What does a tarantula do when it comes across a slippery surface in its travels ... It spins silk out of its feet to aid in locomotion. It is believed that tarantulas are the only animal to use silk in locomotion. The study was written by 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.
The study can be found in the current issue of Nature, which if you don't have a university paying for it, costs a fortune.