Birds, bats and many insects can tuck their wings against their bodies at rest and deploy them to power flight. Whereas birds and bats use well-developed pectoral and wing muscles and tendons, how insects control these movements remains unclear, as mechanisms of wing deployment and retraction vary among insect species. Beetles (Coleoptera) display one of the most complex wing mechanisms. For example, in rhinoceros beetles, the wing deployment initiates by fully opening the elytra and partially releasing the hindwings from the abdomen. Subsequently, the beetle starts flapping, elevates the hindwings at the bases, and unfolds the wingtips in an origami-like fashion. Whilst the origami-like fold have been extensively explored, limited attention has been given to the hindwing base deployment and retraction, which are believed to be driven by thoracic muscles. Using high-speed cameras and robotic flapping-wing models, here we demonstrate that rhinoceros beetles can effortlessly elevate the hindwings to flight position without the need for muscular activity. We show that opening the elytra triggers a spring-like partial release of the hindwings from the body, allowing the clearance needed for subsequent flapping motion that brings the hindwings into flight position. The results also show that after flight, beetles can leverage the elytra to push the hindwings back into the resting position, further strengthening the hypothesis of a passive deployment mechanism. Finally, we validate the hypothesis with a flapping microrobot that passively deploys its wings for stable controlled flight and retracts them neatly upon landing, which offers a simple yet effective approach to the design of insect-like flying micromachines.

翻译：鸟类、蝙蝠及多种昆虫在静止状态下可将翅膀收拢于体侧，并在飞行时展开以提供动力。鸟类和蝙蝠利用发达的胸肌、翼肌及肌腱实现这一过程，而昆虫控制这些运动的机制尚不明确，因为不同昆虫物种的翅膀展开与收拢机制存在差异。甲虫（鞘翅目）展现出最为复杂的翅膀机制之一。例如，在犀牛甲虫中，翅膀展开始于完全打开鞘翅并将后翅从腹部部分释放。随后，甲虫开始扑动，抬升后翅基部，并以类似折纸的方式展开翅尖。尽管这种折纸式折叠结构已得到广泛研究，但对于后翅基部的展开与收拢机制关注有限，传统观点认为这一过程由胸部肌肉驱动。本研究通过高速摄像与扑翼机器人模型，首次证明犀牛甲虫无需肌肉活动即可轻松将后翅抬升至飞行位置。我们发现，打开鞘翅会触发后翅从身体中如弹簧般部分释放，从而为后续扑动提供所需空间，使后翅进入飞行位置。结果还表明，飞行结束后，甲虫可利用鞘翅将后翅推回静止位置，这进一步支持了被动展开机制的假说。最后，我们通过一款扑翼微型机器人验证了该假说：该机器人能够被动展开翅膀以实现稳定可控飞行，并在着陆后整齐收拢翅膀，这为设计类昆虫飞行微型机器提供了一种简洁而有效的方案。