Mystery of Flea’s Jump Resolved

February 18, 2011- Nick Engelfried

Fleas are famous for their ability to jump vast distances in comparison to their body size.  However for decades the question of exactly how they jump so far as eluded scientists.  By examining the anatomy of dead fleas, researchers could make educated guesses about how the insects might propel themselves into the air, and came up with at least two viable hypotheses.  However the problem is that fleas are so small and move so quickly during a jump that it was impossible to observe their exceptional leaping in action.  Only now, thanks to modern high speed recording equipment, have scientists been able to solve the mystery of the jump of the flea.

Last year Malcolm Burrows and Gregory Sutton of Cambridge began studying the jump of the hedgehog flea using a high-speed camera.  Even with modern equipment it was difficult to capture the flea’s jump on film simply because the creatures wouldn’t hold still.  However eventually Burrows and Sutton realized fleas tended to be more active in the light, and by darkening the room they managed to slow them down until camera equipment could be set up.  Videos recorded by the researchers eventually showed the part of a flea’s anatomy essential to a successful jump is the tarsus—basically the insect’s toe.  This disproved a previous hypothesis that fleas rely on their knees to jump.

Of course, pushing of with the tarsus is just one part of what allows fleas to jump so far.  For many years scientists have known the power of the flea’s leap could be attributed to an internal spring made of a substance called resilin.  The mystery was in exactly how the spring is set off and what the flea’s final movements on the ground are before it takes begins a jump—and two widely respected scientists of the twentieth century had come up with competing hypotheses.  Henry Bennet-Clark predicted, correctly it turns out, that the toes were used to launch a flea into the air.  Entomologist Miriam Rothschild believed the knees were used.

As is so often the case in science, Burrows and Sutton ended up confirming the observations they made with high-speed photography by using a mathematical model.  The Bennet-Clark and Rothschild hypotheses each came with their own mathematical predictions about how fast a jumping flea would accelerate.  Burrows and Sutton compared those models to evidence from their own photographical observations, which largely agreed with Bennet-Clark’s formula. 

The extraordinary jumping ability of parasitic fleas allows them leap from one host animal to another, or to find their way back onto their host if they are dislodged.  Their ability to jump is especially important because, unlike most insects, fleas do not have wings and can’t fly.  Fleas can sometimes jump for a distance of up to four feet, although most of their jumps will be much shorter than that.  Once lodged on a warm-blooded animal fleas tend to hide amongst fur or feathers, using their piercing mouthparts to draw the blood on which they feed.

Though today fleas are regarded mainly as a nuisance in countries like the United States, once they shaped the fate of civilizations by transmitting diseases like the “black death,” or bubonic plague.  Modern medicine has led to cures for plague and many other diseases spread by fleas, and today’s sanitation systems make outbreaks of flea-born illness rare.  However these tiny insects apparently still have some secrets to share, as evidenced by the length of time it took to discover exactly how fleas manage to jump so far.

Photo credit: Jeff Keyzer

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