0:00:01 > 0:00:04No matter how well we think we know our planet, the natural world still
0:00:04 > 0:00:06has the ability to surprise us,
0:00:06 > 0:00:09to shock us and maybe sometimes even
0:00:09 > 0:00:13to scare us with its extraordinary events and bizarre behaviour.
0:00:13 > 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 > 0:00:23So we're going to bring you
0:00:23 > 0:00:26the strangest stories our world has to offer.
0:00:48 > 0:00:53To kick off, we're going to look at some of nature's weirdest romantics.
0:01:01 > 0:01:05The shores of Lake Erie on America's beautiful border with Canada
0:01:05 > 0:01:09have always been a tranquil place of peace and quiet.
0:01:10 > 0:01:14Until, early in the summer of 2010,
0:01:14 > 0:01:19it became the setting for a swarm of phenomenal proportions.
0:01:19 > 0:01:25This gas station is being attacked by...something.
0:01:25 > 0:01:27And that lady won't even get out of her car.
0:01:27 > 0:01:29It's like it's snowing.
0:01:29 > 0:01:33A swarm of literally billions stretched over a mile inland
0:01:33 > 0:01:36and for miles along the western shore.
0:01:37 > 0:01:42Local resident Greg Stewart recalls the experience.
0:01:42 > 0:01:45They were all over the wall of the city,
0:01:45 > 0:01:49and I didn't know if I should even get out of my car, it was that bad.
0:01:49 > 0:01:53And, as I got out, they started crunching under my feet.
0:01:53 > 0:01:55Then, within days,
0:01:55 > 0:01:59they spontaneously started to die in their billions.
0:02:01 > 0:02:02Seriously, a pile of bugs.
0:02:08 > 0:02:12The drifts of dead bodies got so deep that the local authorities
0:02:12 > 0:02:15had to use snow ploughs to unblock the roads.
0:02:23 > 0:02:27And, as they started to break down, they left another treat, too.
0:02:29 > 0:02:35It smelled of motor oil and vomit.
0:02:37 > 0:02:39So what were these insects,
0:02:39 > 0:02:43and what could have caused such an extraordinary plague?
0:02:50 > 0:02:54Don Schloesser is an expert in the wildlife of Lake Erie
0:02:54 > 0:02:57The big swarms are really the result of the life history pattern
0:02:57 > 0:02:59of the western Lake Erie mayflies.
0:03:02 > 0:03:06They live in the mud for about two years and they grow and they moult.
0:03:06 > 0:03:08About the middle of May, the first of June,
0:03:08 > 0:03:11they all come out of the water at one time.
0:03:11 > 0:03:13They mate, and then the females
0:03:13 > 0:03:15go back out into the water to lay the eggs.
0:03:15 > 0:03:19And then the whole process starts all over again.
0:03:19 > 0:03:22Mayfly spend about 99% of their lives
0:03:22 > 0:03:25as aquatic larvae at the bottom of ponds and rivers.
0:03:27 > 0:03:30They spend their time feeding and growing
0:03:30 > 0:03:33until, in a cunning plan to avoid getting eaten,
0:03:33 > 0:03:36they all emerge en masse to mate.
0:03:36 > 0:03:39The first few are easy pickings.
0:03:45 > 0:03:50But soon the sheer numbers overwhelm predators -
0:03:50 > 0:03:53they simply can't make a dent in the overall population.
0:03:56 > 0:03:59After about two days, there's a swarm,
0:03:59 > 0:04:02a swirling swarm like a little funnel cloud
0:04:02 > 0:04:04that's formed by the mayflies.
0:04:04 > 0:04:08And what happens is the females jump into that swarm,
0:04:08 > 0:04:10they are fertilized in the air.
0:04:12 > 0:04:16Once they have mated, the male dies and the female heads out
0:04:16 > 0:04:20over the water to release her fertilised eggs
0:04:20 > 0:04:23before she too passes away.
0:04:23 > 0:04:27The entire process takes just a matter of days.
0:04:30 > 0:04:33Each year, as the event comes to an abrupt end,
0:04:33 > 0:04:37it's all hands on deck for the task of clearing up the dead.
0:04:37 > 0:04:41But there's still a lot of questions surrounding their mass emergence.
0:04:41 > 0:04:44When they come out is still a mystery to us.
0:04:44 > 0:04:48We can't predict very well in that two- or three-week period
0:04:48 > 0:04:51when they are actually going to be coming out.
0:04:51 > 0:04:52Sometimes it is related to storm events,
0:04:52 > 0:04:56sometimes it is related to rain events, but somehow
0:04:56 > 0:05:01the mayflies all get a cue when they are down in the bottom of the lake.
0:05:01 > 0:05:04But why are there so many in Lake Erie?
0:05:05 > 0:05:07Lake Erie supplies the types of sediment
0:05:07 > 0:05:09that this critter likes to burrow into.
0:05:09 > 0:05:11It used to have mayflies many years ago,
0:05:11 > 0:05:14then they went away for many years due to pollution.
0:05:14 > 0:05:16Now they're back and they've come back with sort of a vengeance
0:05:16 > 0:05:18in terms of the numbers and the abundances
0:05:18 > 0:05:20that we see come out of the water.
0:05:20 > 0:05:24So this almighty insect orgy is all down
0:05:24 > 0:05:27to a particularly perfect set of conditions.
0:05:27 > 0:05:32The enormous size of the lake and its newly clean waters contribute to
0:05:32 > 0:05:38a swarm so large that it can bring a whole city to a grinding halt.
0:05:42 > 0:05:46No-one likes a relationship that's all give and no take.
0:05:46 > 0:05:49Coming up next, a few love affairs
0:05:49 > 0:05:52that have become a little bit too one-sided -
0:05:52 > 0:05:55from the worm with an eye on a new home
0:05:55 > 0:05:59to the fly whose young play hard to get out.
0:05:59 > 0:06:03We investigate nature's weird world of the unwanted guest.
0:06:06 > 0:06:11Back in 2009, climbing expert Tim Fogg arrived back in the UK
0:06:11 > 0:06:14from a trip to the Central African Republic.
0:06:14 > 0:06:19Nothing odd to report, until one day...this happened.
0:06:22 > 0:06:26Suddenly, my hand swelled up for no apparent reason.
0:06:26 > 0:06:30Then it went down, then about
0:06:26 > 0:06:30ten days later my arm swelled up
0:06:30 > 0:06:33and then it went down. Just bits of me kept swelling up.
0:06:38 > 0:06:41As a rope access specialist, Tim has travelled
0:06:41 > 0:06:46to some of the world's most bizarre and extreme environments,
0:06:46 > 0:06:50but never before had his body parts randomly swollen
0:06:50 > 0:06:52for no apparent reason.
0:06:53 > 0:06:57This bizarre bodily behaviour continued for two years.
0:07:00 > 0:07:03So what could be causing these spontaneous swellings?
0:07:07 > 0:07:11After several medical tests, Tim was diagnosed as having
0:07:11 > 0:07:15contracted loa loa, or the African eye worm.
0:07:17 > 0:07:19It gets its gruesome name from
0:07:19 > 0:07:23the only time it becomes visible in infected humans -
0:07:23 > 0:07:27as it passes through its host's eyeballs.
0:07:30 > 0:07:34It's an incredible parasite that's carried by certain types
0:07:34 > 0:07:38of day biting flies in the swamps of west Africa,
0:07:38 > 0:07:43exactly where Tim had returned home from two years earlier.
0:07:43 > 0:07:46I think I got it wading through a load of mud in the forest where
0:07:46 > 0:07:50mango flies live, which is the thing that transmits it.
0:07:50 > 0:07:53Infection occurs when the larvae of the worm
0:07:53 > 0:07:55are passed to a human as the fly bites.
0:07:57 > 0:08:01The larvae then develop under the skin until they become adults
0:08:01 > 0:08:03and start their travels around the body.
0:08:06 > 0:08:10As they move about under the skin, the immune system
0:08:10 > 0:08:13starts to react and it's this that causes the swelling.
0:08:13 > 0:08:16I guess it was in my hand to start with,
0:08:16 > 0:08:19it presumably went up one arm then my other arm swelled up,
0:08:19 > 0:08:23so presumably somehow it got right across my shoulder and down into the other arm.
0:08:23 > 0:08:25Or maybe it was another worm. I have no idea.
0:08:27 > 0:08:32Incredibly, the worm can grow to be seven centimetres long and live
0:08:32 > 0:08:32for 17 years creeping around under the surface of the host's body.
0:08:32 > 0:08:38for 17 years creeping around under the surface of the host's body.
0:08:38 > 0:08:42The worst thing about this thing wandering about under your skin
0:08:42 > 0:08:45is its habit of coming up to your eye
0:08:45 > 0:08:49and wandering across your eye and across the bridge of your nose and into the other eye.
0:08:49 > 0:08:53And that is apparently very, very painful.
0:08:53 > 0:08:56And I did have one incident where the side of my face swelled up
0:08:56 > 0:08:59which meant it was there, it was getting close
0:08:59 > 0:09:00and thinking about going across my eye.
0:09:00 > 0:09:03Luckily, it changed its mind.
0:09:03 > 0:09:06The beauty of this parasite is that it doesn't hurt you at all,
0:09:06 > 0:09:08and it didn't make me feel ill.
0:09:08 > 0:09:12It was just the swelling, so it's very clever.
0:09:12 > 0:09:14I mean, it just wants to feed off me,
0:09:14 > 0:09:18it doesn't want to give me bother if it can, cos I might get rid of it.
0:09:18 > 0:09:23After he was diagnosed in 2011, Tim's doctor put him
0:09:23 > 0:09:28on an intensive course of drugs, and a year later in June 2012
0:09:28 > 0:09:33he was deemed tentatively clear of his tenacious little body mate.
0:09:38 > 0:09:43Our last story is more body burrowing than bunny boiling,
0:09:43 > 0:09:47a gruesome but truly ingenious example of nature's
0:09:47 > 0:09:49weird relationships gone bad.
0:09:51 > 0:09:55And so to Panama, where an innocent traveller has picked up
0:09:55 > 0:09:57a couple of unwanted passengers.
0:09:57 > 0:10:00Do you see it? Right there.
0:09:57 > 0:10:00SHRIEKING
0:10:00 > 0:10:05What started as two small insect bites has become swollen and angry.
0:10:05 > 0:10:09SHRIEKING
0:10:05 > 0:10:09It's ready to come out.Yeah, it is.
0:10:09 > 0:10:12And there was something inside.
0:10:12 > 0:10:16Whatever they were simply had to be extracted.
0:10:16 > 0:10:20They are big. I can feel it trying to pull back in. Gross.
0:10:20 > 0:10:23You mean it's still alive?
0:10:20 > 0:10:23GASPS AND LAUGHTER
0:10:25 > 0:10:27That's huge!
0:10:32 > 0:10:34So, what on earth are they?
0:10:37 > 0:10:41Dr Mark Rowland works at the London School Of Hygiene and Tropical Medicine
0:10:41 > 0:10:44and has travelled the world studying parasites.
0:10:44 > 0:10:47Those insects that we are trying to pull out of people's bodies are
0:10:47 > 0:10:53the larvae of the botfly and I have some here, pickled inside this jar.
0:10:53 > 0:10:58They are quite large. They are about one and a half centimetres long.
0:10:58 > 0:11:02But how does something this big get under your skin in the first place?
0:11:02 > 0:11:05The botfly itself is quite large, it's about the size
0:11:05 > 0:11:08of a bumblebee, so if it were to actually land on a host itself,
0:11:08 > 0:11:13it would probably be detected by the human or by the cattle or pig
0:11:13 > 0:11:14and be brushed away.
0:11:14 > 0:11:17That makes it less likely for the fly
0:11:17 > 0:11:20to succeed in laying its eggs successfully on the host.
0:11:20 > 0:11:24So the botfly has come up with a very sneaky tactic.
0:11:24 > 0:11:28What the fly has cleverly done is to grab,
0:11:28 > 0:11:33usually an insect like a mosquito or a tick or even a housefly.
0:11:33 > 0:11:36After a quick air ambush, the botfly pins down the fly
0:11:36 > 0:11:39and quickly attaches its eggs.
0:11:41 > 0:11:47And then off it goes to do the botfly's dirty work.
0:11:47 > 0:11:53On contacting the human, or animal host, the small botfly larvae inside the egg will be able
0:11:53 > 0:11:57to detect the warmth of the host, and it will hatch at that point.
0:11:57 > 0:11:59And it does this very quickly indeed.
0:11:59 > 0:12:02The larvae is able to penetrate and embed itself
0:12:02 > 0:12:04in the skin of the host.
0:12:04 > 0:12:08Over the course of several weeks, it will grow
0:12:08 > 0:12:10and eat its way into the flesh.
0:12:10 > 0:12:13And just in case you were thinking of getting rid of it at that stage,
0:12:13 > 0:12:18it has spiny bristles that hold it in
0:12:18 > 0:12:20and make it impossible to pull out.
0:12:20 > 0:12:22Oh, my God! Oh, God!
0:12:22 > 0:12:25That definitely is the trick, man, overnight.
0:12:25 > 0:12:29The only way to win this tug of war is to play dirty.
0:12:29 > 0:12:33One trick that you can do to make it easier is to
0:12:33 > 0:12:38smear a gel or fat over the rear end of the larvae.
0:12:38 > 0:12:41This will block the breathing tubes of the larvae.
0:12:41 > 0:12:45That makes it easier to actually draw the larvae from the body.
0:12:45 > 0:12:48GROANING
0:12:50 > 0:12:53SHOUTS AND GROANS
0:12:53 > 0:12:57Only when you've cut off its air supply will the botfly let go.
0:12:59 > 0:13:02Of course, the other option is to let nature take its course
0:13:02 > 0:13:05and wait six weeks for the larva to become a maggot,
0:13:05 > 0:13:11eat its way out and drop onto the ground before becoming an adult fly.
0:13:13 > 0:13:16It's a nasty business, however they exit.
0:13:16 > 0:13:22But after all of this, you should just end up with a little scar - no problem.
0:13:22 > 0:13:25What all of the stories in this programme seem to illustrate
0:13:25 > 0:13:30is that a bit of understanding and tolerance help in all of our relationships.
0:13:30 > 0:13:36So, if we can implement a bit of love and respect towards all of nature's wonders,
0:13:36 > 0:13:41there's absolutely no doubt that the world would be a richer place.
0:13:41 > 0:13:44And of course, the world is always getting smaller.
0:13:44 > 0:13:49So as we welcome more and more of these bizarre creatures into our own back-yards,
0:13:49 > 0:13:53what we think of as weird now
0:13:53 > 0:13:56might be a lot weirder in the future.