Protection in the wings
Beetles have hardened forewings for the protection of their bodies and hindwings, and their use during crawling or burrowing is well understood. However, the behavior of the larger hindwings during collisions in flight has not been clear because they do not readily flex. Phan and Park present a detailed study of the folding and unfolding mechanisms of the hindwings in free-flying rhinoceros beetles in which the wings were impacted during flight to simulate a cluttered environment (see the Perspective by Sun). They found that origami-like folds in the wing could rapidly collapse on impact and then spring back, thus acting as shock absorbers and stabilizers. The authors replicated this behavior in a flapping-wing robot, enabling it to fly safely after collisions.
At rest, beetles fold and tuck their hindwings under the elytra. For flight, the hindwings are deployed through a series of unfolding configurations that are passively driven by flapping forces. The folds lock into place as the wing fully unfolds and thereafter operates as a flat membrane to generate the aerodynamic forces. We show that in the rhinoceros beetle (Allomyrina dichotoma), these origami-like folds serve a crucial shock-absorbing function during in-flight wing collisions. When the wing collides with an object, it collapses along the folds and springs back in place within a single stroke. Collisions are thus dampened, helping the beetle to promptly recover the flight. We implemented this mechanism on a beetle-inspired wing on a flapping-wing robot, thereby enabling it to fly safely after collisions.