A leaf-mimicking moth uses nanostructures to create 3D leaf shape appearance

Abstract

Nature provides many astonishing examples of visual deception, from fish that resemble leaves to spiders and butterfly pupae that look like bird droppings or moth larvae that bear a striking resemblance to the head and neck of a tree snake.^1,2 Most types of camouflage rely on preventing object detection, but this strategy of resemblance, known as masquerade, operates by fooling the viewer into misidentifying the animal as an inedible or unprofitable object rather than as predator or prey.³ As masquerade hinders object identification, the masquerader must have coloration that recreates the visual features of the object being mimicked. Here, we report a leaf-mimicking nocturnal moth, Eudocima aurantia (Noctuidae), that mimics not only leaf coloration but also a leaf's surface highlights and appearance. The three-dimensional (3D) leaf-like appearance, which is accentuated by the apparent presence of a 3D midrib, is achieved with a featureless planar wing featuring uniformly oriented scales that combine structural and pigmentary coloration. Remarkably, these specialized nanostructures occur in those regions of the wing surface that correspond to the convex parts of a leaf. These structures and pigments combine scattering, absorption, and additive color mixing to produce a leaf-like brown coloration. E. aurantia has exploited the inherent mirror-like properties of thin-film reflectors to produce directional reflections that are usually associated with highlights on smooth, curved surfaces. Specular reflections provide a strong indicator of surface curvature to visual systems,⁴ suggesting that 3D shape mimicry is an integral part of the visual deception.

Keywords: camouflage; gloss; interference; iridescence; masquerade; mimicry; shape perception; structural coloration; thin-film interference; visual illusion.