The mystery of jumping fleas has been solved

Posted by David Gomez

For a long time scientists have been trying to figure out the physics behind the flea’s jumping ability. New research that was recently published has clarified the science of how fleas jump.

The scientific evidence of the mechanics of a flea’s jump comes from the University of Cambridge. According to their press release some fleas can reach speeds as fast as 1.9 meters per second by jumping.
    
Scientist Henry Bennet-Clark discovered in 1967 that fleas store the energy they need to spring themselves into the air in a pad made of a springy, unique protein called resilin. However, in the following decades, debate raged on about how fleas are able to harness this explosive energy. Scientists constructed different hypotheses, but it was only recently that the technology necessary to record and analyze the data became available.
    
Using high-speed video equipment and complicated mathematical models, Professor Malcolm Burrows and Dr. Gregory Sutton from the University's Department of Zoology, were able to confirm that fleas use their toes to push off and launch themselves into the air, solving the 44 year old mystery. Their findings were published last Thursday, in the Journal of Experimental Biology.
    
"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.
    
He and Burrows discovered that the fleas stayed perfectly still in the dark and that they only jumped when the lights went on. By focusing the camera on the stationary insects in low light, the duo were able to successfully film 51 jumps from 10 animals. This was when they received their first clue into the world of how the insects jump so high.
    
In most of the jumps, two parts of the flea's leg - the tarsus (toe) and trochanter (knee) - were touching the ground for the push off, but in 10% of the jumps, only the tarsus (toe) touched the ground. If 10% of the jumps didn't utilize the trochanter (knee), was it really necessary, or were the fleas using two methods to get elevated?
    
Analysing their high-speed videos, the scientists could observe that the insects kept accelerating during take-off, even when the trochanter (knee) was no longer pushing down. And the insects that jumped without using the trochanter (knee) accelerated in the same way as the insects that jumped using the trochanter (knee) and tarsus (toe). Additionally when Burrows and Sutton viewed the flea's leg with a scanning electron microscope, the tibia (shin) and tarsus (toe) had gripping claws, but the trochanter (knee) was totally smooth, preventing it from getting a good grip for pushing off.
    
Sutton and Burrows believed that the insects push down with the tibia (shin) onto the tarsus (toe). Using a mathematical model that could fully recreate the flea's trajectory, the researchers were able to verify that the insects transmit the force from the spring in the thorax into leg segments functioning as levers to push down on the tarsus (toe), effectively solving the 44 year old mystery.