Geckos aren’t the only animals that use van der Waals force to stick to the ceiling. Scientists in Germany and Switzerland have been using electron microscopes to look at the feet of jumping spiders. There they’ve found the same hairs-covered-by-hairs combination that gecko feet have. Once again the hairlets are so small that they can fit into the force fields around molecules and stick fast. Calculations show that the total sticking power of their feet could theoretically hold 173 times their weight.
The jumping spiders – hunters, not web builders – have an added twist to their use of van der Waals force fields. They don’t simply make passive use of the force. The structure of the setules, the smaller hairlets on their feet, allows their van der Waals forces to combine into a very strong overall force on each foot. The spiders are producing their own adhesion, not just making use of the existing forces in the ceiling.
Like geckos, jumping spiders can stick to the ceiling even if it’s wet or oily, no matter how smooth it is. That’s because the setules and the molecules of the ceiling meet in spaces so small that concepts of roughness and wetness simply don’t compute.
This research opens up interesting possibilities for adhesives. Dry, all-purpose, all-weather, reusable duct tape comes to mind.
Jumping spiders sound like the nightmares of the small world. Unlike some other species of spiders, which can have their eight eyes arranged all around their heads, hunting spiders tend to have theirs clustered on the front. All the better to focus on their prey, I imagine. Some of them also bungee jump. They go after flying prey, including birds for some larger spiders, by jumping into the open air. If they miss they haul back up the strand of web to where it’s attached at their launch site and wait for the next meal on wings.
All this and sticky feet, too. Their ability to cling to any surface, focus acutely on moving objects and jump great distances add up to an extremely efficient hunter. It makes you wonder if any of them hunts geckos. Hunter and prey running across the same molecular force field.