Episode 1 Nature's Weirdest Events

No matter how well we think we know our planet, the natural world still

has the ability to surprise us,

to shock us and maybe sometimes even

to scare us with its extraordinary events and bizarre behaviour.

And new technology means that nature's weirdest phenomena

are being caught ever more readily on camera.

So, we're going to bring you the strangest stories our world has to offer.

From the biblical swarm that took Lake Erie by storm...

That is really creepy.

..and the bears with a taste for the poolside...

There is a bear in my hot tub!

..to the amphibian with a frog in its throat...

..and a toad with a skin-crawling secret.

Oh, my God! Look at her! Here they come. There they come. Get them.

With the help of scientists, experts and eyewitnesses,

we're going to try and unravel exactly what on earth is going on.

To kick off, we're going to look at some of nature's weirdest romantics,

stories of bizarre and sometimes fatal attraction.

From the eerie vibrations that shook the shores of San Francisco Bay

to an extreme case of opposites attract.

But first we're heading to America's Great lakes where some

very bizarre romantics are dying to find love, before it's too late.

The shores of Lake Erie on America's beautiful border with Canada

have forever been a tranquil place of peace and quiet.

Until, early in the summer of 2010,

it became the setting for a swarm of phenomenal proportions.

This gas station is being attacked by...something.

And that lady won't even get out of her car.

It's like it's snowing.

A swarm of literally billions stretched over a mile inland

and for miles along the western shore.

Every surface, every inch of air was filled with winged insects.

That is really creepy.

Local resident Greg Stewart recalls the experience.

They were all over the wall of the city and I didn't know if I should even

get out of my car, it was that bad.

And as I got out, they all started crunching under my feet.

Then, within days, they spontaneously started to die in their billions.

Seriously, a pile of bugs.

The drifts of dead bodies got so deep that the local authorities

had to use snow ploughs to unblock the roads.

And as they started to break down, they left another treat, too.

It smelled of motor oil and vomit.

So what were these insects, and what could have caused such an extraordinary plague?

Don Schloesser is an expert in the wildlife of Lake Erie

The big swarms are really the result of the life history pattern of the western Lake Erie mayflies.

They live in the mud for about two years and they grow and they moult.

About the middle of May, the first of June,

they all come out of the water at one time.

They mate, and then the females go back out into the water to lay the eggs.

And then the whole process starts all over again.

Mayfly spend about 99% of their lives

as aquatic larvae at the bottom of ponds and rivers.

They spend their time feeding and growing

until, in a cunning plan to avoid getting eaten,

they all emerge en masse to mate.

The first few are easy pickings.

But soon the sheer numbers overwhelm predators -

they simply can't make a dent in the overall population.

After about two days, there's a swarm,

a swirling swarm like a little funnel cloud that's formed by the mayflies.

And what happens is the females jump into that swarm, they are fertilized in the air.

Once they have mated, the male dies and the female heads out

over the water to release her fertilised eggs

before she too passes away.

The entire process takes just a matter of days.

Each year as the event comes to an abrupt end,

it's all hands on deck for the task of clearing up the dead.

But there is still a lot of questions surrounding their mass emergence.

When they come out is still a mystery to us.

We can't predict very well in that two- or three-week period

when they are actually going to be coming out.

Sometimes it is related to storm events,

sometimes it is related to rain events, but somehow

the mayflies all get a cue when they are down in the bottom of the lake.

But why are there so many in Lake Erie?

Lake Erie supplies the types of sediment that this critter likes to burrow into,

it used to have mayflies many years ago, then they went away for many years due to pollution.

Now they're back and they've come back with sort of a vengeance

in terms of the numbers and the abundances that we see come out of the water.

So this almighty insect orgy is all down to a particularly perfect set of conditions.

The enormous size of the lake and its newly clean waters contribute to

a swarm so large that it can bring a whole city to a grinding halt.

There are 51 different species of mayfly here in the UK.

They are all members of the Ephemeroptera,

which quite literally means "lived for a very short time".

Our mayfly here in the UK do provide an impressive spectacle,

albeit on a somewhat reduced scale to that seen Lake Erie.

And if you want to experience this for yourself,

head to the River Tweed in Scotland or to the Wye in Wales.

An easy way to increase your chances of seeing some emergence

is to time your trip with the flowering of hawthorn trees

and bushes in the area.

And the really bizarre thing about all mayfly is that once

they are in their adult form, they have no mouthparts to feed.

It's a race against time to mate before they starve to death.

Nature at its weirdest.

For our next crazy romance, we head to America's west coast

where it's not insects that fill the air at night

but the lover's serenade of another American beauty.

Sausalito is an exclusive neighbourhood of houseboats,

kissed by the gently lapping waves of San Francisco Bay.

It's a high-class haven of tranquillity -

until the sun goes down

and the peace and serenity of the summer months is absolutely shattered.

AGGRESSIVE HUM

GROWLING HUM

LOW HUM

If you've ever had a sound system with a hum in it, it's that sound.

GROWLING HUM

It sounds like a low-flying flock of B-52s. It's a low hum.

LOW, STEADY HUM

What you can hear now is a recording of the sound itself.

And, yes, it's very loud indeed.

Just imagine shelling out for your dream home

and then having to listen to this all night long!

HUM CONTINUES

Residents likened the volume to that of a low-flying jet air craft.

No-one knew where the sound was coming from,

but everybody had a theory.

Secret navy communication systems, telephone systems run amuck,

pacemakers going off at the same time from old people's homes.

I mean, you can imagine just about anything.

They would run sewer pumps here at night

cos they didn't want the tourists to see the effluent

going out during the daytime in downtown Sausalito,

so they only ran the pumps at night, and the sound was only heard at night.

We would put our hands around the light poles

and they would be vibrating with this sound.

And that's why I was convinced it was electrical. It had to be electrical.

In the early days, this was sort of a bohemian community,

and nobody really wanted to admit that they'd heard it,

because it was just part of the proverbial buzz,

and then as wealthier people moved in and began to say, "What is that noise?

-"That's bothering me? Who can I sue?" And that sort of thing.

-HE LAUGHS

Some of the folks were really angry.

They'd spent half a million dollars to buy a houseboat here,

and they couldn't sleep in it, and so they were quite upset

with all this noise, and they wanted something done about it.

So what on earth could be the cause of these otherworldly sounds?

The state of California sent in the experts.

ELECTRONIC GURGLE

After spending a year and a lot of money analyzing sound waves,

and testing a range of completely bonkers theories, the experts were spent.

So, in a last ditch attempt to find an answer

they called biologist Professor John McCosker.

I received a call from the head of the noise abatement bureau, in Marin County.

He said, "You know, I can't believe I'm even wasting my time asking you this question.

"Is it possible that a fish could make so much noise it would keep people awake?"

I said, "What are you talking about?"

He said, "Well, the houseboat owners are complaining.

"They say that they can't sleep at night and somebody told us that it

"could be an animal underwater and they told us to call you."

So I said, "Sure, play the sound over the phone."

He did, and I said "Oh, yeah, that's the Porichthys notatus,

"the Batrachoidid, it's a Midshipman, they make a noise, it's also called a humming fish."

And he said, "You know what that is?"

I said, "Of course, they do that during the summer,

"starts probably about sundown, ends about daybreak, right?"

And he said, "Oh, my God! Don't tell anybody."

LOW, STEADY HUM

Identifying the culprit was the easy part,

but convincing the city of Sausalito that it was a fish,

that was a lot more difficult, because people just didn't want to believe it.

I knew they were lying. I knew they were lying.

It's a fish. It's a fish.

I thought, this could not be a fish, they have to be out of their minds.

However unbelievable it might be,

this is the culprit - the humble humming toadfish.

The toadfish is an extraordinary fish.

It's one of 30,000 species of fish living on earth,

but because of its appearance and its behaviour,

I'd say it's a little more extraordinary than most other fishes.

The toadfish is a bottom-dwelling ambush predator, superbly adapted to life in the mud and sand,

and one of the many types of fish that use sound in their daily lives.

And when we heard it, we thought it must be something the size of a seal

or a blowfish or something gigantic that would be out there

that was buried in the water with just its eyes peeking out.

But it turned out it was this little, stupid, little, ugly fish.

And it really doesn't look like much,

but it could make enough noise to keep us awake all night.

It spends most of its life living buried in the sand, buried in the mud.

Not that attractive.

So, in order to attract a mate, it has to display,

and in so doing, it displays vocally.

A lot of fishes make noise, and most of them use either

the grinding their teeth, like that... HE GRINDS TEETH

or their body slapping against the water,

and you can hear that noise, or they use their gas bladder or swim bladder.

The swim bladder is a special air-filled organ found in most bony fish.

It allows them to regulate their buoyancy

in the water without having to expend the energy swimming.

But the toadfish has modified its swim bladder to become

an amazing instrument.

That little sac has very strong muscles along the sides of it,

and those muscles vibrate as many as 150 times a second,

so you have this resonating chamber that makes a...

HE HUMS

..that can be heard from a significant distance.

Sound carries very well underwater.

But why the phenomenal racket? And why only during the summer months?

Toadfish spend the majority of their life in the ocean.

They enter the Bay at the beginning of summer and get into the shallow

waters so that they can make their nests, usually against large rocks,

large wooden structures, or against the edge of a houseboat hull.

The water is very murky, it's dark,

and they start trying to attract a female.

A good song can be so irresistible that the male could end up

guarding the eggs of numerous females.

Apparently it's very sexy to another fish,

but it's terrible for us.

Such a small fish is able to generate such an enormous sound

and create such a giant ruckus as a result.

How wonderful! That's what nature can do.

It's an amazing fish.

Incredibly, the old humming toadfish has more than one call.

It hums to attract a mate but it also emits a sharp grunt to discourage potential rivals.

But what's even more surprisingly is it's not the only fish with a song in the piscatorial charts.

Listen to this.

LOW CHIRRUPING

That is the chirruping of a sergeant major fish.

It's a small species which lives on tropical reefs, and it seems

to be more vocal when it's aggressively defending its territory.

LOW CHIRRUPING

RASPING CLICK

That is the sound of the famous pufferfish,

that species which expands its body covered with spines

so it can't be eaten by any larger fish.

But my favourite by far is this one.

DEEP, PULSING BASS SOUND

That is the song of the cod.

I wonder how much longer will be able to hear that in our seas,

given that we're battering its population with over fishing.

Perhaps we could see that this species has had its chips

when it comes to being an oceanic pop star.

The hunt for our next set of outlandish lovers

takes us deep into the unexplored depths of our planet,

where finding that perfect date can seem almost unfathomable.

The deep sea, possibly the weirdest environment in the world.

Life down here is hard - it is vast and empty,

and the simple tasks of finding food and love are very difficult indeed.

To cope, evolution has produced some of its weirdest creations.

Like this appropriately named vampire squid from hell.

And this sea angel - it's a snail that has lost its shell

and taken to a life above the sea bed.

Not to mention Gigantocypris, a leviathan of its kind,

the size of a grape.

And not exempt from the issues of life in the abyss

is our curious romantic, the deep sea anglerfish.

Anglerfish are highly accomplished ambush predators

with a glowing lure on their back that they use for hunting prey in the unending dark.

They have been attracting the attention of scientists

and naturalists for years.

But until recently, one thing baffled them more than any other.

All the fish they found were female.

So, where in the perpetual darkness could all the males be hiding?

Adding to the mystery, many of the fish they studied

had a small passenger attached to their underside.

Then the scientists discovered something almost unbelievable -

that this passenger was in fact the male of the species!

To help us understand this discovery is James Maclaine,

expert of all things fishy from London's Natural History Museum.

If you see a large anglerfish, it's always gong to be female.

They've gone for very, very extreme version of what we call sexual dimorphism.

Which is where the males and females look different,

and they look very, very different indeed in anglerfish.

In fact, for a long time, people thought that male anglerfish

were a completely different kind of thing, didn't even realise they

were anglerfish for a long time because they look so different to the females.

Incredibly, this huge difference in size is a solution

to the problems of life in the deep, where there is very little food.

As demonstrated by this female taken from the water with her stomach still full.

The anglerfish doesn't want to catch something

and then realise it's too big to eat.

So it just has to try and force it in no matter how large it is.

The fish that it's eaten is probably twice as long as the anglerfish,

and what it is, it's sort of curled it up so the head is here

and the fish curves round and then the tail is kind of in there.

So the female has all the specialist kit she needs

for life down here, but what about the male?

He doesn't have any of the fancy paraphernalia of the female,

so in a place where you need to be highly specialized to find food,

how on earth is he going to survive?

The male anglerfish's life is actually quite desperate.

It starts off really nicely. The eggs hatch and they go up to the surface

and the baby anglerfish have a little brief moment in the sunshine.

Once they've left the surface water, they stop feeding and it just becomes

this desperate race against time to find a female before they starve

to death, and if they don't find one within a few weeks, they will starve.

But in the dark emptiness of this deep sea, how does he achieve this?

Well, with a pair of super sensitive nostrils he is able to detect

and follow a faint trail of pheromones that she leaves.

They find the female, and when they do they will actually attach

themselves to her and connect to her blood supply,

the sort of bite on and almost plumb themselves in,

and then they feed off her blood, and she carries them around like a parasite.

It's a sort of deep sea economy measure. Because the male is

so small, he requires only a fraction of the food that the female needs,

so a male and female anglerfish can survive on a fraction of

the amount of food that would be required if they were both the same size.

That's a fabulous tactic in a world where food is very hard to find,

but what's in it for her? After all, she is feeding him with her own blood.

Once they are attached, that's it for life, and it's quite gruesome.

The skin of the female will actually grow out over the male's face,

and he basically becomes like an organ that she carries around.

And he's attached underneath, so he's right there in the right place for when she lays the eggs.

She can literally turn him on, she can send him

a little message through her blood, a hormonal single,

so that when she lays the eggs he can fertilise them as they come out.

It's amazing - when the extreme pressures of life make finding that

special someone almost impossible, it's best to make sure

that you remain joined at the hip forever.

An incredible example of sexual dimorphism,

where, in a species, there is a very distinct difference between the male and female.

Of course, in those anglerfish it's principally size,

but in these black grouse you can see that the male is a lot more

flamboyant than the rather dowdy female,

and that's because he is using those plumes to attract a mate.

But it doesn't only occur in birds.

Look at these splendid stag beetles.

The females on the right here lack those remarkable antlers of the males.

The males need those, of course, for aggressive encounters with rivals.

These bizarre stories of nature's weirdest romantics show the extreme

lengths that some species will go to to find their perfect partner.

From the toadfish whose sweet serenade could bring him

many lovers, to the connection that means that the anglerfish

will never have to find another.

And those mayflies, that are literally dying to mate.

The weird and wacky ways that nature finds love will never cease to amaze.

Now, even though you might be able to choose your lover,

who you end up living next to is an entirely different matter.

Coming up next, we look at some stories where neighbourly understanding is essential.

We'll investigate the curious events that could lead you

to sharing your favourite spot in the garden.

But first, one incredible encounter that has led to a surprising

and beautiful Platonic relationship.

Churchill, on the shores of the Hudson Bay in the Canadian sub-arctic.

Each year, starving polar bears roam around town

waiting for the sea to freeze so they can hunt seals.

Dog breeder and Churchill resident

Brian Ladoon keeps 150 sled dogs on the shores of Hudson Bay.

Just a complete city of dogs.

Brian keeps his dogs on a spit of land jutting out into the sea.

It's isolated and the best place to keep Eskimo dogs on earth.

It's isolated and it's controllable, except for the other locals.

You see, one day in 1992, Brian watched helplessly as a starving

polar bear strolled onto his land

and headed straight for his dogs. He knew all too well that bears

regularly kill and eat dogs where they come into contact.

When I first seen things playing out, I did have great concerns.

I was frightened, and I wasn't sure what to do.

He was unable to move a muscle as half a tonne of malnourished

mega-predator closed in on his faithful companions.

Then, as these photos show,

something truly unbelievable happened.

The pair began to play.

It is extraordinary to see them play together.

Actually you got a privileged position

when you are right in the front row seat and you're watching them

and they are only, like, metres away from you.

Amazingly this particular bear started an annual ritual,

returning to visit the dogs each year just before the sea freezes.

So why on earth did this hungry polar bear feel that

playing with its potential dinner

was better than satisfying its aching hunger?

Clinical psychiatrist Dr Stuart Brown has analysed these incredible photos.

What was amazing to me

was that the polar bear, as he approached this female sled dog

that was tethered, was in a predatory gait,

with fixed eyes, headed toward that sled dog.

Which anyone who's ever seen a predatory animal

recognises as a very powerful signal that says, "I'm going to kill you."

The dog went down into a play bow, and the bear immediately

picked this up, changed his gait and started dancing.

And was gambolling. The hair went flat, the eyes went soft,

and in a moment the bear was standing upright over the sled dog.

The sled dog was staying there wagging her tail.

They looked up at each other

and they started into this wonderful ballet of rough-and-tumble play

which went on for 20 minutes. It was magical.

Dr Brown is a world authority on play,

and has been studying its effects and benefits for over 20 years.

The smarter the animal, the more they play.

It's very important for survival

and for adaptation in a constantly changing environment and world.

Animals that are capable of play are also capable of innovation

and flexibility under unexpected circumstances.

Rough-and-tumble play, which is universal among social mammals,

is extremely beneficial, complex and very, very important.

What does it do?

It teaches the animal their own strength, speed, capabilities.

It puts them in competition with other animals,

tells them where they fit in the hierarchy of the pack.

It also teaches them empathy.

So that makes sense for animals of the same species,

but bears and dogs are competitors at best.

At worst, Brian's dogs are a tasty snack-sized mouthful for a hungry bear.

So there must be something more to it,

but what need could be more urgent than hunger?

I think the power of play signals is so intense

and so important for survival, of both birds and mammals

and human beings, that the signals that herald play are capable

of being interpreted across species, which is quite remarkable.

I've seen a magpie play with a bear.

And they each were able to interpret the signals between each other

that this was play, and they frolicked like crazy.

Well, that's really quite significant, and when you look

at that more deeply, you'll find that the survival drive that is a part

of each of those animals' survival drive, is linked to play behaviour.

So it seems that when the signals are strong enough,

the urge to play can become irresistible.

What's really incredible, though, is that this one exceptional bear

started to bring its mates back with it.

So what started out with just one rogue

doing something out of the ordinary, is now an annual social event.

Up to seven bears from the Churchill population have all

built relationships with Brian's dogs.

And over the years they have become local celebrities.

First you think that the dogs are being attacked, and then you realise

that, you know, he's holding his head in his mouth because he wants to.

You'd think the bear would be right in there eating the dog

straight away, but they have some kind of companionship going on,

and it's amazing. It beautiful.

They look like they are having a great time.

They are happy to see their buddy, you know?

DOG WHINES AND BARKS

I think the dogs get sad when they see the bears go in the fall.

They miss them.

But, you know, come a certain day, the polar bears leave on the ice.

Leaving the dogs hopeful that they will return next year to renew their friendship.

BARKING AND GROWLING

When you really take a close look at what's happening in something

just as magical as a polar bear and a sled dog, you begin to get

an understanding that there is something deeper going on here.

Incredible stuff. But, you know, in we humans,

play is far more important than learning how to survive in the wild.

It's also about learning empathy

and a great range of other social behaviours.

So, for we humans at least, play isn't just practice for hunting and fighting.

For our next story we look at some bizarre neighbourly

relationships that go way past sharing the odd cup of sugar.

The American black bear.

Shy and retiring, they prefer their own company...

..foraging for berries and grubs in their favourite habitats -

the forests, marshes and rugged mountains across North America.

They are brilliantly adapted to life in the wild.

However, some US house owners have been witnessing some very peculiar behaviour.

There's a bear in my hot tub!

Please don't pee in there.

Hey, get out of there! Get out of there!

And it's not just the odd individual taking a dip

Even fiercely protective mothers with cubs are getting in on the action.

I got them swimming in my pool. They use the pool more than us.

-Why didn't they go in Dr Bob's pool?

-I don't know.

But why would such a shy creature decide to party in a human's pool?

You have to call the cops, Daddy. You have to.

Bear expert Dr Ted Oakes believes he might have an explanation.

Black bears spend all winter in dens, which are often very,

very cold places, and so they have thick, thick fur.

But in the summer, because the fur is black, the fur absorbs heat

almost like no other material, and they really, really heat up.

I remember somebody I work with stuck at the moment in the fur

of a black bear in full sun, and it was just below boiling point.

It was about 80 or 90 degrees Celsius.

So, their first line of defence in the heat is to remove themselves from the sun.

The second line of defence in the heat is to start panting.

And black bears will pant when they are very, very hot.

But when a black bear is panting,

it's really in a situation where it's got to do something else

to cool down, and that's usually seeking water.

So, they take the plunge to cool off, but aren't black bears

shy and elusive animals that stay away from humans?

There are nearly a million black bears living in North America,

and 300 million people.

In fact, I would say now that most people are never more than

a few miles from a black bear in most parts of North America.

Black bears, yet, are rarely seen, and the reason for that is they are quite shy.

They don't want to be around people. They like to avoid people, and usually people are trouble for them.

But if there is not much food in the forest,

they will take the opportunity to find food near human habitation.

If it's a choice between starving to death and finding

food from humans, bears can sometimes come to town.

They might not actually come to a house to find water to cool down,

they might actually come to a house to find a bird feeder.

But once they are at the house and they see that the house not only has a bird feeder

but a swimming pool, that's when the party could start for a black bear.

Put that down! Quit tearing it up!

But there is something even more amazing about these intriguing beasts.

In some places where bears make trips into town, they make sure they do so on bin collection day,

making their trips as fruitful as possible.

Having a caring approach for our wild neighbours isn't something

that's restricted to people living in far-flung places.

Yes, they might have bears in hot tubs, but we have foxes on trampolines.

There are about 250,000 adult red foxes in Britain...

..and just like black bears they are intelligent,

opportunistic mammals,

happy to treat our property as their own.

And occasionally use our gardens for a little play, too.

What all these weird relationships show us is that as our population

expands, it gets ever more important to treat those around us with a bit

of humility, whoever they are.

Even if it does mean some of us must accept that man might not always be a dog's best friend.

In nature's weird world, it pays to have a good relationship with your neighbours.

Now, sticking with the subject of population expansion, next up

we take a look at some of nature's weirdest ways of bringing up baby.

We will examine a very unlikely tale of maternal care.

But first we look at an odd animal that has an even odder way

of keeping her little angels safe.

Back in 2007, this bizarre

and gruesome behaviour was caught on camera.

Now it's moving a lot.

Here they come! Here they come!

Get them! Oh, my God! Look at her!

No, your eyes aren't deceiving you,

those are tiny animals erupting from the back of a toad.

But what on earth could these alien beasts be?

In fact they were the offspring of this creature,

the Surinam toad.

But why would she want to turn her back

into a skin-crawling care facility?

Dr Ian Stephen from the Zoological Society of London

might just be able to shed some light on this.

The problem with amphibian eggs is that they are highly nutritious

bundles of food, so lots of things like to eat them.

Things such as snakes, fish, birds and invertebrates,

all find them incredibly tasty.

They also have another problem in that they are completely

defenceless, so even when they turn into tadpoles, they tend to be

restricted to small water bodies so they are very easy prey.

So one strategy that amphibians use is to put all their resources

and energy into incredibly large broods,

so they might lay hundreds maybe thousands of eggs, just in the hope

that one or two individuals go on to reproduce in the next generation.

Obviously this works well for hundreds of species,

but it is a very crude strategy.

There are other amphibians that have come up with more involved ways

of protecting their offspring.

Some frogs will construct a foam nest above a water body.

And quite literally this is a meringue-like foam.

What's fascinating about the nest itself is it's comprised of

different layers, and each layer has its own function,

so the core layer has the eggs and the developing tadpoles themselves,

and then you also have protective layers on the outside

that protect the nest from UV and drying out effects of the sun.

The eggs will take maybe a week to develop,

and the tadpoles will drop into the water body below.

OK, it's a very good way to protect your eggs, but the tadpoles

then still enter the water as helpless and very tempting bite-sized mouthfuls,

trapped in their pools with no way to escape hungry predators.

So there must be better ways to offer protection.

The Darwin's frog takes reproduction to the next level.

They actually take their eggs inside their bodies.

The female frog lays their eggs in damp leaf litter.

The male then takes up the eggs four to five days later

and actually takes the eggs themselves into its vocal sac,

and that's where the eggs then go on to develop into tadpoles.

About 70 days later, the male quite literally coughs up the tiny little froglets.

And, yes - they are complete,

fully formed frogs coming out of his mouth.

Obviously the vocal sacs aren't huge,

so we're only looking at about 15 to 20 in total.

It's an inspired solution for a small brood like that, but what about

if you need to protect hundreds of babies, what happens then?

Well, this takes us neatly back to our friend

with the erupting back, the Surinam toad.

The Surinam toad has taken things to an absolute other level,

When the females spawns, the male takes the eggs themselves

and presses them onto the female's back.

This might be 200, 250 eggs.

What's incredible is that a layer of skin then develops over those eggs.

About 70 days later, tiny fully formed froglets actually emerge from

the female's back, almost like something from the scene of an alien film.

Who'd have thought that life could be so complicated for amphibians?

But then, it does illustrate some of the dangers and difficulties

when it come to getting your genes into the next generation.

When it comes from getting between tadpole and frog.

The issues of providing for the kids are at the forefront of every

parent's mind, but our next mother might just have nature's

weirdest way of bringing up baby.

Shark researcher Stewart Springer was undertaking

an inspection of a pregnant sand tiger shark.

Carefully inserting a hand into the shark's body,

Stewart groped around feeling for any babies.

Then from deep inside the shark's body, something attacked,

tearing at his finger with a set of razor sharp teeth!

But the only thing inside the shark was her unborn offspring.

So why on earth would a baby that is still in the womb have teeth,

let alone know how to use them?

Biologist Dr Matt Gollock is one man who can help answer this.

When producing juveniles within any species, it's a numbers game.

You might recognise mermaids purses,

these are egg cases of species such as cat sharks.

Obviously once the eggs are laid,

these eggs are then vulnerable to predation.

Some species of shark give birth to live young.

The blue shark, for example, produce up to 150 juveniles.

This might mean that more will be killed, but because there is

a greater number, it's more likely that some of them survive.

However, sand tiger sharks have a really amazing reproductive strategy.

They produce eggs into the womb which grow into embryos.

We find out that the juveniles actually develop very quickly,

and within the first few months they actually develop teeth.

And the largest of these embryos will actually kill its brothers and sisters.

Now, come on - that's beyond weird. It's eating its own siblings inside the womb!

After it's eaten its brothers and sisters,

the female will actually produce eggs which keeps the juvenile growing

until it's almost a metre long, after which point it's born into the wild.

It's believed that eating their brothers and sisters in the womb actually is an evolutionary

advantage for the sand tigers that are ultimately born.

They think there is about 20 embryos produced into each uterus,

and so by the time each of the juveniles are born,

they will have maybe up to 20 times,

And that, on top of eating abound 17,000 eggs,

so when they are actually born, they are very, very experienced at hunting their prey.

This strategy means that the juveniles are independent

almost from the minute they are born,

and this means there is a much higher chance of survival.

And when so few young are being produced, this is very, very important.

A pretty unorthodox way of providing for baby,

but nevertheless, absolutely ingenious.

It's totally amazing what weird wonders nature has come up with

to offer babies their best start in life.

From the amphibians who use their own bodies as childcare facilities,

to the mother who sacrifices hundreds of potential young for the sake of just the eldest.

It seems that keeping the kids inside your body

for as long as possible is one way to ensure their safety.

No one likes a relationship that's all give and no take.

Our last collection of stories looks at a few love affairs that have become a little too one-sided.

From the worm with an eye on a new home,

to the fly whose young play hard-to-get-out,

we investigate nature's weird world of the unwanted guest.

But first, a tropical romance gone bad -

a relationship where only one partner likes kissing.

All across South America in the run down parts of towns and cities,

millions of dark forms lurk in the shadows waiting till nightfall to emerge.

But these are no ordinary moth or dainty mosquito,

these are kissing bugs.

And when caught by scientists, they exhibit an unnerving ability

to sense the presence of humans.

So where does this super sense come from?

Dr Matt Yeo from the London School of Tropical Medicine has some answers.

They are really quite nasty bugs.

If they are hungry, you can actually see them.

They will be attracted to the heat of my finger,

so they are quite vicious hungry.

And similarly, if I breathe on them, they become very agitated,

and that's the carbon dioxide from my breath.

And if I breathe a bit more...

Again, you can see them probing through the net.

So these bugs are attracted to warmth and carbon dioxide,

and feed on the blood of larger animals, like us humans.

They sink their needle-like mouth parts into their victims' flesh to draw

long and hard on their blood whilst we sleep away, blissfully unaware.

But that doesn't explain their name.

One of the reasons they're called kissing bugs

is that they tend to come out at night when the lights are off

and your face tends to be the most exposed area.

So they can crawl all over the face

but generally kiss around the mouth area or the facial areas.

They can be so hungry that night after night,

they can really take their toll.

So if you've got a family and they're being fed on every night,

particularly the children can actually become anaemic.

But they have another, darker legacy,

darker even than sucking children into a state of anaemia.

You see, whilst kissing you on the cheek they might well leave you

with the life-threatening Chagas disease,

a condition caused by a tiny parasite

carried by the kissing bugs that can eventually lead to heart failure.

When they take a blood meal, they defecate

and you can scratch it into the bite wound or you can rub your eyes

or put your fingers to your mouth and that's how you become infected.

What an incredible species. Brilliant things.

And you've got to remember that aside from biting us

and sucking a little of our blood, they don't actually do us any harm.

It's the parasite that they transport around that causes that Chagas disease.

Now, kissing bugs do actually have some cousins living here in the UK,

we call them assassin bugs.

But before you lock up your children,

don't worry, they don't feed on humans. They primarily feast on insects.

For nature's next weirdly one-sided union, we look at a hitchhiker

that's desperate to dive deep into a long-term relationship.

Back in 2009, climbing expert Tim Fogg arrived back in

the UK from a trip to the Central African Republic.

Nothing odd to report, until one day this happened.

Suddenly my hand swelled up for no apparent reason.

Then it went down, then about ten days later my arm swelled up

and then it went down. Just bits of me kept swelling up.

As a rope access specialist, Tim has travelled to

some of the worlds most bizarre and extreme environments,

but never before had his body parts randomly swollen for no apparent reason.

This bizarre bodily behaviour continued for two years.

So, what could be causing these spontaneous swellings?

After several medical tests, Tim was diagnosed as having

contracted Loa loa, or the African eye worm.

It gets its gruesome name from

the only time it becomes visible in infected humans -

as it passes through its host's eyeballs.

It's an incredible parasite that is carried by certain types

of day biting flies in the swamps of west Africa,

exactly where Tim had returned home from two years earlier.

I think I got it wading through a lot of mud in the forest where

mango flies live, which is the thing that transmits it.

Infection occurs when the larvae of the worm are passed to a human as the fly bites.

The larvae then develop under the skin until they become adults

and start their travels around the body.

As they move about under the skin, the immune system starts to

react and it's this that causes the swelling.

I guess it was in my hand to start with,

it presumably went up one arm then my other arm swelled up,

so presumably somehow it got right across my shoulder and down into the other arm.

Or maybe it was another worm. I have no idea.

Incredibly, the worm can grow to be seven centimetres long and live

for 17 years creeping around under the surface of the host's body.

The worst thing about this thing wandering about under your skin

is its habit of coming up to your eye

and wandering across your eye and across the bridge of your nose and into the other eye.

And that is apparently very, very painful.

And I did have one incident where the side of my face swelled up

which meant that it was there, it was getting close

and thinking about going across my eye.

Luckily it changed its mind.

The beauty of this parasite is that it doesn't hurt you at all,

and it didn't make me feel ill.

It was just the swelling so it's very clever.

I mean, it just wants to feed off me,

it doesn't want to give me bother if it can, cos I might get rid of it.

After he was diagnosed in 2011, Tim's doctor put him

on an intensive course of drugs, and a year later in June 2012

he was deemed tentatively clear of his tenacious little body mate.

Our last story is more body burrowing than bunny boiling,

a gruesome but truly ingenious example of nature's

weird relationships gone bad.

And so to Panama where an innocent traveller has picked up

a couple of unwanted passengers.

Do you see it? Right there. SHRIEKING

What started as two small insect bites has become swollen and angry.

-SHRIEKING

-It's ready to come out.

-Yeah, it is.

And there was something inside.

Whatever they were simply had to be extracted.

They are big. I can feel it trying to pull back in. Gross.

-You mean it's still alive?

-GASPS AND LAUGHTER

That's huge!

So, what on earth are they?

Dr Mark Rowland works at the London School Of Hygiene and Tropical Medicine

and has travelled the world studying parasites.

Those insects that we are trying to pull out of people's bodies are

the larvae of the botfly and I have some here, pickled inside this jar.

They are quite large. They are about one and a half centimetres long.

But how does something this big get under your skin in the first place?

The botfly itself is quite large, it's about the size

of a bumblebee, so if it were to actually land on a host itself

it would probably be detected by the human or cattle or pig

and brushed away, so that makes it less likely for the fly

to succeed in laying its eggs successfully on the host.

So the botfly has come up with a very sneaky tactic.

What the fly has cleverly done is to grab

an insect like a mosquito or a tick or even a housefly.

After a quick air ambush, the botfly pins down the fly

and quickly attaches its eggs.

And then off it goes to do the botfly's dirty work.

On contacting the human or animal host, the small botfly larvae inside the egg will be able

to detect the warmth of the host, and it will hatch at that point.

And it does this very quickly indeed.

The larvae is able to penetrate and embed itself

in the skin of the host.

Over the course of several weeks, it will grow

and eat its way into the flesh.

And just in case you were thinking of getting rid of it at that stage,

it has spiny bristles that hold it in

and make it impossible to pull out.

Oh, my God! Oh, God!

That definitely is the trick, man, overnight.

The only way to win this tug of war is to play dirty.

One trick that you can do to make it easier is to smear a gel or fat

over the rear end of the larvae.

This will block the breathing tubes of the larvae.

And that makes it easier to actually draw the larvae from the body.

GROANING

SHOUTS AND GROANS

Only when you've cut off its air supply will the botfly let go.

Of course, the other option is to let nature take its course

and wait six weeks for the larva to become a maggot,

eat its way out, and drop onto the ground before becoming an adult fly.

It's a nasty business, however they exit.

But after all of this, you should just end up with a little scar - no problem.

Amazing that a maggot that size does so little damage in the end.

From the bug with a super sense for the human body

to the worm that is just dying to get under your skin

and the botfly who knows how to play tough,

it's obvious that the further we travel the more likely we are

to bring home the unwanted baggage of a holiday romance.

What all of the stories in this programme seem to illustrate

is that a bit of understanding and tolerance help in all of our relationships.

So, if we can implement a bit of love and respect towards all of nature's wonders,

there's absolutely no doubt that the world would be a richer place.

And of course, the world is always getting smaller.

So as we welcome more and more of these bizarre creatures into our own backyards,

What we think of as weird now might be a lot weirder in the future.

Next time on Nature's Weirdest Events,

there is an island awash under a tide of tiny crabs...

..a town terrorized by rampaging elk,

and a community primed for an unbelievable invasion of insects.

Subtitles by Red Bee Media Ltd