The Secret Life of Fleas

Caren B. Les, caren.les@photonics.com

If you’ve ever wondered whether fleas jump using primarily their toes or their knees, wonder no more. Gregory P. Sutton and Malcolm Burrows at the University of Cambridge in the UK have solved the mystery. Using a high-speed camera, they filmed 10 leaping fleas, proving that the creatures push off with their toes.

Since 1967, there had been a somewhat heated debate among scientists as to whether fleas, in their energetic frenzy, push off with their knees or toes.

Upon realizing that fleas remain perfectly still in the dark and resume their jumping antics when the lights are on, Sutton and Burrows focused their camera on the insects in low light, capturing 51 jumps from their newly acquired set of adult hedgehog fleas. They found that, in the majority of jumps, the toe and the knee were in contact with the ground for the push-off, but in 10 percent of the jumps, only the toe touched the ground. They asked themselves whether the knee really was necessary to gain altitude or whether the fleas used both toe and knee in their hopping activity.

The researchers used scanning electron microscopy to view the fleas’ legs and discerned that the shins and toes were equipped with gripping claws, but that the knees were completely smooth – not suitable for getting a good grip for push-off. They began to suspect that the insects push down through their shins onto their toes.

In the end, to attain scientific certainty, Sutton generated mathematical equations that could be used to calculate the insects’ trajectory. He compared the jumping activity visualized in the film with his calculations to see how well they agreed and, as a result, determined that the creatures transmit the force from the spring in the thorax through leg segments acting as levers to push down on the toe and launch their 0.7-mg selves at speeds as high as 1.9 m/s.

We hope that no fleas were harmed in the experiment.