

The Australian common crow caterpillar first spins a silk thread, from which it hangs.

Beneath its skin it has secreted a new and different one.

The old skin splits and rolls off, taking with it the hard parts for which there's no more use,

the tiny claws from the legs and those hard-worked jaws.

The new skin hardens and in a few hours becomes mirror-like,

reflecting the foliage around it for better camouflage.

The body of a butterfly may take months to rebuild,

or as little as a week.

The wings are crumpled bags, but the insect pumps blood into them

and slowly they expand.

The wings dry and harden, and the Australian orchard butterfly is ready for flight.

The primary task now of all these butterflies is to find a mate.

Scent is used to locate their mates over long distances,

and now their gorgeous wings carry them on the search,

proclaiming with their colours and patterns their identities

and so attracting mates of the same species at close range.

They still feed on nectar to provide them with the energy to fly,

but they don't need any food to build or renew their tissues.

The time for growth is over.

The birdwing butterflies of the Far East are among the largest and most graceful.

Male and female butterflies meet and courtship begins.

Successful males couple with females by joining abdomens.

These marvellous, elaborate structures, the wings,

each clothed by thousands of microscopic scales arranged in intricate patterns,

have, within a few days, in some species within a few hours,

completed their purpose.

Male and female have found one another

and the cycle will begin again.

The atlas moth is one of the biggest of all butterflies and moths.

But its body, of course, is small compared with that of a bird.

The reason is because of another limitation to the basic insect body design.

This moth, like all insects, breathes through a series of holes along its flank.

They're the openings of tubes, with many branches,

that extend throughout the body

and carry oxygen to every individual organ.

It's a system that works by diffusion.

It works very well over short distances.

But as the length of the tube increases, it becomes less efficient,

and eventually it becomes impossible.

That's why there are no moths or butterflies the size of eagles.

The insects have, however, found one way of transcending

this problem of the limitation of size.

Numbers. In this one single termite hill,

there must live two or three million insects.

But there are good reasons for considering them not as individuals

but as together constituting one single great super-organism.

A super-organism that simply in terms of animal tissue alone

must weigh as much as an antelope

and which certainly crops the surrounding vegetation as heavily as an antelope.

And when you look at these super-organisms

out here in Western Australia,

they seem to dominate the landscape just as powerfully

as antelope dominate the plains of East Africa.

This type of colony is not just a haphazard collection of individuals

who've decided to share the same dwelling,

like human beings in a tower block.

For one thing, they're all one family. All the children of a single, gigantic female.

For another, they're all incomplete creatures.

Not one of them could survive by itself for long.

These workers are all sterile.

The soldiers, which defend the community, have such huge jaws

that they can't feed themselves.

And the queen, in the middle of the colony, is so huge

that she can't move and has to have food brought to her.

She's a gigantic egg machine.

The workers bring food to one end and collect eggs from the other

which she produces at the almost unbelievable rate of 30,000 a day.

The male, the size of a wasp, lies alongside her.

She has a controlling effect on the activity of the colony.

She sweats a chemical substance which the workers obtain by licking her body,

and this in effect gives them their instructions.

It stimulates them to do certain things.

To feed the young grubs on a particular diet,

to move the eggs into special places.

At one moment, either because of a change in the queen's instructions

or because the eggs she lays are slightly different,

they hatch not into sterile workers but into sexually mature adults,

both male and female.

And then, suddenly, the colony seems to smoke

as thousands upon thousands of individuals emerge to fly off and colonise the surrounding country.

When they land, their wings break off. They won't be needed again.

Now the male and female begin their courtship dances.

Once they've paired,

they find a crevice and start to build themselves a nest.

He fertilises her, she will lay eggs,

and so together they will found a new colony.

A new royal egg machine will go into full production and the various castes of individuals

will hatch and grow.

Highly organised social behaviour like this seems to have evolved several times among insects.

Once among termites, related to cockroaches,

and several times among the ants, bees and wasps.

All three groups have mouth parts

adapted for chewing so they can easily build nests.

The wasps also use theirs for manipulating prey.

Having paralysed their prey with a sting,

some wasps pack them into their cells with the eggs

so their young will have fresh meat when they hatch.

Not all wasps and bees are social.

Many of them are solitary,

digging and stocking only their own cells.

Sometimes, however, the scarcity of suitable nesting places

causes otherwise solitary bees to breed close to one another.

When these adult bees of this species emerge from their pupae,

the males fight one another in order to mate with the females.

Other species of bee that nest in similar sites

are little more socially inclined.

By this Kansas river, a group of little sweat bees are nesting in a burrow with one entrance hole.

A guard bee stands like a sentry at the entrance and allows only its own species to enter.

New arrivals appear to be instructed what to do

by the bee that is moving backwards.

She appears to be the dominant bee in the small colony.

Other bees that seem to be identical in form

apparently accept subordinate roles,

taking on such jobs as building new chambers.

Other chambers are complete.

They already contain eggs or larvae at various stages of development,

together with a ball of pollen for food.

While all the work goes on,

one dominant bee appears to control the group's activities.

This bee can probably recognise others by their smell.

Certainly, taste and smell play a vital part in the coordination

of really big and complex insect colonies

like those of the honey bee.

Workers here are continually collecting chemical substances from the queen.

She is the particularly large insect here inspecting new cells before depositing eggs in them.

The chemical messages she produces circulate throughout the colony

because of the workers' habit of exchanging spittle.

Unlike termites, who travel over land to find food, bees fly.

So they're unable to lay a scent trail on the ground.

Bees have had to evolve a different method of telling co-workers where the food is.

When a worker returns from a new, rich source of food,

it goes onto the vertical cones,

its satchels on its legs packed with yellow pollen.

After exchanging spittle, it dances.

That waggling dance is about 20 degrees to the left of vertical,

and that means that the flower she's discovered can be found by flying

about 20 degrees to the left of the sun.

The other workers "read" the dance,

which is accompanied by noises which some people believe also carry information.

On leaving the hive, the workers remember the angle of the dance

and set off at the same angle to the left of the sun.

Because they can see polarised light,

the bees don't even have to wait for a cloudless day.

The origin of these colonies of insects presents quite a puzzle.

It's a basic principle of evolution by natural selection

that individual animals are engaged in a struggle

to survive, to breed and pass on their genes to the next generation.

How could it have been, then, that in the past there was some insect

that actually gave up that right and laboured to help another insect

pass on her genes to the next generation?

The answer seems to lie in the particular way that these insects reproduce.

Before the queen began laying, she was fertilised by several males called drones.

She stored their sperm in her body, but withheld it when laying to produce males

so they would carry only her genes.

When she lays in cells to produce female workers, she fertilises the eggs by releasing some sperm.

Occasionally, one of these females is allowed to develop into a new queen,

and eventually the old queen will leave in a swarm with her sister workers to start a new colony.

The net result of this complicated system

is that the female workers and their nieces by their new sister queen

are unusually closely related.

In other words, they share a high proportion of common genes.

And so, when these sterile workers labour away for the benefit of a colony,

in order to help the queen pass on her genes to the next generation,

they are in fact labouring on behalf of their own genes.

The insects that have brought this to a particularly high level

are the ants.

Their similar methods of reproduction and skill at manipulation

seems to be the reason why they too have evolved amazing social systems.

The green tree ants of Southeast Asia

cooperate in a most complex way to build their nests.

Groups of workers hold two leaves together, gripping them with their legs and jaws

to form a living bond.

Other workers bring the young grubs from the centre of the nest,

and by giving them little squeezes, stimulate them to produce silk.

Then, using them like tubes of glue,

they move them back and forth between the two leaves

until they fasten them together with a sheet of silk.

The cooperative behaviour of the ants holding the leaf

starts usually with one isolate individual who succeeds in bending over part of the leaf,

usually near the tip, where it's easy.

This seems to act as a signal for other ants to join in,

leaving whatever other tasks they're engaged in.

In these ants, the workers are divided into a major and a minor caste.

The major castes consists of workers who go out and do the foraging

and the minor castes are employed as nurses, looking after the larvae.

In South America, the parasol ants strip trees of their leaves,

cutting them up into pieces and carrying them one by one

into their vast underground nests.

The work goes on night and day,

hundreds of thousands of ants swarming all over the trees.

The technique of carrying a leaf many times bigger than the ant

depends on the worker tucking its head down onto its thorax before taking a grip.

Sometimes they carry these segments for 100 yards,

along trails that have been worn smooth by millions of tiny footsteps, day after day.

The ants will not eat these leaves. They can't.

Unlike termites, which have single-celled organisms in their guts to enable them to digest cellulose.

The ants are collecting leaves in order to chew them up and make a kind of compost.

On that, they cultivate a fungus in their underground galleries.

The fungus supplies the ants with special juicy branches for their food,

and the ants garden it with their own faeces and a special antibiotic dressing for a good yield.

The ants have regular refuse tips on the surface, not far from the nest.

Every now and then, the workers will suddenly stop dismantling trees

and turn their attention to cleaning out the nest.

The fungus which the parasol ants grow can survive nowhere else.

They are utterly dependent on one another.

Other ants have similar relationships with trees,

with the trees actually encouraging the ants to take up residence.

Some acacia trees in Central America have thorns for defence.

But these needle-sharp thorns are doubly dangerous

because inside them live colonies of aggressive stinging ants.

Each pair of thorns has an entrance hole near the tip of one of them.

The spongy cells that once filled the thorns

have been chewed away to make a strong and safe brood chamber

that becomes crammed with eggs and developing larvae.

The ants never have to leave the tree to feed,

for the acacia provides the colony with a beautifully balanced diet.

The tiny reddish-brown beads on the leaflet tips are rich in fats, proteins and vitamins.

Ideal food for developing insects,

although they have no real function for the tree.

The beads develop on the new leaves and at the tips of the shoots,

so the attendant ants are in a perfect position to protect the most vulnerable part of the plant.

The acacia also has nectaries,

but these are not part of its flowers.

The nectaries are situated at the base of the leaves,

and the sole function is to provide the ants with the sugary liquid of which they're extremely fond.

What, then, does the acacia get in return for these services?

The answer is defence. The ants are particularly ferocious

and defend the tree against any other insects that come to feed on it.

What's more, they also drive off any grazing animal that tries to eat the foliage.

And even mutilate and kill climbing vines that try to cover the host tree.

As a result, in tropical areas where competition is intense,

the acacia trees and their ants are a particularly successful team.

The most aggressive ants of all are the army ants

that build no permanent nest at all.

They also have one of the most advanced societies of all insects.

This colony has been temporarily camped overnight.

Somewhere in the middle of this living ball

is the queen and immature ants protected by the bodies of the workers.

They make their own bivouac by linking their legs and bodies together

with strong tiny claws.

At first light, in the morning, the colony will begin to disperse.

Between 150 and 170,000 workers may be present,

and some of them must carry the queen and larvae as the column moves off on a foray

guarded by the huge soldiers, whose only job is defence.

For two or three weeks, the army ants make a new bivouac each night.

Then their behaviour will change

and they will make a semi-permanent home,

often in a hollow tree.

The queen is now ready to lay eggs.

Over a few days, protected by her living shelter of workers,

she will lay between 100,000 and 300,000 eggs.

After three weeks, the larvae hatch.

And because of chemical secretions produced by these new recruits,

the colony is once more galvanised into great activity.

Now the nomadic phase begins again and the army goes to war.

They will kill every living creature in their path that can't run from them.

Normally they hunt other insects, but they will take small reptiles

and even kill dogs and cows if they're tethered and can't escape.

If the termite colony could be compared to an antelope,

then this formidable super-organism must be the insect equivalent of a beast of prey.

As powerful, ferocious and long-lived as many hunters of the jungle.

Whatever limitations there may be in being small,

these army ants and other social insects

seem to have overcome them.

Indeed, the more closely one watches insects, the more deeply impressed one is by their efficiency.

No matter what man may wish to believe, insects are still masters of great parts of the world.

They were, after all, the first animals to emerge onto dry land.

Then they lived by exploiting plants.

Hundreds of thousands of species of them still do so today,

chewing the leaves, gnawing the seeds and drinking the sap.

And when other animals joined the insects on dry land,

the insects exploited them too.

They drank their blood, burrowed into their skins,

they actually found a home within the tissues of living animals.

Man has been doing battle with the insects

ever since he first picked off the first flea and, I dare say, long before.

Today we continue the fight, with fire, with radioactivity,

with the most lethal poisons our chemists have been able to devise.

And yet, so far, we have not managed to exterminate a single species.