Flea mystery solved

A debate that has raged on for 44 years has finally been settled by scientists in Cambridge: a serendipitous set of hedgehog fleas has shown exactly how the insects harness the energy needed to jump at the extraordinary speed they do.

In 1967 Henry Bennet-Clark discovered that fleas store the elastic energy needed to catapult themselves into the air in a pad –part of their skeletal structure – made of the unique protein resilin. However, Miriam Rothschild suggested fleas pushed off with the knee – but neither had the ability to prove their hypothesis correct.

Now, 44 years later, Professor Malcolm Burrows and Dr Gregory Sutton used a high-speed camera to film 51 jumps from 10 fleas to settle the raging debate – fleas use their toes to push off.

“We were always very puzzled by this debate because we’d read the papers and both Henry and Miriam put a lot of evidence for their hypothesis in place and their data were consistent with each other but we couldn’t understand why the debate hadn’t been settled,” said Sutton.

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

Burrow and Sutton’s films showed two parts of the flea’s complicated leg – the tarsus (toe) and trochanter (knee) – were in touch with the ground for the push off in 90% of jumps, but in 10% only the tarsus touched the ground. The insects also continued accelerating during take-off – even when the knee wasn’t used. Analysis using a scanning electron microscope revealed the tibia and toe were equipped with gripping claws, but the knee was smooth.

Using a mathematical model that could reproduce the flea’s trajectory, the scientists confirmed the insects transmit the force from the spring in the thorax through leg segments acting as levers to push down on the tarsus and launch the animals as high as 1.9m/s.