David Attenborough's Natural Curiosities

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 myth 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 is famously quoted that cheetahs can run at speeds

of 70mph.

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,

who 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 were actually named

"flea glasses" after these pests.

And the fleas were excellent creatures to demonstrate a newly-visible

microscopic world. Fleas appear to be extraordinarily strong.

After all, this little badger flea, here,

pulling this chariot, what an extraordinary thing.

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

This tiny merry-go-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

travelling hosts when they get the chance.

There are more than 2,500 species worldwide,

62 of 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.

He then published his discoveries that he made using it

in a marvelous book called Micrographia.

It became one of the first scientific bestsellers.

Samuel Pepys mentioned it in his diary.

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 marvellously 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 six 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 he does.

A flea's jump takes just one thousandth 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 worldwide.

One parcel from America had a special surprise,

the tiny fleas were dressed as Mexicans.

Miriam, Charles's 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 than 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 eight metres.

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 1960s, 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 locusts'

wings and legs.

Using ultraviolet light, it is possible to see it,

as in this picture of the 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% 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 is so robust it lasts a lifetime

and it is 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 breakthrough 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 built

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 closest segment of its hindmost legs towards the body

and hesitated for about a 10th of a second.

Carefully, he dissected fleas and found a pad of 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 will 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.