44-year-old mystery resolved: Fleas jump from toes, not knees

WASHINGTON - A 44-year-old mystery about how fleas are able to jump so high has now been resolved - they push off the ground from their toes, not from their knees as previously thought.

While Henry Bennet-Clark in 1967 discovered that fleas store the energy needed to catapult them into the air in a pad made of an elastic protein called resilin, they didn’t know exactly how.

For years, debate raged between academics as to how fleas harness this explosive energy.

“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,” said Professor Malcolm Burrows and Dr Gregory Sutton from the University of Cambridge.

Using high-speed camera footage and sophisticated mathematical models, they found that jumping fleas take off from their toes (tarsus).We were concerned about how difficult it would be to make the movies because we are used to filming locusts, which are much bigger than fleas,” said Sutton, but he and Burrows realised that the fleas stayed perfectly still in the dark and only jumped when the lights went on.

Focusing the camera on the stationary insects in low light, the duo successfully filmed 51 jumps from 10 animals; and this was when they got their first clue as to how the insects jump.

In the majority of the jumps, two parts of the flea’s complicated leg - the tarsus (toe) and trochanter (knee)- were in contact with the ground for the push off, but in 10 percent of the jumps, only the tarsus (toe) touched the ground.

Analysing the movies, Burrows and Sutton could see that the insects continued accelerating during take-off, even when the trochanter (knee) was no longer pushing down.

They suspected that the insects push down through the tibia (shin) onto the tarsus (toe), as Bennet-Clark had suggested, but the team needed one more line of evidence to clinch the argument.

Using a mathematical model that could reproduce the flea’s trajectory, the scientists were able to confirm that the insects transmit the force from the spring in the thorax through leg segments acting as levers to push down on the tarsus (toe) and launch the 0.7mg animals at speeds as high as 1.9m/s.

The discovery has been published in The Journal of Experimental Biology. (ANI)