Original subtitles

NARRATOR: They're watching you.

More than 5,000 satellites circle the Earth.

Every day, they uncover new

mysterious phenomena that defy explanation.

Discovered from the skies,

code of the Norse gods.

This is, without a doubt, the strangest thing I've seen

in archaeology.

NARRATOR: Something big and weird over Missouri.

If I was in St. Louis, I would be worried

NARRATOR: And America's toxic time bomb.

This place is so polluted that even

the rabbit droppings are radioactive.

NARRATOR: Baffling phenomena.

Mysteries from space.

What on Earth are they?

**

**

Aerial archaeologists take to the skies

over remote wooded hills in central Norway,

an on-board camera fires

laser pulses at the ground to produce a LIDAR image of what

lies hidden beneath the icy landscape.

This LIDAR image really reveals

some incredible structures on the ground here.

RUBEN: We're seeing all these strange formations,

circles and what look like three-pointed stars.

The whole thing looks so weird.

It looks like something out of a cell biology textbook.

NARRATOR: The aerial image has uncovered

dozens of structures lost to history.

They're clearly manmade,

and so that makes me wonder, how old are these things?

And who made them and why?

NARRATOR: Archaeologist David Hill is heading to the site

to investigate.

HILL: I'm very excited about the structures

that you can see on the LIDAR image.

Some of them I really can't explain.

I haven't seen them before.

NARRATOR: Hill thinks some of the structures

in the image are longhouses,

timber buildings built over 1,000 years ago.

It suggests the mystery shapes our legacies of

the Norse warriors who rose

from these lands at the end of the eighth century A.D.

I suspect they might be Viking.

The thing that I'm really unsure about, though,

is their star-shaped formations.

I honestly don't know what they are.

We seem to be getting up to the site.

NARRATOR: According to the LIDAR data,

deep beneath this undulating land

lies a vast array of circles and stars.

Absolutely fantastic.

Many,

many sites have been altered, have been plowed over,

but not here. What we're seeing is intact.

Several of the circular structures are poking

through the Earth,

more evidence, Hill believes, that this is a Viking site.

It seems to be quite a well-defined ditch.

I think this is a burial mound.

Ditches were very important.

They delineate the sacred area.

Within the grave mound, it's the realm of the dead.

Outside, it's the realm of the living.

So I'm now stepping into the realm of the dead.

What we're seeing is a burial site from the Viking period.

NARRATOR: The image suggests this realm of

the dead contains the remains of over 100 Vikings.

I can see 1, 2,

3, 4,

5, 6.

I can't even count them.

This site is incredible.

Fiercely pagan,

the Norsemen would often cremate their dead in

the belief that the smoke would carry them to

the afterlife.

For others, burial mounds are

seen as gateways to another world,

one inhabited by those who had died before them

and the gods they worshiped yet also feared.

HILL: What these mounds represent is

the cosmology of the Vikings.

This is where the living

would commune with the ancestors and the gods.

Wow! Look at that.

Up there on the ridge.

NARRATOR: Two carved slabs of granite crown

the largest of the burial mounds.

This is enormous.

Stone of this size would have

been certainly for somebody very important.

NARRATOR: The Norsemen would often inscribe

gravestones like this with runes,

mystical symbols, which they believed were

originally discovered by the great god, Odin.

They could be used as a means of communication between this

world and the next, or as spells.

This stone was built to convene with the gods,

the spirit world.

It was raised as a gift to them.

NARRATOR: According to Norse beliefs,

half the warriors killed in battle go to Valhalla.

The rest head to Folkvangr,

ruled over by the goddess of sex and war, Freya.

And recent research suggests the Vikings' desire to appease

their gods as they prepare for

these journeys has its origins in a really historical event.

JANULIS: We've got a lot of tantalizing clues that

at the end of 535 A.D.,

there was a massive famine,

and millions of people died all across Europe.

NARRATOR: Geological records reveal that in that year,

dust from a massive volcanic eruption plunges Europe into

months of darkness,

causing crops to fail and killing

a third of the entire population of Scandinavia.

All those natural phenomena that

we today understand by science,

back in the Viking age,

they would understand by relating the gods to them.

NARRATOR: As stories of this catastrophe are passed down

over generations,

it inspires the tales of destruction and vengeful gods

that dominate Viking myths and sagas.

JANULIS: In mythology, this is described as Ragnarok

or the apocalypse.

And when that happens, things go dark, and it takes

several hundred years for the population to build back up.

NARRATOR: What puzzles Hill is how the giant star shapes in

the image are connected to the Vikings'

beliefs in their gods and the afterlife.

This is, without doubt, the strangest thing

I've seen an archeology.

I'm walking down one of the arms of the star-shaped

structure -- remarkable.

Absolutely remarkable.

NARRATOR: Hill knows that three was

a magical number for the Vikings.

The arms

have to mean something.

Odin, the God who created

the first humans, was one of three brothers.

And before the Viking apocalypse, Ragnarok,

there were three winters without summers.

NARRATOR: What's more, the God Loki has three children,

Thor, three weapons, and Fenrir,

the monstrous wolf of the apocalypse,

is bound by three chains.

This is clearly a link between the world in

which we live and the realm of the gods.

What went through the...

the minds of the people who built this?

NARRATOR: Coming up, decoding the Viking cipher.

If I'm right, it connected the Earth to the spirit world.

NARRATOR: And teleporting ships.

They are 60 miles inland, so why are they there?

NARRATOR: An aerial laser survey in Norway

has revealed what appears to be a vast Viking burial ground.

Mystery star-shaped structures sit in its midst...

..perhaps symbolizing the sacred number

three found in Viking mythology.

David Hill is investigating.

I've just discovered

some images and some documents that relate to

the burial, and this material is absolutely spectacular.

NARRATOR: Hill has learned that several years ago, a vessel

was recovered from a grave near the star-shaped mounds.

It originates from the northeast of England,

a favorite hunting ground for Viking raiders.

Yet what puzzles the archaeologist isn't where

the object comes from, but its age.

HILL: This is actually very, very interesting.

It was produced at least 40 years before

the Viking Age began -- that I really wasn't expecting.

NARRATOR: According to historical texts,

the Viking Age begins in 793 A.D.,

when warriors attack the Lindisfarne Monastery in

northeastern England.

They wrought absolute destruction.

The monastery was burned and broken down.

It's a complete bloodbath.

NARRATOR: A raid spurs a wave of pillage and slaughter

through Europe's churches and monasteries that will last

270 years.

Because the Vikings got such

a reputation of brutalizing their victims,

the fear of them spread throughout the land.

We see this appeal across the Christian monasteries.

"Save us, oh, Lord, from the Norsemen."

NARRATOR: The age of the vessel is hugely significant,

because it means those buried at the site played a key

role in the rise of one of

the greatest warrior races the world has seen.

This means that they were out navigating the seas

over 20 years before the Viking Age officially began.

NARRATOR: The years leading up to the Viking Age are shrouded

in mystery.

It is a time when much of Scandinavia is ruled

by groups of warrior peoples known as the Vendals.

JANULIS: The history of the pre-Vikings is fascinating.

We don't exactly know what was going on.

It was sort of a dark time,

not a lot of communication, not a lot of travel.

NARRATOR: What is known from historical records is that

the Vendals were renowned horse-mounted warriors

and traders.

But during the eighth century A.D.,

something happens, which transforms

them into seafaring raiders.

The Vendals move more than

25 to 50 miles away from home.

They are not adventurous.

But the Vikings, the very word "vikingr" means

sea traveler and wanderer.

NARRATOR: Some academics believe the Norsemen's transformation

was fueled by the desire

to protect their pagan beliefs.

In the late eighth century, the King of the Franks, Charlemagne,

is pushing his Catholic forces into Scandinavia,

slaughtering thousands.

This propels the Norsemen to

seek Christian blood and riches overseas,

aided by an unusual climatic event.

It's called the Viking Warm Period,

and a lot of the Arctic Sea starts to melt,

and as a result,

the Vikings start going further

and further away from land in their ships.

They became the most famous seafaring

pirates in the history of the world.

HORTON: They extended right away across Russia,

to Greenland, and eventually into North America itself.

NARRATOR: Before embarking on these long, perilous voyages,

the Viking warriors would need all the protection and strength

their pagan gods could afford them.

They must also prepare for

the afterlife should they perish in battle.

For these reasons, Hill thinks the three-limbed

structures likely represent

the most important and venerated symbol in all Norse mythology.

If I'm right,

this makes the site very sacred place for the Viking.

The number three has special significance,

but the one I think that has the most significance for

this site is the Viking world tree, Yggdrasill.

It had three roots, and it connected the Earth to

the spirit world.

NARRATOR: The great world tree, Yggdrasill,

supports the nine realms of the Norse cosmos.

It connects the mortal and immortal worlds,

and its three routes are pathways to Asgard,

the land of the gods

and Helheim, the underworld.

1,200 years after the Viking age of plunder began,

these extraordinary ritual structures are rediscovered

from the heavens, surrounded by

the graves of the warriors who once worshiped here.

I am convinced that this was a site where the clan

convened with the gods

and their ancestors and the spirit world.

But until a full archaeological investigation

takes place, the stars are gonna hold on to their secrets.

NARRATOR: Coming up, Hitler's ghost ships.

HEIMLER: These are giant.

Why are they here in the middle of a field?

And a mutant craft in the Mojave.

I'm no pilot, but there seems

to be something wrong with this image.

NARRATOR: May 4th, 2018,

the WorldView-2 satellite scans

the province of North Brabant in the Netherlands.

At first glance, this aerial image

of the Netherlands looks like regular farmland.

But zooming in,

there are unusual shapes here in this field.

They definitely look like boats.

It makes no sense at all.

NARRATOR: The ghostly vessels are almost 200 feet in length.

These are not rowboats, they're ships,

and if you zoom out a little bit,

they are 60 miles inland.

So why are they there?

NARRATOR: Anywhere else,

ships buried this far inland would be an unlikely discovery.

But the unique geography of

the Netherlands makes it a real possibility.

About a third of the Netherlands is actually below sea level.

We know that huge amounts of land reclamation

has taken place.

Dams were created to hold back

the North Sea, and the land was drained.

And people are always finding remains of medieval boats

that really sank out in the open sea

in these open fields.

NARRATOR: Historic images of the same location reveal

the mystery craft have a different origin.

They appear for the first time in aerial photographs taken

during the Nazi occupation of the country

during World War II.

Another big clue is the fact that, within the immediate

vicinity of these shapes,

there are craters, and that's suggestive of it having been

a bombing practice range.

But it doesn't really make sense.

I mean, I could think of boats for targets,

but on the water and not inland.

In the run-up to World War II, the Netherlands attempts

to remain neutral on and is ill-equipped

to resist the Nazi threat,

possessing just one tank to repel 2,400 invading German

war machines.

The destruction was total.

The victory was swift, and it was astonishing.

CADDICK-ADAMS: The battle is over

by the end of May 1940, the Germans

have taken just days to overrun the entire country.

NARRATOR: Declassified Nazi files

reveal the role the mystery ships played

in the extraordinary events which followed.

MORGAN: After the 1940 campaign, Germans began to

stage up for an invasion of the United Kingdom.

WALTERS: Of course, the British aren't gonna

roll over to Hitler,

so he's gonna have to do the really tough job of invading

a massively strong and well-defended island.

What Hitler's trying to do is something that

hasn't succeeded since William the Conqueror in 1066,

and that's what these shapes and shadows are all about.

NARRATOR: In June 1940, Hitler commences Operation Sea Lion,

the code name for his plan to invade the island nation.

But Britain presents a very different challenge from

the European countries who had

fallen so quickly to the Nazi tactic of blitzkrieg,

or lightning war.

MORGAN: At the heart of blitzkrieg

was the idea that an attack would come

without warning and would involve

the close coordination of mechanized units on

the ground that could range over vast distances.

Hitler's plans for invading other countries

worked really well across land,

but you can't drive a tank across the English Channel.

NARRATOR: In order for Operation Sea Lion to succeed,

Hitler plans to neutralize the Royal Air Force and launch

an amphibious invasion of England's south coast.

But the fuhrer knows that Royal Navy ships

outnumber Germany's 2 to 1.

So if Germany is gonna defend her invading fleet,

her aircraft have got to take out the boats of the Royal Navy

that's gonna attack the German fleet.

The Luftwaffe is the most powerful air force in

the world,

but only around 10% of the bombs they drop

hit their targets and much less

against moving ones.

You gotta remember, you are in a German plane

traveling around 200 miles an hour,

shuddering and shaking in the sky,

and you're trying to drop a bomb on a boat no more than

the width of a couple of houses.

That is incredibly hard to hit.

HEIMLER: In order for Operation Sea Lion to work,

the Luftwaffe is going to have to increase their accuracy on

hitting ships tremendously.

NARRATOR: The Nazis' solution is to build

a replica harbor and ships next to an inland airfield

and use it to prepare the bomber crews for their

assault on the Royal Navy.

CADDICK-ADAMS: When we look at the image closely,

there's a mock port there,

and there's actually two submarines, as well, and this is

all being crafted so they get it right,

but away from the stress of combat.

NARRATOR: Munitions cost money,

so practice runs are carried out

with concrete bombs filled with phosphor.

They're exactly the same size and weight as a high

explosive bomb -- when they drop and they hit the target,

they crack open, and the phosphor reacts

and sends off smoke.

NARRATOR: Yet the Luftwaffe pilots never get

the chance to put their training to the test.

During the Battle of Britain, the Royal Air Force

deals a hammer blow to Operation Sea Lion,

destroying 1,800 German planes

and killing 2,500 airmen.

WALTERS: There's no way that you could

launch on invading force across the channel

if the RAF and the Royal Navy could just take them out.

It would be slaughter.

The English Channel would have run red with Nazi blood.

NARRATOR: Today, the ships remain as

a chilling memorial to the great invasion that never was.

These are kind of a metaphor, because

they're built at a time when Nazi Germany had grand

ambitions, and all of those

grand ambitions would ultimately fall into ruin,

sort of like these ships.

NARRATOR: Coming up, the mystery mega plane.

This thing is super-sized.

It doesn't even fit on the runway.

And the experiment that changed the world.

This is not your ordinary military site.

This place has an extraordinary history.

NARRATOR: January 9th, 2019.

Flying high above the barren expanses of the Mojave Desert,

the GeoEye-1 satellite captures

something weird sitting on a remote runway.

I'm no pilot, but there seems

to be something wrong with this image.

It almost looks like two airplanes sort of

smushed together.

MORAN: It actually looks like the love child

of, like, a 747 and a catamaran.

NARRATOR: Ken Joyce scans the strange craft

using Maxar's SecureWatch technology.

JOYCE: I started to think that

this image had been somehow manipulated.

I can see a single shadow with two fuselages.

I don't think that it's an error in the image.

I think that this is just one giant aircraft.

NARRATOR: Joyce's analysis reveals

the monster plane has a 38-foot wingspan,

twice that of a 747,

And the largest in the history of aviation.

KOUROUNIS: This thing is super-sized.

It doesn't even fit on the runway.

The wingtips extend over the sides.

MORAN: It doesn't look like it could be

a passenger plane or even a cargo plane.

So what is the purpose of this thing?

NARRATOR: Analysts turn to historical aircraft designs

for clues to the monster plane's purpose.

There's a really deep history in aviation of

building gigantic aircraft

that push the limits of what we think is possible.

And the most iconic of these is the Spruce Goose,

built by the billionaire Howard Hughes.

NARRATOR: The colossal 320-foot wingspan Spruce Goose is

followed three decades later by the Antonov 225,

which holds the world record for the biggest ever payload,

280 tons, equivalent to 45 African elephants.

But the aircraft in the image has

a very different design from these monster planes.

The Antonov has a very large

fuselage to carry large amounts of stuff.

When we look at our mystery aircraft, it has two fuselages,

both of which are very skinny.

It looks more like it's built

to carry something underneath the aircraft.

NARRATOR: Experts consider if the plane's location

could shed some light.

KOUROUNIS: This is the Mojave Air and Space Port

in California -- this is a facility that's used

to test all kinds of experimental spacecraft.

LINSELL: And that gives us a clue that this plane

is probably designed to haul rockets

into the air and then launch them into space.

NARRATOR: By carrying a rocket between the two fuselages

and launching it high up into the atmosphere,

engineers could solve a problem that has plagued

the aerospace industry since before the Apollo program --

how to reduce the cost of reaching orbit.

The United States spent tens of billions of dollars on

the Apollo program,

and if you count for inflation today, that would be

hundreds of billions of dollars.

NARRATOR: To get the Apollo astronauts into orbit,

their Saturn V rocket burns a large

swimming pool's worth of fuel every nine seconds

to reach speeds four times faster than a bullet.

And even today, it costs $10,000 to

get just one pound of payload into orbit.

KOUROUNIS: Any edge that the aerospace industry can get

in terms of getting payloads up,

out of our atmosphere and into space,

whether it's people, satellites, who knows what,

well, that's the Holy Grail

of the space industry.

The plane in the image, called

the Stratolaunch, is custom-built

to overcome this challenge.

MOSHER: The airplane takes off from the runway

with the rocket in the middle, goes up to altitude,

drops the rocket, which then fires and takes a payload

all the way to orbit.

LINSELL: If you launch the rocket from high altitude,

the air resistance is much lower,

and this means that you need less fuel,

and the rockets can therefore be cheaper.

NARRATOR: The Stratolaunch's maximum take-off weight is

1.3 million pounds, the same as 110 Apache helicopters.

To carry a rocket towards space,

it needs six turbo fan jet engines and wings so big

they're nine times the distance

of the Wright Brothers' first flight.

This airplane is so mind-bogglingly large,

they had to create a custom-built hangar

to just house the thing.

The megaplane requires a two-mile-long runway to

get airborne.

By carrying a rocket to 35,000 feet before releasing it,

engineers hope to reduce the cost

of getting hardware into orbit by 50%,

transforming the future of space travel.

It's very rare that we catch

a glimpse of this extraordinary plane,

and there's a bit of, I guess, poetic irony

if you consider that we're looking at something from space

that one day could bring us

into space and give us that seemed vantage.

NARRATOR: Coming up, the long-buried secrets

of the Manhattan Project.

What we're actually looking at here is a nuclear graveyard.

NARRATOR: And the invisible monster blob.

Something seems to be moving across the terrain,

but nobody can see it.

NARRATOR: July 31st, 2019 --

flying over Washington State,

an aerial survey plane scanning the 600-square-mile

Hanford military facility captures something out of place.

Sitting right in the middle,

there is some kind of strange arrangement of objects.

These structures are almost like the keyboard

on the computer.

NARRATOR: The weird keyboard consists of

more than 120 monster barrels,

each 40 feet long and 30 feet wide.

These barrels are literally the size of a house.

They appear to be storing something, but what could it be?

NARRATOR: Elsewhere, a line of supersized storage cylinders

would be a strange anomaly,

but because this is Hanford, they could be evidence of

something much more disturbing.

This is not your ordinary military site.

This place has an extraordinary history.

Some say this is actually the most polluted place

in America, so maybe this has something to do

with these shapes we're seeing in this image.

NARRATOR: Declassified government files

reveal that Hanford's deadly legacy

has its origins in the most secretive and pivotal

military experiment of the 20th century.

It was actually established in World War II as part of

the Manhattan Project.

That was the U.S. development

of the world's first nuclear bomb.

It was here that the world's

first big nuclear reactor was built.

NARRATOR: Such is the secrecy surrounding

the Manhattan Project that of the 120,000 people working

on it, less than 1% know that they are developing the most

catastrophically powerful weapon in history.

ANNOUNCER: At Hanford, Washington, is produced one of

the explosive materials used in the atomic bomb.

[explosion blasts]

It's the same plutonium that ends up going into

the Fat Man atomic bomb that's dropped on Nagasaki.

So you cannot overestimate how important this site is.

NARRATOR: During the Cold War, the military installs

an additional eight atomic reactors at Hanford,

which produce enough plutonium to arm 60,000 nuclear weapons.

More than 56 million gallons of

toxic waste seeps into the soil,

enough to fill 85 Olympic-sized swimming pools.

This place is so polluted that

even the rabbit droppings are radioactive.

So maybe these giant cylindrical barrels are

a way of storing this radioactive waste.

NARRATOR: Journalist Carlo Munoz suspects the giant

cylinders are part of a cleanup program,

but one dealing with radiation from an unexpected source.

MUNOZ: If you count the number of structures,

it's about 120 -- now,

interestingly enough, the United States has

decommissioned roughly 120 nuclear submarines.

NARRATOR: The size of each giant cylinder also

corresponds to that of a submarine's nuclear core.

For all the benefits of nuclear submarines,

their service life really runs about 25 to 30 years.

At that point, they have to be decommissioned.

The problem with that is,

what do you do with the nuclear core

used to power these boats?

NARRATOR: It's a challenge that has been facing

the military since 1959,

when they decided to replace the nuclear reactor on the

USS Seawolf.

The Navy's solution is to simply tow the old reactor

out to sea and drop it to the ocean floor.

And you don't even have to be the most concerned

environmentalist to think that could be a really bad idea.

You're gonna slowly turn

the world's oceans radioactive with obviously

devastating consequences.

LINSELL: Pressure mounted to find a better solution,

and the practice was eventually banned,

and what replaced it was this facility at Hanford.

NARRATOR: Before the cores arrive at Hanford,

the Navy begins the decommissioning process

at the Puget Sound Naval Shipyard,

160 miles to the west.

They basically take the sub out the water,

and they chop it like a sausage into three.

You've got the middle section,

which is gonna house the reactor.

That's the bit you've gotta deal with in order to make it safe.

The first thing they do is remove

the actual nuclear fuel rods from the reactor core.

Then you have what's left is the reactor core itself.

NARRATOR: The core's medals, after years of

neutron bombardment, are still highly radioactive.

After arriving at Hanford,

the cores are lined up at the site in the image,

code-named Trench 94.

What we're actually looking at here is a nuclear graveyard.

At some point, the U.S. government

is going to have to bury this

in order to prevent nuclear radiation from seeping out.

NARRATOR: When buried, these barrels will join 24 million

cubic feet of radioactive waste already entombed

at Hanford,

enough to create 1,800 bombs the size

that destroyed Nagasaki.

They claimed that this is a safe way

of storing and getting rid of nuclear waste.

But we've seen accidents happen in the past.

For now, the only thing we can do

is cross our fingers and hope that nothing happens.

NARRATOR: Coming up,

a monster over the Midwest.

We're having some kind of an explosion out of the central

St. Louis area.

NARRATOR: Satellites play a vital role in

tracking severe weather systems around the globe.

By combining their data with

the technology known as Doppler radar,

meteorologists create images that map the speed

and intensity of an approaching storm in

astonishing detail.

Doppler radar works by sending pulses up into the atmosphere

and seeing whether the pulses bounce off anything

on their way.

CERVENY: Doppler radar is a fascinating tool

for meteorologists, because it becomes almost

an X-ray machine that we can use to examine

the inside of storms.

NARRATOR: On September 19th, 2014,

Doppler data captures what appears to be

a colossal weather front in the skies over Missouri.

It almost looks like we're having some kind of

an explosion that is taking place

out of the central St. Louis area.

If I was in St. Louis, I would be worried.

NARRATOR: The blob's location fuels fears

that the city's 300,000 inhabitants are about

to face the wrath of one of the planet's most destructive

weather phenomenon.

Missouri sits in the middle of several

states that comprise what's called Tornado Alley.

That's where most of the tornadoes

in the U.S. take place.

NARRATOR: Yet accounts from local residents reveal

that the mystery blob is no tornado.

Here's the weird twist.

There's absolutely no reports of any bad weather in the area.

Something seems to be shifting and changing and moving across

the terrain, but nobody can see it.

So what's going on?

NARRATOR: Biologist Adam Ruben studies the data in more detail.

The low signal strength shows that we're dealing with a mass

of very small things, all moving together.

Things seems like it has to be some kind of swarm.

NARRATOR: If this is a swarm, it's a monster,

around 300 miles wide.

Ruben thinks the images have

captured one of the most incredible events in nature.

RUBEN: Not only is Missouri right in the middle

of Tornado Alley,

it's also on the path of one of the most impressive

migrations of any animal on

the planet, the monarch butterfly.

NARRATOR: Every fall, vast numbers of the monarch butterfly

migrate up to 30 miles southward across the U.S.

to escape the freezing winters of the Great Plains and Canada.

These amazing insects travel all the way down

to Mexico on wings that are thinner than paper.

The monarch migration is

the longest insect migration in the world.

It is truly remarkable.

NARRATOR: The monarch butterfly has a bizarre life cycle.

Between April and September, four generations

of the critters live and die

in their North American summer homes.

But as winter looms, something weird happens.

Most monarch butterflies, when they emerge from

the chrysalis, live only 2 to 6 weeks.

But there is this super generation of monarchs that

live up to eight months,

and these ones make this annual migration.

NARRATOR: Triggered by decreasing

day length and temperatures,

the super generation head towards the Mexican border,

covering up to 100 miles a day.

SCHUTTLER: They're traveling from one end

to the continent to the other.

This would be a long flight for us,

even on an airline, and these are just

these little tiny insects.

And they're making it all on their own.

NARRATOR: Flying up to two miles high,

battling storms, predators, and starvation,

it takes months to reach their destination,

but for those that make it here,

the danger is far from over.

RUBEN: Monarch butterflies face a lot of threats,

but there's a new one that's a little bit unexpected.

Monarch butterflies are being killed by Mexican drug cartels.

NARRATOR: Before flying back to North America in the spring,

the monarchs spend five months clustered around oyamel

fir trees in the mountains of Central Mexico,

and that puts them in the firing line

of the local narcos.

The butterflies specifically need the trees in this one place

in Michoacan province,

and the drug cartels have moved in, because the wood in

these forests has become incredibly valuable.

SZULGIT: Drug cartels are branching out now into other

illicit activities,

be it kidnapping, land theft, illegal mining,

and now, illegal logging.

[chainsaw revs]

In Mexico alone, illegal logging is worth

$15 billion a year to criminal enterprises.

After slaughtering an estimated 150,000

people over the past two decades,

the cartels may be about to add

another grim statistic to their reign of terror.

If you destroy the wintering range,

the fate of the monarch butterfly is

basically doomed throughout much of North America.

RUBEN: There's that old saying that if a butterfly flaps

its wings in Central Park that there's snow in Siberia.

But what if millions of butterflies

all stopped flapping their wings?

We don't know what could happen.