Original subtitles

A Summer evening on the Korus river in central Europe.

Its waters are mirror- smooth - but on this particular day of the year,

all that is about to change.

Giant mayflies - Europe's largest -

are starting to rise to the surface and struggle out of

the skins in which they lived as larvae.

At first they come in ones and twos.

Soon there will be millions.

For two years, they've lived underwater.

Now they must fly - to find a mate.

This should be the climax of their lives.

The first to appear are quickly taken by predators.

But soon the swarms are so huge

that neither fish nor birds can make any impact on them.

The first mayflies to emerge in this mass hatching

on this river in Hungary are all males.

As soon as they free themselves from the larval skin on the surface,

they take off and seek safety in the banks

and there they hang on trees and bushes -

or indeed on my finger and the reason they have to rest like this is

because they still have to make one final molt.

Their wings that were transparent now have a handsome blue tinge;

and the elegant filaments at the end of

their abdomens are even longer than before.

They're looking for mates - but they have a problem.

They can't feed for they have neither mouth nor stomach.

They have to fuel their flight entirely

from the reserves of fat that they built up

when they were larvae feeding in the river.

But that fat will only last them for about half an hour of flight time.

So the race to mate now becomes a frantic one.

The females begin to rise to the surface

and the males fly up and down the river searching for them.

As soon as they find one, they all pounce on her,

competing to be the one to fertilize her eggs.

But the struggle of doing so saps their limited energy.

Before long they begin to run out of fuel

and though they flutter despairingly,

they can't maintain themselves in the air.

Win or lose, their lives are almost over

and dead bodies start to litter the surface of the water.

But the females are still in the air.

They're flying up-stream,

judging the depth of the river and the currents in it,

to find a place where they can lay their eggs

so that they will float back down-river to the same sort of place

where the adults themselves lived as larvae.

The ancestral mayflies were among the first creatures

of any kind to take to the air about three hundred

and twenty million years ago.

For them, as for their living descendants,

flight was a brief but invaluable way of finding a mate

and expanding their breeding territories.

The river has also been the home of another kind of insect

with an equally ancient ancestry

and it too is beginning to emerge from the water.

Bigger and more ferocious than the mayfly larvae,

it has been feeding on tadpoles and even small fish.

But that phase of its life is over.

Now each one has to haul itself out of the water

and into the air.

On the top of its thorax it carries a bulging back-pack.

It hunches itself and its outer skin splits.

A very different creature begins to appear.

White threads are drawn out of its flanks.

They are the linings of thin tubes that penetrate deep into its body -

air tubes that will enable the insect to breathe,

now that it is out of water.

It gulps air - inflating its body,

forcing fluid into the bundle on its back.

Its wings begin to unfurl.

Ten minutes later - the wings open. They'll never close again.

Next, the huge muscles within its thorax

must be exercised to prepare them for action.

And it's away.

Dragonflies, like mayflies,

belong to the most ancient group of insects

that flew over the land and here in the Museum

in Harvard there are fossils of them that are 150 million years old.

They're almost identical with species that are still flying today.

However they are by no means the oldest.

We know that there were other dragonflies even earlier -

225 million years ago -

that were flying through the Coal Measure swamps.

We don't have complete specimens of any of those

but there are some tantalizing and amazing fragments -

and here's one.

This marvelously preserved wing has very much

the same pattern of veins supporting panels of membrane as living species.

The thing that makes it different is its size.

From base to tip it measures twelve inches -

30 centimeters.

Little imagination is needed to replace the membrane that must have been there.

This insect must have had a wing-span as big as a seagull's.

Vibrating these wings, preparing for flight,

must have been a formidable business.

A creature this size must have been at least ten times heavier

than the largest insect flying today.

How did it manage to get into the air?

One suggestion is that in those far-off times

there was much more oxygen in the air -

and that would have given the extra power

needed to beat these huge wings.

But it's a fair guess that this ancient pioneer of the skies flew

with much the same technique as dragonflies do today.

Living dragonflies can reach speeds of nearly 40 miles

an hour and fly several miles in their search for new territory.

They're all aerial hunters,

relying on their supreme aeronautical skills

to snatch their prey from the sky.

Their great agility in the air comes

from being able to beat each of their two pairs

of wings quite independently.

You can see clearly that they do this,

when the camera slows down the action four hundred times.

This one is coming in to its perch.

Perfect control is essential to make all the tiny adjustments needed

for an accurate pin-point touch-down.

All dragonflies, when they perch, hold their wings outstretched.

But they have close relations - damselflies -

and they perch with their wings closed above their backs.

Mosquitoes stand little chance when damsels go hunting.

But flight for damsels, as for dragonflies and mayflies,

is primarily the means to find a mate and to breed -

and to do that they, like the others, need water.

Flight is itself an important element in their courtship.

These blue males must first establish a territory

for themselves above open water -

and that involves aerial jousts that can last for hours.

Mature females -

whose wings in this species are not blue but golden brown -

are attracted to those males who control good places for egg-laying.

But the males must nonetheless display the correct wing signals.

This one, patrolling his territory,

is using a special flight to flaunt his handsome wings,

inviting females to join him.

A female signals her willingness

to consider doing so with a flick of her wings.

So now he treats her to his full display.

The female's tail-up posture is apparently a signal

that declares that she's not yet sufficiently impressed.

Now, it seems, he's got it right - her tail is pointing downwards.

He grabs the back of her neck

with the claspers at the end of his abdomen.

She brings her abdomen forward to reach

a chamber under his thorax where he stores his sperm.

His first action, though,

is to scour out her genital tract to remove any sperm

that might be there from a previous mating.

Only when he's done that, will he inject his own sperm.

And now he must show her the best places in his territory for laying eggs.

He flies up and down, with his tail curled

and lands on a suitable piece of vegetation.

The female settles down to lay,

cutting slits in the plant stems with her ovipositor

and inserting an egg into each one.

She may lay as many as thirty.

And all the time,

the male keeps guard lest rival males should try to mate with her.

In other damsel species,

the males make sure that no other male can reach their partners

by keeping hold of them throughout the whole process.

The young that hatch from the eggs of these insects -

the larvae - look very unlike their parents.

This is a dragonfly larva -

and it's in this form that dragonflies spend most of their lives.

The larvae of both dragonfly and damselfly are savage predators.

They'll even feed on their own kind if they get the chance.

This particular larva has a very special problem.

It's a cascade damsel and it has to snatch prey that is swept past it

by the rushing water.

Cascade damsels are very rare and live around

just a few central American waterfalls,

like this one in the mountains of Costa Rica.

The adult male has to perform

his courtship flight under very difficult conditions indeed.

Somehow, he's able to fly even when he's dripping wet

and he shows off to the females

by actually flying through the cascades of water.

To be a good breeding territory,

the vertical rock surface has to be covered

by just the right amount of water.

Too deep and prey may be out of reach;

too shallow and the larvae could be picked off by birds.

A female will only mate with a male

if she approves of his choice of territory.

And this one, it seems, does.

This is it - and she carefully fixes her eggs to the rocks.

But not all damsels need great areas of open water for breeding.

In the rain forests of Central America,

like this one here in Costa Rica,

there's a damselfly that has managed to break the link

with open expanses of water like rivers and ponds.

It's also one of the most spectacular members of the entire family.

The helicopter damselfly,

the largest in the world with a wing-span of up to 20 centimeters.

The males tend to frequent sunlit patches

where the females can see them easily

and they have a special lazy flapping way of flying that is,

in itself, an invitation.

But although helicopter damsels can live away from rivers and streams,

the females nonetheless require a little water

in which to lay their eggs and there is just enough

in this little hollow here - and with luck she'll come down.

And into the water they go.

But these eggs have water-tight casings,

so they can be laid in air.

They are butterfly eggs.

The link with water has been broken.

Butterflies fly in a very different way from dragonflies.

They overlap their two pairs of wings so that they flap as a single pair.

They can't fly as fast or as aerobatically

as dragonflies but they nonetheless are tireless in their search

for the particular food that will suit their young -

and in the case of the cabbage white - that's cabbage.

Now on the surface of this cabbage leaf there's a patch

of tiny little pill-box-shaped eggs.

And when they hatch,

the baby caterpillars will emerge and make an instant meal of the greenery.

And they are already stirring.

But the first dish on the menu is not vegetables.

It's the shells of their own egg capsules -

protein-rich and far too nourishing to be wasted.

That first course, however, doesn't last long.

Now for the main dish - cabbage leaves.

When cabbage plants are damaged,

their leaves release a smell and that quite often attracts

the attention of a rather different insect.

It's a tiny wasp called Cotesia.

She too is trying to make sure

that her young have food immediately available -

but they like living flesh.

So she injects her eggs into the butterfly's caterpillars.

She does this with such surgical precision

that her victims are not mortally injured

and they continue feeding as if nothing had happened to them.

But now much of what the caterpillars

so laboriously gather goes to nourish the wasp grubs

that are developing within them.

As the caterpillars grow, they shed their skins.

They do so five times until ultimately

they are eight hundred times heavier

than they were when they first hatched.

This fully-grown caterpillar must now find shelter.

A strand of silk of silk trails behind it -

silk with which it ties itself to a twig.

And here, over a couple of days, it changes into a chrysalis.

Those caterpillars that were injected

by the Cotesia wasp don't get that chance.

The grubs within them are now emerging.

They too spin silk which hardens to

form a cocoon beneath the caterpillar's empty skin.

Inside, the wasp grubs are transforming themselves

and two weeks later - out come the adult wasps.

A different future awaits the chrysalis.

Within its shell and over a similar two weeks,

the caterpillar's body has been broken down and reassembled -

and now the adult is ready to emerge.

Its wings, like those of a newly-emerged dragonfly,

need pumping up with liquid.

The creature that was once an egg, then a caterpillar,

then a chrysalis has attained its final incarnation.

So another generation of cabbage whites set off

to find good places for their young.

With their fragile- looking wings and apparently erratic flight,

butterflies might not seem to be the most powerful of flyers,

but in fact they are extremely accomplished aeronauts

and they can fly hundreds of miles

if necessary to find the food they need.

Some butterflies use the power of flight for another purpose -

to escape bad weather.

These lush sub-tropical valleys in southern Taiwan are warm

and green all year round and in winter,

they're filled by literally millions of butterflies.

They've all come from the north of this great island,

five hundred miles away,

for there the cold weather has killed off the plants

on which they fed during the summer.

In the mornings they take off from their roosts

and head for the forest canopy,

to warm themselves in the rays of the rising sun.

They have to conserve as much energy as they can,

so instead of using their stores of fat to warm themselves,

they absorb the sun's heat.

There are four species of crow butterflies here

as well as two species of blue tiger butterflies -

and all find enough food to sustain themselves

in these warm and fertile valleys.

Butterflies feed on liquid -

nectar and the juices of rotting fruit -

and to suck it up they have, instead of jaws,

an extraordinarily long but extremely thin tube.

In a newly-emerged butterfly this tube is in two pieces,

for it is in fact a highly modified pair of mouthparts.

Each half has its own muscles and nerve supply

so that the whole unit is fully movable and controllable.

As the young butterfly prepares for adult life,

these two sections are zipped together to

form a tube like a miniature drinking straw.

A special fluid cements the two halves together.

The tube is largely made of a material called resilin which,

when distorted,

springs back to its original shape -

in this case a spiral like a watch spring.

When the muscles within it contract,

it straightens into a long probe that the butterfly can

then insert deep into a flower.

Butterflies and moths have the largest of all insect wings

and their great size means that they can be used very effectively

as bill boards on which to display patterns proclaiming

the species of their owner.

The patterns are produced by tiny scales

that cover the wings like tiles on a roof.

Some have a microscopic structure that refracts

the light and gives the wing a brilliant iridescent shimmer.

Others contain chemical pigments.

With these lovely advertisements,

a male butterfly displays to females and warns off rivals.

Vivid patterns and bright colors

are used to a much lesser degree by moths -

for many are only active at night when colors,

of course, are not easily seen.

Moths also feed primarily on nectar which they suck up

in the same way as butterflies do.

But one moth manages to tap a food source no butterfly has yet exploited.

It comes from lantern bugs which feed by drilling

into the bark of a tree

with their proboscis and sucking out the sap.

This contains a little protein, which the bug wants,

but a lot of sugar, most of which it doesn't want.

So it squirts out the sweet excess

and to make sure that this doesn't attract ants that might attack it,

it fires the droplets well away from the tree trunk

with a tiny spring- loaded spatula at the end of its abdomen.

One enterprising species

of moth regularly sits behind the bug all night

with the curled tip of its proboscis delicately placed

in the stream of droplets.

As sugar water accumulates, so the moth sucks it up.

Most moths, however,

feed by the rather more laborious method

of flying from flower to flower.

A few - the busiest -

do so not only at night but during the day as well.

These are the hawk moths and there are several species

of them gathering nectar

from this buddleia bush in the south of France.

This hawk moth can fly very fast indeed when it wants to but it can also hover,

as it's doing now, to sip nectar from each one of these small flowers.

Beating its wings as fast as this, of course, takes a great deal of energy,

so these hawk moths have to spend much of their day going

from flower to flower sipping the nectar which is so rich

in the carbohydrates they need to power their flight.

They have huge forward- pointing eyes that enable them

to aim their proboscis with such accuracy

that it slips into the exact center of each tiny flower.

With so many minute flowers so closely bunched together,

it would be easy for the moth to visit some twice.

But that would waste energy and if we mark each flower

as the moth drinks from it, it's clear that the moth,

somehow or other, never does this.

Hummingbird hawk moths have no difficulty in hovering.

Bee hawks however,

have heavier bodies and they sometimes use their legs

to help support themselves as they work.

Their need to keep drinking is so pressing

that a female will continue to do that even

when the male with whom she is mating seems

to be trying to fly in the opposite direction.

The Buddleia plant may be a particular favorite

of hawk moths but it is, of course, a foreigner,

introduced into our gardens from China in the nineteenth century.

The hawk moth's original supplies of nectar came

from the flowers of the meadows.

And they still feed there,

alongside many other insects.

This is a carpenter bee.

Bees also have two pairs of wings but they are hooked together so,

like those of butterflies, they operate as one.

Bumblebees have particularly large and heavy bodies and flight,

for them, can be a real effort.

That's particularly so in spring when the mornings are cold

and queen bumblebees are just emerging from their winter sleep.

It's only a few degrees above freezing,

but a queen needs to get started early to look for food.

The thick furry hairs on her body help to conserve

what heat she manages to generate.

At the moment she's only a few degrees warmer

than the surrounding vegetation - as a thermal camera clearly shows.

Her body is only marginally more pink

than the blue leaves and moss around her.

But she has a special way of warming up for flight.

She can put her wings out of gear so that,

without moving them,

she can revv up the wing muscles inside -

and that raises the temperature within her thorax

by twenty degrees centigrade or even more -

as the expanding yellow image on the thermal camera indicates.

Her body temperature is now over 30 degrees centigrade.

At last, she has a chance of lift-off.

She will now be able to visit the spring flowers

while it's still too cold for others to do so.

The long trumpets of the daffodils retain heat very well

and they're still warm even after their hot-bodied visitors have left.

Flies, back in their distant evolutionary past,

also had two pairs of wings,

but their back pair have been reduced to simple knob-ended rods.

These are particularly long on crane flies.

They're part of the fly's flight instrumentation.

Microscopic sensors on their upper and lower surfaces tell their owner

about the air currents around its body and so help in flight control.

They start up even before take-off.

Flies are such accomplished flyers

that they can land upside-down on a ceiling -

or, in this case, the underside of a twig.

Only when you slow down a fly's flight -

here by a hundred times -

can you fully appreciate what superb aerial control they have.

Some species, like these long-legged flies,

flaunt their wings in courtship, just as damselflies do.

These dance flies are voracious hunters

and it's particularly important for them

that they perform their dance correctly.

If one doesn't get it right its partner might well eat it.

This performance, however, seems to have been up to standard.

For hoverflies -

arguably the most accomplished of all insect aviators -

immaculate aerial control is what makes a male attractive to a female.

A male lays claim to a mating territory by trying to stay

in exactly the same position in space for as long as possible.

That's not easy when there are others all around you,

trying to do precisely the same thing.

It might seem that he's absolutely motionless,

but in fact he's having to make continual changes

to adjust for slight currents in the air.

It's an amazing piece of acrobatics -

far better than anything that we could do in a helicopter.

And it's all done in order to impress the female -

to show her that he is superb at holding his territory.

Having to chase away rivals that come too close is an exhausting business -

and when you're trying to maintain your hold on a particular point in mid-air,

even a small midge has to be chased away.

After a morning spent doing this,

a male hoverfly may have lost as much as a third of his body weight.

Little wonder that he takes a break at mid-day in order to rest and refuel.

He dabs up nectar with mouth-parts that are shaped like a pad.

Having refilled his fuel tank,

the male returns to his territory for the afternoon's session of hovering,

in the hope of attracting yet another female and mating with her.

Once again, with his superb eyesight,

he's ready to spot anything that might whiz by him

at high speed that could be a female.

And I might just be able to fool him with a pea-shooter.

Although there may seem to be an extraordinarily large number

of different flies in the world,

it's actually the beetles that are the most varied of all insect groups.

There are 300,000 species of them.

Most find their food by crawling and burrowing on the ground

and to prevent their wings from being damaged in the process,

they've turned the front pair into protective shields.

Some, like weevils,

keep their wing-covers permanently closed

and before take-off push their functional wings out of special slits.

Ladybirds, like most other beetles,

raise their wing covers and hold them clear

of the hind wings throughout their flight.

The result could hardly be called aerodynamic

and consequently their flight is rather lumbering.

Blister beetles are scarcely any better.

When a flight is over,

the hind wings have to be packed away beneath the covers - a process

that can be so complex that it demands all the skills

of a Japanese master of origami.

With flight playing a relatively small part in their lives,

many beetles have grown very large.

This one, the titan beetle that lives in the forests of the Amazon,

is almost certainly the biggest of all insects.

I have to handle him with considerable care

because those huge mandibles at the front are,

powerful enough it's said,

to be able to cut straight through a pencil.

He can fly, but he can't get into the air from the ground.

He's too heavy to do that, so he has to climb trees

and launch himself into the air that way,

and that's why he's got such powerful legs,

armed with sharp claws.

The titan is now known to be the biggest of all beetles.

The champion is seven inches long from the tip of

the mandibles to the tip of its abdomen.

The larva of this great monster has not yet been found

but it must be at least twice as big as the beetle -

a really huge grub.

Beetles and many other insects spend so much

of their lives as flightless larvae that it'd be more accurate

to think of them as creatures of the earth rather than the sky.

Flight for them - as it is for the mayflies -

is a relatively brief episode at the end of their lives.

These cicadas in the eastern United States,

spend seventeen whole years below ground,

sucking sap from tree roots.

And then - within a few days - a whole population emerges.

There may be millions of them in a single acre of land.

They clamber up the trees whose roots have provided them

with sap for all of those seventeen years.

And here they change into their adult costume.

Now they have the wings they need to search for a partner.

Empty larval cases cover the tree trunks and the ground beneath.

And above, in the branches, the millions have started to sing.

The noise is ear-splitting.

After seventeen years of living underground,

the cicadas are now approaching the climax of their lives,

and for the males, that means this.

The call is his way of attracting a female.

The females reply with a quite different sound.

A click made by flicking her wings -

so that's what the males are listening out for.

I can imitate the female's wing flick with a snap of my fingers -

and that causes them to follow me anywhere;

because they're so determined to find a female.

Now can I bring you back.

How about coming this way.

Oh! The noise is awful. Come this way. Come on.

Yes, I can hear you.

Ooo. - Quite right.

At last, a male finds his partner and as he does his call alters.

He's indicating to her that after seventeen years

the time has come to get down to business.

How do these cicadas all emerge simultaneously

after seventeen long years?

Well, we know that they can appreciate changes in the contents of tree sap,

so they're able to detect the passing of a year.

But how do they count up to seventeen? We have no idea.

But even if we did,

this surely would remain one of the most astonishing,

amazing events in the insect world -

and it'll all be over in a couple of weeks for another seventeen years.