Abstract
BackgroundUltrastructures in butterfly wing scales can take many shapes, resulting in the often striking coloration of many butterflies due to interference of light. The plethora of coloration mechanisms is dazzling, but often only single mechanisms are described for specific animals.ResultsWe have here investigated the male Rajah Brooke’s birdwing, Trogonoptera brookiana, a large butterfly from Malaysia, which is marked by striking, colorful wing patterns. The dorsal side is decorated with large, iridescent green patterning, while the ventral side of the wings is primarily brown-black with small white, blue and green patches on the hindwings. Dense arrays of red hairs, creating a distinct collar as well as contrasting areas ventrally around the thorax, enhance the butterfly’s beauty. The remarkable coloration is realized by a diverse number of intricate and complicated nanostructures in the hairs as well as the wing scales. The red collar hairs contain a broad-band absorbing pigment as well as UV-reflecting multilayers resembling the photonic structures of Morpho butterflies; the white wing patches consist of scales with prominent thin film reflectors; the blue patches have scales with ridge multilayers and these scales also have centrally concentrated melanin. The green wing areas consist of strongly curved scales, which possess a uniquely arranged photonic structure consisting of multilayers and melanin baffles that produces highly directional reflections.ConclusionRajah Brooke’s birdwing employs a variety of structural and pigmentary coloration mechanisms to achieve its stunning optical appearance. The intriguing usage of order and disorder in related photonic structures in the butterfly wing scales may inspire novel optical materials as well as investigations into the development of these nanostructures in vivo.
Highlights
Ultrastructures in butterfly wing scales can take many shapes, resulting in the often striking coloration of many butterflies due to interference of light
We recently reported the coloration mechanisms of the Ornithoptera, a genus of birdwings closely related to Trogonoptera sp. [1], with colorful scales consisting of a large membrane stack that acts as a chirped multilayer [7], where the reflected light is filtered by papiliochrome pigments
We focus at the optics of T. brookiana’s green reflecting scales, but we analyze the interplay of pigmentary and structural coloration realized in other wing scale types, using spectrophotometry, imaging scatterometry, and transmission and scanning electron microscopy
Summary
Ultrastructures in butterfly wing scales can take many shapes, resulting in the often striking coloration of many butterflies due to interference of light. The plethora of coloration mechanisms is dazzling, but often only single mechanisms are described for specific animals. Butterflies are a hallmark of biodiversity and multifunctionality in nature. Of particular beauty are the birdwing butterflies of Australasia, which are noted by their exceptional size and a birdlike flight [1, 2]. An especially attractive butterfly is Rajah Brooke’s birdwing, Trogonoptera brookiana, the national butterfly of Malaysia. A detailed explanation of the striking coloration has yet to be made. Recent studies on butterfly coloration have revealed a multitude of optical mechanisms that strongly alter the composition of incident light and reflect strong colors.
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