STRUCTURAL COLOUR: STAR SPECIES NUMBER 1
Name: Morpho (butterfly)
Special Power: iridescence
The Morpho butterflies are Neotropical butterflies found mostly in South America, Mexico, and Central America. There are over 29 accepted species and 147 accepted subspecies of butterflies in the genus Morpho. Morphos range in wingspan from the 7.5-cm (3-in) M. rhodopteron to the imposing 20-cm (8-in) sunset morpho, M. hecuba.
The genus name Morpho comes from an Ancient Greek epithet μορφώ, roughly “the shapely one”, for Aphrodite, goddess of love and beauty.
Many morpho butterflies are coloured in metallic, shimmering shades of blues and greens. These colours are not a result of pigmentation, but are an example of iridescence through structural colouration. Specifically, the microscopic scales covering the morpho’s wings reflect the falling light repeatedly through successive layers, leading to interference effects that depend on both wavelength and the angle of incidence/observance. Thus, whilst the colours appear to vary depending on the viewing angle, they are actually surprisingly uniform, perhaps due to the tetrahedral (diamond-like) structural arrangement of the scales or the diffraction of light from overlying cell layers.
The wide-angle blue reflection property can be explained by exploring the nanostructures in the scales of the morpho butterfly wings. These optically active structures integrate three design principles leading to the wide-angle reflection: alternative lamellae layers (or layers of thin plates), Christmas tree-like shape, and zigzag pattern of the ridges. The reflection spectrum is found to be broad (about 90 nm) for alternating layers and is controlled by variations in the design pattern. The Christmas tree-like pattern helps to reduce or control the directionality of the reflectance by creating an impedance that matches blue wavelengths. In addition, the zigzag pattern of ridges destroys the unwanted interference for other wavelengths in wide angle. This structure may be likened to a photonic crystal.
The lamellate (plate like) structure of their wing scales has been studied as a model for the development of biomimetic fabrics, dye-free paints, and anti-counterfeit technology used in currency.