Wednesday 06 May 2015

Flea's jump analysed by scientists

The age-old mystery of how fleas jump 100 times their height has been solved - and it's their toes not legs that are key.

It has long been known that fleas store the energy needed to catapult themselves up in an elastic-like pad above the hind legs.

But there has been 44 years of constant debate about how the tiny insects use this energy to travel around 100 times their height.

And now, in the first study of its kind, two researchers used high speed recording equipment to examine the exact movements involved and proved that they push off using their toes.

Using hedgehog fleas, they filmed 51 jumps from 10 of the animals.

In the majority of jumps, two parts of the flea's complicated legs - the toe and knee - were in contact with the ground for the push off.

But in 10 per cent of the jumps, only the toe touched the ground.

The duo could see that the insects continued accelerating during take-off - even when the knee was no longer pushing down - and those that jumped without using the knee accelerated in exactly the same way as those that jumped using both the knee and toe.

Furthermore, when they looked at the flea's leg with scanning electron microscopy - a microscope in which a finely focused beam of electrons is scanned across them - the shin and toe had gripping claws but the knee was completely smooth - so it couldn't get a good enough grip to push off.

They suspected that the insects push down through the shin onto the toe, as previous research has suggested, but they needed a mathematical model to reproduce the flea's movement and prove their argument.

Doctor Gregory Sutton conducted the research with Professor Malcolm Burrows at Cambridge University.

Speaking of past conflicting studies on the subject - from Doctor Henry Bennet-Clark in 1967 and then zoologist Dame Miriam Rothschild - Professor Burrows said: "We have finally shown, after all these years, how they do it.

"We were aware of the descriptions of how they were thought to do it and there were these two different ideas so we decided to use the expertise and the technology we had to see if we could solve it.

"We had the biology point of view from myself, and Greg is an engineer for we had that perspective as well.

"We built the models and found that one of the proposed methods could not work.

"They have to use more than their legs, because they have to use a catapult mechanism.

"There are virtually no insects, except those with long legs like the bush cricket, which can jump using just their legs.

"Their toes press on the ground, using the lever system of their legs.


"We found Rothschild's model to be wrong because she was saying they were basically jumping from their hips, not their feet."

He added: "We were always very puzzled by this previous debate because we'd read the papers and both Henry and Miriam put in a lot of evidence for their hypotheses in place and their data were consistent with each other but we couldn't see why the debate hadn't been settled.

"We had a serendipitous set of hedgehog fleas show up so we figured we'd take a crack at it and try to answer the question."

Dr Sutton built Dame Rothschild's model - as a simple mass attached to a spring pushing down through the knee - and Dr Bennet-Clark's model as a spring transmitting the spring's force through as system of levers pushing on the toe.

He then came up with the equations that could be used to calculate the insect's movement and compared the results from his calculations with the films to see if they agreed.

Both models correctly predicted the insect's take-off speed at 1.35 metres/second, but then the Rothschild model began to go wrong - predicting that the insect's acceleration peaked a colossal speed.

Dr Sutton's calculations with the Bennet-Clark level model, however, worked perfectly, accurately predicting the insect's movement and acceleration pattern.

So Sutton and Burrows finally concluded that fleas transmit force from the spring in the thorax - just behind the head - through leg segments acting as levers to push down on to the toe and launch their jump at speeds as high as 1.9metres/second.

The study is published in The Journal of Experimental Biology.


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