Geckos tend to get a lot of attention from scientists, thanks to their fascinating feet. A gecko's feet are padded with microscopic hairs that create an attraction between the atoms in its feet and the surface (called van der Waal forces), which is what lets them stick to surfaces and climbs up walls and trees. Roboticists try to copy gecko feet to build bots that can scale vertical surfaces.
But what happens when a gecko's feet get wet? Plenty of geckos live in wet, tropical habitats, so they must have the ability to find their footing in those environments as well.
Recently, a few scientists at the University of Akron in Ohio led by Alyssa Stark decided to see how good a gecko's traction in the wet really is. (Their study appears in The Journal of Experimental Biology.)
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Stark's team started by anchoring the tiny creatures with a leash and harness attached to a motor that measures exactly how much force is exerted on the gecko. At first, they tested how much force it takes to pull the little guys from dry glass. It turns out geckos can hang on for dear life—the scientists had to pull with the force of about 20 times a gecko's body weight to get them unstuck.
Things changed once the glass was misted. The geckos couldn't keep their footing for more than a couple steps before they were pulled away. The results were the same when the lizards were placed into a shallow container with a little room-temperature water covering the glass bottom. Although the gecko's toes remained dry thanks to tiny air bubbles that encircled the water-repelling digits, the hair on its feet weren't so lucky, Stark says. Once its feet were soaked, the gecko lost its sticking power.
For the team's final experiment, they soaked the gecko's feet in water for 90 minutes before placing it on a dry piece of glass. The lizard could hang on only until the motor pulled it with just the force of the gecko's body weight.
All of this means that even though geckos can walk in wet environments for a time, if their sticky feet get too wet, they can't hold fast. The moisture overpowers the attractive forces produced by its microscopic hairs.