(Photograph) - Hans Mathes reaches for a hair-fine string of copper wire and twists it into a braid until only a tiny loop is left. Then he fetches one of his artistes. They are magnificent athletes: they can kick balls more than 30 times as heavy as themselves, or turn a carousel 20,000 times their weight. Yet they are barely bigger than a grain of sand - they are human fleas.
Mr Mathes carefully holds a flea between his thumb and index finger, moving the little copper wire loop over its head and first pair of legs. Then he delicately squeezes the loop to hold in the flea - too much pressure, and it meets its maker.
Flea circuses were common in medieval Europe, an attraction at just about every county fair. Everybody had fleas, and anybody able to handle them could create his or her own circus in a box. The Mathes family has been in the business for 150 years, and performed for the Pope and the Russian Tsar. But times have changed, and these days the director of Europe's last flea circus works a day job as a janitor in a semiconductor factory in Nuremberg.
The flea circus leaves its little box only two weeks a year to perform at Munich's famous Oktoberfest. The fleas are versatile performers: they can play soccer, pull carriages, turn carousels, juggle, and dance.
But how do you train a flea? Mr Mathes uses their natural instincts and enormous physical capacities. But there's also conditioning involved, something many biologists considered impossible, until recently, for such simple creatures. "You have to observe them carefully," Mr Mathes explains. "Some of them tend to jump, some prefer to just walk."
The "natural jumpers" become soccer players. n the circus, the football fleas are held by their wire harnesses to a little styrofoam ball. "I'm using the flight instinct of the insects," says Mr Mathes. "They want to get away from light." When the fleas feel the ball under their feet, they interpret it as the ground and try to jump - kicking the ball into a tiny soccer goal.
Fleas can jump heights of more than 20cm and distances of more than 35cm, incredible feats for their size. If they were as big as humans, they would be able to jump over a cathedral, and in a thousandth of a second. No vertebrate muscle can contract that rapidly. Fleas do the trick with two tiny spheres made of a protein called resilin, a substance more elastic than rubber, which is attached just above the hind legs. They squeeze these protein rubber balls using the muscles on their hind legs, then lock the legs with a hook located under their bellies, like a crossbow ready to fire. The hook is released and the insect jumps with an acceleration more than 20 times that of the space shuttle.
It takes a lot more training to keep fleas from jumping and to turn them into the dedicated performers Mr Mathes needs for his delicate carriages and carousels. "I have a set of boxes for them," he says. "First, I put them into relatively high boxes so they can jump around a little, then the boxes become ever lower. Finally, they completely give up jumping."
Weblinks Flea biology and health risks: http:www.uos.harvard.eduehshot_topicspom_fleas.html
Fun electrical fleas experiment: www.exploratorium.edusnackselectrical_fleas.html
Fleas and the Black Death: http:www.insecta-inspecta.com
Photograph by Volker Steger