From BBC News:
The mystery of how frogs cling to surfaces – even if their feet are wet – may have been solved by scientists. A study of tree frogs has revealed their toe pads are covered in tiny bumps that can directly touch a surface to create friction. The scientists found this direct contact occurs even though the pads are covered with a film of watery mucus. The findings, published in the journal Interface, may aid the development of anti-slip devices.
“The toe pads are patterned with a fine structure of hexagonal cells with channels running between them,” explained Dr Jon Barnes, an author on the paper and a zoologist from Glasgow University. “One imagines if you are sticking to a leaf, that each cell, even if it is separate from the other cells, can form its own closest orientation.”