Itching To Know How Fleas Flee? Mystery Solved A 40-year-old controversy about how a flea jumps has now been resolved: Fleas take off from their feet, not from their knees. The key? Structures in their legs that act like tiny springs and ground-gripping hooks on their feet.
NPR logo

Itching To Know How Fleas Flee? Mystery Solved

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript
Itching To Know How Fleas Flee? Mystery Solved

Itching To Know How Fleas Flee? Mystery Solved

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript


OK. There are big controversies in science. And there are small ones. This is a story about a small one, a really small one: a debate about the way a flea jumps off the ground. And as NPR's Joe Palca reports, after 40 years, the controversy has been resolved.

JOE PALCA: Before you dismiss this story as trivial and esoteric, just be aware that what scientists have learned from studying flea jumping may someday be useful in building robots or sophisticated control systems. Now, on with the story.

Gregory Sutton is at the University of Cambridge in England. He's interested in how insects control the way they jump.

Dr. GREGORY SUTTON (University of Cambridge): Because it's an incredibly fast, incredibly precise motion, and they don't have enough time for any neurofeedback to fix mistakes.

PALCA: In other words, no way to make midcourse corrections.

Dr. SUTTON: It's got to be set up, and it's got to go off perfectly the first time, every time.

PALCA: Sutton has studied how insects like locusts use their legs to leap. But locusts have their legs out to the side, whereas fleas have them under their bodies.

Dr. SUTTON: So I wanted to see: How do fleas control which direction they jump?

PALCA: The energy for a flea leap comes from what amounts to a spring inside the flea's leg. The flea's muscles compress the spring, and when it's time to jump, the spring is released. The key to understanding the speed and direction of the jump is understanding how the forces released by the spring are transmitted through the leg to the ground.

Forty years ago, two scientific papers came out on this topic.

Dr. SUTTON: And these two papers had differing hypotheses as to how the forces were getting to the ground.

PALCA: One paper, by a scientist named Miriam Rothschild - of�the�Rothschilds, by the way - suggested that the force was exerted through the flea's trochanter.

Dr. SUTTON: A trochanter is like a knee to a flea.

PALCA: The other paper, by Henry Bennet-Clark, argued that the force went through the flea's tarsus - essentially, its foot. Sutton decided to see who was right.

Dr. SUTTON: The first thing was to get the fleas.

PALCA: And where does someone working in Cambridge, England get a supply of fleas?

Dr. SUTTON: We got it from a hedgehog hospital called St. Tiggywinkles.

PALCA: Come again?

Dr. SUTTON: St. Tiggywinkles hedgehog hospital.

PALCA: What is a hedgehog hospital?

Dr. SUTTON: They rescue animals from around the countryside - mostly hedgehogs, but also badgers and deer and other things in the countryside - and they nurse them back to health.

PALCA: The hospital staff removed some fleas from their patients and sent them to Sutton.

Dr. SUTTON: And then we filmed them with high-speed video.

PALCA: The videos clearly showed that the fleas could jump when their knees weren't even touching the ground. Sutton and his colleagues also looked at the fleas with an electron microscope.

Dr. SUTTON: We were looking for things to give the animal traction. And we found there were hooks to give the animal traction on the foot, but we didn't find any of these hooks on the knees.

PALCA: And finally, Sutton made a mathematical model for how a flea jump would work if it started from the knee or the foot.

Dr. SUTTON: The numerical model of the Bennet-Clark mechanism produced a much better fit for the velocities and accelerations we saw than did the Miriam Rothschild model.

PALCA: These results appear in�The Journal of Experimental Biology.

Penn State's Jim Marden says Sutton has proven that Bennet-Clark, the foot guy, was right.

Dr. JIM MARDEN (Pennsylvania State): Oh, slam-dunk. I mean, the movie images alone show very conclusively what the takeoff pattern is.

PALCA: The numerical model and the electron microscope images are icing on the cake.

So how does Henry Bennet-Clark feel about being proven correct after all these years?

Dr. HENRY BENNET-CLARK (Zoology, Oxford University): Let's put it this way: It leaves me unsurprised, because I always thought that the trochanter idea of Miriam Rothschild was as silly as the statement I'm about to make, which is: I'm about to jump off my chair by clinching my buttocks.

PALCA: He's right about that. You can try yourself if you don't believe him.

Joe Palca, NPR News, Washington.

(Soundbite of music)

INSKEEP: This must be NPR News.

Copyright © 2011 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.