UK researchers have figured out how the tiny flea can leap vast distances through the air with the greatest of ease
WHITE MEN can’t jump, or so the movie of the same name tells us, but fleas certainly can – and very efficiently. Now scientists at the University of Cambridge have settled a 44-year-old dispute over how the tiny insects manage to launch themselves into the blue.
How fleas jump might not seem like a compelling issue in the world of science given alternative issues of concern such as global warming, loss of the rain forests and curing disease. Yet a scientific finding is a scientific finding, which in this case was pursued by UK academics at Cambridge, currently ranked the number one university in the world. And the findings are published this morning in the Journal of Experimental Biology.
The researchers involved, Prof Malcolm Burrows and Dr Gregory Sutton, also relied on highly elaborate methods, first filming the critters with specialised high speed cameras and then confirming what they saw by constructing mathematical models that predicted how the flea moved.
If nothing else, learning how the little bug manages to leap such vast distances in relation to its size has finally brought to an end a dispute about how it does this, which began back in 1967.
In that year researcher Henry Bennet-Clark solved at least one part of the flea mystery. The energy needed to launch in search of a hot meal - in the case of a flea, fresh blood - was stored in a highly springy protein pad made of a substance called resilin. Once cocked and ready to fire the resilin triggered in an explosive movement, transferring energy from the pad and down the leg. Here however agreement amongst the scientists ended.
Bennet-Clark held that the force for jumping was delivered by the insect’s toe or “tarsus”. Another researcher Miriam Rothschild came up with a compelling alternative, that in fact the force worked through the flea’s knee or “trochanter”.
Both parts of the bug’s leg were in contact with the surface just before it jumps, but for 44 years dispute remained over whether the toe or knee provided the insect’s launchpad.
The two Cambridge researchers were aware of the unanswered issue but admitted to being “very puzzled” about why it had never been settled. “We had a serendipitous set of hedgehog fleas show up so we figured we would take a crack at it and try to answer the question,” Dr Sutton said.
They were familiar with high speed camera equipment, using it to film locusts. So it was a major scale down to switch to filming jumping fleas, they said. The filming worked however because of a flea peculiarity. They stay completely still while in the dark and only begin jumping when the lights go on.
This meant the researchers could set the camera and focus before throwing on the lights and letting the bugs do their thing. The researchers filmed 51 jumps taken by 10 fleas and then analysed the results. They found that in five jumps only the toe was in contact with the ground while in the rest both joints touched the ground. Yet there was no difference in the quality of jumps.
They then analysed the bugs’ acceleration and found that they continued to accelerate during take-off, even after the knee was off the ground, implying the knee was not the platform for the jump.
Demanding the most conclusive results the scientists went a step further, producing mathematical models to describe knee-launched versus toe-launched flight, and finally the question was answered. There was a perfect match between the models of the Bennet-Clark toe-launch theory and what the researchers saw in the films. So if you are a flea, the only way to go is toe.
The insects achieve a significant speed, as high as 1.9meters per second on the basis of the filming, or 6.84km per hour. That might not sound like much of an accomplishment, but it is worth remembering that the flea weighs less than a thousandth of a gram and is little bigger than a grain of sugar.
