Abstract: Some tribological behavior between mature Gampsocleis gratiosa foot pads and vertical flats of different materials were studied in this work. stereomicroscope (SMS) and scanning electron microscope (SEM) were used to measure the morphology of the Gampsocleis gratiosa foot pads. An atomic force microscope (AFM) was used to measure the morphologies of the surfaces of glass and a wall doped with calcium carbonate material. The attaching behavior of Gampsocleis gratiosa feet on the two vertical surfaces was observed. The attaching force (perpendicular to the vertical surface) and the static frictional force (along the direction of gravitation) of Gampsocleis gratiosa foot pads on a vertical glass were measured. It was shown that the average attaching force is 50.59 mN and the static frictional force is 259.10 mN. The physical models of the attaching interface between Gampsocleis gratiosa foot pads and the two vertical surfaces were proposed. It was observed that the foot pads are smooth in macroscale; however, the pad surface is composed by approximate hexagonal units with sizes of 3 μm to 7 μm in microscale; the adjacent units are separated by nanoscale grooves. The Observations showed that the Gampsocleis gratiosa can not climb the vertical calcium carbonate wall; in contrast, they can easily climb the vertical glass surface. Based on the features of the geometrical morphologies of the foot pads and the glass surface, we speculate that the attaching force and strong static frictional force are attributed to the inter-inlays between the deformable Gampsocleis gratiosa foot pads and the nanoscale sharp tips of the glass surface.

Key words: foot pad, Gampsocleis gratiosa, surface microstructure, static friction, tribology