Like the comic book hero Spider-Man, who shoots webs from his wrists to swing through the city, real-life tarantulas spin silk from their feet to walk on slippery surfaces, according to a new study.
"To my knowledge, no other animals are using silk for locomotion," said Stanislav Gorb, a biologist at the Max Planck Institute for Metals Research in Stuttgart, Germany.
Gorb and colleagues found that zebra tarantulas secrete tiny bits of silk from nozzlelike structures in their feet. These tethers allow the arachnids to scale vertical surfaces.
The discovery supports a hypothesis that ancient spiders first evolved to produce silk from their feet before changing to the modern configuration of producing it in their abdomens.
"It makes sense actually," Gorb said. "We know that all the extremities of ancestor arachnids probably had this possibility to adhere during locomotion, for example, or during prey capture."
Alternatively, the foot secretions may have evolved independently in tarantulas to help the relatively large spiders move around safely, he adds.
(Related interactive feature: tarantula anatomy and life cycle.)
Gorbs team reports the discovery in tomorrow's issue of the science journal Nature.
Silk Tethers
Fritz Vollrath is a zoologist and expert on spider silk at the University of Oxford in England, who was not involved in the research.
He says silk production was long thought to have evolved from glands found on the legs of early spiders.
Until now no one had so clearly shown evidence that the glands actually exist on the feet of a living spider.
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