Geckos in harnesses keep grip even in some wet spots, study finds

Scientists studying the secrets of gravity-defying geckos have discovered that the lizards’ toes can grip certain surfaces even when wet.

The findings, published in Proceedings of the National Academy of Sciences, could help scientists design sticky tape that even works under water.

Geckos are a remarkable and diverse group of lizards — there are more than 1,400 species worldwide, and many live in wet, tropical environments. Researchers have studied the ability of the gecko to cling to ceilings and walls without using very sticky substances. In 2002, they discovered that the gecko foot’s microscopic topography — made of tiny hairlike structures called setae, which themselves have even smaller “split ends” called spatulae — take advantage of a weak electrostatic force called the van der Waals force.

And even though scientists have used their discoveries to design wall-climbing robots, and even “gecko tape,” scientists still don’t understand much about how gecko feet work — including how well they work under water.

To answer this question, researchers from the University of Akron in Ohio had six tokay geckos climb several different types of surfaces — both when dry and when covered in a centimeter of water — while they were in harnesses and pulled on them until they slipped.

They found that the geckos were able to stick to surfaces that were wet or dry, so long as those surfaces were hydrophobic. A hydrophobic surface repels water, which is why water droplets on waxy leaves form tight little beads rather than spreading out in a little puddle.

On a wet glass surface, however, the geckos struggled to maintain their grip. Glass is a hydrophilic surface (on which water happily spreads out).

Water-repellent surfaces, then, appear to be key to the gecko foot’s power. This makes sense, the researchers reasoned, given that geckos should be able to navigate those waxy leaves in their natural, often tropical environments.

Wet glass, however, hasn’t been an issue until quite recently in evolutionary history.

“Our findings highlight the importance of considering the natural environments in which geckos use their adhesive system,” the authors wrote.

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