0:00:03 > 0:00:06The natural world is full of extraordinary animals
0:00:06 > 0:00:08with amazing life histories.
0:00:09 > 0:00:12Yet certain stories are more intriguing than most.
0:00:15 > 0:00:20The mysteries of a butterfly's life cycle or the strange biology
0:00:20 > 0:00:24of the emperor penguin, some of these creatures were surrounded
0:00:24 > 0:00:28by myth and misunderstandings for a very long time.
0:00:30 > 0:00:33And some have only recently revealed their secrets.
0:00:34 > 0:00:37These are the animals that stand out from the crowd,
0:00:37 > 0:00:42the curiosities I find particularly fascinating.
0:00:50 > 0:00:54Some animals can perform amazing physical feats.
0:00:54 > 0:00:56A flea's jump is said to be the equivalent of
0:00:56 > 0:00:59a man leaping over St Paul's Cathedral.
0:01:00 > 0:01:03And it is famously quoted that cheetahs can run at speeds
0:01:03 > 0:01:05of 70mph.
0:01:07 > 0:01:09But are these claims really true?
0:01:27 > 0:01:29Quick, look!
0:01:29 > 0:01:35This is a real live flea circus and you can see this one pulling
0:01:35 > 0:01:38along this tiny chariot.
0:01:38 > 0:01:42There are very few circuses like this these days.
0:01:42 > 0:01:46The whole business of performing fleas dates back into
0:01:46 > 0:01:50the 16th century and it was used by watchmakers,
0:01:50 > 0:01:53who used them to demonstrate how they themselves could work on
0:01:53 > 0:01:55a near miniature scale.
0:01:55 > 0:02:00They used thin gold wires to harness fleas and then link the fleas
0:02:00 > 0:02:02to tiny chains.
0:02:03 > 0:02:06Early magnifying devices like this were actually named
0:02:06 > 0:02:10"flea glasses" after these pests.
0:02:10 > 0:02:15The fleas were excellent creatures to demonstrate a newly-visible
0:02:15 > 0:02:21microscopic world. Fleas appear to be extraordinarily strong.
0:02:21 > 0:02:23After all, this little badger flea, here,
0:02:23 > 0:02:28pulling this chariot, what an extraordinary thing.
0:02:28 > 0:02:33That's the equivalent of me trying to pull a jumbo jet single-handed.
0:02:33 > 0:02:37This tiny merry-go-round, that too is completely powered by fleas.
0:02:40 > 0:02:44The secret of the flea's strength and ability to move such
0:02:44 > 0:02:49equipment lies in their powerful walking and jumping techniques.
0:02:49 > 0:02:54They have the ability to store and then release energy and that
0:02:54 > 0:02:57enables them to leap upwards with great acceleration.
0:03:00 > 0:03:03Fleas need to be good jumpers.
0:03:03 > 0:03:07They live on the skin of mammals and birds, sucking their blood.
0:03:07 > 0:03:10So they have to be able to quickly leap on board their
0:03:10 > 0:03:13travelling hosts when they get the chance.
0:03:14 > 0:03:19There are more than 2,500 species worldwide,
0:03:19 > 0:03:2162 of which live in Britain.
0:03:21 > 0:03:25Fortunately, only a few feed on us.
0:03:31 > 0:03:33Rat fleas were said to be responsible for
0:03:33 > 0:03:39the spread of the Black Death, in 1665, which killed millions.
0:03:41 > 0:03:43But it wasn't until the invention of the magnifying
0:03:43 > 0:03:48glass that we were able to see these tiny creatures face-to-face.
0:03:49 > 0:03:55In 1665, Robert Hooke, an inventor and natural philosopher,
0:03:55 > 0:03:58made one of the first compound microscopes.
0:03:58 > 0:04:01This is a later reproduction of it.
0:04:01 > 0:04:05He then published his discoveries that he made using it in
0:04:05 > 0:04:08a marvellous book called Micrographia.
0:04:08 > 0:04:12It became one of the first scientific bestsellers.
0:04:12 > 0:04:15Samuel Pepys mentioned it in his diary.
0:04:15 > 0:04:19It contained magnificent detailed drawings that revealed
0:04:19 > 0:04:23biological structures that had never been seen before.
0:04:23 > 0:04:27He saw that plant tissue was made up of little units that
0:04:27 > 0:04:29he called cells, the word we still use.
0:04:30 > 0:04:34And he drew this marvellously detailed flea,
0:04:34 > 0:04:37showing its great strikingly long legs.
0:04:39 > 0:04:42He also watched it through the microscope and
0:04:42 > 0:04:47he described how a flea jumped. This is what he says.
0:04:47 > 0:04:50"When the flea intends to leap,
0:04:50 > 0:04:53"he folds up these six legs together,
0:04:53 > 0:04:57"then springs them all out at the same instant and thereby
0:04:57 > 0:05:00"exerting his whole strength at once,
0:05:00 > 0:05:04"carries his little body to a considerable distance."
0:05:05 > 0:05:06Indeed he does.
0:05:11 > 0:05:16A flea's jump takes just one thousandth of a second
0:05:16 > 0:05:20so Hooke must have had very sharp eyesight to see it.
0:05:23 > 0:05:27Many researchers have been fascinated by fleas,
0:05:27 > 0:05:30and for one particular family they became an obsession.
0:05:31 > 0:05:35Charles Rothschild, a banker and keen naturalist, amassed
0:05:35 > 0:05:41over 30,000 specimens and identified more than 500 new species.
0:05:45 > 0:05:49He purchased them from specialist traders worldwide.
0:05:49 > 0:05:53One parcel from America had a special surprise,
0:05:53 > 0:05:56the tiny fleas were dressed as Mexicans.
0:06:05 > 0:06:07Miriam, Charles's daughter,
0:06:07 > 0:06:12shared his passion for fleas and catalogued his whole collection.
0:06:12 > 0:06:16She looked closely at the flea's body and the way they jumped and
0:06:16 > 0:06:18was puzzled to find that they could leap far higher than should
0:06:18 > 0:06:21theoretically have been possible.
0:06:21 > 0:06:25But could their reputation for jumping 200 times their body
0:06:25 > 0:06:26length possibly be true?
0:06:32 > 0:06:35Most of the natural world's top jumpers achieve their
0:06:35 > 0:06:38impressive leaps by using straightforward muscle power.
0:06:39 > 0:06:44Kangaroos can make single bounds of almost eight metres.
0:06:44 > 0:06:49And frogs are able to jump more than 20 times their body length.
0:06:55 > 0:06:59The jumping spider's leap is even more impressive,
0:06:59 > 0:07:02100 times its own length.
0:07:02 > 0:07:05It achieves this by exploiting hydraulics.
0:07:06 > 0:07:10And scientists had long suspected that fleas and other insects
0:07:10 > 0:07:15also needed something other than muscle to make their huge jumps.
0:07:20 > 0:07:25In the 1960s, an exciting discovery was made in the insect world
0:07:25 > 0:07:28that helped explain how bigger flying insects, like locusts
0:07:28 > 0:07:33and dragonflies, were able to fly and jump so well.
0:07:33 > 0:07:37A rubbery protein was found in the hinges and joints of locusts'
0:07:37 > 0:07:39wings and legs.
0:07:39 > 0:07:42Using ultraviolet light, it is possible to see it,
0:07:42 > 0:07:47as in this picture of the leg joint of a locust, here,
0:07:47 > 0:07:49that blue is this new substance.
0:07:50 > 0:07:56But just like this rubber, it could bend and then release energy.
0:07:56 > 0:07:58But the newly discovered material
0:07:58 > 0:08:02did that with more than 90% efficiency.
0:08:02 > 0:08:03Remarkably, too,
0:08:03 > 0:08:07it repeatedly snapped back into shape without any deformation.
0:08:07 > 0:08:09It was named resilin.
0:08:11 > 0:08:15This stretchy protein allows insects to bend their stiff bodies
0:08:15 > 0:08:18and stretch their tendons without snapping.
0:08:20 > 0:08:24It is so robust it lasts a lifetime and it is believed to be the
0:08:24 > 0:08:27most efficient elastic protein known.
0:08:30 > 0:08:34The discovery of resilin opened up a whole new area of study,
0:08:34 > 0:08:39and in 1966, Henry Bennet-Clark,
0:08:39 > 0:08:43an expert in insect biomechanics, had a breakthrough moment.
0:08:46 > 0:08:49He had the chance to see some exciting new footage of fleas
0:08:49 > 0:08:52shot on a newly invented high-speed camera.
0:08:55 > 0:08:58Bennet-Clark studied the new flea footage and built
0:08:58 > 0:09:02a mechanical model 400 times bigger than the flea.
0:09:02 > 0:09:06He calculated that the fleas were somehow generating much more
0:09:06 > 0:09:09power than their muscles could actually provide.
0:09:09 > 0:09:12He noticed that just before leaping,
0:09:12 > 0:09:16the flea bent the closest segment of its hindmost legs towards the
0:09:16 > 0:09:20body and hesitated for about a 10th of a second.
0:09:20 > 0:09:25Carefully, he dissected fleas and found a pad of material and
0:09:25 > 0:09:28that proved to be resilin.
0:09:28 > 0:09:31He proposed that fleas stored some of the energy for their jumps
0:09:31 > 0:09:35in this rubberlike tissue and then released it,
0:09:35 > 0:09:37as they pushed off with their shins and feet.
0:09:40 > 0:09:45So the tiny wingless fleas use internal resilin springs, like
0:09:45 > 0:09:48those of other bigger flying and jumping insects.
0:09:49 > 0:09:54And the secret of their huge leaps lies in the efficient way they
0:09:54 > 0:09:59combine muscle, tendons and joints to harness the resilin's energy.
0:10:02 > 0:10:08Only today do we know how a flea jumps and how high it can jump.
0:10:08 > 0:10:12Just as in Hooke's time, a modern technology - a microscope -
0:10:12 > 0:10:16enabled him to see the anatomy of the flea for the very first
0:10:16 > 0:10:22time, so we have a camera now which is recording 5,000 images a second
0:10:22 > 0:10:25which will enable us to see how it jumps.
0:10:25 > 0:10:31The camera is already running, the flea is in that little box there.
0:10:31 > 0:10:35And we can see the image from the camera on this computer.
0:10:35 > 0:10:39I will stop it as soon as I see the flea has jumped.
0:10:42 > 0:10:43There!
0:10:46 > 0:10:52Its legs are already cocked in the jumping position and the cuticle,
0:10:52 > 0:10:54which is fused to the resilin,
0:10:54 > 0:10:56is bent and ready to release its energy.
0:10:56 > 0:11:01Then it lifts itself from the ground and it is catapulted into the air.
0:11:04 > 0:11:09Our story about fleas started 350 years ago with Robert Hooke's
0:11:09 > 0:11:12first microscopic study.
0:11:12 > 0:11:16Today, images from electron microscopes reveal even more
0:11:16 > 0:11:19details than Hooke's beautiful drawings.
0:11:19 > 0:11:23They show the rough hairs on the flea's shins and toes that
0:11:23 > 0:11:26help it grip before thrusting itself into the air with
0:11:26 > 0:11:28a final push from its toes.
0:11:29 > 0:11:34So can fleas jump 200 times their own body length?
0:11:34 > 0:11:36It would seem not.
0:11:36 > 0:11:40Nonetheless, they can leap a respectable 38 times the length
0:11:40 > 0:11:43of their bodies, which is not bad.
0:11:45 > 0:11:51Fleas are extraordinarily strong, and we now know how they jump.
0:11:52 > 0:11:55The flea's story isn't quite over.
0:11:55 > 0:11:59A new discovery has added a twist to their lives and dispelled
0:11:59 > 0:12:00another myth.
0:12:01 > 0:12:05Recently, bodies of people who died of the Black Death were
0:12:05 > 0:12:08uncovered by workers digging a new railway line.
0:12:08 > 0:12:13Close inspection revealed that the Black Death was an airborne
0:12:13 > 0:12:17disease and had nothing to do with rats or their fleas.
0:12:17 > 0:12:22So the flea's good name can at last be restored and we can
0:12:22 > 0:12:27celebrate them as one of the natural world's most spectacular jumpers.
0:12:28 > 0:12:32A springy protein propels fleas with great force.
0:12:34 > 0:12:37Next, we investigate another impossible feat,
0:12:37 > 0:12:42the cheetah's legendary top speed of 70mph.
0:12:44 > 0:12:46Is this really possible?
0:12:50 > 0:12:54Cheetahs are beautiful, athletic-looking cats.
0:12:54 > 0:12:58They have got a streamlined body, small head,
0:12:58 > 0:13:04elongated legs and narrow shoulders and a very long spine.
0:13:05 > 0:13:09This looks like an animal that is built for speed but exactly
0:13:09 > 0:13:11how fast can he run?
0:13:15 > 0:13:18They have been admired for their grace and speed since antiquity.
0:13:19 > 0:13:23The Egyptians were sometimes buried with these cats because they
0:13:23 > 0:13:27believed they could hasten the journey into the afterworld.
0:13:28 > 0:13:32And in more recent times, sports hunters have used cheetahs
0:13:32 > 0:13:33to run down their prey.
0:13:37 > 0:13:39So the cheetah's impressive sprint
0:13:39 > 0:13:41has been known about for some time.
0:13:43 > 0:13:45But where did the magical figure
0:13:45 > 0:13:47of 70mph come from?
0:13:52 > 0:13:55Back in 1957, a cheetah hit the headlines with news of
0:13:55 > 0:13:57a rather unusual experiment.
0:14:06 > 0:14:10A photographer called Kurt Severin filmed and measured the running
0:14:10 > 0:14:16speed of a tame cheetah using an upturned bicycle, rather like this.
0:14:16 > 0:14:20The back wheel was modified so that a strong fishing line could
0:14:20 > 0:14:25be wound through the rim and pull along a meat-scented bag.
0:14:25 > 0:14:29As the cheetah ran the 80 yard, 73 metre, course,
0:14:29 > 0:14:32the pedals of the bike were hand-cranked as fast as humanly
0:14:32 > 0:14:36possible to drag the bag along just ahead of the cheetah.
0:14:36 > 0:14:41The measurements were made manually, using a stopwatch and a pistol.
0:14:42 > 0:14:47Severin wrote that from a deep crouch, the cheetah spurted to the
0:14:47 > 0:14:53end of the course in 2.25 seconds, for an average speed of 71mph.
0:14:53 > 0:14:55So the legend was born.
0:14:58 > 0:15:02This impressive figure was immediately accepted and is still
0:15:02 > 0:15:05often quoted today. But how accurate is it?
0:15:06 > 0:15:09The top speed of any running mammal depends on the power of its
0:15:09 > 0:15:13muscles and the strength of its tendons and bones.
0:15:15 > 0:15:19Human athletes train hard to reach their personal best,
0:15:19 > 0:15:22but there is still a limit to how fast they can run.
0:15:24 > 0:15:28In a 100-metre sprint, a mere two seconds separates
0:15:28 > 0:15:32a good amateur sprinter from a world-class champion.
0:15:33 > 0:15:37The greyhound is similar in size and shape to a cheetah so it is
0:15:37 > 0:15:41a good substitute animal to test out the cheetah's legendary top
0:15:41 > 0:15:43speed of 70mph.
0:15:48 > 0:15:52Their backs flex and extend so greatly that, at times, none of
0:15:52 > 0:15:54their feet touch the ground.
0:15:57 > 0:16:00But when the greyhound's top speed was measured,
0:16:00 > 0:16:08it was found to be 45mph, a whole 25mph slower than the cheetah.
0:16:12 > 0:16:15People argue that the cheetah could nonetheless achieve
0:16:15 > 0:16:19a bigger stride because of extra flexibility in its back.
0:16:23 > 0:16:26But doubts about its top speed were beginning to creep in,
0:16:26 > 0:16:29a new, more accurate, way of testing was needed.
0:16:32 > 0:16:35Here in the Royal Veterinary College,
0:16:35 > 0:16:39they use dogs to help them in their studies of cheetahs.
0:16:39 > 0:16:41Using a lurcher as a stand-in,
0:16:41 > 0:16:45they have developed an extraordinary data collecting collar.
0:16:45 > 0:16:50It has a GPS attachment that will register position to within
0:16:50 > 0:16:51a fraction of a metre.
0:16:51 > 0:16:56It has movement sensors to show how the animal is in fact moving.
0:16:56 > 0:17:00It can be remotely programmed and it has a solar charged battery
0:17:00 > 0:17:02that will last for up to a year.
0:17:04 > 0:17:07The collars were tested and perfected on
0:17:07 > 0:17:10lurchers in Britain, to make sure that they were small and
0:17:10 > 0:17:12light enough not to disturb their wearer.
0:17:14 > 0:17:18Then the collars were put on captive cheetahs to see if they could
0:17:18 > 0:17:20cope with the twisting run of the hunt.
0:17:25 > 0:17:28The results were excellent and the collars were ready
0:17:28 > 0:17:31for the ultimate test in the wild.
0:17:35 > 0:17:39Here was a chance to see if a wild cheetah's special adaptations
0:17:39 > 0:17:44to hunting really enabled it to run at 70mph.
0:17:46 > 0:17:50Wild cheetahs are faster than other larger cats, like lions,
0:17:50 > 0:17:52because of their lighter bones.
0:17:52 > 0:17:55An advantage in a short, high-speed chase.
0:17:57 > 0:17:59They have big nostrils
0:17:59 > 0:18:03so they can take in large amounts of oxygen, and an enlarged heart
0:18:03 > 0:18:06and lungs that increase circulation.
0:18:08 > 0:18:11Their long tails act like rudders,
0:18:11 > 0:18:15to help them steer and assist their balance as they twist and turn.
0:18:16 > 0:18:19They need to be fast and manoeuvrable because the
0:18:19 > 0:18:22prey they hunt is extremely agile
0:18:22 > 0:18:25and able to change direction very quickly.
0:18:25 > 0:18:29A cheetah can mirror such changes of movement in an instant.
0:18:33 > 0:18:36But what would the GPS collars tell us about their speed?
0:18:39 > 0:18:43Data from the collars has revealed fascinating details about
0:18:43 > 0:18:48cheetahs' lives. How they hunt and exactly how fast they can run.
0:18:48 > 0:18:51The GPS measurements collected are accurate to within half
0:18:51 > 0:18:55a metre and can be precisely matched to satellite images
0:18:55 > 0:18:59of the area, so it is possible to see exactly what kind of
0:18:59 > 0:19:01terrain the cheetahs were hunting on.
0:19:01 > 0:19:05Here we can see an 11-hour day in the life of a cheetah.
0:19:05 > 0:19:08And there it starts to hunt.
0:19:09 > 0:19:15The cheetah ran in one circular direction, like this.
0:19:15 > 0:19:20The blue represents deceleration, getting slower, here,
0:19:20 > 0:19:24and there, the red, where it gets faster and accelerates.
0:19:24 > 0:19:28And the arrows represent the power of the force on the cheetah's
0:19:28 > 0:19:33body as it swerves. And there, finally, it made the kill.
0:19:34 > 0:19:38367 hunts were studied and the top speed of
0:19:38 > 0:19:41a chase was calculated to be 58mph.
0:19:49 > 0:19:51For more than half a century,
0:19:51 > 0:19:53we have overestimated the cheetah's speed.
0:19:56 > 0:20:01It is nonetheless still the fastest animal on land and its
0:20:01 > 0:20:03greatest feat is its acceleration.
0:20:05 > 0:20:08Four times that of Usain Bolt.
0:20:38 > 0:20:44The cheetah's legendary 70mph speed record is just a myth.
0:20:44 > 0:20:49But their true top speed of 58mph is still extraordinary.
0:20:49 > 0:20:53A body that is fine-tuned for hunting helps them run in
0:20:53 > 0:20:55a really remarkable way.
0:20:55 > 0:20:59But the cheetah's real impossible feat, so-called...
0:21:03 > 0:21:08..is the ability to change speed so extremely quickly.
0:21:08 > 0:21:12That makes it one of the most manoeuvrable animals alive.
0:21:12 > 0:21:14Aren't you?
0:21:14 > 0:21:15Aren't you?
0:21:18 > 0:21:22We may have overestimated the abilities of the flea and the
0:21:22 > 0:21:26cheetah but both exhibit remarkable feats of acceleration in
0:21:26 > 0:21:27their quest for food.
0:21:28 > 0:21:31The flea, to hop onto a passing host,
0:21:31 > 0:21:35and the cheetah, to outmanoeuvre its prey.