0:00:02 > 0:00:05No matter how well we think we know our planet, the natural world still
0:00:05 > 0:00:07has the ability to surprise us,
0:00:07 > 0:00:09to shock us and maybe sometimes even
0:00:09 > 0:00:14to scare us with its extraordinary events and bizarre behaviour.
0:00:14 > 0:00:18And new technology means that nature's weirdest phenomena
0:00:18 > 0:00:21are being caught ever more readily on camera.
0:00:21 > 0:00:26So, we're going to bring you the strangest stories our world has to offer.
0:00:30 > 0:00:35From the biblical swarm that took Lake Erie by storm...
0:00:35 > 0:00:37That is really creepy.
0:00:37 > 0:00:40..and the bears with a taste for the poolside...
0:00:40 > 0:00:42There is a bear in my hot tub!
0:00:44 > 0:00:47..to the amphibian with a frog in its throat...
0:00:50 > 0:00:55..and a toad with a skin-crawling secret.
0:00:55 > 0:01:00Oh, my God! Look at her! Here they come. There they come. Get them.
0:01:00 > 0:01:03With the help of scientists, experts and eyewitnesses,
0:01:03 > 0:01:07we're going to try and unravel exactly what on earth is going on.
0:01:30 > 0:01:35To kick off, we're going to look at some of nature's weirdest romantics,
0:01:35 > 0:01:40stories of bizarre and sometimes fatal attraction.
0:01:40 > 0:01:45From the eerie vibrations that shook the shores of San Francisco Bay
0:01:45 > 0:01:48to an extreme case of opposites attract.
0:01:50 > 0:01:54But first we're heading to America's Great lakes where some
0:01:54 > 0:01:59very bizarre romantics are dying to find love, before it's too late.
0:02:01 > 0:02:05The shores of Lake Erie on America's beautiful border with Canada
0:02:05 > 0:02:10have forever been a tranquil place of peace and quiet.
0:02:10 > 0:02:13Until, early in the summer of 2010,
0:02:13 > 0:02:18it became the setting for a swarm of phenomenal proportions.
0:02:18 > 0:02:24This gas station is being attacked by...something.
0:02:24 > 0:02:27And that lady won't even get out of her car.
0:02:27 > 0:02:28It's like it's snowing.
0:02:28 > 0:02:32A swarm of literally billions stretched over a mile inland
0:02:32 > 0:02:35and for miles along the western shore.
0:02:36 > 0:02:42Every surface, every inch of air was filled with winged insects.
0:02:42 > 0:02:44That is really creepy.
0:02:44 > 0:02:49Local resident Greg Stewart recalls the experience.
0:02:49 > 0:02:55They were all over the wall of the city and I didn't know if I should even
0:02:55 > 0:02:57get out of my car, it was that bad.
0:02:57 > 0:03:00And as I got out, they all started crunching under my feet.
0:03:00 > 0:03:07Then, within days, they spontaneously started to die in their billions.
0:03:08 > 0:03:10Seriously, a pile of bugs.
0:03:15 > 0:03:19The drifts of dead bodies got so deep that the local authorities
0:03:19 > 0:03:23had to use snow ploughs to unblock the roads.
0:03:30 > 0:03:34And as they started to break down, they left another treat, too.
0:03:37 > 0:03:41It smelled of motor oil and vomit.
0:03:44 > 0:03:50So what were these insects, and what could have caused such an extraordinary plague?
0:03:57 > 0:04:01Don Schloesser is an expert in the wildlife of Lake Erie
0:04:01 > 0:04:07The big swarms are really the result of the life history pattern of the western Lake Erie mayflies.
0:04:09 > 0:04:13They live in the mud for about two years and they grow and they moult.
0:04:13 > 0:04:15About the middle of May, the first of June,
0:04:15 > 0:04:18they all come out of the water at one time.
0:04:18 > 0:04:23They mate, and then the females go back out into the water to lay the eggs.
0:04:23 > 0:04:26And then the whole process starts all over again.
0:04:26 > 0:04:29Mayfly spend about 99% of their lives
0:04:29 > 0:04:32as aquatic larvae at the bottom of ponds and rivers.
0:04:34 > 0:04:37They spend their time feeding and growing
0:04:37 > 0:04:40until, in a cunning plan to avoid getting eaten,
0:04:40 > 0:04:43they all emerge en masse to mate.
0:04:43 > 0:04:46The first few are easy pickings.
0:04:53 > 0:04:57But soon the sheer numbers overwhelm predators -
0:04:57 > 0:05:01they simply can't make a dent in the overall population.
0:05:12 > 0:05:15After about two days, there's a swarm,
0:05:15 > 0:05:20a swirling swarm like a little funnel cloud that's formed by the mayflies.
0:05:20 > 0:05:25And what happens is the females jump into that swarm, they are fertilized in the air.
0:05:27 > 0:05:32Once they have mated, the male dies and the female heads out
0:05:32 > 0:05:35over the water to release her fertilised eggs
0:05:35 > 0:05:38before she too passes away.
0:05:38 > 0:05:42The entire process takes just a matter of days.
0:05:45 > 0:05:49Each year as the event comes to an abrupt end,
0:05:49 > 0:05:53it's all hands on deck for the task of clearing up the dead.
0:05:53 > 0:05:57But there is still a lot of questions surrounding their mass emergence.
0:05:57 > 0:06:00When they come out is still a mystery to us.
0:06:00 > 0:06:03We can't predict very well in that two- or three-week period
0:06:03 > 0:06:06when they are actually going to be coming out.
0:06:06 > 0:06:08Sometimes it is related to storm events,
0:06:08 > 0:06:10sometimes it is related to rain events, but somehow
0:06:10 > 0:06:14the mayflies all get a cue when they are down in the bottom of the lake.
0:06:16 > 0:06:19But why are there so many in Lake Erie?
0:06:20 > 0:06:25Lake Erie supplies the types of sediment that this critter likes to burrow into,
0:06:25 > 0:06:29it used to have mayflies many years ago, then they went away for many years due to pollution.
0:06:29 > 0:06:32Now they're back and they've come back with sort of a vengeance
0:06:32 > 0:06:35in terms of the numbers and the abundances that we see come out of the water.
0:06:35 > 0:06:43So this almighty insect orgy is all down to a particularly perfect set of conditions.
0:06:43 > 0:06:48The enormous size of the lake and its newly clean waters contribute to
0:06:48 > 0:06:53a swarm so large that it can bring a whole city to a grinding halt.
0:06:55 > 0:07:00There are 51 different species of mayfly here in the UK.
0:07:00 > 0:07:02They are all members of the Ephemeroptera,
0:07:02 > 0:07:06which quite literally means "lived for a very short time".
0:07:07 > 0:07:11Our mayfly here in the UK do provide an impressive spectacle,
0:07:11 > 0:07:15albeit on a somewhat reduced scale to that seen Lake Erie.
0:07:15 > 0:07:19And if you want to experience this for yourself,
0:07:19 > 0:07:23head to the River Tweed in Scotland or to the Wye in Wales.
0:07:24 > 0:07:28An easy way to increase your chances of seeing some emergence
0:07:28 > 0:07:32is to time your trip with the flowering of hawthorn trees
0:07:32 > 0:07:33and bushes in the area.
0:07:35 > 0:07:38And the really bizarre thing about all mayfly is that once
0:07:38 > 0:07:43they are in their adult form, they have no mouthparts to feed.
0:07:43 > 0:07:48It's a race against time to mate before they starve to death.
0:07:48 > 0:07:50Nature at its weirdest.
0:07:52 > 0:07:55For our next crazy romance, we head to America's west coast
0:07:55 > 0:07:58where it's not insects that fill the air at night
0:07:58 > 0:08:02but the lover's serenade of another American beauty.
0:08:05 > 0:08:09Sausalito is an exclusive neighbourhood of houseboats,
0:08:09 > 0:08:13kissed by the gently lapping waves of San Francisco Bay.
0:08:15 > 0:08:19It's a high-class haven of tranquillity -
0:08:19 > 0:08:21until the sun goes down
0:08:21 > 0:08:26and the peace and serenity of the summer months is absolutely shattered.
0:08:26 > 0:08:28AGGRESSIVE HUM
0:08:28 > 0:08:29GROWLING HUM
0:08:29 > 0:08:32LOW HUM
0:08:32 > 0:08:37If you've ever had a sound system with a hum in it, it's that sound.
0:08:37 > 0:08:38GROWLING HUM
0:08:38 > 0:08:42It sounds like a low-flying flock of B-52s. It's a low hum.
0:08:42 > 0:08:45LOW, STEADY HUM
0:08:47 > 0:08:52What you can hear now is a recording of the sound itself.
0:08:52 > 0:08:55And, yes, it's very loud indeed.
0:08:55 > 0:09:00Just imagine shelling out for your dream home
0:09:00 > 0:09:03and then having to listen to this all night long!
0:09:03 > 0:09:07HUM CONTINUES
0:09:09 > 0:09:14Residents likened the volume to that of a low-flying jet air craft.
0:09:20 > 0:09:23No-one knew where the sound was coming from,
0:09:23 > 0:09:26but everybody had a theory.
0:09:26 > 0:09:31Secret navy communication systems, telephone systems run amuck,
0:09:31 > 0:09:34pacemakers going off at the same time from old people's homes.
0:09:34 > 0:09:36I mean, you can imagine just about anything.
0:09:36 > 0:09:38They would run sewer pumps here at night
0:09:38 > 0:09:40cos they didn't want the tourists to see the effluent
0:09:40 > 0:09:43going out during the daytime in downtown Sausalito,
0:09:43 > 0:09:48so they only ran the pumps at night, and the sound was only heard at night.
0:09:48 > 0:09:51We would put our hands around the light poles
0:09:51 > 0:09:54and they would be vibrating with this sound.
0:09:55 > 0:10:00And that's why I was convinced it was electrical. It had to be electrical.
0:10:04 > 0:10:06In the early days, this was sort of a bohemian community,
0:10:06 > 0:10:09and nobody really wanted to admit that they'd heard it,
0:10:09 > 0:10:13because it was just part of the proverbial buzz,
0:10:13 > 0:10:17and then as wealthier people moved in and began to say, "What is that noise?
0:10:17 > 0:10:21- "That's bothering me? Who can I sue?" And that sort of thing. - HE LAUGHS
0:10:21 > 0:10:22Some of the folks were really angry.
0:10:22 > 0:10:26They'd spent half a million dollars to buy a houseboat here,
0:10:26 > 0:10:29and they couldn't sleep in it, and so they were quite upset
0:10:29 > 0:10:33with all this noise, and they wanted something done about it.
0:10:35 > 0:10:40So what on earth could be the cause of these otherworldly sounds?
0:10:42 > 0:10:45The state of California sent in the experts.
0:10:46 > 0:10:48ELECTRONIC GURGLE
0:10:48 > 0:10:53After spending a year and a lot of money analyzing sound waves,
0:10:53 > 0:10:59and testing a range of completely bonkers theories, the experts were spent.
0:11:01 > 0:11:04So, in a last ditch attempt to find an answer
0:11:04 > 0:11:08they called biologist Professor John McCosker.
0:11:08 > 0:11:14I received a call from the head of the noise abatement bureau, in Marin County.
0:11:14 > 0:11:20He said, "You know, I can't believe I'm even wasting my time asking you this question.
0:11:20 > 0:11:24"Is it possible that a fish could make so much noise it would keep people awake?"
0:11:24 > 0:11:26I said, "What are you talking about?"
0:11:26 > 0:11:29He said, "Well, the houseboat owners are complaining.
0:11:29 > 0:11:34"They say that they can't sleep at night and somebody told us that it
0:11:34 > 0:11:37"could be an animal underwater and they told us to call you."
0:11:37 > 0:11:40So I said, "Sure, play the sound over the phone."
0:11:40 > 0:11:43He did, and I said "Oh, yeah, that's the Porichthys notatus,
0:11:43 > 0:11:47"the Batrachoidid, it's a Midshipman, they make a noise, it's also called a humming fish."
0:11:47 > 0:11:49And he said, "You know what that is?"
0:11:49 > 0:11:52I said, "Of course, they do that during the summer,
0:11:52 > 0:11:56"starts probably about sundown, ends about daybreak, right?"
0:11:56 > 0:12:01And he said, "Oh, my God! Don't tell anybody."
0:12:01 > 0:12:04LOW, STEADY HUM
0:12:05 > 0:12:07Identifying the culprit was the easy part,
0:12:07 > 0:12:11but convincing the city of Sausalito that it was a fish,
0:12:11 > 0:12:15that was a lot more difficult, because people just didn't want to believe it.
0:12:15 > 0:12:19I knew they were lying. I knew they were lying.
0:12:19 > 0:12:21It's a fish. It's a fish.
0:12:21 > 0:12:25I thought, this could not be a fish, they have to be out of their minds.
0:12:27 > 0:12:29However unbelievable it might be,
0:12:29 > 0:12:33this is the culprit - the humble humming toadfish.
0:12:34 > 0:12:38The toadfish is an extraordinary fish.
0:12:38 > 0:12:42It's one of 30,000 species of fish living on earth,
0:12:42 > 0:12:45but because of its appearance and its behaviour,
0:12:45 > 0:12:50I'd say it's a little more extraordinary than most other fishes.
0:12:50 > 0:12:57The toadfish is a bottom-dwelling ambush predator, superbly adapted to life in the mud and sand,
0:12:57 > 0:13:02and one of the many types of fish that use sound in their daily lives.
0:13:02 > 0:13:05And when we heard it, we thought it must be something the size of a seal
0:13:05 > 0:13:07or a blowfish or something gigantic that would be out there
0:13:07 > 0:13:10that was buried in the water with just its eyes peeking out.
0:13:10 > 0:13:14But it turned out it was this little, stupid, little, ugly fish.
0:13:15 > 0:13:19And it really doesn't look like much,
0:13:19 > 0:13:23but it could make enough noise to keep us awake all night.
0:13:23 > 0:13:28It spends most of its life living buried in the sand, buried in the mud.
0:13:28 > 0:13:29Not that attractive.
0:13:29 > 0:13:32So, in order to attract a mate, it has to display,
0:13:32 > 0:13:35and in so doing, it displays vocally.
0:13:36 > 0:13:41A lot of fishes make noise, and most of them use either
0:13:41 > 0:13:45the grinding their teeth, like that... HE GRINDS TEETH
0:13:45 > 0:13:47or their body slapping against the water,
0:13:47 > 0:13:52and you can hear that noise, or they use their gas bladder or swim bladder.
0:13:52 > 0:13:57The swim bladder is a special air-filled organ found in most bony fish.
0:13:57 > 0:14:00It allows them to regulate their buoyancy
0:14:00 > 0:14:04in the water without having to expend the energy swimming.
0:14:04 > 0:14:08But the toadfish has modified its swim bladder to become
0:14:08 > 0:14:10an amazing instrument.
0:14:12 > 0:14:17That little sac has very strong muscles along the sides of it,
0:14:17 > 0:14:23and those muscles vibrate as many as 150 times a second,
0:14:23 > 0:14:27so you have this resonating chamber that makes a...
0:14:27 > 0:14:30HE HUMS
0:14:30 > 0:14:32..that can be heard from a significant distance.
0:14:32 > 0:14:35Sound carries very well underwater.
0:14:35 > 0:14:41But why the phenomenal racket? And why only during the summer months?
0:14:41 > 0:14:45Toadfish spend the majority of their life in the ocean.
0:14:45 > 0:14:50They enter the Bay at the beginning of summer and get into the shallow
0:14:50 > 0:14:55waters so that they can make their nests, usually against large rocks,
0:14:55 > 0:15:00large wooden structures, or against the edge of a houseboat hull.
0:15:00 > 0:15:03The water is very murky, it's dark,
0:15:03 > 0:15:06and they start trying to attract a female.
0:15:08 > 0:15:13A good song can be so irresistible that the male could end up
0:15:13 > 0:15:14guarding the eggs of numerous females.
0:15:19 > 0:15:24Apparently it's very sexy to another fish,
0:15:24 > 0:15:26but it's terrible for us.
0:15:26 > 0:15:29Such a small fish is able to generate such an enormous sound
0:15:29 > 0:15:32and create such a giant ruckus as a result.
0:15:32 > 0:15:34How wonderful! That's what nature can do.
0:15:34 > 0:15:35It's an amazing fish.
0:15:39 > 0:15:43Incredibly, the old humming toadfish has more than one call.
0:15:43 > 0:15:51It hums to attract a mate but it also emits a sharp grunt to discourage potential rivals.
0:15:51 > 0:15:56But what's even more surprisingly is it's not the only fish with a song in the piscatorial charts.
0:15:56 > 0:15:57Listen to this.
0:15:59 > 0:16:02LOW CHIRRUPING
0:16:02 > 0:16:06That is the chirruping of a sergeant major fish.
0:16:06 > 0:16:10It's a small species which lives on tropical reefs, and it seems
0:16:10 > 0:16:15to be more vocal when it's aggressively defending its territory.
0:16:15 > 0:16:17LOW CHIRRUPING
0:16:17 > 0:16:20RASPING CLICK
0:16:20 > 0:16:22That is the sound of the famous pufferfish,
0:16:22 > 0:16:25that species which expands its body covered with spines
0:16:25 > 0:16:28so it can't be eaten by any larger fish.
0:16:30 > 0:16:33But my favourite by far is this one.
0:16:33 > 0:16:37DEEP, PULSING BASS SOUND
0:16:37 > 0:16:40That is the song of the cod.
0:16:40 > 0:16:45I wonder how much longer will be able to hear that in our seas,
0:16:45 > 0:16:48given that we're battering its population with over fishing.
0:16:48 > 0:16:51Perhaps we could see that this species has had its chips
0:16:51 > 0:16:54when it comes to being an oceanic pop star.
0:16:56 > 0:16:59The hunt for our next set of outlandish lovers
0:16:59 > 0:17:02takes us deep into the unexplored depths of our planet,
0:17:02 > 0:17:08where finding that perfect date can seem almost unfathomable.
0:17:10 > 0:17:16The deep sea, possibly the weirdest environment in the world.
0:17:18 > 0:17:23Life down here is hard - it is vast and empty,
0:17:23 > 0:17:29and the simple tasks of finding food and love are very difficult indeed.
0:17:29 > 0:17:33To cope, evolution has produced some of its weirdest creations.
0:17:36 > 0:17:40Like this appropriately named vampire squid from hell.
0:17:44 > 0:17:48And this sea angel - it's a snail that has lost its shell
0:17:48 > 0:17:51and taken to a life above the sea bed.
0:17:54 > 0:17:58Not to mention Gigantocypris, a leviathan of its kind,
0:17:58 > 0:18:01the size of a grape.
0:18:02 > 0:18:05And not exempt from the issues of life in the abyss
0:18:05 > 0:18:09is our curious romantic, the deep sea anglerfish.
0:18:10 > 0:18:14Anglerfish are highly accomplished ambush predators
0:18:14 > 0:18:20with a glowing lure on their back that they use for hunting prey in the unending dark.
0:18:22 > 0:18:25They have been attracting the attention of scientists
0:18:25 > 0:18:26and naturalists for years.
0:18:28 > 0:18:32But until recently, one thing baffled them more than any other.
0:18:34 > 0:18:37All the fish they found were female.
0:18:40 > 0:18:46So, where in the perpetual darkness could all the males be hiding?
0:18:48 > 0:18:50Adding to the mystery, many of the fish they studied
0:18:50 > 0:18:54had a small passenger attached to their underside.
0:18:56 > 0:19:00Then the scientists discovered something almost unbelievable -
0:19:00 > 0:19:05that this passenger was in fact the male of the species!
0:19:08 > 0:19:12To help us understand this discovery is James Maclaine,
0:19:12 > 0:19:17expert of all things fishy from London's Natural History Museum.
0:19:17 > 0:19:20If you see a large anglerfish, it's always gong to be female.
0:19:20 > 0:19:25They've gone for very, very extreme version of what we call sexual dimorphism.
0:19:25 > 0:19:27Which is where the males and females look different,
0:19:27 > 0:19:30and they look very, very different indeed in anglerfish.
0:19:30 > 0:19:33In fact, for a long time, people thought that male anglerfish
0:19:33 > 0:19:36were a completely different kind of thing, didn't even realise they
0:19:36 > 0:19:40were anglerfish for a long time because they look so different to the females.
0:19:40 > 0:19:44Incredibly, this huge difference in size is a solution
0:19:44 > 0:19:48to the problems of life in the deep, where there is very little food.
0:19:50 > 0:19:55As demonstrated by this female taken from the water with her stomach still full.
0:19:56 > 0:19:58The anglerfish doesn't want to catch something
0:19:58 > 0:19:59and then realise it's too big to eat.
0:19:59 > 0:20:03So it just has to try and force it in no matter how large it is.
0:20:03 > 0:20:07The fish that it's eaten is probably twice as long as the anglerfish,
0:20:07 > 0:20:10and what it is, it's sort of curled it up so the head is here
0:20:10 > 0:20:14and the fish curves round and then the tail is kind of in there.
0:20:15 > 0:20:18So the female has all the specialist kit she needs
0:20:18 > 0:20:22for life down here, but what about the male?
0:20:22 > 0:20:27He doesn't have any of the fancy paraphernalia of the female,
0:20:27 > 0:20:31so in a place where you need to be highly specialized to find food,
0:20:31 > 0:20:34how on earth is he going to survive?
0:20:34 > 0:20:37The male anglerfish's life is actually quite desperate.
0:20:37 > 0:20:41It starts off really nicely. The eggs hatch and they go up to the surface
0:20:41 > 0:20:44and the baby anglerfish have a little brief moment in the sunshine.
0:20:46 > 0:20:51Once they've left the surface water, they stop feeding and it just becomes
0:20:51 > 0:20:54this desperate race against time to find a female before they starve
0:20:54 > 0:20:58to death, and if they don't find one within a few weeks, they will starve.
0:20:59 > 0:21:04But in the dark emptiness of this deep sea, how does he achieve this?
0:21:06 > 0:21:12Well, with a pair of super sensitive nostrils he is able to detect
0:21:12 > 0:21:16and follow a faint trail of pheromones that she leaves.
0:21:17 > 0:21:21They find the female, and when they do they will actually attach
0:21:21 > 0:21:24themselves to her and connect to her blood supply,
0:21:24 > 0:21:27the sort of bite on and almost plumb themselves in,
0:21:27 > 0:21:33and then they feed off her blood, and she carries them around like a parasite.
0:21:33 > 0:21:36It's a sort of deep sea economy measure. Because the male is
0:21:36 > 0:21:41so small, he requires only a fraction of the food that the female needs,
0:21:41 > 0:21:45so a male and female anglerfish can survive on a fraction of
0:21:45 > 0:21:49the amount of food that would be required if they were both the same size.
0:21:49 > 0:21:53That's a fabulous tactic in a world where food is very hard to find,
0:21:53 > 0:22:00but what's in it for her? After all, she is feeding him with her own blood.
0:22:00 > 0:22:03Once they are attached, that's it for life, and it's quite gruesome.
0:22:03 > 0:22:07The skin of the female will actually grow out over the male's face,
0:22:07 > 0:22:10and he basically becomes like an organ that she carries around.
0:22:10 > 0:22:14And he's attached underneath, so he's right there in the right place for when she lays the eggs.
0:22:14 > 0:22:16She can literally turn him on, she can send him
0:22:16 > 0:22:19a little message through her blood, a hormonal single,
0:22:19 > 0:22:24so that when she lays the eggs he can fertilise them as they come out.
0:22:24 > 0:22:28It's amazing - when the extreme pressures of life make finding that
0:22:28 > 0:22:33special someone almost impossible, it's best to make sure
0:22:33 > 0:22:35that you remain joined at the hip forever.
0:22:37 > 0:22:40An incredible example of sexual dimorphism,
0:22:40 > 0:22:44where, in a species, there is a very distinct difference between the male and female.
0:22:44 > 0:22:47Of course, in those anglerfish it's principally size,
0:22:47 > 0:22:50but in these black grouse you can see that the male is a lot more
0:22:50 > 0:22:53flamboyant than the rather dowdy female,
0:22:53 > 0:22:58and that's because he is using those plumes to attract a mate.
0:22:58 > 0:23:00But it doesn't only occur in birds.
0:23:00 > 0:23:03Look at these splendid stag beetles.
0:23:03 > 0:23:09The females on the right here lack those remarkable antlers of the males.
0:23:09 > 0:23:13The males need those, of course, for aggressive encounters with rivals.
0:23:15 > 0:23:20These bizarre stories of nature's weirdest romantics show the extreme
0:23:20 > 0:23:24lengths that some species will go to to find their perfect partner.
0:23:24 > 0:23:28From the toadfish whose sweet serenade could bring him
0:23:28 > 0:23:33many lovers, to the connection that means that the anglerfish
0:23:33 > 0:23:35will never have to find another.
0:23:35 > 0:23:40And those mayflies, that are literally dying to mate.
0:23:40 > 0:23:46The weird and wacky ways that nature finds love will never cease to amaze.
0:23:48 > 0:23:51Now, even though you might be able to choose your lover,
0:23:51 > 0:23:55who you end up living next to is an entirely different matter.
0:23:55 > 0:24:00Coming up next, we look at some stories where neighbourly understanding is essential.
0:24:02 > 0:24:05We'll investigate the curious events that could lead you
0:24:05 > 0:24:08to sharing your favourite spot in the garden.
0:24:09 > 0:24:14But first, one incredible encounter that has led to a surprising
0:24:14 > 0:24:16and beautiful Platonic relationship.
0:24:18 > 0:24:23Churchill, on the shores of the Hudson Bay in the Canadian sub-arctic.
0:24:26 > 0:24:30Each year, starving polar bears roam around town
0:24:30 > 0:24:33waiting for the sea to freeze so they can hunt seals.
0:24:35 > 0:24:38Dog breeder and Churchill resident
0:24:38 > 0:24:42Brian Ladoon keeps 150 sled dogs on the shores of Hudson Bay.
0:24:46 > 0:24:49Just a complete city of dogs.
0:24:49 > 0:24:53Brian keeps his dogs on a spit of land jutting out into the sea.
0:24:57 > 0:25:03It's isolated and the best place to keep Eskimo dogs on earth.
0:25:03 > 0:25:09It's isolated and it's controllable, except for the other locals.
0:25:12 > 0:25:18You see, one day in 1992, Brian watched helplessly as a starving
0:25:18 > 0:25:21polar bear strolled onto his land
0:25:21 > 0:25:26and headed straight for his dogs. He knew all too well that bears
0:25:26 > 0:25:30regularly kill and eat dogs where they come into contact.
0:25:30 > 0:25:35When I first seen things playing out, I did have great concerns.
0:25:35 > 0:25:39I was frightened, and I wasn't sure what to do.
0:25:39 > 0:25:43He was unable to move a muscle as half a tonne of malnourished
0:25:43 > 0:25:47mega-predator closed in on his faithful companions.
0:25:49 > 0:25:51Then, as these photos show,
0:25:51 > 0:25:54something truly unbelievable happened.
0:25:57 > 0:25:59The pair began to play.
0:26:03 > 0:26:05It is extraordinary to see them play together.
0:26:05 > 0:26:07Actually you got a privileged position
0:26:07 > 0:26:10when you are right in the front row seat and you're watching them
0:26:10 > 0:26:13and they are only, like, metres away from you.
0:26:14 > 0:26:19Amazingly this particular bear started an annual ritual,
0:26:19 > 0:26:23returning to visit the dogs each year just before the sea freezes.
0:26:26 > 0:26:30So why on earth did this hungry polar bear feel that
0:26:30 > 0:26:32playing with its potential dinner
0:26:32 > 0:26:35was better than satisfying its aching hunger?
0:26:37 > 0:26:42Clinical psychiatrist Dr Stuart Brown has analysed these incredible photos.
0:26:43 > 0:26:45What was amazing to me
0:26:45 > 0:26:49was that the polar bear, as he approached this female sled dog
0:26:49 > 0:26:53that was tethered, was in a predatory gait,
0:26:53 > 0:26:56with fixed eyes, headed toward that sled dog.
0:26:56 > 0:27:00Which anyone who's ever seen a predatory animal
0:27:00 > 0:27:04recognises as a very powerful signal that says, "I'm going to kill you."
0:27:04 > 0:27:10The dog went down into a play bow, and the bear immediately
0:27:10 > 0:27:14picked this up, changed his gait and started dancing.
0:27:14 > 0:27:18And was gambolling. The hair went flat, the eyes went soft,
0:27:18 > 0:27:23and in a moment the bear was standing upright over the sled dog.
0:27:23 > 0:27:25The sled dog was staying there wagging her tail.
0:27:25 > 0:27:27They looked up at each other
0:27:27 > 0:27:31and they started into this wonderful ballet of rough-and-tumble play
0:27:31 > 0:27:34which went on for 20 minutes. It was magical.
0:27:36 > 0:27:39Dr Brown is a world authority on play,
0:27:39 > 0:27:44and has been studying its effects and benefits for over 20 years.
0:27:44 > 0:27:47The smarter the animal, the more they play.
0:27:47 > 0:27:49It's very important for survival
0:27:49 > 0:27:54and for adaptation in a constantly changing environment and world.
0:27:54 > 0:27:58Animals that are capable of play are also capable of innovation
0:27:58 > 0:28:01and flexibility under unexpected circumstances.
0:28:04 > 0:28:08Rough-and-tumble play, which is universal among social mammals,
0:28:08 > 0:28:12is extremely beneficial, complex and very, very important.
0:28:12 > 0:28:13What does it do?
0:28:13 > 0:28:17It teaches the animal their own strength, speed, capabilities.
0:28:17 > 0:28:21It puts them in competition with other animals,
0:28:21 > 0:28:24tells them where they fit in the hierarchy of the pack.
0:28:24 > 0:28:26It also teaches them empathy.
0:28:27 > 0:28:31So that makes sense for animals of the same species,
0:28:31 > 0:28:34but bears and dogs are competitors at best.
0:28:34 > 0:28:39At worst, Brian's dogs are a tasty snack-sized mouthful for a hungry bear.
0:28:41 > 0:28:43So there must be something more to it,
0:28:43 > 0:28:46but what need could be more urgent than hunger?
0:28:48 > 0:28:51I think the power of play signals is so intense
0:28:51 > 0:28:56and so important for survival, of both birds and mammals
0:28:56 > 0:29:01and human beings, that the signals that herald play are capable
0:29:01 > 0:29:05of being interpreted across species, which is quite remarkable.
0:29:05 > 0:29:09I've seen a magpie play with a bear.
0:29:09 > 0:29:13And they each were able to interpret the signals between each other
0:29:13 > 0:29:16that this was play, and they frolicked like crazy.
0:29:16 > 0:29:19Well, that's really quite significant, and when you look
0:29:19 > 0:29:24at that more deeply, you'll find that the survival drive that is a part
0:29:24 > 0:29:27of each of those animals' survival drive, is linked to play behaviour.
0:29:28 > 0:29:32So it seems that when the signals are strong enough,
0:29:32 > 0:29:35the urge to play can become irresistible.
0:29:35 > 0:29:40What's really incredible, though, is that this one exceptional bear
0:29:40 > 0:29:42started to bring its mates back with it.
0:29:44 > 0:29:47So what started out with just one rogue
0:29:47 > 0:29:52doing something out of the ordinary, is now an annual social event.
0:29:52 > 0:29:57Up to seven bears from the Churchill population have all
0:29:57 > 0:30:01built relationships with Brian's dogs.
0:30:01 > 0:30:04And over the years they have become local celebrities.
0:30:04 > 0:30:08First you think that the dogs are being attacked, and then you realise
0:30:08 > 0:30:12that, you know, he's holding his head in his mouth because he wants to.
0:30:12 > 0:30:15You'd think the bear would be right in there eating the dog
0:30:15 > 0:30:18straight away, but they have some kind of companionship going on,
0:30:18 > 0:30:20and it's amazing. It beautiful.
0:30:20 > 0:30:23They look like they are having a great time.
0:30:23 > 0:30:26They are happy to see their buddy, you know?
0:30:26 > 0:30:31DOG WHINES AND BARKS
0:30:33 > 0:30:37I think the dogs get sad when they see the bears go in the fall.
0:30:37 > 0:30:38They miss them.
0:30:38 > 0:30:43But, you know, come a certain day, the polar bears leave on the ice.
0:30:43 > 0:30:48Leaving the dogs hopeful that they will return next year to renew their friendship.
0:30:55 > 0:30:58BARKING AND GROWLING
0:31:03 > 0:31:06When you really take a close look at what's happening in something
0:31:06 > 0:31:11just as magical as a polar bear and a sled dog, you begin to get
0:31:11 > 0:31:14an understanding that there is something deeper going on here.
0:31:19 > 0:31:23Incredible stuff. But, you know, in we humans,
0:31:23 > 0:31:27play is far more important than learning how to survive in the wild.
0:31:27 > 0:31:30It's also about learning empathy
0:31:30 > 0:31:32and a great range of other social behaviours.
0:31:32 > 0:31:38So, for we humans at least, play isn't just practice for hunting and fighting.
0:31:41 > 0:31:45For our next story we look at some bizarre neighbourly
0:31:45 > 0:31:49relationships that go way past sharing the odd cup of sugar.
0:31:53 > 0:31:55The American black bear.
0:32:00 > 0:32:06Shy and retiring, they prefer their own company...
0:32:08 > 0:32:11..foraging for berries and grubs in their favourite habitats -
0:32:14 > 0:32:18the forests, marshes and rugged mountains across North America.
0:32:21 > 0:32:24They are brilliantly adapted to life in the wild.
0:32:27 > 0:32:33However, some US house owners have been witnessing some very peculiar behaviour.
0:32:36 > 0:32:38There's a bear in my hot tub!
0:32:40 > 0:32:42Please don't pee in there.
0:32:45 > 0:32:48Hey, get out of there! Get out of there!
0:32:48 > 0:32:52And it's not just the odd individual taking a dip
0:32:54 > 0:32:57Even fiercely protective mothers with cubs are getting in on the action.
0:32:59 > 0:33:03I got them swimming in my pool. They use the pool more than us.
0:33:03 > 0:33:06- Why didn't they go in Dr Bob's pool? - I don't know.
0:33:09 > 0:33:14But why would such a shy creature decide to party in a human's pool?
0:33:14 > 0:33:16You have to call the cops, Daddy. You have to.
0:33:18 > 0:33:22Bear expert Dr Ted Oakes believes he might have an explanation.
0:33:24 > 0:33:26Black bears spend all winter in dens, which are often very,
0:33:26 > 0:33:30very cold places, and so they have thick, thick fur.
0:33:30 > 0:33:35But in the summer, because the fur is black, the fur absorbs heat
0:33:35 > 0:33:39almost like no other material, and they really, really heat up.
0:33:39 > 0:33:42I remember somebody I work with stuck at the moment in the fur
0:33:42 > 0:33:46of a black bear in full sun, and it was just below boiling point.
0:33:46 > 0:33:50It was about 80 or 90 degrees Celsius.
0:33:50 > 0:33:55So, their first line of defence in the heat is to remove themselves from the sun.
0:33:55 > 0:33:58The second line of defence in the heat is to start panting.
0:33:58 > 0:34:03And black bears will pant when they are very, very hot.
0:34:03 > 0:34:06But when a black bear is panting,
0:34:06 > 0:34:08it's really in a situation where it's got to do something else
0:34:08 > 0:34:11to cool down, and that's usually seeking water.
0:34:16 > 0:34:20So, they take the plunge to cool off, but aren't black bears
0:34:20 > 0:34:23shy and elusive animals that stay away from humans?
0:34:26 > 0:34:30There are nearly a million black bears living in North America,
0:34:30 > 0:34:31and 300 million people.
0:34:31 > 0:34:35In fact, I would say now that most people are never more than
0:34:35 > 0:34:39a few miles from a black bear in most parts of North America.
0:34:39 > 0:34:43Black bears, yet, are rarely seen, and the reason for that is they are quite shy.
0:34:43 > 0:34:48They don't want to be around people. They like to avoid people, and usually people are trouble for them.
0:34:48 > 0:34:51But if there is not much food in the forest,
0:34:51 > 0:34:56they will take the opportunity to find food near human habitation.
0:34:56 > 0:34:58If it's a choice between starving to death and finding
0:34:58 > 0:35:01food from humans, bears can sometimes come to town.
0:35:03 > 0:35:07They might not actually come to a house to find water to cool down,
0:35:07 > 0:35:10they might actually come to a house to find a bird feeder.
0:35:10 > 0:35:13But once they are at the house and they see that the house not only has a bird feeder
0:35:13 > 0:35:17but a swimming pool, that's when the party could start for a black bear.
0:35:19 > 0:35:22Put that down! Quit tearing it up!
0:35:22 > 0:35:27But there is something even more amazing about these intriguing beasts.
0:35:27 > 0:35:33In some places where bears make trips into town, they make sure they do so on bin collection day,
0:35:33 > 0:35:36making their trips as fruitful as possible.
0:35:38 > 0:35:42Having a caring approach for our wild neighbours isn't something
0:35:42 > 0:35:45that's restricted to people living in far-flung places.
0:35:45 > 0:35:49Yes, they might have bears in hot tubs, but we have foxes on trampolines.
0:35:55 > 0:35:59There are about 250,000 adult red foxes in Britain...
0:36:01 > 0:36:03..and just like black bears they are intelligent,
0:36:03 > 0:36:06opportunistic mammals,
0:36:06 > 0:36:10happy to treat our property as their own.
0:36:10 > 0:36:14And occasionally use our gardens for a little play, too.
0:36:24 > 0:36:29What all these weird relationships show us is that as our population
0:36:29 > 0:36:33expands, it gets ever more important to treat those around us with a bit
0:36:33 > 0:36:35of humility, whoever they are.
0:36:37 > 0:36:43Even if it does mean some of us must accept that man might not always be a dog's best friend.
0:36:45 > 0:36:51In nature's weird world, it pays to have a good relationship with your neighbours.
0:36:54 > 0:36:57Now, sticking with the subject of population expansion, next up
0:36:57 > 0:37:02we take a look at some of nature's weirdest ways of bringing up baby.
0:37:03 > 0:37:07We will examine a very unlikely tale of maternal care.
0:37:09 > 0:37:13But first we look at an odd animal that has an even odder way
0:37:13 > 0:37:15of keeping her little angels safe.
0:37:19 > 0:37:21Back in 2007, this bizarre
0:37:21 > 0:37:23and gruesome behaviour was caught on camera.
0:37:23 > 0:37:25Now it's moving a lot.
0:37:25 > 0:37:28Here they come! Here they come!
0:37:28 > 0:37:30Get them! Oh, my God! Look at her!
0:37:31 > 0:37:34No, your eyes aren't deceiving you,
0:37:34 > 0:37:38those are tiny animals erupting from the back of a toad.
0:37:42 > 0:37:46But what on earth could these alien beasts be?
0:37:48 > 0:37:52In fact they were the offspring of this creature,
0:37:52 > 0:37:54the Surinam toad.
0:37:56 > 0:37:59But why would she want to turn her back
0:37:59 > 0:38:02into a skin-crawling care facility?
0:38:04 > 0:38:08Dr Ian Stephen from the Zoological Society of London
0:38:08 > 0:38:10might just be able to shed some light on this.
0:38:13 > 0:38:16The problem with amphibian eggs is that they are highly nutritious
0:38:16 > 0:38:18bundles of food, so lots of things like to eat them.
0:38:18 > 0:38:21Things such as snakes, fish, birds and invertebrates,
0:38:21 > 0:38:23all find them incredibly tasty.
0:38:24 > 0:38:28They also have another problem in that they are completely
0:38:28 > 0:38:31defenceless, so even when they turn into tadpoles, they tend to be
0:38:31 > 0:38:34restricted to small water bodies so they are very easy prey.
0:38:39 > 0:38:43So one strategy that amphibians use is to put all their resources
0:38:43 > 0:38:46and energy into incredibly large broods,
0:38:46 > 0:38:49so they might lay hundreds maybe thousands of eggs, just in the hope
0:38:49 > 0:38:53that one or two individuals go on to reproduce in the next generation.
0:38:54 > 0:38:58Obviously this works well for hundreds of species,
0:38:58 > 0:39:01but it is a very crude strategy.
0:39:01 > 0:39:04There are other amphibians that have come up with more involved ways
0:39:04 > 0:39:06of protecting their offspring.
0:39:08 > 0:39:11Some frogs will construct a foam nest above a water body.
0:39:12 > 0:39:16And quite literally this is a meringue-like foam.
0:39:16 > 0:39:19What's fascinating about the nest itself is it's comprised of
0:39:19 > 0:39:22different layers, and each layer has its own function,
0:39:22 > 0:39:25so the core layer has the eggs and the developing tadpoles themselves,
0:39:25 > 0:39:27and then you also have protective layers on the outside
0:39:27 > 0:39:31that protect the nest from UV and drying out effects of the sun.
0:39:33 > 0:39:35The eggs will take maybe a week to develop,
0:39:35 > 0:39:38and the tadpoles will drop into the water body below.
0:39:40 > 0:39:44OK, it's a very good way to protect your eggs, but the tadpoles
0:39:44 > 0:39:50then still enter the water as helpless and very tempting bite-sized mouthfuls,
0:39:50 > 0:39:56trapped in their pools with no way to escape hungry predators.
0:39:56 > 0:39:59So there must be better ways to offer protection.
0:40:02 > 0:40:05The Darwin's frog takes reproduction to the next level.
0:40:05 > 0:40:09They actually take their eggs inside their bodies.
0:40:11 > 0:40:15The female frog lays their eggs in damp leaf litter.
0:40:15 > 0:40:18The male then takes up the eggs four to five days later
0:40:18 > 0:40:22and actually takes the eggs themselves into its vocal sac,
0:40:22 > 0:40:27and that's where the eggs then go on to develop into tadpoles.
0:40:27 > 0:40:31About 70 days later, the male quite literally coughs up the tiny little froglets.
0:40:35 > 0:40:37And, yes - they are complete,
0:40:37 > 0:40:41fully formed frogs coming out of his mouth.
0:40:44 > 0:40:46Obviously the vocal sacs aren't huge,
0:40:46 > 0:40:48so we're only looking at about 15 to 20 in total.
0:40:50 > 0:40:54It's an inspired solution for a small brood like that, but what about
0:40:54 > 0:40:58if you need to protect hundreds of babies, what happens then?
0:41:00 > 0:41:03Well, this takes us neatly back to our friend
0:41:03 > 0:41:06with the erupting back, the Surinam toad.
0:41:08 > 0:41:11The Surinam toad has taken things to an absolute other level,
0:41:11 > 0:41:15When the females spawns, the male takes the eggs themselves
0:41:15 > 0:41:17and presses them onto the female's back.
0:41:17 > 0:41:20This might be 200, 250 eggs.
0:41:20 > 0:41:24What's incredible is that a layer of skin then develops over those eggs.
0:41:30 > 0:41:34About 70 days later, tiny fully formed froglets actually emerge from
0:41:34 > 0:41:38the female's back, almost like something from the scene of an alien film.
0:41:58 > 0:42:02Who'd have thought that life could be so complicated for amphibians?
0:42:02 > 0:42:05But then, it does illustrate some of the dangers and difficulties
0:42:05 > 0:42:08when it come to getting your genes into the next generation.
0:42:08 > 0:42:13When it comes from getting between tadpole and frog.
0:42:17 > 0:42:20The issues of providing for the kids are at the forefront of every
0:42:20 > 0:42:25parent's mind, but our next mother might just have nature's
0:42:25 > 0:42:27weirdest way of bringing up baby.
0:42:33 > 0:42:35Shark researcher Stewart Springer was undertaking
0:42:35 > 0:42:38an inspection of a pregnant sand tiger shark.
0:42:41 > 0:42:44Carefully inserting a hand into the shark's body,
0:42:44 > 0:42:46Stewart groped around feeling for any babies.
0:42:50 > 0:42:54Then from deep inside the shark's body, something attacked,
0:42:54 > 0:42:59tearing at his finger with a set of razor sharp teeth!
0:43:02 > 0:43:07But the only thing inside the shark was her unborn offspring.
0:43:09 > 0:43:15So why on earth would a baby that is still in the womb have teeth,
0:43:15 > 0:43:17let alone know how to use them?
0:43:21 > 0:43:25Biologist Dr Matt Gollock is one man who can help answer this.
0:43:26 > 0:43:30When producing juveniles within any species, it's a numbers game.
0:43:31 > 0:43:33You might recognise mermaids purses,
0:43:33 > 0:43:37these are egg cases of species such as cat sharks.
0:43:37 > 0:43:38Obviously once the eggs are laid,
0:43:38 > 0:43:43these eggs are then vulnerable to predation.
0:43:43 > 0:43:45Some species of shark give birth to live young.
0:43:45 > 0:43:49The blue shark, for example, produce up to 150 juveniles.
0:43:49 > 0:43:52This might mean that more will be killed, but because there is
0:43:52 > 0:43:56a greater number, it's more likely that some of them survive.
0:43:59 > 0:44:04However, sand tiger sharks have a really amazing reproductive strategy.
0:44:04 > 0:44:07They produce eggs into the womb which grow into embryos.
0:44:09 > 0:44:12We find out that the juveniles actually develop very quickly,
0:44:12 > 0:44:17and within the first few months they actually develop teeth.
0:44:17 > 0:44:22And the largest of these embryos will actually kill its brothers and sisters.
0:44:22 > 0:44:28Now, come on - that's beyond weird. It's eating its own siblings inside the womb!
0:44:29 > 0:44:32After it's eaten its brothers and sisters,
0:44:32 > 0:44:35the female will actually produce eggs which keeps the juvenile growing
0:44:35 > 0:44:39until it's almost a metre long, after which point it's born into the wild.
0:44:45 > 0:44:49It's believed that eating their brothers and sisters in the womb actually is an evolutionary
0:44:49 > 0:44:53advantage for the sand tigers that are ultimately born.
0:44:53 > 0:44:58They think there is about 20 embryos produced into each uterus,
0:44:58 > 0:45:01and so by the time each of the juveniles are born,
0:45:01 > 0:45:03they will have maybe up to 20 times,
0:45:03 > 0:45:07And that, on top of eating abound 17,000 eggs,
0:45:07 > 0:45:12so when they are actually born, they are very, very experienced at hunting their prey.
0:45:13 > 0:45:16This strategy means that the juveniles are independent
0:45:16 > 0:45:18almost from the minute they are born,
0:45:18 > 0:45:21and this means there is a much higher chance of survival.
0:45:21 > 0:45:24And when so few young are being produced, this is very, very important.
0:45:26 > 0:45:29A pretty unorthodox way of providing for baby,
0:45:29 > 0:45:34but nevertheless, absolutely ingenious.
0:45:34 > 0:45:38It's totally amazing what weird wonders nature has come up with
0:45:38 > 0:45:41to offer babies their best start in life.
0:45:41 > 0:45:45From the amphibians who use their own bodies as childcare facilities,
0:45:45 > 0:45:50to the mother who sacrifices hundreds of potential young for the sake of just the eldest.
0:45:52 > 0:45:55It seems that keeping the kids inside your body
0:45:55 > 0:45:59for as long as possible is one way to ensure their safety.
0:46:03 > 0:46:07No one likes a relationship that's all give and no take.
0:46:07 > 0:46:15Our last collection of stories looks at a few love affairs that have become a little too one-sided.
0:46:15 > 0:46:18From the worm with an eye on a new home,
0:46:18 > 0:46:21to the fly whose young play hard-to-get-out,
0:46:21 > 0:46:26we investigate nature's weird world of the unwanted guest.
0:46:27 > 0:46:30But first, a tropical romance gone bad -
0:46:30 > 0:46:34a relationship where only one partner likes kissing.
0:46:35 > 0:46:40All across South America in the run down parts of towns and cities,
0:46:40 > 0:46:45millions of dark forms lurk in the shadows waiting till nightfall to emerge.
0:46:48 > 0:46:52But these are no ordinary moth or dainty mosquito,
0:46:52 > 0:46:54these are kissing bugs.
0:46:57 > 0:47:01And when caught by scientists, they exhibit an unnerving ability
0:47:01 > 0:47:03to sense the presence of humans.
0:47:09 > 0:47:12So where does this super sense come from?
0:47:16 > 0:47:21Dr Matt Yeo from the London School of Tropical Medicine has some answers.
0:47:21 > 0:47:23They are really quite nasty bugs.
0:47:23 > 0:47:25If they are hungry, you can actually see them.
0:47:25 > 0:47:28They will be attracted to the heat of my finger,
0:47:28 > 0:47:30so they are quite vicious hungry.
0:47:30 > 0:47:33And similarly, if I breathe on them, they become very agitated,
0:47:33 > 0:47:35and that's the carbon dioxide from my breath.
0:47:35 > 0:47:37And if I breathe a bit more...
0:47:38 > 0:47:42Again, you can see them probing through the net.
0:47:42 > 0:47:46So these bugs are attracted to warmth and carbon dioxide,
0:47:46 > 0:47:51and feed on the blood of larger animals, like us humans.
0:47:51 > 0:47:55They sink their needle-like mouth parts into their victims' flesh to draw
0:47:55 > 0:48:01long and hard on their blood whilst we sleep away, blissfully unaware.
0:48:01 > 0:48:04But that doesn't explain their name.
0:48:04 > 0:48:06One of the reasons they're called kissing bugs
0:48:06 > 0:48:10is that they tend to come out at night when the lights are off
0:48:10 > 0:48:13and your face tends to be the most exposed area.
0:48:14 > 0:48:16So they can crawl all over the face
0:48:16 > 0:48:19but generally kiss around the mouth area or the facial areas.
0:48:20 > 0:48:23They can be so hungry that night after night,
0:48:23 > 0:48:24they can really take their toll.
0:48:24 > 0:48:29So if you've got a family and they're being fed on every night,
0:48:29 > 0:48:32particularly the children can actually become anaemic.
0:48:32 > 0:48:35But they have another, darker legacy,
0:48:35 > 0:48:39darker even than sucking children into a state of anaemia.
0:48:39 > 0:48:43You see, whilst kissing you on the cheek they might well leave you
0:48:43 > 0:48:46with the life-threatening Chagas disease,
0:48:46 > 0:48:48a condition caused by a tiny parasite
0:48:48 > 0:48:52carried by the kissing bugs that can eventually lead to heart failure.
0:48:54 > 0:48:57When they take a blood meal, they defecate
0:48:57 > 0:49:01and you can scratch it into the bite wound or you can rub your eyes
0:49:01 > 0:49:04or put your fingers to your mouth and that's how you become infected.
0:49:06 > 0:49:09What an incredible species. Brilliant things.
0:49:09 > 0:49:12And you've got to remember that aside from biting us
0:49:12 > 0:49:15and sucking a little of our blood, they don't actually do us any harm.
0:49:15 > 0:49:19It's the parasite that they transport around that causes that Chagas disease.
0:49:19 > 0:49:24Now, kissing bugs do actually have some cousins living here in the UK,
0:49:24 > 0:49:27we call them assassin bugs.
0:49:27 > 0:49:29But before you lock up your children,
0:49:29 > 0:49:34don't worry, they don't feed on humans. They primarily feast on insects.
0:49:35 > 0:49:40For nature's next weirdly one-sided union, we look at a hitchhiker
0:49:40 > 0:49:44that's desperate to dive deep into a long-term relationship.
0:49:47 > 0:49:51Back in 2009, climbing expert Tim Fogg arrived back in
0:49:51 > 0:49:55the UK from a trip to the Central African Republic.
0:49:55 > 0:50:00Nothing odd to report, until one day this happened.
0:50:03 > 0:50:07Suddenly my hand swelled up for no apparent reason.
0:50:07 > 0:50:11Then it went down, then about ten days later my arm swelled up
0:50:11 > 0:50:14and then it went down. Just bits of me kept swelling up.
0:50:19 > 0:50:22As a rope access specialist, Tim has travelled to
0:50:22 > 0:50:27some of the worlds most bizarre and extreme environments,
0:50:27 > 0:50:33but never before had his body parts randomly swollen for no apparent reason.
0:50:34 > 0:50:38This bizarre bodily behaviour continued for two years.
0:50:41 > 0:50:45So, what could be causing these spontaneous swellings?
0:50:48 > 0:50:52After several medical tests, Tim was diagnosed as having
0:50:52 > 0:50:56contracted Loa loa, or the African eye worm.
0:50:58 > 0:51:00It gets its gruesome name from
0:51:00 > 0:51:04the only time it becomes visible in infected humans -
0:51:04 > 0:51:08as it passes through its host's eyeballs.
0:51:11 > 0:51:15It's an incredible parasite that is carried by certain types
0:51:15 > 0:51:19of day biting flies in the swamps of west Africa,
0:51:19 > 0:51:24exactly where Tim had returned home from two years earlier.
0:51:24 > 0:51:27I think I got it wading through a lot of mud in the forest where
0:51:27 > 0:51:31mango flies live, which is the thing that transmits it.
0:51:31 > 0:51:37Infection occurs when the larvae of the worm are passed to a human as the fly bites.
0:51:38 > 0:51:42The larvae then develop under the skin until they become adults
0:51:42 > 0:51:44and start their travels around the body.
0:51:47 > 0:51:51As they move about under the skin, the immune system starts to
0:51:51 > 0:51:54react and it's this that causes the swelling.
0:51:54 > 0:51:57I guess it was in my hand to start with,
0:51:57 > 0:52:00it presumably went up one arm then my other arm swelled up,
0:52:00 > 0:52:04so presumably somehow it got right across my shoulder and down into the other arm.
0:52:04 > 0:52:06Or maybe it was another worm. I have no idea.
0:52:08 > 0:52:13Incredibly, the worm can grow to be seven centimetres long and live
0:52:13 > 0:52:19for 17 years creeping around under the surface of the host's body.
0:52:19 > 0:52:23The worst thing about this thing wandering about under your skin
0:52:23 > 0:52:26is its habit of coming up to your eye
0:52:26 > 0:52:30and wandering across your eye and across the bridge of your nose and into the other eye.
0:52:30 > 0:52:34And that is apparently very, very painful.
0:52:34 > 0:52:37And I did have one incident where the side of my face swelled up
0:52:37 > 0:52:40which meant that it was there, it was getting close
0:52:40 > 0:52:42and thinking about going across my eye.
0:52:42 > 0:52:43Luckily it changed its mind.
0:52:44 > 0:52:48The beauty of this parasite is that it doesn't hurt you at all,
0:52:48 > 0:52:49and it didn't make me feel ill.
0:52:49 > 0:52:53It was just the swelling so it's very clever.
0:52:53 > 0:52:55I mean, it just wants to feed off me,
0:52:55 > 0:53:00it doesn't want to give me bother if it can, cos I might get rid of it.
0:53:00 > 0:53:04After he was diagnosed in 2011, Tim's doctor put him
0:53:04 > 0:53:09on an intensive course of drugs, and a year later in June 2012
0:53:09 > 0:53:14he was deemed tentatively clear of his tenacious little body mate.
0:53:19 > 0:53:24Our last story is more body burrowing than bunny boiling,
0:53:24 > 0:53:28a gruesome but truly ingenious example of nature's
0:53:28 > 0:53:30weird relationships gone bad.
0:53:33 > 0:53:36And so to Panama where an innocent traveller has picked up
0:53:36 > 0:53:38a couple of unwanted passengers.
0:53:38 > 0:53:41Do you see it? Right there. SHRIEKING
0:53:41 > 0:53:47What started as two small insect bites has become swollen and angry.
0:53:47 > 0:53:51- SHRIEKING - It's ready to come out.- Yeah, it is.
0:53:51 > 0:53:53And there was something inside.
0:53:53 > 0:53:57Whatever they were simply had to be extracted.
0:53:57 > 0:54:01They are big. I can feel it trying to pull back in. Gross.
0:54:01 > 0:54:05- You mean it's still alive? - GASPS AND LAUGHTER
0:54:06 > 0:54:08That's huge!
0:54:13 > 0:54:15So, what on earth are they?
0:54:18 > 0:54:22Dr Mark Rowland works at the London School Of Hygiene and Tropical Medicine
0:54:22 > 0:54:25and has travelled the world studying parasites.
0:54:25 > 0:54:28Those insects that we are trying to pull out of people's bodies are
0:54:28 > 0:54:34the larvae of the botfly and I have some here, pickled inside this jar.
0:54:34 > 0:54:39They are quite large. They are about one and a half centimetres long.
0:54:39 > 0:54:43But how does something this big get under your skin in the first place?
0:54:43 > 0:54:46The botfly itself is quite large, it's about the size
0:54:46 > 0:54:49of a bumblebee, so if it were to actually land on a host itself
0:54:49 > 0:54:54it would probably be detected by the human or cattle or pig
0:54:54 > 0:54:58and brushed away, so that makes it less likely for the fly
0:54:58 > 0:55:01to succeed in laying its eggs successfully on the host.
0:55:01 > 0:55:05So the botfly has come up with a very sneaky tactic.
0:55:05 > 0:55:09What the fly has cleverly done is to grab
0:55:09 > 0:55:14an insect like a mosquito or a tick or even a housefly.
0:55:14 > 0:55:18After a quick air ambush, the botfly pins down the fly
0:55:18 > 0:55:20and quickly attaches its eggs.
0:55:23 > 0:55:26And then off it goes to do the botfly's dirty work.
0:55:28 > 0:55:34On contacting the human or animal host, the small botfly larvae inside the egg will be able
0:55:34 > 0:55:38to detect the warmth of the host, and it will hatch at that point.
0:55:38 > 0:55:40And it does this very quickly indeed.
0:55:40 > 0:55:43The larvae is able to penetrate and embed itself
0:55:43 > 0:55:45in the skin of the host.
0:55:45 > 0:55:49Over the course of several weeks, it will grow
0:55:49 > 0:55:51and eat its way into the flesh.
0:55:51 > 0:55:55And just in case you were thinking of getting rid of it at that stage,
0:55:55 > 0:55:57it has spiny bristles that hold it in
0:55:57 > 0:56:00and make it impossible to pull out.
0:56:02 > 0:56:03Oh, my God! Oh, God!
0:56:03 > 0:56:06That definitely is the trick, man, overnight.
0:56:06 > 0:56:09The only way to win this tug of war is to play dirty.
0:56:11 > 0:56:17One trick that you can do to make it easier is to smear a gel or fat
0:56:17 > 0:56:20over the rear end of the larvae.
0:56:20 > 0:56:22This will block the breathing tubes of the larvae.
0:56:22 > 0:56:26And that makes it easier to actually draw the larvae from the body.
0:56:26 > 0:56:29GROANING
0:56:29 > 0:56:33SHOUTS AND GROANS
0:56:33 > 0:56:38Only when you've cut off its air supply will the botfly let go.
0:56:40 > 0:56:43Of course, the other option is to let nature take its course
0:56:43 > 0:56:47and wait six weeks for the larva to become a maggot,
0:56:47 > 0:56:52eat its way out, and drop onto the ground before becoming an adult fly.
0:56:54 > 0:56:57It's a nasty business, however they exit.
0:56:57 > 0:57:02But after all of this, you should just end up with a little scar - no problem.
0:57:04 > 0:57:09Amazing that a maggot that size does so little damage in the end.
0:57:11 > 0:57:15From the bug with a super sense for the human body
0:57:15 > 0:57:19to the worm that is just dying to get under your skin
0:57:19 > 0:57:24and the botfly who knows how to play tough,
0:57:24 > 0:57:28it's obvious that the further we travel the more likely we are
0:57:28 > 0:57:33to bring home the unwanted baggage of a holiday romance.
0:57:35 > 0:57:38What all of the stories in this programme seem to illustrate
0:57:38 > 0:57:44is that a bit of understanding and tolerance help in all of our relationships.
0:57:44 > 0:57:49So, if we can implement a bit of love and respect towards all of nature's wonders,
0:57:49 > 0:57:54there's absolutely no doubt that the world would be a richer place.
0:57:54 > 0:57:57And of course, the world is always getting smaller.
0:57:57 > 0:58:03So as we welcome more and more of these bizarre creatures into our own backyards,
0:58:03 > 0:58:09What we think of as weird now might be a lot weirder in the future.
0:58:12 > 0:58:16Next time on Nature's Weirdest Events,
0:58:16 > 0:58:20there is an island awash under a tide of tiny crabs...
0:58:23 > 0:58:27..a town terrorized by rampaging elk,
0:58:27 > 0:58:30and a community primed for an unbelievable invasion of insects.
0:58:35 > 0:58:38Subtitles by Red Bee Media Ltd