44-year-old mystery of how fleas jump resolved (w/ Video)

February 10, 2011, The Company of Biologists
This image shows the anatomy of a flea showing sections of the leg. Credit: Gregory Sutton

If you thought that we know everything about how the flea jumps, think again. In 1967, Henry Bennet-Clark discovered that fleas store the energy needed to catapult themselves into the air in an elastic pad made of resilin. However, in the intervening years debate raged about exactly how fleas harness this explosive energy. Bennet-Clark and Miriam Rothschild came up with competing hypotheses, but neither had access to the high speed recording equipment that could resolve the problem. Turn the clock forward to Malcolm Burrows' Cambridge lab in 2010.

'We were always very puzzled by this debate because we'd read the papers and both Henry and Miriam put a lot of evidence for their hypotheses in place and their data were consistent with each other but we couldn't understand why the debate hadn't been settled,' says Burrows' postdoc, Gregory Sutton. He adds, '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'. Filming leaping fleas with a high-speed camera, Sutton and Burrows found that fleas push off with their toes (tarsus) and publish their discovery in The .

'We were concerned about how difficult it would be to make the movies because we are used to filming , which are much bigger than fleas,' admits 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% of the jumps, only the tarsus (toe) touched the ground. Sutton explains that Rothschild had suggested that fleas push off with the trochanter (knee), but if 10% of the jumps didn't use the trochanter (knee) was it really necessary, or were the fleas using two mechanisms to get airborne?

Burrows and Sutton needed more evidence. Analysing the movies, the duo could see that the insects continued 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 exactly the same way as the insects that jumped using the trochanter (knee) and tarsus (toe). Also, when Burrows and Sutton looked at the flea's leg with scanning electron microscopy, the tibia (shin) and tarsus (toe) were equipped with gripping claws, but the trochanter (knee) was completely smooth, so it couldn't get a good grip to push off. Sutton and Burrows 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: a mathematical model that could reproduce the flea's trajectory.

'I looked at the simplest way to represent both models,' explains Sutton. Building Rothschild's model as a simple mass attached to a spring pushing down through the trochanter (knee) and Bennet-Clark's model as a spring transmitting the spring's force through a system of levers pushing on the tarsus (toe), Sutton generated the equations that could be used to calculate the insect's trajectory. Then he compared the results from his calculations with the movies to see how well they agreed.

Both models correctly predicted the insect's take-off velocity at 1.35m/s, but then the Rothschild model began to go wrong. It predicted that the insect's acceleration peaked at a colossal 22,000m/s2 (2200g), whereas the acceleration of the insects in the movies only peaked at 1500m/s2 (150g). However, Sutton's calculations based on the Bennet-Clark lever model worked perfectly, accurately predicting the insect's trajectory and acceleration pattern.

So Sutton and Burrows have finally settled the argument and resolved how jump. The 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.

Explore further: Male water fleas observed for first time

More information: Sutton, G. P. and Burrows, M. (2011). Biomechanics of jumping in the flea. J. Exp. Biol. 214, 836-847. jeb.biologists.org/cgi/content/abstract/214/5/836

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4.8 / 5 (6) Feb 10, 2011
I saw a flea jump once. I had just gotten out of the shower and was toweling in front of a window and the sun was shining in just right to see him perfectly. He jumped from the floor to my thigh to my chest and then to my head in about a half second. So fast I couldn't even react. Amazing, especially considering they tumble through the air. (I owned a dog at the time)

Another time there was an unoccupied cottage where I lived. A caretaker and his dog lived there before but no one had gone in there for a few months. I wanted to see what was inside and went in. Within 30 seconds of walking in both my ankles started to burn. I pulled my pants leg up, didn't see anything. The burning was under my sock. I rolled one sock down and under the top inch of the sock was a black band of fleas, hundreds biting my ankle. They all went to the same place on both legs in around 30 seconds. I ran outside and ripped off all my clothes, my room mates thought I was nuts running across the yard naked..

5 / 5 (1) Feb 10, 2011
Moebius... your story instantly made me itch!
not rated yet Feb 10, 2011
Moebius, i commend you for sharing your story!
not rated yet Feb 10, 2011
They all went to the same place on both legs in around 30 seconds

Yep... I'm a veterinarian and I see this kind of thing all the time. Vacated home where previous occupants had pets. New people move in and they and their pets have a flea tsunami to deal with. Turns out that fleas develop to the pupa stage and then remain suspended. When stimulated by vibrations they very rapidly hatch and attack. I commonly have people in my office pleading with me to help them do something to deal with this problem.

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