National Geographic News
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Matt Kaplan

for National Geographic News

Published February 11, 2011

It was no small task, but researchers have solved a long-term mystery—how fleas jump. Now high-speed video (watch above) confirms the insects take off using their toes, scientists announced Thursday.

Silly as it might sound, catching fleas mid-leap is hard, mostly because they're just too fast to capture on film—until now.

Without good photographic evidence, scientists' only alternative has been to examine dead fleas' body parts.

Such flea dissections—combined with the limited high-speed video technology available in the past—revealed that the insects powered their leap with energy stored in one spring inside their bodies.

But how the critters were pushing off the ground remained a total unknown.

Some experts had proposed that fleas push off with their knees, while others had speculated that the insects push off with their toes.

(Related: "Froghopper Bug Crowned 'World's Greatest Leaper.'")

Fleas Keep Team on Their Toes

For the new study, Gregory Sutton and Malcolm Burrows, both of the U.K.'s University of Cambridge, modeled how a flea would have to move to jump from its toes versus its knees.

"I'm a mechanical engineer by training, and, when looked at as a machine, the insect jump is an almost unbelievably fast, precise, and reliable motion," Sutton said.

"It made me really curious about how insects used their bodies to do this."

(Also see "How Snakes Can 'Fly.'")

The team then compared these models to the new high-speed film footage, which had captured live fleas leaping.

The team worked with a flea species that stayed mostly still in darkness, which proved to be an advantage. That's because the researchers could keep the lights off and more easily focus the camera on the flea.

Then, the moment the team turned the lights back on, the flea would jump with the camera already focused.

Fleas' movements on camera were completely consistent with the idea of fleas jumping from their toes, the experts say.

For instance, in 12 percent of the insects' jumps, knees never even made contact with the ground, the results showed.

Ain't that the fleas' knees.

Flea-jumping study published online in February in the Journal of Experimental Biology.

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