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The Tortoise beetle Charidotella egregia is able to modify the structural colour of its cuticle reversibly, when disturbed by stressful external events. After field observations, measurements of the optical properties in the two main stable colour states and SEM and TEM investigations, a physical mechanism is proposed to explain the colour switching on this insect. It is shown that the gold colouration (rest state) arises from a chirped multilayer reflector maintained in a perfect coherent state by the presence of humidity in the porous patches within each layer, while the red colour (disturbed state) results from the destruction of this reflector by the expulsion of the liquid from the porous patches, turning the multilayer into a translucent slab that leaves a view on a deeper-lying pigmental red substrate. This mechanism not only explains the change of hue but also the change of scattering mode from specular to diffuse. Quantitative modelling is developed in support of this analysis.

The three-dimensional structure that causes the coloration of the tropical weevil Pachyrrhynchus congestus pavonius was studied, using a combination of electron microscopy, optical spectroscopy, and numerical modeling. The orange scales that cover the colored rings on the animal's body were opened, to display the structure responsible for the coloration. This structure is a three-dimensional photonic polycrystal, each grain of which showing a face-centered cubic symmetry. The measured lattice parameter and the observed filling fraction of this structure explain the dominant reflected wavelength in the reddish orange. The long-range disorder introduced by the grain boundaries explains the paradoxical observation that the reflectance, although generated by a photonic crystal, is insensitive to changes in the viewing angle.

Recent advances in the photonics and optics industries have produced great demand for ever more sophisticated optical devices, such as photonic crystals. However, photonic crystals are notoriously difficult to manufacture. Increasingly, therefore, researchers have turned towards naturally occurring photonic structures for inspiration and a wide variety of elaborate techniques have been attempted to copy and harness biological processes to manufacture artificial photonic structures. Here, we describe a simple, direct process for producing an artificial photonic device by using a naturally occurring structure from the wings of the butterfly Papilio blumei as a template and low-temperature atomic layer deposition of TiO2 to create a faithful cast of the structure. The optical properties of the organic-inorganic diffraction structures produced are assessed by normal-incidence specular reflectance and found to be well described by multilayer computation method using a two-dimensional photonic crystal model. Depending on the structural integrity of the initially sealed scale, it was found possible not only to replicate the outer but also the inner and more complex surfaces of the structure, each resulting in distinct multicolor optical behavior as revealed by experimental and theoretical data. In this paper, we also explore tailoring the process to design composite skeleton architectures with desired optical properties and integrated multifunctional (mechanical, thermal, optical, fluidic) properties.