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The natural world is full of extraordinary animals, with amazing life histories.

Yet, certain stories are more intriguing than most.

The mysteries of a butterfly's life cycle,

or the strange biology of the emperor penguin.

Some of these creatures were surrounded by myths

and misunderstandings for a very long time.

And some have only recently revealed their secrets.

These are the animals, that stand out from the crowd.

The curiosities I find particularly fascinating.

Some animals can perform amazing physical feats.

A flea's jump is said to be the equivalent of a man

leaping over St.Paul's Cathedral.

And it's famously quoted, that cheetahs

can run at speeds of 70 miles an hour.

But are these claims really true?

Quick. Look

This is a real, live, flea circus,

and you can see this one, pulling along this tiny chariot.

There are very few circuses like this, these days.

The whole business of performing fleas,

dates back into the 16th century, and it was used by watchmakers.

They used them, to demonstrate how they

themselves could work on a near-miniature scale.

They used thin gold wires, to harness fleas,

and then link the fleas to tiny chains.

Early magnifying devices like this

where actually named "flea glasses", after these pests.

And the fleas where excellent creatures

to demonstrate a newly visible, microscopic world.

Fleas appear to be extraordinarily strong,

after all, this little flea here,

pulling this chariot,

was an extraordinary thing.

That's the equivalent of me, trying to pull a jumbo jet single-handed.

And this tiny merry-to-round, that too, is completely powered by fleas.

The secret of the flea's strength and ability, to move such equipment,

lies in their powerful walking and jumping techniques.

They have the ability, to store and then release energy,

and that enables them to leap upwards, with great acceleration.

Fleas need to be good jumpers.

They live on the skin of mammals and birds, sucking their blood.

So they have to be able, to quickly leap on board

their traveling hosts, when they get the chance.

There are more than 2,500 species worldwide,

62 or which, live in Britain.

Fortunately, only a few feed on us.

Rat fleas were said to be responsible,

for the spread of the black death, in 1665,

which killed millions.

But it wasn't until the invention of the magnifying glass,

that we were able to see these tiny creatures, face to face.

In 1665, Robert Hooke,

an inventor and natural philosopher

made one of the first compound microscopes.

This is a later reproduction of it.

And he then published his discoveries,

that he made, using it,

in a marvelous book, called "Micrographia ".

It became one of the first scientific best-sellers.

Samuel Pepys mentioned it in his diary.

And it contained magnificent, detailed drawings,

that revealed biological structures, that had never been seen before.

He saw that plant tissue, was made up of

little units, that he called cells.

The word we still use.

And he drew this marvelously detailed flea,

showing its great, strikingly long legs.

He also watched it through the microscope,

and he described, how a flea jumped.

This is what he says:

"When the flea intends to leap",

"he folds up these 6 legs together"

"then springs them all out, at the same instant"

"and thereby exerting his whole strength at once,"

"carries his little body, to a considerable distance."

Indeed it does.

A flea's jump, takes just 1/1000th of a second.

So Hooke, must have had very sharp eyesight to see it.

Many researchers have been fascinated by fleas,

and for one particular family, they became an obsession.

Charles Rothschild, a banker and keen naturalist,

amassed over 30,000 specimens,

and identified more than 500 new species.

He purchased them from specialist traders, world wide.

and one parcel from America, had a special surprise.

The tiny fleas were dressed as Mexicans.

Miriam, Charles' daughter, shared his passion for fleas,

and catalogued his whole collection.

She looked closely at the flea's body

and the way they jumped,

and was puzzled to find, that they could leap far higher

then should theoretically have been possible.

But could their reputation for jumping 200 times

their body length, possibly be true.

Most of the natural world's top jumpers

achieve their impressive leaps,

by using straightforward muscle power.

Kangaroos can make single bounds, of almost 8 meters.

And frogs are able to jump

more than 20 times their body length.

The jumping spider's leap is even more impressive,

100 times its own length.

It achieves this, by exploiting hydraulics.

And scientists had long suspected,

that fleas, and other insects,

also needed something other than muscle,

to make their huge jumps.

In the 1960's an exciting discovery was made

in the insect world, that helped explain,

how bigger flying insects, like locusts and dragonflies

were able to fly and jump so well.

A rubbery protein was found in the hinges

and joints of locust wings and legs.

Using ultra-violet light, it's possible to see it,

as in this picture of a leg joint, of a locust.

Here, that blue, is this new substance.

But, just like this rubber, it could bend,

and then, release energy.

But the newly discovered material did that,

with more than 90 percent efficiency.

Remarkably too, it repeatedly snapped

back into shape, without any deformation.

It was named: Resilin.

This stretchy protein allows insects, to bend their stiff

bodies and stretch their tendons, without snapping.

It's so robust, it lasts a lifetime,

and it's believed to be the most

efficient elastic protein known.

The discovery of Resilin, opened up a whole new area of study.

And in 1966, Henry Bennet-Clark,

an expert in insect bio-mechanics,

had a break-through moment.

He had the chance, to see some exciting new footage of fleas,

shot on a newly invented high-speed camera.

Bennet-Clark studied the new flea footage, and build

a mechanical model, 400 times bigger than the flea.

He calculated, that the fleas were somehow generating

much more power, than their muscles could actually provide.

He noticed, that just before leaping,

the flea bent the closed segment, of its hind-most legs,

towards the body, and hesitated for about 1/10th of a second.

Carefully, he dissected fleas, and found a pad material.

And that proved to be Resilin.

He proposed, that fleas stored some of the energy for their jumps,

in this rubber-like tissue, and then released it,

as they pushed off, with their shins and feet.

So the tiny wingless fleas, use internal Resilin springs,

like those of other bigger, flying and jumping insects.

And the secret of their huge leaps,

lies in the efficient way, they combine muscle,

tendons and joints, to harness the resilin's energy.

Only today, do we know how a flea jumps, and how high it can jump.

Just as in Hooke's time, a modern technology, a microscope,

enabled him to see the anatomy of the flea, for the very first time,

so, we have a camera now, which is recording 5,000 images a second,

which enable us to see how it jumps.

The camera is already running.

The flea is in that little box, there.

And we can see the image from the camera, on this computer.

I will stop it, as soon as I see, the flea has jumped.

There.

Its legs are already cocked in the jumping position,

and the cuticle which has fused the Resilin,

is bent, and ready to release its energy,

and then, it lifts itself from the ground, and it's catapulted into the air.

Our story about fleas started 350 years ago,

with Robert Hooke's first microscopic study.

Today, images from electron microscopes

reveal even more details, than Hooke's beautiful drawings.

They show the rough hairs, on the flea's shins and toes,

that help it grip, before thrusting itself into the air

with a final push from its toes.

So, can fleas jump 200 times their own body length?

It would seem not.

Nonetheless, they can leap a respectable 38 times

the length of their bodies, which is not bad.

Fleas are extraordinarily strong.

And we now know how they jump.

The flea's story isn't quite over.

A new discovery has added a twist to their lives,

and dispelled another myth.

Recently, bodies of people, who died of the black death,

were uncovered by workers, digging a new railway line.

This inspection revealed, that the black death was an airborne disease,

and had nothing to do with rats, or their fleas.

So, the flea's good name can at last be

restored, and we can celebrate them,

as one of the natural world's

most spectacular jumpers.

Next, meet an animal that performs another amazing feat.

The Cheetah,

that, they say, can run at over 70 miles an hour.

Fleas can't jump as high as some say,

but they can make extraordinary leaps.

Next, we investigate another amazing claim.

The Cheetah's ability to run at speeds of 70 miles an hour.

Is that really possible?

Cheetahs are beautiful, athletic looking cats

They've got a streamlined body, small head,

elongated legs, narrow shoulders

and a very long spine.

This looks like an animal, that's build for speed.

But exactly how fast can he run?

They've been admired for their grace and speed, since antiquity.

The Egyptians were sometimes buried with these cats,

because they believed, that they could hasten the journey to the after-world.

And in more recent times, sports hunters

have used cheetahs, to run down their prey.

So, the cheetah certainly has an impressive sprint.

But where did the magical figure of 70 miles an hour come from?

Back in 1957, a cheetah hit the headlines

with news of a rather unusual experiment.

A photographer, called Kurt Severin

filmed and measured the running speed of a tame cheetah

using an upturned bicycle, rather like this.

The back wheel was modified,

so that a strong fishing line

could be wound through the rim

and pull along a meat scented bag.

As the cheetah ran the 80 yard, or 73 meter course,

the pedals of the bike were hand-cranked as fast as humanly possible,

to drag the bag along, just ahead of the cheetah.

The measurements were made manually,

using a stopwatch and a pistol.

Severin wrote, that from a deep crouch,

the cheetah spurted to the end of the course, in 2,25 seconds,

for an average speed of 71 miles an hour.

So, the legend was born.

This impressive figure was immediately accepted,

and is still often quoted today.

But how accurate is it?

The top speed of any running mammal,

depends on the power of its muscles,

and the strength of its tendons and bones.

Human athletes train hard, to reach their personal best,

but there's still a limit to how fast they can run.

In a 100 meter sprint, a mere 2 seconds

separates a good amateur sprinter,

from a world class champion.

The greyhound is similar in size and shape, to a cheetah,

so it's a good substitute animal,

to test out the cheetah's legendary top speed

of 70 miles an hour.

Their backs flex and extend so greatly,

that at times, none of their feet touch the ground.

But when the greyhound's top speed was measured,

it was found to be 45 miles an hour;

a whole 25 miles an hour

slower than the cheetah.

People argued, that the cheetah could nonetheless achieve

a bigger stride, because of extra flexibility in its back.

The doubts about its top speed, were beginning to creep in.

A new, more accurate way of testing, was needed.

Here in the Royal Veterinary College,

they use dogs, to help them in their studies of cheetahs.

Using a lurcher as a stand-in,

they've developed an extraordinary, data collecting collar.

It has a GPS attachment, that will register

position, to within a fraction of a meter.

It has movement sensors, to show

how the animal is in fact moving.

It can be remotely programmed,

and it has a solar charged battery,

that will last for up to a year.

The collars were tested and perfected,

on lurchers in Britain

to make sure that they were small and light enough,

no to disturb their wearer.

Then the collars were put on captured cheetahs,

to see if they could cope with the twisting, while at the hung.

The results were excellent,

and the collars were ready for the ultimate test:

in the wild.

Here was a chance, to see if a wild cheetah's special adaptations to hunting,

really enabled it, to run at 70 miles an hour.

Wild cheetahs are faster than other larger cats, like lions,

because of their lighter bones.

An advantage in the short, high-speed chase.

They have big nostrils, so they can take in large amounts of oxygen,

and an enlarged heart and longs, that increase circulation.

Their long tails act like rudders, to help them steer,

and assist their balance as they twist and turn.

They need to be fast and maneuverable, because the prey they hunt

is extremely agile and able to change direction very quickly.

A cheetah can mirror such changes of movements in an instant.

But what would the GPS-collars tell us, about their speed?

Data from the collars, has revealed fascinating details about cheetahs lives,

How they hunt, and exactly how fast they can run.

The GPS measurements collected, are accurate to within half a meter,

and can be precisely matched to satellite images of the area.

So, it's possible to see exactly what kind

of terrain, the cheetahs were hunting on.

Here, we can see an 11-hour day in the life of a cheetah,

and there, it starts to hunt.

The cheetah ran in one circular direction, like this.

The blue represents deceleration, getting slower here,

and there, the red, where it gets faster and accelerates.

And the arrows, represent the power of the force

on the cheetah's body, as it swirls.

And there, finally, it made the kill.

367 hunts were studied, and the top speed of

a chase, was calculated to be 58 miles an hour.

For more than half a century, we have

overestimated the cheetah's speed.

It is nonetheless, still the fastest animal on land,

and it's greatest feat, is its acceleration.

Four times that, of Usain Bolt.

The cheetah's legendary, 70 miles an hour,

speed record, is just a myth.

But their true top speed of 58 miles

an hour, is still extraordinary.

A body, that is fine tuned for hunting

helps them run, in a really remarkable way.

But the cheetah's real impossible feat, so-called,

is the ability to change speed so extremely quickly.

And that makes it one of the most maneuverable animals alive.

Aren't you? Aren't you.

We may have overestimated the abilities of the flea, and the cheetah.

But both exhibit remarkable feats of acceleration, in their quest for food.

The flea, to hop on to a passing host,

and the cheetah, to outmaneuver its prey.

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