Functional characteristics of the rigid elytra in a bamboo weevil beetle Cyrtotrachelus buqueti

Gripping performance in the stick insect Sungaya inexpectata in dependence on the pretarsal architecture

Insect attachment devices and capabilities have been subject to research efforts for decades, and even though during that time considerable progress has been made, numerous questions remain. Different types of attachment devices are known, alongside most of their working principles, however, some details have yet to be understood. For instance, it is not clear why insects for the most part developed pairs of claws, instead of either three or a single one. In this paper, we investigated the gripping forces generated by the stick insect Sungaya inexpectata, in dependence on the number of available claws. The gripping force experiments were carried out on multiple, standardized substrates of known roughness, and conducted in directions both perpendicular and parallel to the substrate. This was repeated two times: first with a single claw being amputated from each of the animals' legs, then with both claws removed, prior to the measurement. The adhesive pads (arolia) and frictional pads (euplantulae) remained intact. It was discovered that the removal of claws had a detractive effect on the gripping forces in both directions, and on all substrates. Notably, this also included the control of smooth surfaces on which the claws were unable to find any asperities to grip on. The results show that there is a direct connection between the adhesive performance of the distal adhesive pad (arolium) and the presence of intact claws. These observations show collective effects between different attachment devices that work in concert during locomotion, and grant insight into why most insects possess two claws.

Numerical Simulations of the Effect of the Asymmetrical Bending of the Hindwings of a Hovering C. buqueti Bamboo Weevil with Respect to the Aerodynamic Characteristics

The airfoil structure and folding pattern of the hindwings of a beetle provide new transformation paths for improvements in the aerodynamic performance and structural optimization of flapping-wing flying robots. However, the explanation for the aerodynamic mechanism of the asymmetrical bending of a real beetle's hindwings under aerodynamic loads originating from the ventral and dorsal sides is unclear. To address this gap in our understanding, a computational investigation into the aerodynamic characteristics of the flight ability of C. buqueti and the large folding ratio of their hindwings when hovering is carried out in this article. A three-dimensional (3D) pressure-based SST k-ω turbulence model with a biomimetic structure was used for the detailed analysis, and a refined polyhedral mesh was used for the simulations. The results show that the fluid around the hindwings forms a vortex ring consisting of a leading-edge vortex (LEV), wing-tip vortex (TV) and trailing-edge vortex (TEV). Approximately 61% of the total lift is generated during the downstroke, which may be closely related to the asymmetric bending of the hindwings when they are subjected to pressure load.