Original subtitles

Every spring, a tiny hero of the insect world undertakes a journey that almost defies belief.

Weighing less than a gram,

the intrepid Painted Lady butterfly migrates a staggering 2,000 miles

from the Atlas Mountains in Morocco, all the way to the UK and beyond.

Right now, across Britain,

hundreds and thousands of butterflies

are arriving on our shores after an epic journey.

I'll be following that incredible journey

as it advances across Europe.

Painted Lady.

With the help of insect expert Dr James Logan,

we'll be unpacking the science

behind a migration of immense proportions.

That's amazing. It's actually following your finger.

I'm going to be charting the progress

of our butterfly spotters from across the country

with the help of this fantastic team.

Quick, quick, quick. Painted Lady.

And we have a dedicated army of butterfly enthusiasts on the ground

helping us.

Working closely with leading butterfly experts

and using hi-tech experiments and the very latest science,

we're unravelling one of nature's greatest migratory mysteries

and perhaps revealing for the first time

the answer to the greatest puzzle of all -

just why do they migrate in the first place?

This is the story of the greatest insect migration on Earth.

This programme contains scenes of Repetitive Flashing Images.

Rothamsted Research Centre in Hertfordshire

is the world's leading centre in insect science.

Here, they unlock mysteries from the insect world

with some quite extraordinary technology.

So where better to track this year's migration of the Painted Lady?

In their grounds, we've set up a special butterfly hub,

which we're sharing with more than 700 Painted Ladies,

so we can really get up close and personal

with these extraordinary creatures.

Alongside our butterfly hub,

James has set up a communications centre to chart their arrival.

All over the country,

the public are getting involved by sending in their videos and pictures

as Painted Ladies appear in Britain.

She's the first one we've found in the garden this year.

It's almost, like, magical when you actually see one.

Painted Lady.

And I'm going to be doing some incredible experiments

to unlock the secrets of the Painted Lady migration,

finding out exactly how and why they do what they do.

Got it.

Yes! Yes, I've done it.

Is that OK? That's absolutely right. Brilliant.

This extraordinary migration begins

in the North African deserts in winter.

After breeding and building up their numbers,

they set off in spring,

heading across the Mediterranean to Europe and into the UK

on a quite remarkable journey

for a creature as fragile as a butterfly.

The Painted Lady story is a fascinating one.

I came to love butterflies through bees.

I kept hives for many years

and used to spot them out in wildflower meadows.

Like most people, I'm enchanted by their colours and variety,

but how many realise what this one species manages to achieve?

The Painted Lady is a pretty familiar sight

in most of our gardens,

which makes it easy to take for granted.

So here's everything you need to know

about these mini marvels in just a minute.

Painted ladies are 5cm in length and weigh a mere 200mg,

which is a tenth of the weight of a paperclip.

Yet amazingly, they can fly 100 miles in a single day,

the equivalent of us running four marathons,

and do so at speeds of up to 30mph.

They lay their eggs on thistles and nettles,

the preferred food choice for hatching caterpillars.

Painted Ladies are a global phenomenon,

the most widely distributed and most successful butterfly in the world.

They really are amazing creatures, and supreme travellers, of course.

But why do they go on such a long journey

and, actually, a really dangerous one?

I've been to find out where it all begins.

I've travelled over 1,200 miles to Morocco in North Africa.

Flanked by the Sahara Desert and Atlas Mountains,

Morocco is a dry and unforgiving place.

It's early March,

and the Painted Ladies have been busy

mating and laying eggs here.

Driving through this incredibly parched landscape,

it's just so hard to imagine that this is where the butterflies

that we see fluttering around our green English gardens come from.

But they do. One man has a special fascination with them.

Constanti Stefanescu is the world's leading expert on Painted Ladies

and has been coming here for many years to find them.

He's a Spanish lepidopterist from the Natural History Museum

in Granollers, in Catalonia.

Constanti has had many scientific papers published on the Painted Lady

and is working on his latest one.

Since I was a boy, I was very interested in animals in general,

and butterflies in particular.

Well, the Painted Lady is really a very special butterfly,

because it's one of the very few that can move long distances.

So to understand the butterfly,

you have to deal with populations moving between continents,

which is quite exceptional.

Constanti is piecing together

why Painted Ladies fly from their breeding grounds here

to northern Europe each year

and is getting close to a breakthrough

in understanding why they make the migration.

I've come here to find out more and to help where I can,

using essential butterfly technology.

I've been issued with some state-of-the-art equipment here.

And here we have what every good butterfly collector needs -

a good old-fashioned...

..butterfly net.

OK.

I'm really hoping that we might see some butterflies today.

Do you think there's any chance?

The weather is very windy today, so...

It's not the best time to catch Painted Ladies,

but there is still an opportunity.

The odds are against us - not only is it windy, but it's also March.

Conditions are still good for Painted Ladies,

but they're already beginning to leave.

Migration is a risky business, and many will perish along the way.

If there's somewhere which seems safe and plenty of plants and so on,

why would they take the risk of moving on

when so many of them die? Yeah...

Painted Lady. Ah!

Two. Two Painted Ladies.

One. Is it?

BLEEP, BLEEP, BLEEP!

There, there... Here.

Stop, stop, stop.

It was here. I think it went...

It was incredibly close. I think I saw it go off that...

Oh, there it is, there it is. Is that it?

Got it.

Fantastic! You got one. I got one, yeah. Brilliant!

Brilliant!

So you see that they exist.

They do exist.

Can I touch it?

No, no. The wings not, because the scales will be lost.

Oh, right, and you need those. You only have to touch the body.

That's so brilliant that you got one. Yeah.

How did you see that? It's so tiny, that one.

Well, I am always thinking about the Painted Lady,

so I saw the colour passing by

and the kind of flight that these butterflies have.

What are you going to do now?

I will keep it in this envelope

and the wings will be used for analysis.

That really was quite extraordinary

when Constanti just leapt off cos he'd seen a Painted Lady.

It reminded me of those great butterfly collectors

you see in old photos with their nets,

determined to go anywhere in pursuit of their prey.

I leave Constanti to it, but I'll be back in the morning.

We'll be going on a hunt for the Painted Lady's arch enemy

to gather vital evidence

which I hope will help us understand the riddle

of why these butterflies migrate in the first place.

When I left Morocco, the Painted Ladies were preparing

to head off on their extraordinary journey,

but how on earth do they know where to go to once they leave Africa?

James has been trying to find out.

So how do our Painted Ladies navigate

over such incredible distances?

Scientists here at Rothamsted have been trying to solve that mystery

and, apparently, all you need is a barrel, some glue,

a computer and, of course, a Painted Lady butterfly.

Rebecca Nesbit is a scientist with a passion for Painted Ladies.

She specialises in butterfly migration,

and here at Rothamsted, she's part of an elite entomology team.

For this experiment, first, you have to prepare your butterfly.

This one has been in the fridge, so it's... Nice and cold. Exactly.

Sleepy, easy to handle.

Get it out of the pot.

And butterflies

are really obliging.

If you just touch the outside of their thorax,

they flick their wings down.

Oh, yeah.

And we can very gently trap them on this sponge.

Just put this mesh over so they're exposed like that.

This experiment is going to involve attaching a Painted Lady to a wire

suspended in the barrel.

We're hoping to show that Painted Ladies

work out which direction to go when leaving Morocco

by using the sun as a compass.

But before this can happen, though,

you have to do something rather bizarre.

Next step is to shave...

Shave the butterfly. Shave the butterfly.

Just really gently rub my finger across it.

OK, all right, so there's not

a mini butterfly razor blade, then, that you use?

Which is what I was expecting, I have to be honest.

Sadly not. It's a bit disappointing,

but just rub it away.

You're basically taking the hairs off of the cuticle there,

just sort of making a smooth surface,

presumably so you can stick the glue on.

Exactly. This is just normal contact adhesive.

Does it harm the butterfly? No, not at all.

A tiny metal rod is glued to the butterfly's back.

What are we hoping to get out of this experiment?

What we're hoping to look at is give the butterfly a view of the sky

and use the sun to find out which direction it's going in,

so using the sun as a compass.

Painted Ladies might be travelling vast distances

by taking cues from the sun's position in the sky

and combining it with the time of day.

To prove this, we need to go outside.

This is the set-up, then. Yes.

So I think the first thing we'll do...

I'll just show you the flight simulator. OK.

Yeah. Or big white barrel.

So how does this work, then?

That rod we put on the butterfly... Yeah.

..that will attach to this really tiny bit of plastic tubing.

Once we put it on, it is free to turn,

so the butterfly's flapping

and it can turn in any direction it likes.

So it has to be able to see the sun

and then will orientate when it sees the sun. Exactly.

It's a bit fiddly. Really need a steady hand to do this.

I also need my glasses on.

Yes!

So what we need now is to calibrate it,

so if you could just hold on to the butterfly by the rod

and come in underneath with a compass.

Can I use my phone compass? Yes, please. Yes, that's perfect.

I'm holding my mobile phone

underneath this tethered butterfly as a compass,

which is a little bit strange - I've never done that before.

But the idea is we're going to see

where this butterfly heads in relation to the sun.

Once I let it go, it should take its lead from the sun

and fly in a northerly direction, unless it wants to play a bit first.

Sometimes you can get them to follow a finger.

That's amazing. It's actually following your finger.

Why is it doing that? I don't really know.

Its legs are out. Maybe it is looking to... To land.

Yes. But, yeah, they often do follow. Ah!

Are you sure you haven't trained this one?

This is actually my pet butterfly!

With the butterfly ready, it's time to do the experiment.

So the data's been fed in from the barrel to this box,

and then what happens?

The information that that box provides,

I'm then able to analyse it and plot out the flight path

that the butterfly would have taken if it wasn't inside the barrel.

These are some migratory flight paths,

so you can see that these are relatively straight.

So how does that tell you how it uses the sun to navigate?

So what I can do is I can compare a situation like this,

where it can see the sky,

with a situation where I've put a lid on the barrel,

so the butterfly can't see the sky. OK.

And by doing that,

you can tell whether it's using the sun to navigate by?

Exactly. OK.

If it can't see the sun, it doesn't know where it's going,

whereas when it can see the sun, it's got a clear flight path,

then we know there's a difference.

The map on the left clearly shows a Painted Lady

heading in the same general direction,

whereas by blocking the sun, the map on the right

shows the Painted Lady moving in random directions.

So does this experiment definitively prove

that the Painted Lady butterfly uses the sun to navigate?

That's certainly what our evidence is suggesting,

that when they can see the sun, then they know where they're going.

If you put a lid on the barrel,

then they aren't going in the right direction you'd expect

and, actually, they spin around a bit more, they appear more confused.

What a really neat experiment, demonstrating that the sun

is like an in-built sat nav for our butterflies -

an essential piece of kit for our Painted Ladies on the move.

They're getting very excited

by your experiment as well, aren't they?

I mean, it's remarkable, isn't it,

the way that they manage to use the sun

to travel these immense distances?

Yes, it is, and it's such a simple experiment that we did.

We used a barrel and the sun, essentially, to work it out.

But I couldn't quite understand from the experiment...

So they're using the sun for navigation,

but the position of the sun changes all the time.

That's right, so as the Earth rotates,

the sun moves against the horizon.

We don't actually know

how these butterflies manage to compensate for that.

For other butterfly species,

we know that they have an internal clock.

I mean, we all have biological clocks.

Body clocks. Body clock, yeah.

These guys have a body clock as well,

but it's in their antennae, called a circadian clock.

Basically, what that allows them to do is to tell what time of day it is

so they can adjust their flight direction

based on where the sun is and what time of day it is, essentially.

It's very clever. It is incred...

You think of these as tiny creatures here,

and yet they have this highly sophisticated navigation system.

Yeah, it's a perfect example of evolution

in terms of how to overcome adverse conditions

and make the most incredible journey.

Every single one of these butterflies

has the ability to do that on its own.

I think these butterflies' circadian clocks

are telling them it's breakfast time.

They're having a bit of orange juice, aren't they?

Back in March, Painted Ladies were getting ready for their migration.

In part two of my Moroccan adventure,

I caught up with them before they left.

Early morning in the Moroccan desert,

and the camels are already up.

It's late March,

the end of the Painted Lady breeding season

and the start of their incredible migration.

It's so windy here,

and if I'm having to battle against it,

what on earth is it like for a butterfly?

Yet that's exactly what the Painted Lady does.

They fly over this parched desert terrain

and right over those mountains there

to make it all the way to Europe and, of course, to Britain.

I'm on my way to meet up with Constanti Stefanescu again.

He's the most respected entomologist in his field

and has had over 100 scientific papers published.

From environmental impacts on butterflies

to population declines and Painted Lady migration,

what he doesn't know about butterflies isn't worth knowing.

Constanti's latest work is close to revealing ground-breaking science

that will shed new light on why Painted Ladies migrate.

He's collecting Painted Lady caterpillars.

They're under attack from another insect,

and it's the relationship between them

that he's particularly keen to investigate.

'To find a caterpillar,

'first you have to find the plants they live on.'

This is one of the very good host plants, isn't it?

Yeah, look, there are many nests here.

Host plants provide food for caterpillars.

Each species of butterfly has a specific plant

on which they lay their eggs.

Are there plants that the Painted Lady likes?

Yeah, in fact, the Painted Lady is one of the few butterflies

that can use many different kinds of plants,

even if they prefer these thistles and the mallows.

What's that caterpillar doing now?

I see with the binoculars

that producing some silk and, well, it's building a nest.

Once built, the nest will form a snug tent

from which the caterpillar emerges to feed.

As it grows, so too does the tent.

I'll just get this little caterpillar here.

It's clinging on.

There, is that all right? Not too damaged.

And there's another much smaller one over here.

There we go.

It's astonishing to think that this caterpillar,

once turned into an adult, could fly all the way to Britain

and, who knows, even end up in my back garden.

Collecting Painted Lady caterpillars is easy when you know where to look.

A far greater challenge for Constanti is what lurks within them.

He's looking for signs

that Painted Lady caterpillars have been attacked, but by what?

So this is a mass of cocoons of the main enemy of the Painted Lady.

It's a tiny wasp.

The adult wasp, what it does

is to search for the larvae of the caterpillar of the Painted Lady

and lay the eggs inside the body of the caterpillar.

Once they hatch,

the wasp larvae begin eating the Painted Lady caterpillar

from the inside out,

eventually forming a silky mass around the caterpillar corpse,

before finally emerging as adult wasps.

I estimate that maybe 60%, 70% of the caterpillars of the Painted Lady

are killed by this parasitoid.

But I can tell when you found that,

you were rather excited to find these horrible creatures. Oh, yeah.

So what are you going to do with this now?

I will keep this mass of cocoons inside the vial,

waiting for the adults to emerge.

So our butterflies in Morocco

are under serious attack from a deadly parasite.

It's the possible link between the parasitic wasps

and Painted Lady migration that Constanti's investigating.

One main part of the research

is to see how many of these caterpillars will die

because of the parasitise by the wasps,

and so every night,

we have to check if some of them have already died or not.

So, actually, you're quite interested if one's dead.

Yeah. I hope that some of them will die.

A curious Constanti is compiling his evidence.

He'll take the caterpillars home with him to Spain.

The wasps they might contain

could be a key component in his migration research.

I've got to go home soon,

but I can't leave without catching at least one Painted Lady, can I?

This morning, I'm on a mission.

This is my last chance.

There's one here.

Yeah.

Ha! Got one!

Here's one. Oh, I'm so pleased! I'm so pleased.

Yeah, this butterfly is more easy to catch than a fresh butterfly.

Oh, come on! It's my first Painted Lady.

What are you doing here?

Well, there it is - my first Painted Lady.

And it's an incredible experience,

although I'm glad I'm collecting it for science

rather than just for a collection.

Painted Ladies are definitely out this morning, and my eye is in.

Oh, hang on, there it is.

Oh, yeah. Here's the Painted Lady.

Oh, no, no...

Is it still there? Yeah.

Yeah. Oh, yeah!

OK, your second Painted Lady. Two!

That's great. I know my technique was a bit useless, but I got it.

I did get it. Number two.

Number two, yeah. But you see again, this is a very, very old butterfly.

Show a bit of gratitude! Stop saying it's old and rubbish.

Be pleased I'm doing your work for you!

For free. Thank you. Thank you so much.

It's been a really good day, no? Yeah.

The adults... I think it's time for a tagine, no?

Tagine - now you're talking.

We can celebrate the capture of the Painted Ladies with a nice tagine.

Constanti managed to collect over 100 caterpillars in Morocco

which, depending on how many develop into butterflies

and how many are killed by the wasps,

could shed new light on understanding

the Painted Lady migration.

Scientists like Constanti, at the forefront of lepidoptery,

rely on centuries of research by enthusiastic amateurs.

Many of their specimens

are now in the Natural History Museum in London,

home to the largest collection of Painted Ladies in the world.

This is my very own private night at the museum,

with the echoing walls now all the crowds have gone.

You normally think of dinosaurs like Dippy at the Natural History Museum

but, actually, there are more than 30 million insect specimens,

as well as a whole load of world-renowned experts,

so where better a place to come than here

to find out more about Painted Ladies,

those incredible flying machines?

Well, I'm really looking forward to being able to find out more

about the kind of detailed anatomy of the Painted Lady.

Dr Blanca Huertas is the senior curator

of the museum's butterfly collection.

There are over four million butterflies here,

including Painted Ladies from around the globe.

So is where they all are?

Yeah, this is the corner

in the world's biggest collection of butterflies

where we have the Painted Ladies.

And how many Painted Ladies have you got here?

We have probably about 3,000 specimens.

We have specimens from all over the world in here.

Painted Ladies are found in more countries than any other butterfly,

making them also one of the most successful.

Just in these six, seven boxes,

we have specimens from around 40 countries.

We've got things from Turkey,

we've got things from Morocco, Sri Lanka...everywhere.

And what kind of time span, then, do you have?

We've got collections back into the early 1800s in here.

Do you notice differences in the patterns?

Yeah, that's why we have a long series of butterflies.

Some have differences, say, not just on the upper side,

but also if you look into the underside.

They're very distinctive.

They're very different to how they actually look in the upper sides.

The rich colours are used for courtship and camouflage.

Open wings display your wares to other Painted Ladies.

Closed, they blend in with the background

to help them avoid being eaten by predators like birds.

Interestingly enough,

the females are much bigger, and also kind of faded.

So sometimes you see lots of butterflies,

kind of, really bright colours, and they are only males.

The males are the ones who are really, really bright.

The females are a little bit more dull.

More dull, more faded?

Yeah. It's an expensive business, in evolutionary speaking,

producing colour with all of these pigments.

It implies a lot of energy.

So the females need that energy in other things,

like giving birth to the next butterflies,

to the next generation.

So the males still can afford it,

but the females are very careful how they spend their energy.

So the males are expending all their energy looking good,

and the females are back at base, breeding?

Absolutely.

And if they don't do that, they don't succeed finding a mate.

The males are the ones showing off,

and the females are usually the ones

who select those good-looking males in butterflies.

Our fascination with butterflies goes back centuries.

They were valuable and coveted treasures back in the day.

Dr Hans Sloane was an Irish-born scientist

and keen collector in the 1600s.

He amassed one of the greatest collections

of plants and animals of his time.

His curiosities, as they were known then,

are the founding core of the museum's collections.

We're now in the historical collections.

What an historical collection, as well.

These incredibly big books.

The crown jewels, actually!

We've got the oldest specimens of plants preserved in here.

But not only the oldest specimens of plants

where I've brought you today, because we have in here,

pressed in the herbarium sheets of Hans Sloane,

we've got the oldest Painted Lady ever collected and pressed

and preserved here in the Natural History Museum.

The oldest Painted Lady?

Yes, we're going back into the 1600s.

So even as his snap in time with the plants,

this butterfly was flying around,

and we're going to see it in a minute.

And this is part of this incredible historical collection

which Hans Sloane started?

Yes, that was collected by himself

and preserved by the Reverend Adam Buddle.

OK, let's go and see what Adam Buddle had in his scrapbook.

Adam Buddle was a botanist in the 1600s.

Amateur collectors were rife in those days.

His vast knowledge of plants meant his collections

were more respected and relevant than most.

At the same time the naturalists were collecting plants,

they also pressed some butterflies in here.

This one in particular is a very, very old specimen.

That's amazing. How old is that?

This was collected back in the 1600s, late 1600s.

This is the oldest Painted Lady we have knowledge of

and it's in here in the Natural History Museum collections.

And did you know it was here?

It was kind of a recent discovery for us

and it's very exciting to show you.

I can see that it's a Painted Lady,

and it's been pressed in the same way that we'd press wildflowers.

Yeah. Pre-1700s, that was the method to preserve specimens.

Collected flowers and plants

were pressed onto book pages known as herbarium sheets.

Butterflies were preserved with the flowers they feed on,

a practice that's still done today.

Look here. We have it written in quite shaky handwriting -

"The Painted Lady".

They have a common name. It's still in use after 300 years.

I just love looking at the detail of all of this.

It's almost like a work of art, this.

It's so beautiful,

the way he's placed the butterflies in amongst the grasses.

That was preserved by Reverend Adam Buddle.

You probably have heard about the butterfly bushes, the buddleia.

Yes. That's where the name came from.

Over many years, he compiled a definitive English plant guide

that was never published.

The original manuscript is preserved here.

In later years, the well-known buddleia plant, or butterfly bush,

was named in his honour.

Do you know, all the time that I've talked about buddleia,

I've got buddleia in my garden,

I didn't realise it came from a person,

the person who, all those years ago, collected these butterflies.

A great naturalist.

As you see, lots of care, lots of notes and detail

on this collection - well preserved.

So a very important snap in time?

Absolutely. Probably the only one, really.

It really has been so interesting

to come behind the scenes at the Natural History Museum,

where they've been studying butterflies for generations.

You know, insects are the most successful animals on the planet,

and it's easy to see why Painted Ladies fall into that category.

Back in March,

our Painted Ladies had been breeding in Morocco in large numbers

ahead of travelling across Europe on their epic migration.

The life cycle of the butterfly

is one of the most fascinating in the natural world.

As Painted Ladies only live for up to three weeks, they breed quickly.

When a male finds a female, he has to win her affection.

To do this, he uses perfume.

Chemicals called pheromones

are intoxicating to females at close range.

If she likes it, they settle down to mate.

They stay locked together for up to an hour,

sunbathing at every opportunity.

Eggs no bigger than a pinhead

are laid on plants the caterpillars feed on.

Jewel-encrusted thistles glisten for five days

before bursting into life.

Caterpillars gorge themselves from the moment they hatch,

and begin to grow,

shedding their skin five times before reaching full size.

In just ten days,

the caterpillar is a colossal 100 times bigger than when it hatched.

Suspended on a silk pad, it splits its skin one last time,

revealing a case-like chrysalis or pupa.

Inside the chrysalis,

the caterpillar reduces itself to a DNA soup,

reconstructing into something else entirely.

Two weeks later, a Painted Lady butterfly emerges

and the cycle starts all over again.

We're following this year's Painted Lady butterfly migration,

and our communications centre is buzzing.

Piece by piece, scientific experiments,

eyewitness accounts and the world's leading experts

are helping us unravel the mysteries of an extraordinary journey.

We know it began in Morocco

at the end of the winter breeding season in March.

Our Painted Ladies then touched down in Catalonia, in Spain, to refuel.

And this is where I caught up with them next.

To get to Spain,

our Painted Ladies have had to overcome extreme desert conditions

and to climb to incredible heights,

navigating mountains as high as 13,500 feet.

Many will have died, the voyage taking its toll,

or been eaten by predators.

An exhausted Painted Lady is easy pickings for a hungry frog.

Those that do make it this far are rewarded with better conditions.

These beautiful olive groves

just brimming everywhere you look with spring wildflowers.

I mean, it couldn't be further away, could it,

from the mountainous, rocky deserts of Morocco?

But Catalonia is the first stop for many of the Painted Ladies we saw.

It's 1,500km from their breeding ground

and they're still only halfway from their final destination.

I met up with Constanti

at the Granollers Natural History Museum in Catalonia.

He's been studying the specimens I helped him collect in Morocco

and I'm keen to discover what he's found out,

but not before indulging my passion for all things butterflies

with him first.

I love these old illustrations.

They're incredible, aren't they, the detail on some of these?

Yeah, they are good indeed.

Painted Lady, Peacock.

Do you think it is there's something about the beauty of butterflies

that makes people want to study them?

Oh, yeah, of course.

There are many more people that are attracted by butterflies

than by beetles, for example.

And you've got quite a few collections here in the museum?

Yeah, and one of these collections

is my own collection that I did when I was...

Is this yours? Yeah, this is mine.

Here you are. Ah, gosh.

And, well,

it's very useful to start a butterfly collection

to learn to distinguish the species.

Well, even I can get some of these.

OK, that's Peacock?

That's Peacock. Red Admiral. Red Admiral.

OK, and if I haven't got the Painted Lady by now,

you'd be despairing of me, wouldn't you? Yeah.

Around the world, it's not Constanti's beloved Painted Ladies

that get all the attention.

Until recently,

it was thought the Monarch carried out the longest butterfly migration.

Travelling 3,500km from the US to Mexico,

it often returns to the same trees where its ancestors were born.

Thousands form a spectacular butterfly blanket in the process,

which I've seen myself in the Mexican forest.

The Monarch might be a headline-grabbing superstar,

but it's not a patch on the Painted Lady.

I'm amazed by how much material there is

about the Monarch butterfly,

but really comparatively little about the Painted Lady.

Well, I am quite envious

about how much has been done, and is being done, on the Monarch

and the little research that is being done on the Painted Lady.

But on the other hand,

it means that we still have many, many things to explore

on the Painted Lady, which is nice.

But, actually, the Painted Lady is the champion, isn't it?

I think so. I think...

Well, I know for sure

the Painted Lady can fly more than 4,000km

in the whole cycle of migration,

and the Monarch can do as much as 3,500km,

so at least the Painted Lady can win the Monarch in this sense.

Constanti is trying to solve a migration mystery

that's occupied his work for the last ten years.

After numerous field trips to Morocco,

collecting live caterpillars,

he's slowly unravelling the effect a sinister parasite might have

on the Painted Lady migration.

So all those specimens that you collected

in the heat of the Moroccan desert, you've brought them back here,

and what have you been doing with them?

I brought back all these larvae until they pupate

or until they die because they were attacked by the wasps.

I recognise the cocoon from the caterpillars

that you showed me in Morocco.

And what's emerged from that white mass?

Well, inside this mass, there are many cocoons.

Very small cocoons.

And from each cocoon will emerge one of these wasps.

These are sisters that come from a single female

that lay the eggs inside the caterpillar.

Are you telling me that all these wasps came from one caterpillar?

From one caterpillar, yeah.

Gosh. Maybe there can be between 50, 60, 70, depending.

It's almost as if each one of these

is then able to lay 50 eggs in a caterpillar.

I mean, they could wipe out the Painted Lady, couldn't they?

Yeah. In Morocco, we have seen

that most of the populations of Cotesia, of these wasps,

are composed only by females.

They can reproduce without the males.

So every single wasp can parasitise, can attack,

and lay eggs in a new Painted Lady caterpillar,

so the risk is terribly high.

A good Painted Lady breeding season

inevitably becomes an even better one for the parasitic wasps.

Constanti believes the wasps have a key role to play

in Painted Lady migration.

It won't be long before he can finally reveal his findings.

Outside in Catalonia, the Ladies are already here.

The ones who managed to escape the parasitic wasps

are enjoying the Spanish sun.

So why is it you think

that the Painted Lady has come to places like this?

Well, because here, they find exactly what they need

to have a big success for reproduction.

So you see that everything is green.

There are flowers everywhere, there is nectar for the adults,

there are food plants everywhere.

But this lasts only a short period.

So the next generation has to move to the north,

to track the same situation in central Europe or northern Europe.

So it's the strategy of this long-range migrant

which is the Painted Lady.

So not all Painted Ladies fly to Britain in one go.

Many stop over somewhere like this to feed and breed,

their offspring emerging hard-wired

to continue migrating to Britain and beyond.

It's a relay race,

with one generation passing the baton to the next, and so on.

Some, however, emerge from a chrysalis in Spain

and don't migrate any further at all, choosing instead to stay

and spend their short three-week life breeding,

while food is abundant.

Their main food plant, thistles, are seasonal.

As they die off in one country, they bloom in another.

So it makes sense for some Painted Ladies

to migrate and follow them.

Much of what Constanti had shown me in Spain

involved the Painted Lady's arch enemy wasp.

What he'd kept from me was worth the wait.

So here, I have some of the butterflies

that I raised from the caterpillars that we collected from Morocco.

So these are all... Right, OK. OK?

One of the caterpillars Constanti brought back from Morocco

didn't fall foul of the Cotesia wasps

and instead went through its full transformation

into a butterfly in his office.

Oh, yes, I can see them. Yeah. The legs are moving.

That's a male, so we can release this male at the hilltop.

Oh, great, OK. Probably he will enjoy the place.

I'm very nervous about doing this, because they're so delicate.

OK, all right. So, just...

OK, like this.

Just here, yeah?

Yeah? OK.

OK, that's incredible - this butterfly,

which came from a caterpillar we picked up in Morocco,

has never flown before, and we're just going to let it go.

Off you go. Off you go.

Oh, look. He needs to warm his wings up a little bit first.

Do you think? Well, I think he is more or less ready.

OK, I'm going to let him... You take your time.

A virgin flight is a big deal.

It's really fluttering.

Come on. Oh!

There he goes!

He's doing quite well, huh? Not bad for a first flight.

A hesitant start, maybe,

but this butterfly will be migrating north to the UK

alongside the others within days -

unless, of course, it decides to stay and breed

for its short life instead.

So why are some Painted Ladies driven to migrate and others not?

James is getting exclusive access behind the scenes

here at Rothamsted to find out.

I've been given special permission

to get inside this high-security facility here at Rothamsted

to find out some of the latest cutting-edge research

on insect migration.

I feel quite privileged.

This is pretty awesome.

It's like being in a spaceship in a sci-fi movie

or something like that.

It's also a little bit spooky.

But I believe this is where the magic happens.

Here, they're studying migratory moths

to understand what makes some insects of the same species migrate

and others not.

The results should apply to migrating butterflies as well.

What on earth is going on in this experiment?

Well, we use a number of techniques in our lab

to study insect migration.

And these are our roundabout-style

tethered flight mills.

OK, so roundabouts for moths?

That's right, yes. So, basically, we use this technique

to investigate the flight capability of different individuals

of the same species,

using this technique

to identify good flyers and poor flyers

so we can try to understand the genetic control of migration.

The moths on the roundabouts are flying on their own accord.

It's their natural flight driving them

and their every move is being measured.

OK, so how do you define a good flyer and a poor flyer?

Is it all to do with how far they fly or...?

We place the moth onto this roundabout

and then we just allow the moths to fly overnight

and then those individuals which have flown a long way,

which might be 30km in a single night,

we can put into one category,

and then we might have others that only fly a few hundred metres.

And why do they do that?

Why do you have some long-haul and some short-haul flyers?

Some individuals can be highly migratory

and others hardly move at all.

And they do this in response to different conditions

that promote migration or not, as the case may be. OK.

But something in the environment or something can change

and trigger them to become a long-haul flyer?

That is exactly what happens.

And so it might be the environmental conditions,

the weather, it might be the quality of the host crops

that they're feeding on.

That can turn them into a migratory

or it can turn off the migratory genes.

What are those genes actually doing physically to the insect?

How do they help with the migration?

Well, there's a whole number of genes that are being overexpressed,

but some of them are evolved with the availability of flight fuel

which, in these insects, is body fat.

So a number of genes are associated with turning fat into a fuel

that they can use.

There are also genes which are associated

with the production of strong, very active flight muscles.

And so, again, those long flyers, they have the strongest muscles.

The genes associated with those are turned up to maximum, if you like.

Wow. Does this apply to other insects?

Whatever we learn here would be perfectly transferable

to all butterflies and moths that migrate

and so it would be relevant to the Painted Lady story.

So, what this research is revealing

is that variations in environmental conditions

appear to switch certain migratory genes on or off.

Some are fatter, some are fitter,

some develop bigger flight muscles, and so on.

Fatter ones with stronger muscles

are likely to continue migrating to the next country,

while others are better equipped to stay in one place and breed.

We are monitoring the 2016 migration at Rothamsted,

and know that Painted Ladies left Morocco in March.

By April, they were breeding in Catalonia.

I came back from there

expecting them to be navigating through France

and hitting our shores in early May.

May came, but not many Painted Ladies.

Brutal weather in northern Europe earlier this year

hit them from all sides.

So it's no surprise, then,

that the class of 2016 is late arriving.

In May and early summer,

northern Europe had its highest rainfall for over 100 years.

Rising river levels threatened to decimate towns in Germany,

Paris flooded and the UK had one of its wettest Junes ever.

An average Painted Lady weighs 200mg.

Large raindrops can weigh more than 70mg.

So flying through rain is virtually impossible.

Added to that, butterflies need to warm up

in the sun to fly efficiently,

so bad weather is bad news for Painted Ladies.

Back at Rothamsted, the Painted Ladies in our hub

are making the most of what we put out for them.

The butterflies love the sugar that they get from the oranges,

and that's one reason why they migrate,

why they go from Morocco to Spain,

is because the food plants dry up in one country

and they need to move on to find fresh plants,

like these here, the buddleia,

which you may have in your garden, that the butterflies enjoy so much.

But not all of them travel up through the western Mediterranean.

Some head east instead, as we are going to see.

When Painted Ladies leave Morocco,

they don't all head one way to northern Europe -

some embark on a route to eastern Europe instead.

Each year, the different routes have varying degrees of success.

Through April and May this year,

great numbers descended on Corfu and Crete via the eastern route,

but comparatively few arrived in northern Spain and Britain,

due to bad weather.

By expanding their distribution across different routes,

the butterflies breed successfully in enough countries

to keep their overall numbers up.

While some emerge from their cocoons and continue migrating,

others emerge and do not travel on,

staying instead to breed a further generation.

That is why we see more and more Painted Ladies

as the summer progresses.

In the communications centre,

James has been mapping the progress of our Painted Lady migration

as it has unfolded.

What have you been looking at?

Well, I'm just mapping out the routes, actually,

of some of these butterflies.

You started off here, didn't you, in Morocco?

South of Marrakech, really near to the Sahara desert.

Of course, they can start off pretty much anywhere

across this Northern African belt, here, and sort of head northwards.

Let's draw this out. So, you started about here

and then you moved up to Catalonia, didn't you?

Yes, it's the kind of north of Spain.

Imagine being the size of a butterfly

and having to fly that far.

You'd think it would take a long time, but actually,

scientists have modelled it and they reckon that it could take

as little as 20 to 36 hours.

That's with a tailwind, obviously,

and then flying at an average of 15km per hour.

And then they head on, they just carry the drive northwards?

That's right. So, the ones that you saw in Catalonia

probably will make their way, or already have made their way,

or are starting to make their way, up here.

But over here, on the other hand -

let's do this in another colour, cos it seems to be a second route,

certainly with the sightings -

the butterflies seem to be heading up perhaps from Libya, here,

maybe the coast of Egypt, up to Crete.

So lots of sightings in Crete and other parts of Greece, as well.

So, this seems to be a bit of a hot spot this year

with our butterfly spotters.

I love the idea that there are these butterfly enthusiasts

who are sitting there, waiting in their gardens

for the arrival of the Painted Lady.

The eastern route, having benefited from good weather

throughout the year, is reaping rewards,

and none more so than Crete.

So, Crete has been an absolute hot spot.

Let me prove it to you, actually,

because one of our butterfly spotters

has sent us in a video, and...

This is from a guy called David Cook,

who is on holiday in Crete at the moment,

and he sent in this footage of Painted Ladies.

Hi, I'm Dave Cook,

I'm holidaying on the Greek island of Crete.

It's a bit like a motorway service station for butterflies.

I've never seen so many Painted Ladies in one place!

Actually... So, he's counted them,

and there's between 50 and 100 per bush.

That's amazing. He's only ever seen one or two in the UK,

so he's booked this holiday to Crete,

hoping that the Painted Ladies were going to be there,

and lo and behold they were.

So, he's ditched his family, they're on the beach.

They're on the beach just, you know, having a holiday.

He's out butterfly spotting for us. Yeah. It's brilliant.

I'm feeling a butterfly divorce coming on, you know.

That's exactly what I would do on holiday. Really?

Absolutely, ask my wife. I'm not going on holiday with you!

THEY LAUGH

Coming out of such a horrendous June,

it's no surprise our British spotters

didn't have as much luck as Dave Cook in Crete.

So how can scientists detect when Painted Ladies do arrive in the UK?

James has the answer.

Now, we know that thousands upon thousands

of Painted Lady butterflies

make this incredible journey every single year,

but it's not as if we see them sort of flocking past our heads,

and that's because they do it in a rather efficient way.

I like to think of it as the insect highway in the sky,

flying at these incredible heights, at these incredible wind speeds,

and these things can survive this.

It's actually amazing.

And the way that scientists know this is by using this -

the vertical-looking radar.

It might appear little more than a satellite dish,

but as the old saying goes, never judge a book by its cover.

'Insect migration expert Dr Jason Chapman

'is the custodian of this cutting-edge piece of kit.'

So, this dish is basically reflecting a beam up into the sky?

That's right, yeah. It's like shining a searchlight into the sky.

Basically, we're hoping that insects will pass through that beam

so we can detect them.

It's kind of a cone shape as it's going up in the sky.

Yeah. So, it's a very narrow cone. It just spreads out a little bit,

but by the time it gets to our highest altitude,

which is 1.2km,

it's still only 30 metres wide,

so it is quite a narrow sliver

of the sky that we're sampling.

On a sunny summer's day like today,

we might expect maybe two, three, four...5,000 individuals.

Thousand?! Yes.

'Different insect species fly at different heights.

'Painted Ladies pass through the beam at a much higher altitude

'than most butterflies.

'But it takes more than just the height they fly at

'to confirm they're Painted Ladies.'

The reason that we can identify and classify

different kinds of insects

is because they're different shapes and sizes

and their different wing-beating frequencies

produce very different signals.

So, when you see a butterfly in the sky with the radar,

how do you know it's on the migration?

When you see hundreds of individuals flying over on the same day

in the same direction, then you can see that there must be

a population-level migration going on.

For us to see what the vertical radar sees at altitude,

we need to go inside.

So, this is the computer that controls the operation of the radar.

As insects passes through, we'll get a peak

as an individual flies through the beam. Oh, yeah.

Yeah, so you can see the peaks happening.

They're quite quick, just within a couple of seconds.

This graph represents a Painted Lady butterfly?

That's right. It's a signal that we recorded from a Painted Lady

flying over the radar.

So, that peak tells you how big the insect is?

Yes, so the magnitude of the peak,

the amount of power that is being reflected,

that will give you some indication

about the overall size of the insect.

OK, and along this bottom axis, we've got time,

and it's three seconds here, or so.

So, within a couple of seconds, that insect, of that size,

passed through the beam.

That's right. And so in two seconds, it passed through our beam,

which is about 20 metres' diameter.

Yeah, yeah. So a very quick calculation tells you

that it was travelling at ten metres per second,

that's about 40kmph.

This one clearly was on the move.

Yeah. Must have been part of the migration.

Incredibly, they do so at heights of over 1,000 metres.

Only one type of butterfly travels north in large numbers

and at that height this time of year,

so they can only be Painted Ladies.

Maps from previous years provide confirmation.

Each of those black bars

is related to the numbers of individuals

that were flying in that direction.

And that's what we would expect during the early spring migration

as these butterflies are travelling northwards.

If the Painted Ladies were not migrating north,

the map would look something like this.

Multidirectional flight paths indicate an insect

with no particular place to go.

I've had an insight into what is normally a completely hidden part

of the Painted Lady butterfly's migration and its world.

It's allowed scientists to unravel and unlock

some of the amazing secrets of this incredible migration

that these tiny, fragile butterflies make.

When our Painted Ladies do finally arrive,

they're going to need refreshment.

So, how can we prepare for their arrival?

Long-distance athletes need regular refuelling,

otherwise it affects their endurance.

And, you know, it's exactly the same thing with Painted Ladies.

When they come here after that monumental journey,

they're hungry - they need nectar, sugar, for energy.

And there are all sorts of things

that we can do in our own gardens to help them.

Patrick Barkham is going to show me how.

Patrick is a natural history journalist and author.

He's so obsessed with butterflies that in the space of one year,

he tracked down every British species for a book.

He's turned his Suffolk garden into a wildlife haven.

Why is this so particularly good for butterflies?

Well, it's very simple, really. I've planted some

typical wildflower mixes.

I tried to find mixes that use native species to Britain,

not just exotic mixes.

It looks like a sort of fairly scruffy lawn, to some eyes,

but there's loads of grass-feeding butterflies

that actually lay their eggs,

the caterpillars feed on the grasses.

Then, of course, you chuck in a load of wildflower mix

and you get these lovely wildflowers on which the butterflies can nectar.

And you've got some fantastic daisies here.

These are great, and these surprised me,

because I saw 19 Painted Ladies on these a couple of weeks ago,

just round the corner.

So the Painted Ladies come in on this enormous journey

and it's seen my ox-eye daisies

and it's dropping down to refuel, you know, it's a lovely thing.

And then I went to look for them the next day

and they'd all disappeared again,

so they'd all continued their journey north.

All that effort - you've planted these fantastic wildflowers,

and then they just disappear!

They race through your garden in 30 seconds

and have a quick fuel stop and then zoom off again.

To me, that's great and that's enough,

but the next thing is you want them breeding in your garden.

You really want their food plant, thistle,

and thistle is not such an easy sell, is it?

No. I've got these enormous thistles by my front door.

It's quite hard, isn't it,

to ask keen gardeners to let thistles grow?

It's a real struggle - even I struggle with thistles.

This is a lovely example of how if you do something for butterflies,

it helps all kinds of wildlife, cos I found another caterpillar,

and it's somewhere on this plant here,

and it's the caterpillar of an Angle Shades moth.

I took a little picture of it

and, helpfully, someone identified it for me.

And it's this wonderful insect,

and the caterpillar comes out at night

and munches away at the thistle

and soon it will pupate and become this beautiful, beautiful moth.

Patrick's garden is full of low-maintenance plants

that we can all easily grow in our own gardens.

So, got some buddleias here,

and some slightly smelly garden gloves.

Oh, don't worry, they can't be any worse than mine, I can promise you.

And there is a trowel and some spades

and here's our buddleias.

'I'm not averse to a bit of gardening,

'and I'm keen to lend Patrick a hand replenishing his butterfly oasis.'

So, where do you want me to start?

So, I'd just stick one at the back of the lavender -

more or less where that spade is would be fine.

OK, great. You can dig out these. These are just little weeds.

Don't get stung by the nettles

that I've left there for the small Tortoiseshells.

Do you know, my garden is...

I've left a lot of nettles for butterflies

but, blimey, they do spread, don't they? Yeah, they do.

I really love the idea that you can look out in your garden,

you can see that you've got nettles and thistles

and things like that, and you can think,

"I'm not a lazy gardener,

"I'm doing something that's incredibly moral,

"I'm saving butterflies." Yeah, exactly.

So, are you happy for this to go in here? Yeah, yeah.

Buddleia is by far the most popular nectar plant of British butterflies.

A favourite of 18 species, including the Painted Lady,

it's not called the butterfly bush for nothing.

I just took these from cuttings,

and I just literally take a cutting of buddleia,

stick it in a pot like this, leave it for a few months

and then you get a buddleia

and you don't have to spend £10 at a garden centre for one.

It's really important to think about plants that will keep going

right through the year,

particularly when there aren't so many other flowers around.

That's right. The nectar sources at the end of the summer,

when everything else has died back, they are the real key.

Butterflies in the garden are a marker of a healthy ecosystem.

Get things right for them, you get things right for other wildlife.

The value of caterpillars as a high-protein food source

for breeding birds, for example, is invaluable.

Butterflies are also effective pollinators.

When feeding, pollen sticks to hairs that cover their body

and is passed from flower to flower.

But they're in decline.

Industrial agriculture, habitat loss and changes to the weather

have seen the numbers drop by 70% in recent years.

Anything we can do for butterflies in our gardens

might help buck the trend.

The butterfly flower I wanted to show you, Martha, is this.

Ivy? Yeah. OK.

One of the best things you can have for butterflies in your garden.

It flowers really late in the season, doesn't it?

Yeah, and that's perfect for the butterflies like the Red Admiral

that need energy late in the summer to hibernate through the winter.

The other thing that's brilliant,

this is another great thing for the lazy gardener, isn't it?

I guess it is. THEY LAUGH

All around Patrick's garden is a one-stop butterfly buffet.

So, this is garlic mustard, or jack-by-the-hedge.

This is a weed you'll see under almost any hedgerow,

and it is the food plant for the Orange Tip.

If it has butterflies on it,

then it becomes a really beautiful thing.

Yeah, and it becomes a precious thing, and you start thinking,

"Well, I'd better not cut that back

"because there might be a butterfly egg on it,"

and it does start making you think.

With the UK now basking in summer sunshine,

conditions are perfect for Painted Ladies.

And after such a long wait, they've finally made it here.

They will be hungry,

and with flowers up and down the country in full bloom,

Painted Ladies made it just in time.

It took a while, but in late June, early July,

the class of 2016 eventually hit our shores in significant numbers.

Around the country, our spotters are on a winning streak.

Marie and David Law found their Painted Lady

on the busy streets of Skegness.

Turn the right way round!

We have two today. Two? Two Painted Ladies.

Tell me facts about Painted Lady butterflies.

They fly from Morocco.

Well done.

Yeah? Go on. To here, some of them.

OK, they fly from Morocco.

Yeah. Through Spain.

Yeah. Through France.

Sometimes, yeah. Then here.

Yeah. Or they can fly straight from Morocco to here. Yeah.

Come to me, butterfly, land on my hand.

Oh, wouldn't that be nice? It would!

Marie and David have a knack

for being in the right place at the right time for Painted Ladies.

Oh, look, it's one of the...

Oh, no, there's one there. Yeah, there is.

Very top. Right here.

Oh, another one.

Painted Lady butterfly, definitely. It's definitely a Painted Lady. Definitely.

It's not a Cabbage White. No.

Go on, run up and see.

Is it a brown one? Is it...?

No, it's not, it's a Speckled Wood. Speckled Wood, yeah?

That was a Speckled Wood.

Last year, they witnessed something

even the most experienced butterfly scientists

would be lucky to see.

We're at Skegness Gibraltar Pond nature reserve. Yeah.

We're here... We...

THEY LAUGH

We are here because in June,

we saw two Painted Lady butterflies that were just about to mate.

It was one of those moments where you just happened to walk about

and you just notice that one little thing that is different,

just that one...

They were acting a bit unusual,

that's not normally what butterflies do,

and then you take a close look and, "Oh, there are two of them."

There's two of them here. They could be just about to mate.

They were very close.

He was... He was getting closer and closer and closer to it

and then they just flew off.

They landed together, I got some shots, both flew off,

came back to exactly the same spot.

They did. Which means that was probably the male's territory.

Just right there. It was down here.

Back at Rothamsted,

butterfly migration specialist Rebecca Nesbit

has worked with an incredible piece of kit

that could help us understand what Painted Ladies get up to

now that they're here.

To do this, she tracks Painted Lady flight patterns using radar

and is going to show James how to do it.

Hi, Rebecca. Hello.

So, tell me, how on earth do you put a radio antenna

onto the back of a butterfly?

So, first we have to trap it down.

As with the flight simulator experiment,

you have to shave a Painted Lady before attaching anything to it.

Rebecca showed me earlier, so now it is my turn.

Here is your butterfly. Yeah.

Oh, no, no! Is that OK?

Oh, no. Come back!

Yeah, give it a go. Got it.

It's quite a lively butterfly.

Oh, now, you can do this. Behave.

There we go. Oh, no.

This is embarrassing. I've made such a mess of it.

Yes! Yes, I've done it.

I handle insects all the time,

but I don't know why my hands are completely shaking,

and I think because you did it so professionally,

I'm so nervous about doing it badly.

If you think about it too much, your hands definitely start shaking.

OK, brilliant.

'A gentle rub and my first butterfly haircut is done.'

Once glued on, this tiny radio antenna weighs almost nothing.

What it lacks in size, it makes up for with what it can do.

This technology is the creation of Dr Jason Lim,

one of the world's leading experts in insect tracking devices.

Called a harmonic radar,

it is able to pick up the antenna attached to the Painted Lady's back

using a specific wavelength.

It's then able to track the Painted Lady as it flies.

So, does it come off eventually or...?

It will just fall off after a few days.

This may look heavy,

but it's extremely lightweight and harmless,

and doesn't affect the Painted Lady's ability to fly.

Butterflies require energy to fly,

so topping my one up beforehand is a good idea.

Unravelling the proboscis takes not only skill

but a willing participant.

The proboscis is a long, narrow tube,

a feeding straw designed to get deep into nectar-rich flowers.

In this instance, sugar water on a cloth will do.

It takes a while,

but we do eventually get the butterfly to eat something.

Having had its pre-flight meal,

my butterfly is now ready for takeoff.

And we are heading out to that release box. Yeah.

And then, if it's OK, if you could just whip the string off... OK.

..and that lets the butterfly go free.

Conditions are good. Absolutely perfect,

particularly when the sun comes out.

Well, this one seems OK.

Perfectly happy, looks quite calm.

We put the pot right down on the floor...

Yeah. Tip the butterfly out and then I will close it.

Gosh, she's really active now, isn't she?

Yes, that heat has instantly brought her out.

As the sun comes out, so do our Painted Lady's wings.

Acting like solar panels,

they absorb sunlight to warm up flight muscles,

ready for action.

With my butterfly poised

and Jason Lim's tracking radar spinning into action, we're ready.

DRAMATIC MUSIC PLAYS

OK, you can release the butterfly now, over.

Excellent. OK, he's ready. He's ready? Great. He's ready.

OK, stand back. Stand back. Just so we don't shade it.

OK. And the sun is out. How perfect is this?

Quick. And I just pull? Yeah. Pull.

MUSIC STOPS SUDDENLY

'I obviously peaked too early.

'Taking this chance to sunbathe while it can,

'my Painted Lady needs a little encouragement.'

Fly, come on!

The sun is out. Oh, it's going away again!

Fly, come on!

And then she's off.

Jason, the butterfly is on the move.

OVER RADIO: 'OK, over.

'Butterfly is moving quite fast.

'It's now flying towards the manor garden, over.'

My Painted Lady stops for a refuel.

Back in the van, Jason tracks it as it moves around Rothamsted.

The radar can keep tabs on it from up to a kilometre away.

So, where's our butterfly?

That is the butterfly flying from here,

so it is moving slowly.

Yes, that's the one.

This is a 100-metre ring.

So we know the butterfly is 100 metres away from us.

Away from us. Yeah? Yes.

So, here is our release point.

OK. So we can see the butterfly has flown

about 50 metres away from there.

So it's on the move, then, clearly? Yeah.

That's brilliant that we're able to see this.

It's stopped now, though. Yeah, so we just have to wait.

Maybe it's just foraging below the radar, under the radar,

where the radar couldn't pick up a signal from it.

OK. So the machine allows us to track the position

of the butterflies every three seconds.

So the butterfly could do what they normally do -

sunbathing to warm up the body

and then they forage, flying around different patches of flowers

and potentially looking for a mate as well.

What a great piece of technology this is,

allowing us to see into the life of the Painted Lady butterfly.

And who knows what the future might hold for this?

It might even allow us to unlock even more secrets

of the Painted Lady butterfly migration.

Tracking technology will no doubt advance

and so too the distances that can be covered.

You never know - one day, we might be able to track

a Painted Lady all the way from Morocco to here.

Our butterfly spotters don't need tracking devices.

Now that it's July, Painted Ladies are coming to them.

Dave Cook is back from Crete and out doing what he loves best.

I've come here to the location, Brixton Common,

with the specific intention of finding the Painted Lady

that I found here this morning.

She's still here and she's still nectaring.

It's great. It's absolutely brilliant.

Result.

What it's all about.

And Darcia from Wiltshire is equally pleased to be out and about

spotting her favourite butterfly.

I am Darcia Gingell and this is Morgan's Hill nature reserve,

which is a Wiltshire Wildlife Trust site

in North Wiltshire.

And it's a gorgeous morning this morning,

and we're here to hopefully try and find some Painted Ladies.

It's actually quite difficult to get hold of a picture of a Painted Lady

unless they're actually still and nectaring,

because a lot of the time, they're quite fast flyers,

so they'll zoom into view, maybe come around you,

circle round you, take a look at you and then they're off.

Unless you find them, as I've said, nectaring.

Once they're in one place, maybe on a nice thistle,

they tend to stay there, and you might even, you know,

get a chance to take a glimpse of one for a few seconds,

and they're off again.

Quite a big butterfly there.

No, small Tortoiseshell. Got my hopes up.

About a week ago, me and my partner

were at a place called Ravensroost Wood.

Just walking along the track, next minute, "Whizz!"

Round your head.

Really shocked and surprised to actually see it was a Painted Lady.

Just came and landed and settled on the floor in front of us.

It's a beautiful butterfly.

So, there we go.

It's just flown along behind us and come and landed and settled.

It's quite fascinating

to think where this beautiful butterfly has come from.

I think it's almost, like, magical when you actually see one,

and I think it reminds you of those fairy tales

when you were a child

and you're imagining what a fairy really would be like,

and I think a butterfly is the closest you can get to that.

With Painted Ladies now being seen all over the country,

how do we know just how successful

the migration has been this year overall?

'Richard Fox is part of Butterfly Conservation,

'a definitive authority on British butterflies.

'His migratory maps tell a fascinating story.'

Your volunteers have been looking out for the Painted Lady,

which, of course, we're following.

Yes, so we've got some maps here

of sightings of Painted Ladies from this year.

So, each Painted Lady picture represents a place

where members of the public have reported seeing Painted Ladies.

And this is from... January and February?

I'm amazed there are any Painted Ladies at all!

Exactly. So, you often really wouldn't see any Painted Ladies

in Britain at all over that January, February period in a normal year.

But this year wasn't normal.

We had a very, very mild spell over New Year

and winds from the south,

bringing Painted Ladies from North Africa,

where they normally are at that time of year.

These pioneering Painted Ladies

coming up into southwest England, South Wales...

But not just the south, I mean, there's Isle of Man,

Northern Ireland.

Some in Cumbria as well.

So really amazing influx at that time of year.

Painted Ladies normally start arriving here in May.

But a very warm January meant one bucked the trend.

They react very quickly to conditions around them.

Tropical air blowing in from Africa

saw Britain bask in unseasonably warm weather

at the beginning of the year.

With the warm winds came the first Painted Lady sighting,

in Somerset in south-west England,

as early as January 3rd this year.

It had flown the 2,500km from where I was in Morocco

to here in a matter of days.

But that's not the earliest on record.

Remarkably, one was spotted on New Year's Day in 2013.

Painted Ladies that fly here early in a single journey

are known as pioneers.

Unfortunately, these pioneers will perish

once the weather turns cold again.

And then we come on to the spring, a few more.

Yes, there were a few more,

but the weather really wasn't very good this spring.

It was colder than usual,

it was very wet in some places.

So although we're seeing more butterflies,

as you'd expect, there's nothing very much going on.

So, we move on to the next one - the summer.

And what a summer, albeit delayed.

In late June through July,

sightings erupted across the country.

So, these are Painted Ladies

not coming direct from North Africa,

but coming up from Spain, Portugal, southern France.

It's an explosion of Painted Ladies.

There's barely a part of the country that doesn't have Painted Ladies.

That's right, and indeed,

even the places where they haven't been recorded,

they may well have been there, just not been spotted by people.

These Painted Ladies aren't coming from North Africa,

as the ones in January and February were -

these are moving up from southern parts of Europe,

so they're kind of a generation on.

But, really, all over the country, as you can see.

Yeah, the far north of Scotland - out in the Hebrides.

Really good concentrations

down in the southwest.

We had people on the Isles of Scilly and in west Cornwall

who saw, you know, 50 or even 100 Painted Ladies in a single day,

so there were some quite good numbers around at this time.

So we hear so much about the kind of problems,

the troubles that butterflies are in.

What about Painted Ladies?

Well, Painted Ladies are a very adaptable species.

They are obviously highly mobile, they are nomadic,

they don't live in particular places,

and most importantly, I guess,

the food that their caterpillars need

is mainly thistles, in this country,

that's mainly what the caterpillars are eating

and, of course, they're very common and widespread.

So, actually, Painted Ladies have done really well

in Britain over the past 40 years.

Oh, that's really good to hear.

To get here, Painted Ladies started out from Morocco in late March.

Following the appearance of the foods they feed on,

they arrived in Spain in April to breed,

a new generation carrying out the next stage of the journey

through France in May.

Few made it to Britain in May,

bad weather delaying their arrival in significant numbers

until late June, early July.

The Painted Ladies we see now

are the grandchildren of ones that left Morocco.

Generations born in this country

will then continue to push further north towards the Arctic

before the summer is out.

Basking in the British sunshine in July,

Painted Ladies are a welcome sight.

This is what our spotters have been waiting for.

Like Dave and Agnes in Dorset, who found a beauty.

It's very colourful. Yes!

You can see how fresh she is, she's got that metallic glow on her.

Yeah, she's only been out a day. If not this morning.

Fantastic.

THEY CHUCKLE

The numbers are definitely starting to build.

She is warming up really nicely, isn't she? Yeah. Brilliant.

Dave and Agnes are just the tip of the iceberg.

Spotters from all over the country are seeing our Ladies regularly now,

and the pictures are rolling in.

People have been sending all sorts of pictures - not all butterflies!

But this is a really good one.

And do you know what? This is a guy called Adam Middleton,

and guess what.

He's only 14 years old. That's...

The image is so sharp. Isn't it? You can really see the antennae.

It is absolutely brilliant.

You can see the eye here, the antennae,

and it's got its proboscis out,

it was obviously trying to feed on nectar there.

It's really hard to get a picture like this

of a butterfly in the wild.

And he's 14 years old,

so not only is he a fantastic butterfly spotter,

he's a pretty good photographer as well.

Here's a young man who will be after your job one of these days.

LAUGHING: Yeah, probably.

It's so important that people do this.

You know, scientists are relying on data from people that are, you know,

doing all of this, taking pictures, sightings,

so that they can record them and see what is happening with the migration

from a conservation point of view.

What I like is the way that people have been doing it

in our country for hundreds of years,

so we have the best biological data, don't we?

That's right. We've been doing it for so long.

We're a nation of butterfly spotters.

All the Painted Ladies our spotters are seeing

are this year's Moroccan descendants.

When I joined the world's leading Painted Lady expert,

Constanti Stefanescu, earlier in the year,

he was piecing together the puzzle

of why Painted Ladies migrate in the first place.

It's taken him ten years of extensive research

to establish the facts and reach a definitive conclusion.

After countless expeditions to Morocco

and painstaking data analysis in Spain,

what has he found out?

Well, the butterflies are going absolutely crazy in here,

and it's rather perfect for us to be able to welcome Doctor Constanti.

It seems a long time ago

since we were filming together in Morocco, doesn't it?

Yeah, yeah, it's far away.

But they clearly found you as a butterfly fan.

Now, tell me about your discovery

and all the work that you've been doing,

which I was happy to be a part of.

Well, I started to collect caterpillars of the Painted Lady,

to see which were its natural enemies, many years ago,

maybe ten years ago.

Immediately I realised that these wasps can be very, very important.

And then I thought that maybe migration could be...

..a way to escape this mortality, to these little wasps.

Constanti's research indicates that Painted Ladies leave Morocco

at a specific time of year to escape from their deadly enemy,

the Cotesia wasp.

If they don't, they die.

When I collected the caterpillars in Morocco,

I was afraid that maybe the results would not support the idea.

But when I brought back these caterpillars to Catalonia,

immediately they started to die because of this parasite.

So, yeah, I am very happy about that.

So, how would you sum up your discovery this year?

Well, I would say that the data that we gathered this year

is the first clear demonstration

that natural enemies is also one of the factors

that are important for migration.

Still analysing some data, but the results are very clear,

so I am absolutely confident about what we have found.

Constanti has cracked it.

'His ten-year investigation has revealed astonishing new facts

'about the Painted Lady migration.'

Yes.

'Tiny wasps are the Painted Lady's nemesis in Morocco,

'laying eggs inside caterpillars

'and subsequently killing them on a grand scale.'

As Painted Ladies breed,

so too do the wasps, in huge numbers.

At some point during the breeding season,

Painted Ladies have to leave Morocco to survive.

This is ground-breaking news, a scientific first for Constanti.

His dedicated research has paid off

and added another reason why Painted Ladies migrate

in the first place.

Not only do they move to follow their food source,

as previously known...

..but they also migrate because they are driven out.

Well, that's great that we are able to break the news of your discovery

in our film.

You will appear in the acknowledgements of this paper!

Oh! Well, I never thought I'd end up as a footnote in a scientific paper!

That's fantastic.

But just as suddenly as they appear, usually in May,

Painted Ladies disappear in late October.

For years, it was thought they simply hibernated,

like many other British butterflies, but they don't.

In fact, they don't stop doing anything.

Feeding and breeding throughout the year,

albeit on different continents, they are always on the move.

As northern Europe gets colder, they seek warmer climes.

And where better than where it all began - Morocco?

Incredibly, a final generation makes the 2,500km journey

from Britain back to Morocco in just a few days.

And it's not just from here - they do so from wherever

they have travelled across Europe each year.

In six generations,

Painted Ladies move up to 5,000km in one direction,

towards the Arctic Circle,

and 5,000km back to Morocco.

In a truly remarkable voyage,

they return to Africa

to start their life cycle

and the extraordinary migration all over again.

We've learned so much about the Painted Lady,

and there couldn't be more of a contrast

between the lush green gardens here at Rothamsted

and those rocky deserts in Morocco.

But do you know, I think it's about time

that we let these creatures go free.

And there's enough food plants around here that they could breed

and maybe even send a next generation of butterflies

going back all the way to Morocco.

Right, I think we should go for it, set the butterflies free!

One, two, three, go!

Oh, look, they've been trying to get out all day, I think.

Fantastic, there we go.

Morocco is that way, go!

Yes!

There we go. Oh, look, there we go.

Be free!

WINGS BEAT