Elastic wing deployments in beetles and their folding mechanisms

Foldable hindwings in beetles are one of the ultimate deployable structures. They have sufficient strength and stiffness to tolerate 20-1000 beats per second in the flight position, although they can be folded and unfolded nearly instantly depending on the situation. This study focuses on a group of beetles that have unfolding-stable-type wings and aims to reveal their wing-folding/unfolding mechanisms. These beetles use their wing elasticity for deployment and can therefore quickly take off. First, on the basis of the reports of entomologists, the authors describe the factors related to the actuation of insect wing folding and unfolding. Then, the detailed motions involved in take-off and wing storing in ladybird beetles and rove beetles are observed by a high-speed camera. The analysis of these movies reveals the detailed processes of wing-unfolding and folding in these two species. Intrinsic elasticity plays a major role in wing development in both species. In the case of wing storing, a ladybird beetle folds its hindwings into a symmetric pattern using a simple up- down movement of the abdomen, whereas rove beetles also use their abdomens for wing-folding, but their movements are more complex, and the crease patterns are asymmetric. Finally, the characteristics of each wing-folding mechanism are summarized and the potential for engineering applications are discussed. Wing-folding/unfolding mechanisms in these insects have various unique capabilities which will provide new possibilities for designing deployable structures.