Adaptive adhesion by a beetle: manipulation of liquid bridges and their breaking limits.

A drop brought into contact with a nearby substrate can wet and spread against the substrate, forming a liquid bridge that exerts a capillary force. This force due to surface tension can be used to “grab” the substrate, pulling it toward the drop. “Wet” adhesion results from the parallel action of an array of small liquid bridges. The Florida palm beetle, Hemisphaerota cyanea, uses wet adhesion to defend itself against attacking predators by adhering to the palm leaf using an array of about 120 000 μm-sized liquid bridges. The beetle's survival depends on the strength of adhesion which, in turn, depends on how liquid bridges break. Individual bridges break when they go unstable, according to their response curves. However, the ultimate strength of an individual bridge depends on the class of disturbances to which it is subjected, and it has been speculated that the beetle may have some control over this class. The authors experimentally study families of liquid bridge equilibria for their breaking limits ...