Spiders Are Found to Use Geckos’ Mechanism for Hanging Around
Spiders, it turns out, are very much like geckos -- at least in the way in which they cling to walls and ceilings.
In both cases, the creature’s extraordinary gripping ability has been found to be produced by Van der Waals’ forces generated by literally thousands of microscopic hairs on each of their feet. The discovery provides a remarkable example of evolution providing identical answers to the same problem in widely divergent species.
Researchers pondered for years how the gecko, which is substantially heavier than a spider, was able to scamper across ceilings so easily. In 2000, biologist Robert J. Full of UC Berkeley showed that the clinging ability was produced by minute hairs, or setae, on the animal’s feet. Each gecko toe contains more than 100,000 tiny hairs, and each of those hairs is split at the end into hundreds of even tinier tips.
The individual hairs get so close to whatever surface the gecko is climbing on that they generate a Van der Waals’ force, the same force that holds molecules together. The force generated by each tip is vanishingly small, but added up, they it gives the gecko tremendous clinging ability.
Now a team of German and Swiss researchers has reported in the journal Smart Materials and Structures that it used an electron microscope to show that the foot of the jumping spider, Evarcha arcuata, is covered with similar hairs, which the researchers call setules.
“We found out that when all 600,000 tips are in contact with an underlying surface, the spider can produce an adhesive force of 170 times its own weight,” said researcher Andrew Martin. “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 clinging to his back.”
The researchers speculated that one use of the discovery might be to develop Post-it notes that would cling to even wet or sticky surfaces. It might also be used to help spacesuit-clad astronauts stick to seats or floors in weightless environments.
