Tree frogs use a combination of mucus and molecular forces to walk on vertical glass.

The remarkable climbing ability of tree frogs is primarily attributed to their specialized digital pads. Research led by Dr. Jon Barnes at the University of Glasgow has revealed that these pads are covered in hexagonal epithelial cells roughly 10 micrometers wide. These cells are separated by deep channels that allow mucus to flow evenly across the surface.This mucus layer creates a capillary bridge between the toe pad and the surface. Capillary adhesion is the same force that makes two wet glass slides stick together. Because the mucus is watery rather than glue-like, the frog can detach its feet instantly by simply changing the angle of its toe. This process is known as 'wet adhesion' and is highly efficient even on rough or dirty surfaces.Beyond fluid dynamics, tree frogs also utilize van der Waals forces. These are weak electric attractions between molecules that occur when surfaces are in extremely close contact. This dual-mechanism allows species like the Red-eyed Tree Frog (Agalychnis callidryas) to support up to 50 times their own body weight on a vertical plane.Engineers are currently studying these biological structures to develop new types of reusable adhesives. By mimicking the hexagonal patterns and fluid distribution of frog skin, researchers hope to create tires with better wet-weather grip and medical bandages that stay secure without damaging sensitive skin. This field of biomimicry highlights how evolution has solved complex friction and adhesion problems over millions of years.