0:00:02 > 0:00:04My name's Steve Backshall.
0:00:04 > 0:00:05Woo!
0:00:05 > 0:00:10And this is my search for the Deadly 60.
0:00:10 > 0:00:12That's not just animals that are deadly to me
0:00:12 > 0:00:15but animals that are deadly in their own world.
0:00:17 > 0:00:20My crew and I are travelling the planet
0:00:20 > 0:00:23and you're coming with me! Every step of the way.
0:00:30 > 0:00:32In the natural world, there's one type of animal
0:00:32 > 0:00:35that probably freaks us out more than any other, the parasites,
0:00:35 > 0:00:38those that feed off us and other host species
0:00:38 > 0:00:41in the most grizzly and grotesque ways imaginable.
0:00:41 > 0:00:45In this special Deadly 60, I've come here to find out more.
0:00:47 > 0:00:49We're here to explore the alien world
0:00:49 > 0:00:53of the deadly killer you rarely see, the parasite.
0:00:53 > 0:00:56Ranging from the grotesque to the bizarrely beautiful,
0:00:56 > 0:01:00parasites come in all shapes and sizes.
0:01:00 > 0:01:02They feed on other organisms, or hosts,
0:01:02 > 0:01:07creeping up on their victims looking for a free meal.
0:01:07 > 0:01:11Often the parasite goes completely unnoticed by the host animal
0:01:11 > 0:01:14but sometimes the parasites cause illness
0:01:14 > 0:01:18and in extreme cases, even death.
0:01:25 > 0:01:28One of the weirdest of all parasite and host relationships
0:01:28 > 0:01:32occurs between a mind-bending parasitic worm and its host,
0:01:32 > 0:01:35or should we say victim, a snail,
0:01:35 > 0:01:39in what is a real-life alien takeover.
0:01:39 > 0:01:42This is the zombie snail parasite.
0:01:44 > 0:01:48This unfortunate snail, along with its normal diet of fresh leaves,
0:01:48 > 0:01:51has accidentally eaten some bird droppings.
0:01:51 > 0:01:55In the bird droppings were the eggs of the zombie snail parasite.
0:01:55 > 0:01:58Once inside the snail, these eggs hatch out
0:01:58 > 0:02:03and as the parasites grow, they move up into the snail's antennae.
0:02:03 > 0:02:07But then something even stranger begins to happen.
0:02:07 > 0:02:11Somehow the parasite manages to take control of the snail's brain,
0:02:11 > 0:02:14changing its behaviour so that the snail begins to climb high up
0:02:14 > 0:02:18into an opening in the canopy. Here, high up, in broad daylight
0:02:18 > 0:02:20while most other snails are in hiding,
0:02:20 > 0:02:23this snail is in full view of any passing predator.
0:02:23 > 0:02:26The parasite wriggles around as if sending out a grotesque message
0:02:26 > 0:02:31which catches the attention of a passing bird.
0:02:31 > 0:02:36The bird scoffs the snail down, and the parasite gets munched too.
0:02:36 > 0:02:40Its eggs are released in the bird's gut,
0:02:40 > 0:02:43and dumped in the bird's droppings,
0:02:43 > 0:02:47ready to be eaten by another unlucky snail.
0:02:47 > 0:02:50So the unpleasant cycle continues,
0:02:50 > 0:02:54one of the most revolting but fascinating in nature.
0:02:59 > 0:03:02Parasites are essentially animals that live on,
0:03:02 > 0:03:05or sometimes inside, a host animal,
0:03:05 > 0:03:09living off their tissues or possibly their blood,
0:03:09 > 0:03:15and leeches are an absolute case in point.
0:03:15 > 0:03:17This creature will inch along like this,
0:03:17 > 0:03:19searching for a good place to get stuck in
0:03:19 > 0:03:24and it has genuinely scalpel-sharp teeth.
0:03:24 > 0:03:29As my crew and I discovered on a jungle trek through Borneo.
0:03:32 > 0:03:33It's a tiger leech.
0:03:35 > 0:03:37They'll wait in positions just like this
0:03:37 > 0:03:39for something warm-blooded to wander past
0:03:39 > 0:03:44and then they'll drop off and get stuck in to a nice blood meal.
0:03:44 > 0:03:49They sense the warmth of our bodies. They are absolutely hideous.
0:03:49 > 0:03:52Look, see him start to walk?
0:03:52 > 0:03:57Yep, there you go.
0:03:57 > 0:04:00Now, I want to do a little bit of a scientific experiment here.
0:04:00 > 0:04:02There's six of us here,
0:04:02 > 0:04:06we're going to wander through the forest for about ten minutes
0:04:06 > 0:04:08and see how many of these little beauties we can pick up.
0:04:08 > 0:04:11Come on, guys, I mean at least...
0:04:11 > 0:04:14At least do a little bit, roll your trousers up or something. come on.
0:04:14 > 0:04:15Pale English legs here.
0:04:15 > 0:04:17What about you?
0:04:17 > 0:04:19LAUGHTER
0:04:19 > 0:04:21Right, let's go get 'em!
0:04:23 > 0:04:26When the leech bites, it releases an anaesthetic
0:04:26 > 0:04:29so you don't feel them feeding.
0:04:29 > 0:04:31Its saliva also contains an anticoagulant
0:04:31 > 0:04:35that stops blood clotting so your blood flows freely
0:04:35 > 0:04:38until the leech has gorged itself,
0:04:38 > 0:04:42finally dropping off to wait for another unsuspecting passer-by.
0:04:42 > 0:04:45And I absolutely hate them!
0:04:45 > 0:04:50You see, blood is actually a really nutritious food stuff.
0:04:50 > 0:04:51It's packed full of protein
0:04:51 > 0:04:55and there are loads of blood-sucking terrors that love it!
0:04:58 > 0:05:01Perhaps the most infamous of them all
0:05:01 > 0:05:05is the blood-sucking, spine-chilling vampire bat.
0:05:08 > 0:05:12I was in Costa Rica to see one of them in the flesh
0:05:12 > 0:05:14and they'd set up home deep inside a cave.
0:05:14 > 0:05:16So, just there ahead of us,
0:05:16 > 0:05:22that dark hole is a cave and that's where we're heading.
0:05:24 > 0:05:25Right.
0:05:29 > 0:05:33These parasites hide away in the dark until nightfall
0:05:33 > 0:05:35when they head out in search of food.
0:05:41 > 0:05:43Oh, Lord, look up there.
0:05:43 > 0:05:47I can see fluttering shapes at the top of the cave
0:05:47 > 0:05:51but to see these parasites up close, I need to catch one.
0:05:58 > 0:05:59Got one in?
0:05:59 > 0:06:00Yep, got one.
0:06:02 > 0:06:04The last time I tried to do this,
0:06:04 > 0:06:07it bit clean through the glove and into my finger.
0:06:13 > 0:06:18So up above me now is a roost, about 30 or 40 vampire bats,
0:06:18 > 0:06:22and at night, they'll take wing
0:06:22 > 0:06:28using that remarkable wing membrane
0:06:28 > 0:06:33and fly out in search of a warm blood meal.
0:06:33 > 0:06:37They use the ridiculously sharp teeth
0:06:37 > 0:06:38at the front of the mouth here,
0:06:38 > 0:06:41I don't want to get my finger too close cos I just know
0:06:41 > 0:06:44I'm going to get bitten on camera, but they shave away
0:06:44 > 0:06:48a portion of hair from the animal that they're going to be feeding on
0:06:48 > 0:06:51and then bite a tiny hole and then lap away at the blood
0:06:51 > 0:06:55that leaks out, and their saliva keeps the blood flowing.
0:06:55 > 0:06:57It's what's called an anticoagulant,
0:06:57 > 0:07:00and they take in about a soup spoon of blood,
0:07:00 > 0:07:03which doesn't sound like very much
0:07:03 > 0:07:05but when you look at the size of this tiny bat,
0:07:05 > 0:07:11actually, for its bodyweight, that's an enormous meal.
0:07:11 > 0:07:14It is in fact a third of their bodyweight in blood
0:07:14 > 0:07:15at every meal.
0:07:15 > 0:07:18This is the original Dracula,
0:07:18 > 0:07:23and far more chilling than any vampire of myth or legend.
0:07:29 > 0:07:31Where's he gone, he's not on my back, is he?
0:07:31 > 0:07:32Turn around.
0:07:34 > 0:07:37It's not just that parasites like leeches and bats
0:07:37 > 0:07:41suck our blood, but they also spread disease,
0:07:41 > 0:07:44and this is what makes them so potentially dangerous.
0:07:44 > 0:07:47One tiny blood-sucking parasite
0:07:47 > 0:07:50spread one of the most notorious diseases in history.
0:07:50 > 0:07:52The Black Death, or Bubonic Plague,
0:07:52 > 0:07:55swept through Europe in the 14th century.
0:07:55 > 0:08:00At the time, it was thought that the culprits were rats.
0:08:00 > 0:08:04It turns out, though, that was highly, highly unfair.
0:08:04 > 0:08:08Actually, it was down to something far smaller, fleas!
0:08:08 > 0:08:11The fleas were living and feeding off the rat's blood,
0:08:11 > 0:08:14but because the fleas weren't fussy feeders,
0:08:14 > 0:08:18and the rats were often living alongside humans,
0:08:18 > 0:08:21some fleas took the opportunity to feed on human blood.
0:08:21 > 0:08:25But the flea's saliva contained a lethal disease.
0:08:25 > 0:08:28Whilst feeding, the fleas passed on this infection to humans
0:08:28 > 0:08:31and the results were catastrophic.
0:08:31 > 0:08:35One flea can carry 100 plague bacteria in its gut
0:08:35 > 0:08:38and one bite is all it takes to get infected.
0:08:41 > 0:08:44And it wiped out as much as a third of the population of Europe,
0:08:44 > 0:08:47all down to some tiny hopping fleas!
0:08:51 > 0:08:54One thing all these parasites have in common
0:08:54 > 0:08:57is that they have to find a victim to feed on.
0:08:57 > 0:08:58Many are attracted to body heat
0:08:58 > 0:09:02but for some, just breathing is a dead giveaway that a meal is nearby.
0:09:02 > 0:09:06Check out these Latin American mini monsters.
0:09:06 > 0:09:10And inside here, we've got a whole bunch of what are called
0:09:10 > 0:09:11reduviid bugs.
0:09:11 > 0:09:14Have a look at this, it's pretty grotesque!
0:09:18 > 0:09:23Oh, my goodness, that is horrid!
0:09:25 > 0:09:29They come rushing up to the top
0:09:29 > 0:09:33and stick their sharp little beaks, they're called rostrums,
0:09:33 > 0:09:40right through in search of, well, me, basically.
0:09:40 > 0:09:44So, carbon dioxide particularly is a signal for certain parasites
0:09:44 > 0:09:47to actually hone in on a host species.
0:09:49 > 0:09:52Every single one of those tiny little needles
0:09:52 > 0:09:54could be spreading a killer disease.
0:09:56 > 0:10:01Well, that is certainly the creepiest thing I've seen today!
0:10:06 > 0:10:08Not nearly as creepy but definitely
0:10:08 > 0:10:11one of the most peculiar examples of parasitism I know
0:10:11 > 0:10:14is found in the world of birds.
0:10:14 > 0:10:17It occurs when one animal steals directly from another.
0:10:17 > 0:10:22It's called kleptoparasitism, and the cuckoo is King Klepto.
0:10:22 > 0:10:26In this oddball relationship, the cuckoo tricks the host bird
0:10:26 > 0:10:30into feeding and bringing up her young.
0:10:30 > 0:10:33The adult cuckoo lays her eggs in another bird's nest,
0:10:33 > 0:10:35like this reed warbler.
0:10:35 > 0:10:37Once the cuckoo chick hatches,
0:10:37 > 0:10:40it pushes all the other birds' eggs out of the nest.
0:10:43 > 0:10:45The chick then stays in the nest
0:10:45 > 0:10:47and the parent bird continues to feed the intruder
0:10:47 > 0:10:52as if it was its own, and it gets bigger and bigger.
0:10:52 > 0:10:56Look at the size of that mouth!
0:10:58 > 0:11:02They can get to be six times the size of the surrogate parent.
0:11:02 > 0:11:06How the reed warbler doesn't realise is also pretty weird!
0:11:10 > 0:11:13The food-stealing cuckoo and blood-sucking fleas and bats
0:11:13 > 0:11:17are just some of the weird and wonderful world of parasites,
0:11:17 > 0:11:20but some of the most gruesome are amongst the flesh eaters.
0:11:22 > 0:11:25Flies like the parasitic botfly need to find animals, like cows,
0:11:25 > 0:11:29to lay their eggs on.
0:11:29 > 0:11:32But the botfly is too big and heavy to go unnoticed by the cow.
0:11:32 > 0:11:36So, the botfly cleverly uses a smaller fly
0:11:36 > 0:11:39to take her eggs to the host.
0:11:40 > 0:11:45She carefully lays her eggs on the smaller fly.
0:11:45 > 0:11:48This lighter fly will then visit the cow
0:11:48 > 0:11:50to feed on its sweat unnoticed.
0:11:50 > 0:11:53But as it feeds, the warmth of the cow's body
0:11:53 > 0:11:55causes the botfly eggs to hatch,
0:11:55 > 0:11:59which, armed with small teeth, bore down into the skin of the cow.
0:12:01 > 0:12:06Here, the botfly babies feed on the living flesh of the cow.
0:12:06 > 0:12:09And after merrily munching away for two months,
0:12:09 > 0:12:11the maggots fall to the ground and turn into flies.
0:12:11 > 0:12:16But it's not always cows that are the chosen victim,
0:12:16 > 0:12:19as Jonny, our long suffering cameraman, found out
0:12:19 > 0:12:23after one of his jungle adventures.
0:12:23 > 0:12:25Well, when I was in Guiana,
0:12:25 > 0:12:29I had a botfly on my head, which was particularly nasty.
0:12:29 > 0:12:30It takes quite a few weeks,
0:12:30 > 0:12:33three, four weeks to get to a big, fat size.
0:12:33 > 0:12:36Every night I heard it because it was there on the side of my head
0:12:36 > 0:12:39so I could hear it scratching against my skull at night.
0:12:39 > 0:12:42And we all told you it was just a spot and you should man-up.
0:12:42 > 0:12:45Yes, including the medics. "Man-up, it's a spot",
0:12:45 > 0:12:49and I was going, "Spots don't make noises, you know, every night",
0:12:49 > 0:12:52and eventually, after four or five weeks,
0:12:52 > 0:12:54I got Mandy to get her big Freddy Kruger nails
0:12:54 > 0:12:57and pop it out. Covered her in pus.
0:12:57 > 0:13:00It was absolutely grotesque, and I just remember this,
0:13:00 > 0:13:03this tiny little thing with almost backwards-pointing hair
0:13:03 > 0:13:05so it could keep itself inside your flesh.
0:13:05 > 0:13:08- They are particularly nasty.- And a big breathing snorkel at the end.
0:13:08 > 0:13:11That was good. But I missed it in the end, you know.
0:13:11 > 0:13:13We became friends.
0:13:15 > 0:13:19Our next parasite may be a flesh-eating monster
0:13:19 > 0:13:21with a horrendously painful sting.
0:13:21 > 0:13:22Oh, there's one, look.
0:13:22 > 0:13:25But at least it won't eat me alive.
0:13:25 > 0:13:30It's the tarantula hawk wasp, and we found one in Mexico.
0:13:30 > 0:13:31As the name suggests,
0:13:31 > 0:13:36this parasite has as its host, tarantula spiders.
0:13:36 > 0:13:39And our best chance of catching one
0:13:39 > 0:13:42was as it emerged from a tarantula's hole.
0:13:48 > 0:13:49OK.
0:13:50 > 0:13:53Oh! And he's off. No, come back!
0:13:53 > 0:13:56Catching one was tricky, to say the least.
0:13:59 > 0:14:00Ah.
0:14:00 > 0:14:03But, I wasn't giving up.
0:14:04 > 0:14:07Got it, got it, got it, got it, got it, got it, got it.
0:14:11 > 0:14:13Oh no, he went out the hole!
0:14:13 > 0:14:16Oh no! I can't believe it, that's so frustrating.
0:14:16 > 0:14:19You come back here now!
0:14:19 > 0:14:21I had him,
0:14:21 > 0:14:24but I've got a great big hole in my net
0:14:24 > 0:14:28and he just flew straight out through it.
0:14:28 > 0:14:29- He's coming this way, Steve.- Right.
0:14:29 > 0:14:32Finally, I out-manoeuvred the wasp.
0:14:32 > 0:14:36Got her, got her. Right, now this time,
0:14:36 > 0:14:39you are not getting away.
0:14:40 > 0:14:43I've got to be ever so careful for, I don't want to damage her,
0:14:43 > 0:14:48but also, her sting is absolutely paralysing.
0:14:50 > 0:14:51There she is.
0:14:53 > 0:14:54That...
0:14:55 > 0:15:00..is the tarantula hawk wasp, or pepsis wasp,
0:15:00 > 0:15:03and she is...
0:15:04 > 0:15:09..one of the most incredible predators
0:15:09 > 0:15:11found anywhere in the world.
0:15:12 > 0:15:14Look at the size of her sting.
0:15:16 > 0:15:19(Right, there we go.)
0:15:19 > 0:15:22Look at that. Glorious, glorious colour.
0:15:22 > 0:15:27Very vibrant metallic blue with bright orange wings,
0:15:27 > 0:15:31but don't let her beauty fool you.
0:15:31 > 0:15:34This is one of the most grotesque killers
0:15:34 > 0:15:37in the whole of the animal kingdom. But she is incredible.
0:15:37 > 0:15:41Look at the mandibles, look at the size of these jaws here.
0:15:41 > 0:15:45This creature here has a strength way beyond her size,
0:15:45 > 0:15:50and a sting that, well, if I was to get stung by this,
0:15:50 > 0:15:53I would be able to think about nothing else for at least 24 hours.
0:15:53 > 0:15:55And it's these formidable attributes
0:15:55 > 0:15:57that make it a potent parasite.
0:16:00 > 0:16:02When the wasp finds a tarantula,
0:16:02 > 0:16:04it will out-manoeuvre it,
0:16:04 > 0:16:08before delivering a single, paralysing sting.
0:16:08 > 0:16:11The spider's still alive, but completely defenceless.
0:16:11 > 0:16:15This is only half the story.
0:16:15 > 0:16:19The paralysed spider is then dragged by the wasp to its burrow,
0:16:19 > 0:16:23where it will lay an egg which will hatch into a maggot.
0:16:23 > 0:16:26This maggot slowly devours the spider
0:16:26 > 0:16:28from the inside out while it's still alive.
0:16:34 > 0:16:38Not many creatures would take on a tarantula.
0:16:38 > 0:16:41Even more tricky though would be the bullet ant,
0:16:41 > 0:16:44the largest ant on Earth with a fearsome sting.
0:16:44 > 0:16:49But there's a remarkable parasite that's neither plant nor animal
0:16:49 > 0:16:53that can kill whole colonies of this fearsome ant.
0:16:54 > 0:17:00I've now got the world's most painful stinging insect on my hand
0:17:00 > 0:17:02and I have to say I am very nervous.
0:17:02 > 0:17:05Although I've been stung by this before,
0:17:05 > 0:17:07I can remember how badly it hurt.
0:17:07 > 0:17:11It is just extraordinary that an animal of this size
0:17:11 > 0:17:13has a sting that's powerful enough
0:17:13 > 0:17:16to incapacitate an animal the size of me.
0:17:16 > 0:17:20I mean, think how many times bigger I am than this ant,
0:17:20 > 0:17:25but one little sting will have me absolutely crying on the floor.
0:17:25 > 0:17:28So, what parasite is going to take on
0:17:28 > 0:17:30this seemingly indestructible insect?
0:17:32 > 0:17:35Well, it's not a bird or even another insect.
0:17:35 > 0:17:37It's a fungus.
0:17:37 > 0:17:40Even its brutal sting can't save it from our next parasite.
0:17:40 > 0:17:44This bullet ant is acting rather strangely.
0:17:44 > 0:17:50Fungal spores have infiltrated its body and taken over its mind.
0:17:50 > 0:17:54The ant becomes disorientated and climbs to the top of a stem.
0:17:54 > 0:17:58Those that are infected are quickly carried away by other ants
0:17:58 > 0:18:01in the family so as not to infect the rest of the colony,
0:18:01 > 0:18:04and for very good reason.
0:18:05 > 0:18:09Once the fungus matures and the fruiting body begins to emerge,
0:18:09 > 0:18:13nothing can stop its fatal, terrifying progress.
0:18:14 > 0:18:19The parasitic fungus cordyceps has taken over the ant's body.
0:18:19 > 0:18:23This parasite is so effective, it can wipe out whole colonies,
0:18:23 > 0:18:27and it's not just ants that fall victim to this parasite.
0:18:28 > 0:18:31It's peculiarly beautiful,
0:18:31 > 0:18:35but brutal, like some grim, fatal fairytale.
0:18:37 > 0:18:40One of the creepiest body-snatching parasites around.
0:18:40 > 0:18:44It's just a good job they don't infect us humans.
0:18:49 > 0:18:52So far in this Deadly 60 special,
0:18:52 > 0:18:55we've been exploring the world of parasites,
0:18:55 > 0:18:56from the big to the small.
0:18:56 > 0:19:02How they can live on the surface of their host as well as inside.
0:19:02 > 0:19:05What they feed on and how they track down their victims.
0:19:07 > 0:19:11But when parasites get inside us human beings
0:19:11 > 0:19:13the results can be astonishing.
0:19:15 > 0:19:18There's no doubt that the parasites we find most creepy
0:19:18 > 0:19:21are the ones that live inside us.
0:19:21 > 0:19:24Things like the tapeworm.
0:19:24 > 0:19:27Now, tapeworms are found in many different kinds of animals.
0:19:27 > 0:19:30This one here was found inside a human being
0:19:30 > 0:19:33in their intestine feeding on our food.
0:19:33 > 0:19:36Now, that is pretty grim,
0:19:36 > 0:19:40but actually, as tapeworms go, it's absolutely nothing.
0:19:42 > 0:19:45The biggest tapeworm that was ever found inside a human being was,
0:19:45 > 0:19:47well, I'll show you how long it was.
0:19:49 > 0:19:50It wasn't this long.
0:19:51 > 0:19:52It wasn't this long.
0:19:55 > 0:20:00It was a staggering 21 metres long,
0:20:00 > 0:20:03and that was just one of 18 different tapeworms
0:20:03 > 0:20:06found inside just one boy.
0:20:06 > 0:20:08It's enough to put you off your lunch.
0:20:10 > 0:20:12The tapeworm gets inside us
0:20:12 > 0:20:16when we eat something contaminated with tapeworm eggs.
0:20:16 > 0:20:19It's more common in places with poor hygiene, but once inside us,
0:20:19 > 0:20:23the tapeworm makes its home inside our digestive system.
0:20:23 > 0:20:27Its head attaches to our intestines with tiny little hooks
0:20:27 > 0:20:30and here, it feeds off the food we eat.
0:20:30 > 0:20:35For the parasite, it's the perfect environment for it to grow.
0:20:35 > 0:20:38Warm, full of food and safe from predators.
0:20:38 > 0:20:40They can go unnoticed for ages
0:20:40 > 0:20:43living in side us for up to 20 years,
0:20:43 > 0:20:46but large infestations can cause serious stomach problems.
0:20:46 > 0:20:49However, once discovered, they're easily dealt with
0:20:49 > 0:20:52with a dose of medicine.
0:20:53 > 0:20:55Many of the parasites we've seen so far
0:20:55 > 0:20:59take over the bodies and minds of their hosts, sucking their blood,
0:20:59 > 0:21:03but there's one parasite that's deadlier than all the others.
0:21:03 > 0:21:08In fact, it's such a big killer it's not just the deadliest parasite,
0:21:08 > 0:21:11it's the deadliest animal to us on the planet.
0:21:11 > 0:21:14So, what is it?
0:21:14 > 0:21:16Well, there is a very definite answer to that.
0:21:16 > 0:21:19It's a creature that kills hundreds of thousands of times
0:21:19 > 0:21:21more human beings than any shark.
0:21:23 > 0:21:25It's not a spider,
0:21:25 > 0:21:28or a snake, far from it.
0:21:28 > 0:21:32It is the creature that's lurking behind these doors.
0:21:32 > 0:21:36Are you, um, are you sure you want to come in here, mate?
0:21:36 > 0:21:37No, I'm not surprised.
0:21:39 > 0:21:42It is in fact the mosquito.
0:21:42 > 0:21:44No more than two centimetres in size
0:21:44 > 0:21:47but far more dangerous to us than any larger beast.
0:21:47 > 0:21:51There are 3,000 species, but only one carries the disease
0:21:51 > 0:21:54that kills millions of human beings every year.
0:21:54 > 0:21:59That disease is malaria, a parasite that's transmitted to humans
0:21:59 > 0:22:02when an infected mosquito sucks our blood.
0:22:05 > 0:22:09Well, here they are, the deadliest animals on earth.
0:22:09 > 0:22:11I know they don't look like much,
0:22:11 > 0:22:14but mosquitoes are certainly not to be underestimated.
0:22:14 > 0:22:18There is no animal that causes more human deaths than this.
0:22:18 > 0:22:23Now, they actually start off like these little wriggling worms,
0:22:23 > 0:22:24these are mosquito larvae,
0:22:24 > 0:22:29and they will hatch out and live in still, stagnant water.
0:22:29 > 0:22:33The adults eventually erupt into this winged form.
0:22:34 > 0:22:38It's only the females that actually bite you and they do that
0:22:38 > 0:22:41when they're ready to produce eggs and when they do,
0:22:41 > 0:22:45that's when all hell breaks loose because they carry a parasite
0:22:45 > 0:22:49in their saliva which can create the disease malaria.
0:22:50 > 0:22:53The mosquitoes in this lab don't carry malaria,
0:22:53 > 0:22:55so I'm gonna get one to bite me.
0:22:55 > 0:22:57Do you have any preference where you'd like to be bitten?
0:22:57 > 0:23:00Right there. That's my favourite spot.
0:23:00 > 0:23:03With our special macro lens, you'll be able to see
0:23:03 > 0:23:06how exactly this hungry little girl goes to work.
0:23:08 > 0:23:11The mosquito injects me with its incredibly sharp,
0:23:11 > 0:23:13needle-like mouth parts.
0:23:13 > 0:23:16These are made up of two tubes,
0:23:16 > 0:23:19one to inject an enzyme that inhibits blood clotting,
0:23:19 > 0:23:23and the other to suck blood into their body.
0:23:23 > 0:23:25They also inject an anaesthetic
0:23:25 > 0:23:28so you can't feel any pain of the bite until it's too late.
0:23:28 > 0:23:32And once it bites, you it gets bigger and bigger
0:23:32 > 0:23:34as it fills up with blood.
0:23:39 > 0:23:42Though there are some treatments for malaria the disease,
0:23:42 > 0:23:45the best thing is simply not to get bitten,
0:23:45 > 0:23:48and to avoid getting bitten, there are repellents.
0:23:48 > 0:23:51Now, we've come up with a special Deadly experiment
0:23:51 > 0:23:52to see if these work.
0:23:52 > 0:23:55Just over there is a sealed room
0:23:55 > 0:23:58and the whole crew will go in there using one of these repellents.
0:23:58 > 0:24:00We'll fill it up with mosquitoes
0:24:00 > 0:24:02and see how many times we get bitten.
0:24:02 > 0:24:04We can't quite believe we're going to do this.
0:24:04 > 0:24:08OK, Ruth my director actually reacts quite badly to mosquito bites
0:24:08 > 0:24:11so she's getting the full on repellent
0:24:11 > 0:24:14with a high percentage of the active ingredient, Deet.
0:24:14 > 0:24:17This genuinely does work. So there you go, Ruth.
0:24:17 > 0:24:20OK, next up we have a herbal remedy.
0:24:20 > 0:24:22This one is based on eucalyptus, I'll give this to Ash,
0:24:22 > 0:24:26my cameraman, because it's his job to make me look good
0:24:26 > 0:24:29and I don't want him distracted. So there you go, Ash.
0:24:29 > 0:24:32Now next up, we have some slightly more suspect cures.
0:24:32 > 0:24:33We have garlic.
0:24:33 > 0:24:37Apparently, eating lots of garlic keeps the mosquitoes away,
0:24:37 > 0:24:42so Lizzie, my researcher, is going to cover herself in garlic paste.
0:24:42 > 0:24:44LAUGHS Thank you very much!
0:24:44 > 0:24:48And last of all, B vitamins are said to get rid of mosquitoes,
0:24:48 > 0:24:50so we're going for something that's high in B vitamins.
0:24:50 > 0:24:54Simon the sound recordist is going to cover himself in Marmite.
0:24:54 > 0:24:56- Cover myself?- Yes. - Can't you do it for me?
0:24:56 > 0:24:59Absolutely not, that is not in my job description.
0:24:59 > 0:25:02OK, guys? Get stuck in.
0:25:02 > 0:25:06As the crew cover themselves with repellents,
0:25:06 > 0:25:09I decide I'm going to be the control and go without.
0:25:12 > 0:25:15All right then, come on in. So...
0:25:15 > 0:25:19This is our prison cell for the next few minutes.
0:25:19 > 0:25:22I'm not sure I want to be locked in here with Lizzie, she honks.
0:25:22 > 0:25:25It's your fault.
0:25:25 > 0:25:26OK, James?
0:25:29 > 0:25:31All right. Good luck, guys.
0:25:33 > 0:25:37OK, so the mosquitoes are at large.
0:25:38 > 0:25:42and they're already heading straight for me
0:25:42 > 0:25:45and they're all settling on Ruth's head.
0:25:45 > 0:25:46SHE WINCES
0:25:48 > 0:25:51With the parasites free and hungry,
0:25:51 > 0:25:54who would they decide to feast on?
0:25:54 > 0:25:57It wasn't long before the mosquitoes started to land
0:25:57 > 0:26:00and it was Simon and Lizzie they chose.
0:26:00 > 0:26:06It seems Marmite and garlic are more of an attractant than a repellent.
0:26:09 > 0:26:10And on closer inspection...
0:26:10 > 0:26:11No.
0:26:11 > 0:26:15..Ruth, Ash and me were of no interest to the mosquitoes.
0:26:15 > 0:26:18Well, I think it's clear that actually
0:26:18 > 0:26:21only the chemical repellent really works,
0:26:21 > 0:26:23but each individual human being
0:26:23 > 0:26:27definitely has a varying degree of attraction to mosquitoes,
0:26:27 > 0:26:31and I seem to be a living, walking mosquito repellent!
0:26:31 > 0:26:34Well, it's all good news.
0:26:38 > 0:26:42This was just a fun experiment. Well, not that much fun,
0:26:42 > 0:26:44but in reality, the developments
0:26:44 > 0:26:47on repellents for this parasite are really important.
0:26:47 > 0:26:51The mosquito is one of the biggest killers on the planet
0:26:51 > 0:26:53and is definitely the deadliest parasite on Earth.
0:26:53 > 0:26:56Parasites certainly aren't going to win any popularity contests,
0:26:56 > 0:27:00but that doesn't mean they don't deserve a place on the Deadly 60.
0:27:00 > 0:27:04Their incredible and often complex relationships with their hosts
0:27:04 > 0:27:07are some of the most remarkable in the natural world.
0:27:09 > 0:27:12Parasites may seem horrid and pointless,
0:27:12 > 0:27:14but they're some of the most important
0:27:14 > 0:27:17and influential things on the planet.
0:27:17 > 0:27:19We're continually evolving to stay ahead of them
0:27:19 > 0:27:22and they're continually evolving to better feast on us.
0:27:22 > 0:27:25Whatever, there's no doubt the parasites are definitely Deadly.
0:27:28 > 0:27:33Join me next time as I continue my search for the Deadly 60.
0:27:33 > 0:27:37Ow! That was my toe!
0:27:55 > 0:27:57Subtitles by Red Bee Media Ltd