Smart joints: auto-cleaning mechanism in the legs of beetles

The auto-cleaning system in digging forelegs of the Congo rose chafer Pachnoda marginata femoro-tibial joint is described. The cleaning system consists of four subsystems: three external ones represented by microsetal pad, hairy brush and scraper and one internal one. They work proactively not only removing contaminants, but also preventing them from entering the joint. The principle of functioning of the cleaning system is based on the sliding of the contacting surfaces of the joint, equipped with hairs, bristles and scrapers. The mutual movement of such surfaces leads to the shift of contaminating particles and, ultimately, to their removal from surfaces of the joint. The key feature of the joint cleaning system is its complete autonomy, in which cleaning is performed constantly with each movement of the femoro-tibial joint without special actions required from the insect. The difference between the auto-cleaning system and self-cleaning and active grooming is also discussed.