Friction Coefficient Evolution of Drying Lubricant in the Joints of Beetles by Friction Force Microscopy

Abstract Recent studies suggest that the joints of beetles and other insects comprise micro-structured surfaces in combination with lubricants. Here, we utilize friction force microscopy (FFM) to analyse the tribological properties of the femoro-tibial leg joints by the example of Coelorrhina aurata (metallic green flower beetle) and Otiorhynchus sulcatus (black vine weevil). To preserve the original state of the lubricant as well as the microstructures, the FFM measurements were conducted in silicone oil, which satisfies our requirements of transparency, customizable viscosity, absent health risks and lower density compared to the expected density of the lubricant. Microscopic friction was measured on fresh and air-dried samples to stress the change of the lubricant properties over time. Despite the similarity of the two beetle joints, the FFM measurements reveal different frictional properties of the respective lubricants.