The Role of Microstructures in Eclosion and Wing Expansion of Butterflies

Eclosion is the critical process of the butterfly transforming from a pupa into an adult. During this process, the morphology of the lepidopteran wings undergoes drastic changes, as the butterfly rapidly transitions from a wingless pupa to an adult with large-scale wings, resulting in a several-fold or even dozen-fold expansion in wing surface area. Although the lepidopteran wings undergo drastic morphological changes within a short period, this process does not cause damage to the butterfly’s body. The reason lies in the pupal developmental stage, where the wing membrane, veins, tracheae, and membranous tissues gradually differentiate into numerous micron-scale foldable units. They are double-layered, foldable structures and capable of providing a several-dozen-fold expansion in surface area—far exceeding the actual requirement for wing expansion—thus supplying sufficient surface area reserves for wing flattening. During eclosion, the foldable units are progressively unfolded under wing expansion forces, with the stored area being utilized as the foldable units are flattened sequentially. At the macroscopic level, this results in rapid expansion of the surface area. The unfolding process of lepidopteran wings is influenced by the structure and arrangement of wing veins, exhibiting a change trend where length increases first, followed by width. Therefore, the morphological changes of lepidopteran wings are the result of cumulative deformations in foldable units. In summary, these foldable units serve not only as the constituent units of the wings but also as functional units, regulating wing deformation and the unfolding process.