Australian tree frogs hang from tilted surfaces using the same physics as adhesive tape, experiments have found.
White’s tree frogs (Litoria caerulea) secrete mucus from their toe pads to hold on to steep surfaces through capillary forces, similar to the way a wet piece of tissue sticks to a window. In this video, the researchers place a frog on a platform and begin to tilt the platform up to a vertical position (90° in the counter at top left) and then continue rotating until the frog is hanging upside down and eventually falls off (typically at around 150°).
The frog starts out in a crouching position with its legs tucked under its body. As the challenge increases, however, the amphibian engages in a sprawling dance.
The researchers found that this splaying behavior is rooted in the same physical principle that applies to adhesive tape. The easiest way to peel tape away from a surface is by pulling one corner away at the largest possible angle from the sticking surface; pulling the tape at a shallow angle makes it virtually impossible to get unstuck. Australian tree frogs mimic this effect by stretching their limbs to maintain a shallower angle with respect to the platform as it rotates, the researchers write in Journal of the Royal Society Interface.
“This experiment shows the maximum adhesive force a frog can take,” says Thomas Endlein, a biologist at the University of Glasgow, UK, who led the study. “But usually frogs would avoid overhanging surfaces to avoid such difficult sprawling positions.”