Tree frogs need to adhere to surfaces of various roughnesses in their natural habitats; these include bark, leaves and rocks. Rough
surfaces can alter the effectiveness of their toe pads, due to factors such as a change of real contact area and abrasion of the pad
epithelium. Here, we tested the effect of surface roughness on the attachment abilities of the tree frog Litoria caerulea. This was
done by testing shear and adhesive forces on artificial surfaces with controlled roughness, both on single toe pads and whole animal
scales. It was shown that frogs can stick 2–3 times better on small scale roughnesses (3–6 µm asperities), producing higher adhesive
and frictional forces, but relatively poorly on the larger scale roughnesses tested (58.5–562.5 µm asperities). Our experiments
suggested that, on such surfaces, the pads secrete insufficient fluid to fill the space under the pad, leaving air pockets that would
significantly reduce the Laplace pressure component of capillarity. Therefore, we measured how well the adhesive toe pad would
conform to spherical asperities of known sizes using interference reflection microscopy. Based on experiments where the conformation
of the pad to individual asperities was examined microscopically, our calculations indicate that the pad epithelium has a low
elastic modulus, making it highly deformable