Ladybirds – exemplified by their cherry red regalia – have been hiding an incredible secret beneath the brightness of their shell. They have the flexibility to furl their wings into a tight space, yet also deploy them with enough stiffness and strength for flight. This is not just a simple case of origami, but a marvelous anatomical adaptation.
The findings of the new study, published in the Proceedings of the National Academy of Sciences, may inform a wide range of structures in robotics, mechanics, and aerospace engineering.
Underneath a ladybird’s cherry red shell is a pair of veined wings that unfurl for flight. The shell, known as an elytra, acts as a pair of modified forewings while also protecting the delicate, transparent hindwings when at rest. Yet how do ladybirds fold and deploy their hindwings without sacrificing too much flexibility and strength?
To test how ladybirds accomplish this complex engineering feat, the team led by Professor Kazuya Saito of the University of Tokyo made a transparent replica of the beetle's bright red elytra using UV-cured resin. They then anesthetized the ladybirds, fastened the artificial elytra, and used high-speed video and micro-CT scanning to observe the wings at work.
"From an engineering standpoint, the most interesting aspect of hindwings in beetles is how they can achieve the compatibility between the deformability (or instability) required for the wing storage and the strength properties (or stability) required for flying," the authors write. "These two properties generally demonstrate a trade-off relationship, and thus are difficult to combine."
Yet ladybirds have successfully resolved this issue with the evolution of thick veins relative to their body size and two folding lines in the longitudinal direction of the wing. The veins increase the strength, while the folds reduce stiffness. Yet, one would think these folds would also decrease the strength of the wing.
"Our results show that ladybird beetles solve this problem by using tape spring-like veins as the main wing-supporting structures," the team write. "This structure becomes elastically stable when it is extended and can be stored into a compact form only by elastic folding; therefore, it is widely used in the extension booms and hinges of space-deployable structures."
In a sense, the origami-like folds act like a hinge for wing storage and deployment. Most transformable objects need joints, hinges, and rigid parts to achieve the same ends, but these little beetles use the flexibility and elasticity of their wings to achieve a complex transformation with relatively simple structures.
These findings may go on to inform a range of designs, from satellite antennas to medical instruments to solar panels – essentially anything that needs to fold into a small space, yet retain its durability and rigidity when unfurled.