0:00:04 > 0:00:09The natural world is full of fantastically small animals.
0:00:09 > 0:00:12Hello! Where are you going?
0:00:12 > 0:00:14And I mean REALLY small.
0:00:15 > 0:00:20Some you'll recognise because millions of us watch them online.
0:00:21 > 0:00:24Some are rare and unusual...
0:00:25 > 0:00:30..and others look like big animals that have shrunk in the wash.
0:00:30 > 0:00:32Despite initial appearances,
0:00:32 > 0:00:35these animals aren't the underdogs you might think they are.
0:00:37 > 0:00:41In fact, new science is revealing that these small-scale superheroes
0:00:41 > 0:00:45are perfectly adapted to deal with the challenges
0:00:45 > 0:00:49of the big, wide world in their own unique ways.
0:00:52 > 0:00:55I'm Patrick Aryee and as a biologist,
0:00:55 > 0:00:58I want to find out what makes these super small creatures
0:00:58 > 0:01:02some of the most successful animals on the planet.
0:01:02 > 0:01:03HE CHUCKLES
0:01:03 > 0:01:07That is brilliant! This is the first time I've seen anything like this.
0:01:11 > 0:01:14We're going to travel the world to meet the leading experts
0:01:14 > 0:01:18on these incredible creatures and discover the secrets
0:01:18 > 0:01:21behind these pint-sized superstars,
0:01:21 > 0:01:26revealing the huge benefits that being small can bring,
0:01:26 > 0:01:29as well as the challenges that small creatures face
0:01:29 > 0:01:31and the ingenious ways they overcome them.
0:01:31 > 0:01:33Look at that.
0:01:33 > 0:01:35And I'll also show you how some miniature animals
0:01:35 > 0:01:38punch way above their weight.
0:01:39 > 0:01:43They've all turned being small into a HUGE advantage.
0:01:43 > 0:01:45And we're going to find out why.
0:01:59 > 0:02:02This is a leaf chameleon.
0:02:02 > 0:02:04It lives in northern Madagascar
0:02:04 > 0:02:06and as its name suggests,
0:02:06 > 0:02:09it goes about the leaf litter eating tiny insects.
0:02:10 > 0:02:14Weighing less than a quarter of a gram, it's minuscule
0:02:14 > 0:02:17and one of the smallest lizards in the world.
0:02:17 > 0:02:23Pound for pound, they are 3,500 times smaller than this guy.
0:02:25 > 0:02:26The Parson's chameleon.
0:02:27 > 0:02:29The weight difference between them
0:02:29 > 0:02:33is the same between me and ten elephants.
0:02:33 > 0:02:35I can't get them too close together
0:02:35 > 0:02:37because the Parson's chameleon's prey
0:02:37 > 0:02:40is bigger than the leaf chameleon.
0:02:40 > 0:02:43But despite the size difference,
0:02:43 > 0:02:45these two are remarkably similar.
0:02:45 > 0:02:49They both have all the classic chameleon characteristics...
0:02:51 > 0:02:54..independently moving, rotating eyes...
0:02:56 > 0:02:58..specialised gripping feet
0:02:58 > 0:03:00with toes that point forward and backwards...
0:03:01 > 0:03:06..and a super-powered tongue that shoots out and suckers prey.
0:03:09 > 0:03:13The leaf chameleon has all the same complex attributes,
0:03:13 > 0:03:16just miniaturised.
0:03:16 > 0:03:18But why?
0:03:18 > 0:03:21Nothing ever happens by accident in nature.
0:03:21 > 0:03:26This guy obviously wouldn't be this size if it didn't make sense.
0:03:26 > 0:03:29If anything, it means that it's easier to hide,
0:03:29 > 0:03:31it needs less food and less space.
0:03:32 > 0:03:33So, by being small,
0:03:33 > 0:03:38this chameleon has overcome some of life's biggest challenges -
0:03:38 > 0:03:40finding food, keeping out of danger
0:03:40 > 0:03:44and finding its own space in this big, wide world.
0:03:45 > 0:03:46And it's not alone.
0:03:51 > 0:03:55Animals all over the globe are using their small size
0:03:55 > 0:03:57to solve life's problems.
0:04:00 > 0:04:02And one of the biggest problems
0:04:02 > 0:04:06is finding enough food in a fiercely competitive world.
0:04:12 > 0:04:14The island of Madagascar,
0:04:14 > 0:04:17home to over 100 species of lemur.
0:04:20 > 0:04:23Just like us, they're primates,
0:04:23 > 0:04:25and they come in all different shapes,
0:04:25 > 0:04:28colours and sizes.
0:04:31 > 0:04:34But I'm here to meet the smallest.
0:04:36 > 0:04:37Mouse lemurs.
0:04:39 > 0:04:41They're barely the size of an apple.
0:04:47 > 0:04:50Now, this guy probably weighs about 70g
0:04:50 > 0:04:53which is surprising when you think that the largest primates,
0:04:53 > 0:04:57the gorilla, weighs over 3,000 times as much.
0:04:57 > 0:04:59And even the largest lemur, the indri,
0:04:59 > 0:05:02is still over 100 times this lemur's weight.
0:05:04 > 0:05:08Despite this, when it comes to a special source of food,
0:05:08 > 0:05:09they come out on top.
0:05:14 > 0:05:17All lemurs eat fruits, seeds and leaves.
0:05:19 > 0:05:22And with so much competition for the tastiest treats,
0:05:22 > 0:05:27you'd think the tiny mouse lemur would be at the back of the queue.
0:05:27 > 0:05:31But this little lemur uses its size to its advantage.
0:05:35 > 0:05:37Whilst other lemurs are just too heavy...
0:05:39 > 0:05:40..because they're small,
0:05:40 > 0:05:43mouse lemurs can head straight for the ends
0:05:43 > 0:05:45of the highest, flimsiest branches.
0:05:46 > 0:05:48And the special food they're after?
0:05:49 > 0:05:51Flowers.
0:05:51 > 0:05:54Rich in sugars, they make one of the best meals
0:05:54 > 0:05:58and these tiny lemurs get to them with ease.
0:06:01 > 0:06:03Their larger, heavier cousins
0:06:03 > 0:06:06have to compete for food on bigger branches...
0:06:08 > 0:06:10..but mouse lemurs avoid the competition
0:06:10 > 0:06:12by reaching the unreachable.
0:06:19 > 0:06:22Lemurs aren't the only ones using their size to secure a snack.
0:06:25 > 0:06:27On the other side of the globe,
0:06:27 > 0:06:29in the cloud forests of Ecuador,
0:06:29 > 0:06:33another tiny animal is muscling in on its next meal.
0:06:39 > 0:06:42Hummingbirds are the smallest birds on the planet.
0:06:44 > 0:06:47They are incredibly appealing
0:06:47 > 0:06:49and when it comes to viral videos,
0:06:49 > 0:06:51they are an internet sensation.
0:06:54 > 0:06:58The smallest are the same size as a large bee.
0:06:58 > 0:07:01And take a look at how tiny their nests are.
0:07:04 > 0:07:07Hummingbirds are well-known for the incredible speed
0:07:07 > 0:07:09with which they move their wings.
0:07:10 > 0:07:13They can beat them up to 15 times a second.
0:07:16 > 0:07:20But it uses a huge amount of energy, so they feed on sugar-rich nectar.
0:07:23 > 0:07:26And because they need to consume a lot of calories,
0:07:26 > 0:07:30access to the best flowers is worth fighting for.
0:07:33 > 0:07:35But in this world of tiny birds,
0:07:35 > 0:07:40size still matters and it turns out that being even smaller
0:07:40 > 0:07:41is even better.
0:07:43 > 0:07:48The booted racket-tail is tiny, no bigger than your little finger.
0:07:50 > 0:07:54So, while the big boys are fighting over the flowers,
0:07:54 > 0:07:57the smaller, more agile racket-tail can sneak in...
0:07:59 > 0:08:03..feed and fly off before being spotted by the bigger birds.
0:08:05 > 0:08:08A cheeky move proving that being the smallest of the small
0:08:08 > 0:08:12can sometimes offer big payoffs in the fight for food.
0:08:17 > 0:08:21Going unseen is another huge advantage of being miniature.
0:08:23 > 0:08:26And it's something that my next super small animal
0:08:26 > 0:08:28has taken to the extreme.
0:08:32 > 0:08:36The ocean is a perilous place for little creatures.
0:08:37 > 0:08:41They're easy pickings for hundreds of larger predators.
0:08:43 > 0:08:47In fact, less than 1% of fish reach maturity.
0:08:48 > 0:08:52So, to survive, you need a strategy.
0:08:56 > 0:09:00On the reefs of Australia and Southeast Asia,
0:09:00 > 0:09:01a super-small creature,
0:09:01 > 0:09:04living in this sea fan coral,
0:09:04 > 0:09:07has just that.
0:09:07 > 0:09:10But first, we have to find it.
0:09:16 > 0:09:19The pygmy seahorse,
0:09:19 > 0:09:21the smallest of its kind.
0:09:23 > 0:09:27So small they could fit on your fingernail...
0:09:27 > 0:09:29or the end of a pencil.
0:09:31 > 0:09:35Truly tiny and perfectly camouflaged to their coral home.
0:09:35 > 0:09:40Which makes these little seahorses almost impossible to spot.
0:09:40 > 0:09:46In fact, they were unknown to science until 1969
0:09:46 > 0:09:49when they were discovered completely by accident.
0:09:49 > 0:09:52Nobody knew they existed until one of the corals was collected
0:09:52 > 0:09:54and when they brought it up to look at the coral,
0:09:54 > 0:09:56they saw something small and moving on it.
0:09:56 > 0:09:59And when they looked closely, they realised it was a tiny seahorse
0:09:59 > 0:10:01that looked exactly like the arms of the coral.
0:10:02 > 0:10:06These little seahorses are actually born smooth and brown.
0:10:07 > 0:10:12But as they develop, they transform to match the colour and texture
0:10:12 > 0:10:14of the sea fan they land on,
0:10:14 > 0:10:17regardless of the colour of their parents.
0:10:17 > 0:10:19Within 24 hours,
0:10:19 > 0:10:20they would clearly change colour
0:10:20 > 0:10:23and change in characteristics to match that coral,
0:10:23 > 0:10:26and that was a pretty amazing thing to see happen.
0:10:27 > 0:10:30These miniature marvels then spend their entire life
0:10:30 > 0:10:33on that one piece of coral,
0:10:33 > 0:10:35which can be over a metre tall and wide.
0:10:39 > 0:10:41When you're that small,
0:10:41 > 0:10:44that's plenty of space to make a home.
0:10:44 > 0:10:47The pygmy seahorse has evolved to be so small to take advantage
0:10:47 > 0:10:48of a piece of real estate
0:10:48 > 0:10:51that nobody else is really taking advantage of.
0:10:51 > 0:10:55In fact, there could be up to 28 pairs of seahorses
0:10:55 > 0:10:57living on one sea fan...
0:10:58 > 0:11:00..hidden in plain sight.
0:11:02 > 0:11:05But even a secretive seahorse needs to eat.
0:11:08 > 0:11:10The pygmy seahorse is a predatory fish,
0:11:10 > 0:11:13just like the massive great white shark.
0:11:13 > 0:11:15Now, you might think of the shark as having it better,
0:11:15 > 0:11:17but they have to travel hundreds
0:11:17 > 0:11:19if not thousands of miles in search of food,
0:11:19 > 0:11:25whereas pygmy seahorses just wait for a meal to come to them.
0:11:27 > 0:11:30They catch plankton as it passes by,
0:11:30 > 0:11:34or pick it from the polyps of the coral,
0:11:34 > 0:11:37while their bigger relatives, like the weedy sea dragon,
0:11:37 > 0:11:39have to go out in search of food,
0:11:39 > 0:11:42putting themselves in the paths of predators.
0:11:45 > 0:11:48This free delivery service means the pygmy seahorse
0:11:48 > 0:11:50never has to leave home...
0:11:52 > 0:11:54..and that's pretty smart.
0:11:55 > 0:11:58Being miniature means that the pygmy seahorse
0:11:58 > 0:12:01can live in a world that is also miniature.
0:12:03 > 0:12:06When it comes to staying out of sight,
0:12:06 > 0:12:09being small offers a huge advantage.
0:12:09 > 0:12:14But do small animals sacrifice strength and power in return?
0:12:18 > 0:12:21Surely the Goliaths of the animal world have the upper hand
0:12:21 > 0:12:24in terms of sheer muscle and might?
0:12:27 > 0:12:29Well, not quite.
0:12:33 > 0:12:35When it comes to brawn,
0:12:35 > 0:12:38it's the little guys that pack the most serious punch.
0:12:40 > 0:12:43I'm in the African bush to meet one of the most impressive.
0:12:45 > 0:12:48You've probably guessed that this little insect is a dung beetle.
0:12:49 > 0:12:53Now, of course, their diet may be unsavoury to us,
0:12:53 > 0:12:55but it clearly works for them.
0:12:55 > 0:12:59Not only have they evolved to feast on the dung of other animals,
0:12:59 > 0:13:03but they are proportionately one of the strongest animals alive.
0:13:05 > 0:13:07Some of these high rollers
0:13:07 > 0:13:11can push balls that are ten times their own weight,
0:13:11 > 0:13:13even up steep hills.
0:13:15 > 0:13:18A Herculean effort with a huge payoff.
0:13:19 > 0:13:22A single ball of dung can be enough to feed them
0:13:22 > 0:13:24for the rest of their lives.
0:13:29 > 0:13:32And they're not the only super-strong insects.
0:13:34 > 0:13:37These are leafcutter ants.
0:13:37 > 0:13:39They carry pieces of leaf
0:13:39 > 0:13:42up to 50 times their own body weight.
0:13:44 > 0:13:48Now, that would be like me trying to carry a van on my back.
0:13:50 > 0:13:52In terms of weight-to-strength ratio,
0:13:52 > 0:13:55this ant is stronger than an elephant.
0:13:57 > 0:14:00In fact, measured this way,
0:14:00 > 0:14:03all of the strongest animals on Earth are tiny
0:14:03 > 0:14:06and it's all to do with physics.
0:14:09 > 0:14:12The Scaling Law means that if you doubled all the dimensions
0:14:12 > 0:14:16of any living thing, it would become eight times heavier.
0:14:19 > 0:14:21So, weight increases more quickly
0:14:21 > 0:14:23than dimensions or size.
0:14:24 > 0:14:28Because strength is determined by how big your muscles are
0:14:28 > 0:14:29compared to your weight,
0:14:29 > 0:14:33animals get heavier more quickly than they get stronger.
0:14:36 > 0:14:38What's more, larger animals
0:14:38 > 0:14:42have to use more energy simply supporting all their bulk.
0:14:45 > 0:14:47So, smaller, lighter animals
0:14:47 > 0:14:51are proportionately stronger than big animals.
0:14:55 > 0:14:58And one of the strongest animals in the world
0:14:58 > 0:15:00is only the size of a peanut.
0:15:03 > 0:15:05The bull-headed dung beetle.
0:15:10 > 0:15:13Whereas an elephant can't even pull twice its own weight...
0:15:15 > 0:15:18..scientists found that the bull-headed dung beetle
0:15:18 > 0:15:20can pull a staggering
0:15:20 > 0:15:231,141 times their own weight.
0:15:26 > 0:15:27Now, that is the equivalent
0:15:27 > 0:15:31of me pulling six fully-loaded double-decker buses.
0:15:32 > 0:15:36Amazingly, this mighty strength isn't for pushing balls of dung.
0:15:37 > 0:15:40They don't roll their dung away to bury it.
0:15:40 > 0:15:47Instead a pair dig a tunnel directly underneath a big fresh pat
0:15:47 > 0:15:50where the females lay their eggs.
0:15:50 > 0:15:52So, why, then, are they so strong?
0:15:53 > 0:15:55Well, digging might be one reason.
0:15:56 > 0:15:58But there's another more important one.
0:16:00 > 0:16:04A rogue male is searching for a mate down an already-occupied tunnel.
0:16:06 > 0:16:10The horned male needs to keep his mate to himself.
0:16:12 > 0:16:15Intruders have to be pushed out with brute force.
0:16:19 > 0:16:22In their world, strength is king.
0:16:27 > 0:16:30These animals have all found fantastic ways
0:16:30 > 0:16:34of using their small size to solve the big problems
0:16:34 > 0:16:36that all animals face.
0:16:37 > 0:16:41But being small does make some things more difficult.
0:16:43 > 0:16:45I'm going to investigate some of the challenges
0:16:45 > 0:16:49that the smallest animals face because of their size
0:16:49 > 0:16:53and reveal the many ways they've overcome them to succeed.
0:16:56 > 0:16:59One of the biggest problems about being small is temperature.
0:17:01 > 0:17:05Small animals get hot and cold much faster than big animals.
0:17:07 > 0:17:10And this time-lapse footage demonstrates this perfectly.
0:17:12 > 0:17:16There's a good reason why the ice cube on the left is melting faster.
0:17:16 > 0:17:18Because it's smaller.
0:17:19 > 0:17:22It may seem obvious that a small ice cube
0:17:22 > 0:17:24would melt quicker than a large one,
0:17:24 > 0:17:27but have you ever stopped to consider why that happens?
0:17:27 > 0:17:31Well, it all comes down to the amount of surface area an object has
0:17:31 > 0:17:35in comparison to its volume - the physical space that it takes up.
0:17:35 > 0:17:39Because smaller objects have a greater surface area
0:17:39 > 0:17:42in comparison to their volume than larger objects,
0:17:42 > 0:17:43they lose heat quicker.
0:17:47 > 0:17:50That same principle applies to animals too.
0:17:52 > 0:17:55If you're tiny, dealing with temperature extremes
0:17:55 > 0:17:56is a big problem.
0:17:59 > 0:18:04But this hasn't stopped small animals living in extreme places
0:18:04 > 0:18:07because they've found some creative solutions.
0:18:09 > 0:18:11This shovel-snouted lizard
0:18:11 > 0:18:15lives in the blistering heat of the Namibian desert.
0:18:15 > 0:18:19To stop his feet burning on the sand, he's learnt to dance.
0:18:23 > 0:18:25His neighbour, the silver ant,
0:18:25 > 0:18:28has evolved to grow a fine covering of shiny hair
0:18:28 > 0:18:32to reflect the scorching heat.
0:18:32 > 0:18:34But even so, they can only survive
0:18:34 > 0:18:38for up to ten minutes in the midday sun.
0:18:41 > 0:18:44But there's one tiny Namibian mammal
0:18:44 > 0:18:46that's mastered desert survival
0:18:46 > 0:18:49with an impressively large adaptation.
0:18:55 > 0:18:57The fennec is an extraordinary fox.
0:18:59 > 0:19:01Weighing less than a bag of sugar,
0:19:01 > 0:19:04they are the smallest member of the fox family.
0:19:05 > 0:19:09But they've got the biggest ear-to-body ratio of any carnivore.
0:19:11 > 0:19:15These cunning foxes use their oversized ears to radiate body heat.
0:19:16 > 0:19:18Because they're so large and thin,
0:19:18 > 0:19:21they quickly lose heat to the surrounding air
0:19:21 > 0:19:22which cools down their blood
0:19:22 > 0:19:26and stops them from overheating in the searing Sahara sun.
0:19:30 > 0:19:328,000 miles away in Argentina,
0:19:32 > 0:19:36there's one colourful little animal that's taken desert dwelling
0:19:36 > 0:19:38to a whole new level.
0:19:38 > 0:19:41That is, when you can find one.
0:19:41 > 0:19:44I have been working in the desert in Argentina for 15 years
0:19:44 > 0:19:46and I have never seen a pink fairy.
0:19:48 > 0:19:51They would tell me that Mendoza was a hot spot,
0:19:51 > 0:19:54so I wandered around in the desert,
0:19:54 > 0:19:56looking for pink fairies and just couldn't find them.
0:19:59 > 0:20:01No, not an actual fairy,
0:20:01 > 0:20:04a pink fairy armadillo.
0:20:07 > 0:20:10With its pink back and fluffy white body,
0:20:10 > 0:20:15it's one of the oddest and strangely endearing animals on the planet.
0:20:18 > 0:20:21They are the world's smallest armadillo,
0:20:21 > 0:20:24250 times lighter than their largest relatives.
0:20:26 > 0:20:29They're so elusive, they're only captured on camera
0:20:29 > 0:20:32by locals who have stumbled across them by accident.
0:20:34 > 0:20:37It is very difficult to see a pink fairy armadillo
0:20:37 > 0:20:39because they live underground.
0:20:39 > 0:20:42Most sightings that we have recorded
0:20:42 > 0:20:45are from pink fairy armadillos that were crossing a road,
0:20:45 > 0:20:47so we suspect that they are digging
0:20:47 > 0:20:51and they find a hard underground that they cannot dig through.
0:20:54 > 0:20:58Living underground is a clever way to keep cool.
0:21:01 > 0:21:03Unlike many of their larger relatives,
0:21:03 > 0:21:05they don't even emerge to feed.
0:21:07 > 0:21:10We don't even know if they are rare or if they are very abundant.
0:21:10 > 0:21:13We simply don't know because we can't find them.
0:21:15 > 0:21:19But why do these compact critters look so different to their cousins?
0:21:20 > 0:21:22When you look at these two armadillos,
0:21:22 > 0:21:25the most striking difference, other than their size,
0:21:25 > 0:21:27is their shell.
0:21:27 > 0:21:30This bigger one has what many of us would consider to be
0:21:30 > 0:21:33the classic armoured armadillo shell,
0:21:33 > 0:21:36which pretty much covers its entire body.
0:21:36 > 0:21:38Whereas the shell of the pink fairy armadillo
0:21:38 > 0:21:40only covers the top of its back
0:21:40 > 0:21:43and, in fact, it's only connected along the spine.
0:21:44 > 0:21:46So, it's not really armour for defence,
0:21:46 > 0:21:50but instead, it's another perfectly pint-sized solution
0:21:50 > 0:21:52to control their temperature.
0:21:52 > 0:21:54It's thought that when they want to cool down,
0:21:54 > 0:21:56they pump blood into this shell,
0:21:56 > 0:22:00allowing the heat to be given off to the surrounding environment.
0:22:00 > 0:22:01It's a bit like a hot water bottle -
0:22:01 > 0:22:05as the surroundings get warmer, it gets cooler.
0:22:05 > 0:22:07But when they want to do the opposite and stay warm,
0:22:07 > 0:22:09they drain blood out of the shell
0:22:09 > 0:22:13and back into their furry, insulated bodies.
0:22:15 > 0:22:18It's a fabulous way of keeping their body temperature in check
0:22:18 > 0:22:21and the reason why they're pink.
0:22:21 > 0:22:25Their blood vessels are so close to the surface, they show through.
0:22:27 > 0:22:33Underground, their unusual body also performs another fantastic function.
0:22:33 > 0:22:35Pink fairy armadillos have a rump plate,
0:22:35 > 0:22:37or it's sometimes called a butt plate.
0:22:37 > 0:22:42It's very strong and this is used to compact the soil.
0:22:43 > 0:22:46It starts digging forward and then it backs up
0:22:46 > 0:22:49and it compacts the sand behind it.
0:22:51 > 0:22:54These miniature Argentinian architects
0:22:54 > 0:22:56have carved out a very special niche.
0:22:59 > 0:23:03By trading in their protective shell, they've given up a lot.
0:23:03 > 0:23:05But for this subterranean explorer,
0:23:05 > 0:23:09it works because they rarely ever make an appearance above ground
0:23:09 > 0:23:13and that's why you hardly ever see a pink fairy in the desert.
0:23:15 > 0:23:20Temperature control isn't the only problem that tiny creatures face.
0:23:22 > 0:23:26It's a big world out there and if you've got very short legs,
0:23:26 > 0:23:28it takes much longer to get around.
0:23:30 > 0:23:33This is a money spider.
0:23:33 > 0:23:35It's only about five millimetres long.
0:23:37 > 0:23:40They're found all over the UK,
0:23:40 > 0:23:44but these tiny arachnids are also intrepid explorers,
0:23:44 > 0:23:46capable of covering hundreds of miles...
0:23:48 > 0:23:52..because they've turned their size to their advantage
0:23:52 > 0:23:55and made a home in almost every continent.
0:23:57 > 0:23:59So, how has such a tiny creature
0:23:59 > 0:24:02colonised the far corners of the world?
0:24:02 > 0:24:06It has to do with something that all spiders produce
0:24:06 > 0:24:08and that...is silk.
0:24:10 > 0:24:12It's the spiders' secret weapon.
0:24:14 > 0:24:16They use it to build webs...
0:24:19 > 0:24:20..lay traps...
0:24:25 > 0:24:28..and some even use it to ensnare...
0:24:30 > 0:24:32..or lasso their prey.
0:24:39 > 0:24:44But the smaller spiders use their silk in a very special way.
0:24:48 > 0:24:49When they want to travel,
0:24:49 > 0:24:53they send out a stream of silk which they use to catch the wind...
0:24:55 > 0:24:59..and lift themselves up into the air, like a parachute.
0:25:01 > 0:25:06It's called "ballooning" and it enables small spiders
0:25:06 > 0:25:08to migrate hundreds of miles,
0:25:08 > 0:25:11carried by the wind.
0:25:14 > 0:25:18But colonising continents means crossing oceans
0:25:18 > 0:25:21and they can't control where they land,
0:25:21 > 0:25:25so what happens if an unfortunate spider lands on water?
0:25:25 > 0:25:28Surely, that's the end of its adventures?
0:25:30 > 0:25:34Far from it, because these tiny spiders have a solution
0:25:34 > 0:25:38that has made them record-breaking long-distance travellers.
0:25:39 > 0:25:42Dr Sara Goodacre and a team of scientists
0:25:42 > 0:25:44have been studying these tiny explorers...
0:25:44 > 0:25:47- So, we've got one spider, there. - Here it goes.
0:25:47 > 0:25:50..and she's going to show me their special skill.
0:25:52 > 0:25:54So, what you can see is that it's floating,
0:25:54 > 0:25:56it's definitely not sinking.
0:25:56 > 0:25:59It's floating across the surface of the water.
0:25:59 > 0:26:00Because they're so light,
0:26:00 > 0:26:04their weight is supported by the surface tension of the water.
0:26:04 > 0:26:06Their legs make tiny dents in it,
0:26:06 > 0:26:09but, miraculously, don't break through.
0:26:09 > 0:26:13- If you look... Look, it's starting to run.- Isn't that amazing?
0:26:13 > 0:26:17So, for something that's really not supposed to survive on water at all,
0:26:17 > 0:26:19- it's doing rather well.- Yeah.
0:26:20 > 0:26:21But introduce a breeze...
0:26:21 > 0:26:23OK.
0:26:23 > 0:26:25..and they do something even more astonishing.
0:26:28 > 0:26:31- Let's have a look. Can you see those front two legs?- Yes!
0:26:37 > 0:26:42This tiny spider is using its raised legs to catch the wind,
0:26:42 > 0:26:43just like a sail.
0:26:45 > 0:26:49There you go. You can see how, all of a sudden, they go so much faster.
0:26:50 > 0:26:54So, it's all about timing and sensing what the wind is doing?
0:26:54 > 0:26:56Once they make the decision to go,
0:26:56 > 0:26:59they're really at the mercy of the winds.
0:26:59 > 0:27:01And what's even more incredible
0:27:01 > 0:27:04is that different spiders have different sailing styles.
0:27:09 > 0:27:12- That one's doing more with its back legs.- Yeah...
0:27:16 > 0:27:19These are the same species and they're doing different things.
0:27:21 > 0:27:24Sometimes they'll use four legs, sometimes two,
0:27:24 > 0:27:27sometimes the front legs, sometimes the back legs.
0:27:27 > 0:27:28They've got a range of options.
0:27:31 > 0:27:34I guess that kind of gives them their own little personalities.
0:27:34 > 0:27:36Absolutely. And to me, really, it makes perfect sense.
0:27:36 > 0:27:38One strategy doesn't always win.
0:27:43 > 0:27:45By sailing and ballooning in this way,
0:27:45 > 0:27:50these tiny spiders can travel over 40 miles in a single day.
0:27:52 > 0:27:54By utilising the power of the wind,
0:27:54 > 0:27:58they can cross not only whole continents, but the oceans too,
0:27:58 > 0:28:00using virtually no energy.
0:28:00 > 0:28:03And that is what has enabled these tiny spiders
0:28:03 > 0:28:07to colonise almost every part of the globe.
0:28:09 > 0:28:12But not all small animals are international travellers.
0:28:12 > 0:28:18And sometimes, just getting from A to B can be a struggle.
0:28:20 > 0:28:23In the forests of New England in North America
0:28:23 > 0:28:27lives a little squirrel that can fit in the palm of your hand.
0:28:29 > 0:28:33It needs to move from tree to tree in search of food,
0:28:33 > 0:28:36but the trees are widely spaced
0:28:36 > 0:28:40and the forest floor is a dangerous place.
0:28:40 > 0:28:42So, what's a squirrel to do?
0:28:46 > 0:28:48Fly, of course!
0:28:55 > 0:28:58They have a furry parachute-like membrane
0:28:58 > 0:29:00between their wrists and ankles
0:29:00 > 0:29:03that they use to glide effortlessly between trees.
0:29:07 > 0:29:12They're only a quarter of the size of a common grey squirrel,
0:29:12 > 0:29:16but this in-built wingsuit means they can travel much further,
0:29:16 > 0:29:19covering up to 70 metres in a single flight.
0:29:21 > 0:29:26This saves energy and allows them to avoid predators on the ground.
0:29:32 > 0:29:34When trees are close together,
0:29:34 > 0:29:36like in the jungles of Liberia, West Africa,
0:29:36 > 0:29:39travel problems are different.
0:29:40 > 0:29:45Animals like hippos would never be able to get through the trees...
0:29:45 > 0:29:47unless they shrunk.
0:29:48 > 0:29:51And that's exactly what pygmy hippos have done.
0:29:53 > 0:29:55They've evolved a shape and size
0:29:55 > 0:29:59to help them move through the dense jungle.
0:29:59 > 0:30:02It's made for an adorable small animal
0:30:02 > 0:30:05with even more adorable babies
0:30:05 > 0:30:09that have proved to be internet celebrities.
0:30:09 > 0:30:12This pygmy hippo really does look like...
0:30:12 > 0:30:15Hello! ..a scaled-down version of a common hippo.
0:30:17 > 0:30:19But as well as a reduction in size -
0:30:19 > 0:30:21it's about ten times smaller -
0:30:21 > 0:30:23there are a number of other differences
0:30:23 > 0:30:26that make it really well adapted to life in the jungle.
0:30:30 > 0:30:32As well as having much bulkier bodies,
0:30:32 > 0:30:36common hippos' spines are almost parallel to the ground,
0:30:36 > 0:30:39whereas pygmy hippos' backs slope downwards,
0:30:39 > 0:30:42making it easier for them to move through the dense forests.
0:30:44 > 0:30:47While pygmy hippos' eyes are on the sides of their head
0:30:47 > 0:30:49for navigating the jungle floor,
0:30:49 > 0:30:52common hippo eyes are on the tops of their heads,
0:30:52 > 0:30:57for keeping a look out in the water where they spend most of their time,
0:30:57 > 0:31:01which is also why common hippos have webbed feet and pygmies don't.
0:31:05 > 0:31:07Pygmy hippos like this one
0:31:07 > 0:31:10probably weigh about three times as much as I do
0:31:10 > 0:31:14and that just comes down to a diet of leaves, grasses and fruit.
0:31:15 > 0:31:18So, even though they aren't small in terms of sheer weight,
0:31:18 > 0:31:22in comparison to the common hippo, they are miniature.
0:31:23 > 0:31:27Their size and shape means they can effortlessly move
0:31:27 > 0:31:29through the dense forest almost unseen.
0:31:31 > 0:31:35So, by being well adapted to their jungle environment,
0:31:35 > 0:31:39these 300kg animals have almost become invisible.
0:31:43 > 0:31:45Small animals have conquered the problems
0:31:45 > 0:31:46of getting around brilliantly.
0:31:48 > 0:31:51But what about raising the next generation?
0:31:51 > 0:31:54No matter how small you are,
0:31:54 > 0:31:57your offspring will inevitably be even smaller.
0:31:58 > 0:32:01So, if you're pushing the limits of what's possible as an adult,
0:32:01 > 0:32:05having babies that are big enough to survive is going to be a problem.
0:32:06 > 0:32:09But as we'll see, it's another example of how small creatures
0:32:09 > 0:32:11have risen to the challenge.
0:32:11 > 0:32:14This cool little thing
0:32:14 > 0:32:17might look like an earthworm,
0:32:17 > 0:32:20but when you look closely,
0:32:20 > 0:32:23you'll see that it's actually a very tiny snake,
0:32:23 > 0:32:28complete with super small scales and a miniaturised fork tongue.
0:32:29 > 0:32:35These worm-like snakes are found all over the Americas, Asia and Africa.
0:32:35 > 0:32:41This one is a brahminy blind snake and it weighs less than a gram.
0:32:41 > 0:32:43Which is mind-boggling when you consider
0:32:43 > 0:32:47that the largest snakes can weigh more than a fully-grown human.
0:32:49 > 0:32:51And this isn't even the smallest species.
0:32:54 > 0:33:00Thinner than a piece of spaghetti, these thread snakes are even tinier.
0:33:00 > 0:33:03They're 700 times smaller than a large python
0:33:03 > 0:33:07and weigh a staggering 100,000 times less.
0:33:10 > 0:33:13Found only on the Caribbean island of Martinique,
0:33:13 > 0:33:15they've tapped into a food source
0:33:15 > 0:33:18that bigger animals aren't competing for...
0:33:21 > 0:33:24..the eggs and larvae of ants and termites.
0:33:27 > 0:33:31So, their size is an advantage when finding food,
0:33:31 > 0:33:35but being so tiny is an enormous challenge when reproducing.
0:33:37 > 0:33:40Most snakes lay large clutches of eggs -
0:33:40 > 0:33:43in some cases, up to 100 -
0:33:43 > 0:33:46all in the hope that at least some of their hatchlings survive.
0:33:51 > 0:33:54Because they're so short and thin,
0:33:54 > 0:33:57Martinique thread snakes lay just one egg at a time.
0:33:59 > 0:34:01And even though it's only one centimetre long,
0:34:01 > 0:34:04it's still huge compared to the snake's tiny body.
0:34:06 > 0:34:08And that's because when it hatches,
0:34:08 > 0:34:10the single baby snake is already
0:34:10 > 0:34:12half the size of the adults.
0:34:14 > 0:34:17That's in stark contrast to bigger snakes whose hatchlings
0:34:17 > 0:34:19are only around a tenth of their size.
0:34:23 > 0:34:26So, strangely, for their size,
0:34:26 > 0:34:29these tiny snakes have enormous babies.
0:34:30 > 0:34:34And these babies can eat the same food as their parents
0:34:34 > 0:34:36as soon as they're born.
0:34:39 > 0:34:43But this is by no means the only tactic employed by small animals.
0:34:46 > 0:34:49This little critter is a tenrec -
0:34:49 > 0:34:52a hedgehog-like mammal found in Madagascar.
0:34:54 > 0:34:56They feed on insects on the forest floor
0:34:56 > 0:34:59and like all small animals that live on the ground,
0:34:59 > 0:35:02they're vulnerable to predators, even with their protective spines.
0:35:04 > 0:35:06So, to survive as a species,
0:35:06 > 0:35:09tenrecs have taken the absolute opposite approach to babymaking.
0:35:11 > 0:35:14They have more offspring than any other mammal,
0:35:14 > 0:35:17with as many as 32 in a litter.
0:35:18 > 0:35:21And, remarkably, the young can breed themselves
0:35:21 > 0:35:23when they're just 35 days old.
0:35:25 > 0:35:27This brilliant solution means that,
0:35:27 > 0:35:30in contrast to big animals like elephants,
0:35:30 > 0:35:32that are pregnant for nearly two years,
0:35:32 > 0:35:36when conditions are good, tenrecs can have lots of babies.
0:35:42 > 0:35:44But when it comes to bringing up baby,
0:35:44 > 0:35:48there's one species so minuscule it pushes the physical limits
0:35:48 > 0:35:50of being able to reproduce at all.
0:35:55 > 0:36:00Inside this phial is a specimen of the smallest fish in the world.
0:36:03 > 0:36:04In fact, it's so small that it can live
0:36:04 > 0:36:07in nothing more than a mere puddle.
0:36:07 > 0:36:09But miniaturisation on this scale
0:36:09 > 0:36:13comes at an almost unbelievable price.
0:36:16 > 0:36:22Found only in the swamps of Sumatra, Paedocypris progenetica are so rare
0:36:22 > 0:36:25they don't even have a common name.
0:36:25 > 0:36:28They live in a drought-prone world,
0:36:28 > 0:36:30where water comes and goes,
0:36:30 > 0:36:34and for a fish, THAT is a serious challenge.
0:36:37 > 0:36:41The adults are less than eight millimetres long,
0:36:41 > 0:36:44smaller than a 5p piece
0:36:44 > 0:36:47and they have adapted to be this small so a shoal can survive
0:36:47 > 0:36:49in the smallest puddle of water.
0:36:51 > 0:36:55But how is something this tiny still able to bear young?
0:36:58 > 0:37:00The world's smallest fish have evolved
0:37:00 > 0:37:04an astonishingly dramatic physical solution.
0:37:04 > 0:37:08To understand, we have to look at a more average fish.
0:37:09 > 0:37:12The zebrafish is a common aquarium fish
0:37:12 > 0:37:15that scientists often use as a comparison.
0:37:15 > 0:37:18They have a very typical skeleton,
0:37:18 > 0:37:20fully developed bones,
0:37:20 > 0:37:21complete with long ribs,
0:37:21 > 0:37:23and a thick casing around the brain.
0:37:25 > 0:37:28The tiny Paedocypris skeleton is very different.
0:37:28 > 0:37:30The ribs are hardly developed
0:37:30 > 0:37:32and they don't have a proper skull,
0:37:32 > 0:37:34so their brains are actually exposed.
0:37:36 > 0:37:38But here's the weird thing.
0:37:38 > 0:37:41They look remarkably like a zebrafish
0:37:41 > 0:37:43that hasn't fully developed.
0:37:43 > 0:37:44A juvenile.
0:37:46 > 0:37:48And that's no coincidence.
0:37:48 > 0:37:52Because Paedocypris are the Peter Pans of the fish world.
0:37:52 > 0:37:55The fish that never really grows up.
0:37:59 > 0:38:02It's only their reproductive organs that really mature,
0:38:02 > 0:38:04so they can create the next generation
0:38:04 > 0:38:08while keeping as compact as possible to survive through droughts.
0:38:10 > 0:38:14An extreme solution that's extremely clever.
0:38:22 > 0:38:24By finding extraordinary ways
0:38:24 > 0:38:27to overcome the physical barriers of their size,
0:38:27 > 0:38:31all these animals reap the benefits that being little brings.
0:38:33 > 0:38:35But, finally,
0:38:35 > 0:38:37I want to introduce you to some animals
0:38:37 > 0:38:40that refuse to be pigeonholed as small
0:38:40 > 0:38:44and manage to reap the rewards of much larger animals
0:38:44 > 0:38:46in a host of different ways.
0:38:48 > 0:38:54First up, a feisty animal that's found a way of becoming big.
0:38:54 > 0:38:58This is a fire ant and I'm handling it with care
0:38:58 > 0:39:01because they pack a pretty nasty sting.
0:39:02 > 0:39:05Now, as much as they might not be that friendly to me,
0:39:05 > 0:39:08they are, in fact, social insects
0:39:08 > 0:39:10and that means that if one were to sting me,
0:39:10 > 0:39:13that would send a signal to the rest of the colony and, within minutes,
0:39:13 > 0:39:17I could have an entire army on the attack.
0:39:22 > 0:39:25This cooperation is key to overcoming their small size
0:39:25 > 0:39:28and it's crucial where they live.
0:39:30 > 0:39:34They're native to the rainforests of Central and South America
0:39:34 > 0:39:37and with rainforests comes rain.
0:39:38 > 0:39:39Lots of it.
0:39:39 > 0:39:42THUNDER CRASHES
0:39:42 > 0:39:47In fact, one of the biggest problems they face in their underground homes
0:39:47 > 0:39:49is the risk of flooding.
0:39:50 > 0:39:53So, let's see how they deal with getting wet.
0:39:55 > 0:39:58If I gently place this ant in this tank of water...
0:40:00 > 0:40:03We can see that it's not doing particularly well.
0:40:03 > 0:40:08Their exoskeletons do repel water, but other than that,
0:40:08 > 0:40:11they're not particularly well equipped for swimming.
0:40:11 > 0:40:14Just going to fish her out of that water.
0:40:14 > 0:40:16There we go.
0:40:16 > 0:40:19So, I guess the question is, how on earth do these ants cope
0:40:19 > 0:40:23with living in one of the most flood-prone places on the planet?
0:40:25 > 0:40:27That's where working together comes in.
0:40:28 > 0:40:33Inside this beaker are thousands of fire ants.
0:40:33 > 0:40:35And if I just swirl them around...
0:40:35 > 0:40:37Wow.
0:40:37 > 0:40:39They kind of form this ball.
0:40:41 > 0:40:42Wow.
0:40:44 > 0:40:49So, if I keep on moving them around in my hand like this,
0:40:49 > 0:40:54they stay in this cluster and so far, so good.
0:40:54 > 0:40:57Now, watch what happens when I put them in this tank of water.
0:40:57 > 0:40:59Here we go.
0:41:00 > 0:41:05Amazing. So, this ball of ants is staying together...
0:41:06 > 0:41:08..like a raft.
0:41:12 > 0:41:13That is brilliant.
0:41:15 > 0:41:17This is the first time I've seen anything like this.
0:41:17 > 0:41:19Unlike the individual ant,
0:41:19 > 0:41:22they don't have any trouble at all in the water.
0:41:22 > 0:41:26Instead, they form a floating waterproof island.
0:41:28 > 0:41:32And scientists have found that when they raft in this way,
0:41:32 > 0:41:36they can take a force of 400 times their body weight.
0:41:38 > 0:41:41Now, you'd think that the ones at the bottom would be sacrificed.
0:41:41 > 0:41:43But what's happening is that their bodies repel water
0:41:43 > 0:41:47and so that allows for a layer of air to be trapped in the raft
0:41:47 > 0:41:50which means they can still breathe. That is amazing.
0:41:55 > 0:41:57By linking their bodies together,
0:41:57 > 0:41:59they're enhancing their ability to repel water.
0:42:02 > 0:42:05The way they knit together has been likened to the weaving
0:42:05 > 0:42:07of a waterproof fabric.
0:42:10 > 0:42:13These ants are waterproof, flexible,
0:42:13 > 0:42:15and almost completely indestructible.
0:42:18 > 0:42:22In the wild, they can assemble these rafts quickly
0:42:22 > 0:42:25and that's what allows them to endure the epic storms
0:42:25 > 0:42:26in their rainforest home.
0:42:29 > 0:42:31They can survive like this for months,
0:42:31 > 0:42:35spreading out over the water's surface in search of solid ground.
0:42:38 > 0:42:40This is teamwork at its finest.
0:42:40 > 0:42:41When ants behave in this way,
0:42:41 > 0:42:44they display all the hallmarks of a superorganism.
0:42:49 > 0:42:51And they're not the only small animals
0:42:51 > 0:42:53that work together to become bigger.
0:42:57 > 0:43:02Starling murmurations are much more than just hypnotic spectacles.
0:43:04 > 0:43:06They're all about safety in numbers.
0:43:10 > 0:43:13It's much harder for a predator like a peregrine falcon
0:43:13 > 0:43:15to target one small bird
0:43:15 > 0:43:17in the middle of a swirling flock of thousands.
0:43:22 > 0:43:25And when small fish move as one, they're harder to catch,
0:43:25 > 0:43:29so they become much bigger than the sum of their parts.
0:43:32 > 0:43:35But not all small creatures need back up.
0:43:37 > 0:43:40There's one legendary little animal
0:43:40 > 0:43:42that seems to think it's bigger than it is
0:43:42 > 0:43:46and it takes on huge predators all on its own.
0:43:48 > 0:43:50Meet the honey badger.
0:43:52 > 0:43:54It lives on the African plains,
0:43:54 > 0:43:57home to some of the biggest animals that roam our planet.
0:44:00 > 0:44:03Honey badgers live in Southern Africa and Asia
0:44:03 > 0:44:06and they share their home with some of the largest,
0:44:06 > 0:44:08most dangerous predators in the world.
0:44:09 > 0:44:13Lions are the biggest predators in Africa.
0:44:13 > 0:44:16A male can weigh nearly 200kg.
0:44:16 > 0:44:18Whereas a honey badger
0:44:18 > 0:44:19is 20 times smaller,
0:44:19 > 0:44:22weighing in at only 10kg.
0:44:24 > 0:44:25So, when they're out hunting,
0:44:25 > 0:44:28how do they avoid becoming a meal themselves?
0:44:30 > 0:44:34By being a small animal with a seriously big attitude.
0:44:37 > 0:44:41Running or hiding just isn't a honey badger's style.
0:44:41 > 0:44:45For them, the best defence is a good offence.
0:44:48 > 0:44:51The bigger and more intimidating the predator,
0:44:51 > 0:44:53the more feisty the honey badger's response.
0:44:55 > 0:44:58A suicidal strategy, you might think,
0:44:58 > 0:45:01if it weren't for the fact that this fearless fighter
0:45:01 > 0:45:04has a few tricks up its sleeve.
0:45:06 > 0:45:10Aww! What an amazing little guy.
0:45:11 > 0:45:15This is Stompy. He's a hand-reared honey badger
0:45:15 > 0:45:19and he's going to let me show you why honey badgers
0:45:19 > 0:45:21are so resilient,
0:45:21 > 0:45:23very agile
0:45:23 > 0:45:26and also, very muscular,
0:45:26 > 0:45:29which makes them very hard to subdue and pin down.
0:45:29 > 0:45:31Good boy, Stompy.
0:45:31 > 0:45:36This skin is about six millimetres thick in some places
0:45:36 > 0:45:39and it's so tough that even the quills of porcupines
0:45:39 > 0:45:41struggle to get through.
0:45:41 > 0:45:44Not only that, look how loose all that skin is around his body.
0:45:48 > 0:45:50It means that when they're grabbed from behind,
0:45:50 > 0:45:53they're able to twist inside their own skin.
0:45:56 > 0:46:00All this combined means not only can this little honey badger survive
0:46:00 > 0:46:03an attack from a ferocious lion,
0:46:03 > 0:46:05it can actually bite back.
0:46:05 > 0:46:09Their jaws are incredibly strong,
0:46:09 > 0:46:11so not only are they very hard to kill,
0:46:11 > 0:46:13they're also a dangerous opponent.
0:46:18 > 0:46:22Although they're much smaller than many of their adversaries,
0:46:22 > 0:46:25they're built to fight like much larger animals,
0:46:25 > 0:46:29and in my eyes, they're the smallest big predator
0:46:29 > 0:46:31on the African plains.
0:46:31 > 0:46:33HYENAS WHIMPER
0:46:33 > 0:46:36By punching well above their weight,
0:46:36 > 0:46:40honey badgers have found a fantastic way of living alongside
0:46:40 > 0:46:43some of the world's largest predators.
0:46:43 > 0:46:47Their bulletproof build makes up for their small size
0:46:47 > 0:46:52and their big attitude has made them an internet hit.
0:46:52 > 0:46:54Maybe you're one of the 80 million people
0:46:54 > 0:46:56that have watched them online.
0:47:02 > 0:47:04In the depths of the ocean,
0:47:04 > 0:47:07another group of animals reap the benefits
0:47:07 > 0:47:11of being both big and small at the same time.
0:47:13 > 0:47:15Deep-sea anglerfish.
0:47:17 > 0:47:20Ambush predators that entice prey
0:47:20 > 0:47:23with a fantastic bioluminescent lure.
0:47:25 > 0:47:29With those scary-looking teeth and gaping mouths,
0:47:29 > 0:47:33small may not be the first word that springs to mind.
0:47:34 > 0:47:39But in fact, this fearsome-looking fish is hiding a small secret.
0:47:43 > 0:47:46This absolute beast of an animal
0:47:46 > 0:47:49is a female anglerfish
0:47:49 > 0:47:52and it looks quite bizarre.
0:47:52 > 0:47:54What's even more bizarre than that, though,
0:47:54 > 0:47:58is the fact that this is her male counterpart.
0:48:00 > 0:48:02Now, the reason why they look so different
0:48:02 > 0:48:05comes down to something called sexual dimorphism.
0:48:05 > 0:48:08That's where males and females look different.
0:48:08 > 0:48:12In this case, it's an extreme version of exactly that.
0:48:13 > 0:48:18For anglerfish, it's more extreme than in any other animal.
0:48:18 > 0:48:20In some species,
0:48:20 > 0:48:24the males can weigh a staggering half a million times less
0:48:24 > 0:48:27than their female partners.
0:48:27 > 0:48:30So, why on earth are they so small?
0:48:32 > 0:48:36Incredibly, it's to help them survive in the depths of the ocean
0:48:36 > 0:48:39where food is almost impossible to find.
0:48:42 > 0:48:45It is a joint venture and the two sexes
0:48:45 > 0:48:47have very different strategies.
0:48:49 > 0:48:53The females have huge jaws and elastic stomachs,
0:48:53 > 0:48:57so can feast on almost anything they come across.
0:48:57 > 0:48:59They're definitely not fussy eaters.
0:49:00 > 0:49:05The males have also adapted perfectly to deepwater survival,
0:49:05 > 0:49:07but in a completely different way.
0:49:07 > 0:49:11They've evolved to go without food.
0:49:12 > 0:49:15Once they reach adulthood, they stop feeding.
0:49:16 > 0:49:20They use every ounce of energy in their body to find a female.
0:49:25 > 0:49:29The white shape at the front of the male's head are his nostrils
0:49:29 > 0:49:31which are the biggest in proportion
0:49:31 > 0:49:34to their head of any animal on Earth.
0:49:34 > 0:49:38And using these, he sniffs out females in the vast ocean.
0:49:39 > 0:49:44An almost impossible task at which most males probably fail.
0:49:45 > 0:49:49The male's self-sacrifice is a pretty dramatic one,
0:49:49 > 0:49:51but it does make sense.
0:49:51 > 0:49:53Between them, an anglerfish pair
0:49:53 > 0:49:55only need about half the amount of food
0:49:55 > 0:49:58as they would do if they were both large.
0:49:58 > 0:50:01But the question is, how on earth do they mate?
0:50:04 > 0:50:06If he's lucky enough to find a female,
0:50:06 > 0:50:10he bites onto her and releases a chemical
0:50:10 > 0:50:16that fuses his mouth to her body, joining them for life.
0:50:20 > 0:50:25His eyes and fins then waste away
0:50:25 > 0:50:27and he's nourished only by her blood.
0:50:28 > 0:50:32But he still breathes with his own gills and, crucially,
0:50:32 > 0:50:33still produces sperm.
0:50:37 > 0:50:43So, this female has a male attached to her right there.
0:50:43 > 0:50:44You can just make him out.
0:50:44 > 0:50:48And the males pretty much act as a reproductive organ
0:50:48 > 0:50:50that the females carry around.
0:50:50 > 0:50:52Now, when the females want to lay eggs,
0:50:52 > 0:50:54they send a hormonal signal through their blood
0:50:54 > 0:50:56to literally turn him on,
0:50:56 > 0:50:59so that he can fertilise the eggs as they come out.
0:51:01 > 0:51:02Over their lifetime,
0:51:02 > 0:51:05females can collect several males
0:51:05 > 0:51:08who produce sperm season after season.
0:51:08 > 0:51:10By reducing in size,
0:51:10 > 0:51:12the male has given the species
0:51:12 > 0:51:14a better chance of survival
0:51:14 > 0:51:17in one of the most inhospitable places on the planet.
0:51:19 > 0:51:22Another way for small animals to reap some of the benefits
0:51:22 > 0:51:26of being big is, well, to pretend to be big.
0:51:31 > 0:51:34When the white-faced scops-owl feels threatened,
0:51:34 > 0:51:39they make themselves as big and intimidating as they possibly can,
0:51:39 > 0:51:42almost doubling in size.
0:51:45 > 0:51:50Frilled lizards intimidate would-be attackers by opening their mouths
0:51:50 > 0:51:53and expanding the skin around their necks.
0:51:58 > 0:52:02For birds of paradise, it's all about getting a mate.
0:52:02 > 0:52:06They make themselves as big, grand and colourful as they can,
0:52:06 > 0:52:09in the hope of attracting a female.
0:52:13 > 0:52:18There's one final small superstar with an ingenious size solution
0:52:18 > 0:52:21that I want you to meet.
0:52:21 > 0:52:24And it just happens to be the smallest carnivore in the world.
0:52:25 > 0:52:28Hello! Where are you going?
0:52:28 > 0:52:29This little guy...
0:52:29 > 0:52:31HE LAUGHS
0:52:31 > 0:52:33..is Fidget and he's a weasel.
0:52:33 > 0:52:35He's running all over the place!
0:52:37 > 0:52:39They aren't usually this friendly.
0:52:39 > 0:52:43Weasels are actually one of the most ferocious predators out there.
0:52:46 > 0:52:50But Fidget has been hand-reared by wildlife artist Robert Fuller,
0:52:50 > 0:52:53who rescued him when he was abandoned by his mother.
0:52:54 > 0:52:57Robert is obsessed with weasels,
0:52:57 > 0:53:01and he doesn't just paint them, he films them too.
0:53:02 > 0:53:05There's 30 surveillance cameras in the gardens
0:53:05 > 0:53:08covering all the different areas. Nest chambers, pathways.
0:53:08 > 0:53:12So, I'm able to follow the track of the weasels through the garden.
0:53:12 > 0:53:13So, you've got the whole place rigged up?
0:53:13 > 0:53:16- It's a bit like weasel Big Brother! - It is, yeah, exactly.
0:53:16 > 0:53:19All these cameras here, while I'm painting, in my peripheral vision,
0:53:19 > 0:53:22I can see what's happening with the weasels.
0:53:30 > 0:53:32Although, to me, Fidget seems small,
0:53:32 > 0:53:35in comparison to rodents like mice and voles,
0:53:35 > 0:53:37weasels are actually quite big...
0:53:40 > 0:53:43..or at least that's how they first appear.
0:53:45 > 0:53:47But they've got a surprising trick
0:53:47 > 0:53:49that gives them the best of both worlds.
0:53:51 > 0:53:55And this demonstration should help me to explain.
0:53:57 > 0:54:00My silhouette is a pretty good way
0:54:00 > 0:54:02of getting an idea of my overall size.
0:54:02 > 0:54:05How much space I take up.
0:54:05 > 0:54:08But all you need is a change in perspective
0:54:08 > 0:54:11to see things a bit differently.
0:54:11 > 0:54:15From above, you can see that I appear to be much smaller,
0:54:15 > 0:54:17and could fit into some tight places.
0:54:19 > 0:54:21Just like weasels.
0:54:21 > 0:54:25By being long and thin, they're small in just one direction
0:54:25 > 0:54:28and can squeeze into really tiny spaces.
0:54:28 > 0:54:33So, we've got a 50-mill clear pipe here and we can...
0:54:33 > 0:54:36He's obviously designed to go down vole holes, mouse holes.
0:54:36 > 0:54:38So, that's pretty easy for him.
0:54:38 > 0:54:41Straight through there, yeah. We expected that.
0:54:41 > 0:54:44- We go down onto a 40-mill pipe. - Wow, you can see...
0:54:44 > 0:54:47I love how he's able to even spin around.
0:54:47 > 0:54:50Yeah, this is important if they get stuck in a mouse hole,
0:54:50 > 0:54:53they've got to obviously find their way out, or a vole hole.
0:54:53 > 0:54:55So, they can spin, twist.
0:54:55 > 0:54:58- He's so nimble!- Yeah!
0:54:58 > 0:55:01But the challenge for him right now
0:55:01 > 0:55:03is to see if he can make it through...
0:55:04 > 0:55:08- He's halfway through! - So, is 34...millimetres.
0:55:08 > 0:55:09The smallest tube.
0:55:12 > 0:55:16These tubes are smooth inside, so he can't get any traction.
0:55:18 > 0:55:22But take a look at how Fidget handles some of the other obstacles.
0:55:22 > 0:55:26He can squeeze through tiny tunnels and navigate tight spaces.
0:55:34 > 0:55:37And in the wild, it's even more apparent.
0:55:39 > 0:55:41Watch as this winter-coat weasel
0:55:41 > 0:55:46seems to shrink itself down to the same width as its prey.
0:55:48 > 0:55:52They're thin enough to chase down mice and voles in tiny tunnels,
0:55:52 > 0:55:57but strong enough to overpower them and take down much larger prey.
0:56:03 > 0:56:07Weasels like Fidget are small without being small.
0:56:07 > 0:56:10Which, in my opinion, is a pretty ingenious size solution.
0:56:17 > 0:56:22Although being small does bring some big challenges,
0:56:22 > 0:56:26these animals have found impressive ways of overcoming these problems.
0:56:28 > 0:56:32Reaping the benefits that being smaller brings to them...
0:56:35 > 0:56:38..and turning size to their advantage.
0:56:50 > 0:56:52Because they can grow quicker,
0:56:52 > 0:56:57breed earlier and survive with less food and space,
0:56:57 > 0:57:00they're often better than big animals at coping
0:57:00 > 0:57:03with dramatic changes to their environment
0:57:03 > 0:57:05that could threaten their existence.
0:57:13 > 0:57:16So, although this chameleon looks delicate,
0:57:16 > 0:57:19in many ways, it's less fragile
0:57:19 > 0:57:21than some of the biggest animals on the planet.