Want to Climb Walls? Key Is Spider Grip

ByABC News
April 23, 2004, 10:58 AM

April 27 -- The itsy-bitsy spider went up the water spout, goes the nursery rhyme. But how exactly does the spider climb such a slippery vertical surface?

Now scientists think they have the answer hair. It's a simple discovery that may someday lead to innovative new technologies and products, ranging from stickier Post-it notes to space suits that adhere to surfaces in zero gravity.

Using a scanning electron microscope, researchers from Germany and Switzerland discovered small hairs on the feet of the jumping spider, or Evarcha arcuata. Each of the small hairs is covered in even smaller hairs called "setules," which have unique triangular tips.

These tiny setules more than 620,000 in all give spiders their superior ability to climb up water spouts, along walls and across ceilings.

The scientists estimated spiders are able to grip surfaces with a force greater than 170 times their own weight.

"That's like Spider-man clinging to the flat surface of a window on a building by his fingertips and toes only, whilst rescuing 170 adults who are hanging onto his back," says Andrew Martin of the Institute of Technical Zoology and Bionics in Bremen, Germany, co-author of the study, published in the most recent Institute of Physics journal Smart Materials and Structures.

The researchers speculate the force that allows spiders to climb glass and hang on ceilings is something known as the van der Waals force.

This form of attraction, based on the positive and negative charges of individual molecules, acts only when molecules of opposite charges are within a few nanometers of one another.

The triangular-tipped setules on spiders' feet are perfectly designed to take advantage of the van der Waals force because they form hundreds of thousands of flexible contact points.

Because there are many small contact points, spiders can adjust the number of contacts needed for different surfaces, whether vertical, horizontal, smooth or rough.