Parasites Deadly 60

My name's Steve Backshall.

Woo!

And this is my search for the Deadly 60.

That's not just animals that are deadly to me

but animals that are deadly in their own world.

My crew and I are travelling the planet

and you're coming with me! Every step of the way.

In the natural world, there's one type of animal

that probably freaks us out more than any other, the parasites,

those that feed off us and other host species

in the most grizzly and grotesque ways imaginable.

In this special Deadly 60, I've come here to find out more.

We're here to explore the alien world

of the deadly killer you rarely see, the parasite.

Ranging from the grotesque to the bizarrely beautiful,

parasites come in all shapes and sizes.

They feed on other organisms, or hosts,

creeping up on their victims looking for a free meal.

Often the parasite goes completely unnoticed by the host animal

but sometimes the parasites cause illness

and in extreme cases, even death.

One of the weirdest of all parasite and host relationships

occurs between a mind-bending parasitic worm and its host,

or should we say victim, a snail,

in what is a real-life alien takeover.

This is the zombie snail parasite.

This unfortunate snail, along with its normal diet of fresh leaves,

has accidentally eaten some bird droppings.

In the bird droppings were the eggs of the zombie snail parasite.

Once inside the snail, these eggs hatch out

and as the parasites grow, they move up into the snail's antennae.

But then something even stranger begins to happen.

Somehow the parasite manages to take control of the snail's brain,

changing its behaviour so that the snail begins to climb high up

into an opening in the canopy. Here, high up, in broad daylight

while most other snails are in hiding,

this snail is in full view of any passing predator.

The parasite wriggles around as if sending out a grotesque message

which catches the attention of a passing bird.

The bird scoffs the snail down, and the parasite gets munched too.

Its eggs are released in the bird's gut,

and dumped in the bird's droppings,

ready to be eaten by another unlucky snail.

So the unpleasant cycle continues,

one of the most revolting but fascinating in nature.

Parasites are essentially animals that live on,

or sometimes inside, a host animal,

living off their tissues or possibly their blood,

and leeches are an absolute case in point.

This creature will inch along like this,

searching for a good place to get stuck in

and it has genuinely scalpel-sharp teeth.

As my crew and I discovered on a jungle trek through Borneo.

It's a tiger leech.

They'll wait in positions just like this

for something warm-blooded to wander past

and then they'll drop off and get stuck in to a nice blood meal.

They sense the warmth of our bodies. They are absolutely hideous.

Look, see him start to walk?

Yep, there you go.

Now, I want to do a little bit of a scientific experiment here.

There's six of us here,

we're going to wander through the forest for about ten minutes

and see how many of these little beauties we can pick up.

Come on, guys, I mean at least...

At least do a little bit, roll your trousers up or something. come on.

Pale English legs here.

What about you?

LAUGHTER

Right, let's go get 'em!

When the leech bites, it releases an anaesthetic

so you don't feel them feeding.

Its saliva also contains an anticoagulant

that stops blood clotting so your blood flows freely

until the leech has gorged itself,

finally dropping off to wait for another unsuspecting passer-by.

And I absolutely hate them!

You see, blood is actually a really nutritious food stuff.

It's packed full of protein

and there are loads of blood-sucking terrors that love it!

Perhaps the most infamous of them all

is the blood-sucking, spine-chilling vampire bat.

I was in Costa Rica to see one of them in the flesh

and they'd set up home deep inside a cave.

So, just there ahead of us,

that dark hole is a cave and that's where we're heading.

Right.

These parasites hide away in the dark until nightfall

when they head out in search of food.

Oh, Lord, look up there.

I can see fluttering shapes at the top of the cave

but to see these parasites up close, I need to catch one.

Got one in?

Yep, got one.

The last time I tried to do this,

it bit clean through the glove and into my finger.

So up above me now is a roost, about 30 or 40 vampire bats,

and at night, they'll take wing

using that remarkable wing membrane

and fly out in search of a warm blood meal.

They use the ridiculously sharp teeth

at the front of the mouth here,

I don't want to get my finger too close cos I just know

I'm going to get bitten on camera, but they shave away

a portion of hair from the animal that they're going to be feeding on

and then bite a tiny hole and then lap away at the blood

that leaks out, and their saliva keeps the blood flowing.

It's what's called an anticoagulant,

and they take in about a soup spoon of blood,

which doesn't sound like very much

but when you look at the size of this tiny bat,

actually, for its bodyweight, that's an enormous meal.

It is in fact a third of their bodyweight in blood

at every meal.

This is the original Dracula,

and far more chilling than any vampire of myth or legend.

Where's he gone, he's not on my back, is he?

Turn around.

It's not just that parasites like leeches and bats

suck our blood, but they also spread disease,

and this is what makes them so potentially dangerous.

One tiny blood-sucking parasite

spread one of the most notorious diseases in history.

The Black Death, or Bubonic Plague,

swept through Europe in the 14th century.

At the time, it was thought that the culprits were rats.

It turns out, though, that was highly, highly unfair.

Actually, it was down to something far smaller, fleas!

The fleas were living and feeding off the rat's blood,

but because the fleas weren't fussy feeders,

and the rats were often living alongside humans,

some fleas took the opportunity to feed on human blood.

But the flea's saliva contained a lethal disease.

Whilst feeding, the fleas passed on this infection to humans

and the results were catastrophic.

One flea can carry 100 plague bacteria in its gut

and one bite is all it takes to get infected.

And it wiped out as much as a third of the population of Europe,

all down to some tiny hopping fleas!

One thing all these parasites have in common

is that they have to find a victim to feed on.

Many are attracted to body heat

but for some, just breathing is a dead giveaway that a meal is nearby.

Check out these Latin American mini monsters.

And inside here, we've got a whole bunch of what are called

reduviid bugs.

Have a look at this, it's pretty grotesque!

Oh, my goodness, that is horrid!

They come rushing up to the top

and stick their sharp little beaks, they're called rostrums,

right through in search of, well, me, basically.

So, carbon dioxide particularly is a signal for certain parasites

to actually hone in on a host species.

Every single one of those tiny little needles

could be spreading a killer disease.

Well, that is certainly the creepiest thing I've seen today!

Not nearly as creepy but definitely

one of the most peculiar examples of parasitism I know

is found in the world of birds.

It occurs when one animal steals directly from another.

It's called kleptoparasitism, and the cuckoo is King Klepto.

In this oddball relationship, the cuckoo tricks the host bird

into feeding and bringing up her young.

The adult cuckoo lays her eggs in another bird's nest,

like this reed warbler.

Once the cuckoo chick hatches,

it pushes all the other birds' eggs out of the nest.

The chick then stays in the nest

and the parent bird continues to feed the intruder

as if it was its own, and it gets bigger and bigger.

Look at the size of that mouth!

They can get to be six times the size of the surrogate parent.

How the reed warbler doesn't realise is also pretty weird!

The food-stealing cuckoo and blood-sucking fleas and bats

are just some of the weird and wonderful world of parasites,

but some of the most gruesome are amongst the flesh eaters.

Flies like the parasitic botfly need to find animals, like cows,

to lay their eggs on.

But the botfly is too big and heavy to go unnoticed by the cow.

So, the botfly cleverly uses a smaller fly

to take her eggs to the host.

She carefully lays her eggs on the smaller fly.

This lighter fly will then visit the cow

to feed on its sweat unnoticed.

But as it feeds, the warmth of the cow's body

causes the botfly eggs to hatch,

which, armed with small teeth, bore down into the skin of the cow.

Here, the botfly babies feed on the living flesh of the cow.

And after merrily munching away for two months,

the maggots fall to the ground and turn into flies.

But it's not always cows that are the chosen victim,

as Jonny, our long suffering cameraman, found out

after one of his jungle adventures.

Well, when I was in Guiana,

I had a botfly on my head, which was particularly nasty.

It takes quite a few weeks,

three, four weeks to get to a big, fat size.

Every night I heard it because it was there on the side of my head

so I could hear it scratching against my skull at night.

And we all told you it was just a spot and you should man-up.

Yes, including the medics. "Man-up, it's a spot",

and I was going, "Spots don't make noises, you know, every night",

and eventually, after four or five weeks,

I got Mandy to get her big Freddy Kruger nails

and pop it out. Covered her in pus.

It was absolutely grotesque, and I just remember this,

this tiny little thing with almost backwards-pointing hair

so it could keep itself inside your flesh.

-They are particularly nasty.

-And a big breathing snorkel at the end.

That was good. But I missed it in the end, you know.

We became friends.

Our next parasite may be a flesh-eating monster

with a horrendously painful sting.

Oh, there's one, look.

But at least it won't eat me alive.

It's the tarantula hawk wasp, and we found one in Mexico.

As the name suggests,

this parasite has as its host, tarantula spiders.

And our best chance of catching one

was as it emerged from a tarantula's hole.

OK.

Oh! And he's off. No, come back!

Catching one was tricky, to say the least.

Ah.

But, I wasn't giving up.

Got it, got it, got it, got it, got it, got it, got it.

Oh no, he went out the hole!

Oh no! I can't believe it, that's so frustrating.

You come back here now!

I had him,

but I've got a great big hole in my net

and he just flew straight out through it.

-He's coming this way, Steve.

-Right.

Finally, I out-manoeuvred the wasp.

Got her, got her. Right, now this time,

you are not getting away.

I've got to be ever so careful for, I don't want to damage her,

but also, her sting is absolutely paralysing.

There she is.

That...

..is the tarantula hawk wasp, or pepsis wasp,

and she is...

..one of the most incredible predators

found anywhere in the world.

Look at the size of her sting.

(Right, there we go.)

Look at that. Glorious, glorious colour.

Very vibrant metallic blue with bright orange wings,

but don't let her beauty fool you.

This is one of the most grotesque killers

in the whole of the animal kingdom. But she is incredible.

Look at the mandibles, look at the size of these jaws here.

This creature here has a strength way beyond her size,

and a sting that, well, if I was to get stung by this,

I would be able to think about nothing else for at least 24 hours.

And it's these formidable attributes

that make it a potent parasite.

When the wasp finds a tarantula,

it will out-manoeuvre it,

before delivering a single, paralysing sting.

The spider's still alive, but completely defenceless.

This is only half the story.

The paralysed spider is then dragged by the wasp to its burrow,

where it will lay an egg which will hatch into a maggot.

This maggot slowly devours the spider

from the inside out while it's still alive.

Not many creatures would take on a tarantula.

Even more tricky though would be the bullet ant,

the largest ant on Earth with a fearsome sting.

But there's a remarkable parasite that's neither plant nor animal

that can kill whole colonies of this fearsome ant.

I've now got the world's most painful stinging insect on my hand

and I have to say I am very nervous.

Although I've been stung by this before,

I can remember how badly it hurt.

It is just extraordinary that an animal of this size

has a sting that's powerful enough

to incapacitate an animal the size of me.

I mean, think how many times bigger I am than this ant,

but one little sting will have me absolutely crying on the floor.

So, what parasite is going to take on

this seemingly indestructible insect?

Well, it's not a bird or even another insect.

It's a fungus.

Even its brutal sting can't save it from our next parasite.

This bullet ant is acting rather strangely.

Fungal spores have infiltrated its body and taken over its mind.

The ant becomes disorientated and climbs to the top of a stem.

Those that are infected are quickly carried away by other ants

in the family so as not to infect the rest of the colony,

and for very good reason.

Once the fungus matures and the fruiting body begins to emerge,

nothing can stop its fatal, terrifying progress.

The parasitic fungus cordyceps has taken over the ant's body.

This parasite is so effective, it can wipe out whole colonies,

and it's not just ants that fall victim to this parasite.

It's peculiarly beautiful,

but brutal, like some grim, fatal fairytale.

One of the creepiest body-snatching parasites around.

It's just a good job they don't infect us humans.

So far in this Deadly 60 special,

we've been exploring the world of parasites,

from the big to the small.

How they can live on the surface of their host as well as inside.

What they feed on and how they track down their victims.

But when parasites get inside us human beings

the results can be astonishing.

There's no doubt that the parasites we find most creepy

are the ones that live inside us.

Things like the tapeworm.

Now, tapeworms are found in many different kinds of animals.

This one here was found inside a human being

in their intestine feeding on our food.

Now, that is pretty grim,

but actually, as tapeworms go, it's absolutely nothing.

The biggest tapeworm that was ever found inside a human being was,

well, I'll show you how long it was.

It wasn't this long.

It wasn't this long.

It was a staggering 21 metres long,

and that was just one of 18 different tapeworms

found inside just one boy.

It's enough to put you off your lunch.

The tapeworm gets inside us

when we eat something contaminated with tapeworm eggs.

It's more common in places with poor hygiene, but once inside us,

the tapeworm makes its home inside our digestive system.

Its head attaches to our intestines with tiny little hooks

and here, it feeds off the food we eat.

For the parasite, it's the perfect environment for it to grow.

Warm, full of food and safe from predators.

They can go unnoticed for ages

living in side us for up to 20 years,

but large infestations can cause serious stomach problems.

However, once discovered, they're easily dealt with

with a dose of medicine.

Many of the parasites we've seen so far

take over the bodies and minds of their hosts, sucking their blood,

but there's one parasite that's deadlier than all the others.

In fact, it's such a big killer it's not just the deadliest parasite,

it's the deadliest animal to us on the planet.

So, what is it?

Well, there is a very definite answer to that.

It's a creature that kills hundreds of thousands of times

more human beings than any shark.

It's not a spider,

or a snake, far from it.

It is the creature that's lurking behind these doors.

Are you, um, are you sure you want to come in here, mate?

No, I'm not surprised.

It is in fact the mosquito.

No more than two centimetres in size

but far more dangerous to us than any larger beast.

There are 3,000 species, but only one carries the disease

that kills millions of human beings every year.

That disease is malaria, a parasite that's transmitted to humans

when an infected mosquito sucks our blood.

Well, here they are, the deadliest animals on earth.

I know they don't look like much,

but mosquitoes are certainly not to be underestimated.

There is no animal that causes more human deaths than this.

Now, they actually start off like these little wriggling worms,

these are mosquito larvae,

and they will hatch out and live in still, stagnant water.

The adults eventually erupt into this winged form.

It's only the females that actually bite you and they do that

when they're ready to produce eggs and when they do,

that's when all hell breaks loose because they carry a parasite

in their saliva which can create the disease malaria.

The mosquitoes in this lab don't carry malaria,

so I'm gonna get one to bite me.

Do you have any preference where you'd like to be bitten?

Right there. That's my favourite spot.

With our special macro lens, you'll be able to see

how exactly this hungry little girl goes to work.

The mosquito injects me with its incredibly sharp,

needle-like mouth parts.

These are made up of two tubes,

one to inject an enzyme that inhibits blood clotting,

and the other to suck blood into their body.

They also inject an anaesthetic

so you can't feel any pain of the bite until it's too late.

And once it bites, you it gets bigger and bigger

as it fills up with blood.

Though there are some treatments for malaria the disease,

the best thing is simply not to get bitten,

and to avoid getting bitten, there are repellents.

Now, we've come up with a special Deadly experiment

to see if these work.

Just over there is a sealed room

and the whole crew will go in there using one of these repellents.

We'll fill it up with mosquitoes

and see how many times we get bitten.

We can't quite believe we're going to do this.

OK, Ruth my director actually reacts quite badly to mosquito bites

so she's getting the full on repellent

with a high percentage of the active ingredient, Deet.

This genuinely does work. So there you go, Ruth.

OK, next up we have a herbal remedy.

This one is based on eucalyptus, I'll give this to Ash,

my cameraman, because it's his job to make me look good

and I don't want him distracted. So there you go, Ash.

Now next up, we have some slightly more suspect cures.

We have garlic.

Apparently, eating lots of garlic keeps the mosquitoes away,

so Lizzie, my researcher, is going to cover herself in garlic paste.

LAUGHS Thank you very much!

And last of all, B vitamins are said to get rid of mosquitoes,

so we're going for something that's high in B vitamins.

Simon the sound recordist is going to cover himself in Marmite.

-Cover myself?

-Yes.

-Can't you do it for me?

Absolutely not, that is not in my job description.

OK, guys? Get stuck in.

As the crew cover themselves with repellents,

I decide I'm going to be the control and go without.

All right then, come on in. So...

This is our prison cell for the next few minutes.

I'm not sure I want to be locked in here with Lizzie, she honks.

It's your fault.

OK, James?

All right. Good luck, guys.

OK, so the mosquitoes are at large.

and they're already heading straight for me

and they're all settling on Ruth's head.

SHE WINCES

With the parasites free and hungry,

who would they decide to feast on?

It wasn't long before the mosquitoes started to land

and it was Simon and Lizzie they chose.

It seems Marmite and garlic are more of an attractant than a repellent.

And on closer inspection...

No.

..Ruth, Ash and me were of no interest to the mosquitoes.

Well, I think it's clear that actually

only the chemical repellent really works,

but each individual human being

definitely has a varying degree of attraction to mosquitoes,

and I seem to be a living, walking mosquito repellent!

Well, it's all good news.

This was just a fun experiment. Well, not that much fun,

but in reality, the developments

on repellents for this parasite are really important.

The mosquito is one of the biggest killers on the planet

and is definitely the deadliest parasite on Earth.

Parasites certainly aren't going to win any popularity contests,

but that doesn't mean they don't deserve a place on the Deadly 60.

Their incredible and often complex relationships with their hosts

are some of the most remarkable in the natural world.

Parasites may seem horrid and pointless,

but they're some of the most important

and influential things on the planet.

We're continually evolving to stay ahead of them

and they're continually evolving to better feast on us.

Whatever, there's no doubt the parasites are definitely Deadly.

Join me next time as I continue my search for the Deadly 60.

Ow! That was my toe!

Subtitles by Red Bee Media Ltd