Scale Creates Broadband Diffuse Silver Reflectivity

Biological Strategy

AskNature Team

Modify Light/Color

Color in living systems comes from pigments and the interaction of light with surfaces. Color serves many purposes for living systems, such as attracting prey or mates, providing warnings, or protecting through camouflage. To create the effects needed for each purpose, living systems must control the expression or visibility of pigments and the interactions (such as reflectance and refraction) of light. To do so, they have strategies that modify color or light to increase or decrease the color’s position, intensity, opacity, and more. Male hummingbirds, for example, have brightly colored feather patches on their throats; the coloring comes from pigments, structures that refract light, or a combination of the two. When a male hummingbird hovers near a potential mate, it modifies the angle of these feathers to create a bright, colorful display. However, when it needs to mute the colors to reduce conspicuousness, such as to avoid a predator, it modifies the angle again.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Wings of the butterfly Argyrophorus argenteus creates silver color via sub-micron thick scales that scatter light and create a range of periodicities parallel to the scale surface.

“The butterfly Argyrophorus argenteus…appears to have overcome the design challenge associated with creating an efficient broadband reflection using very limited reflector thickness.” (Vukusic 2009:S194)

“It is the quasi-random variation in colour between these neighbouring bands and along each band’s length, concurrent with their close juxtaposition, which creates the overall broadband silver appearance of the butterfly’s wings…It is a structural design that not only coherently scatters visible light to produce colour but it simultaneously presents a range of periodicities that run parallel to the scale surface. It is this range that results in the scatter of a broad band of wavelengths and the production of its macroscopic silver hue through additive colour mixing.” (Vukusic 2009:S198)

“Its unusual colour appearance arises from a sub-micron thickness scale design that creates broadband diffuse silver reflectivity by multi-colour addition. This is achieved by incorporation of a unique design variation into its constituent multilayer reflector, one in which the required range of periodicities lies in the direction that is parallel to the surface rather than perpendicular to it as is the case with the much more common forms of natural broadband reflectors. Biomimetically, this A. argenteus scale design offers the basis for ultra-thin synthetic broadband reflectors, across a range of wavelength bands not limited only to visible wavelengths.” (Vukusic 2009:S200)