Invertebrate biodiversity has inspired technological advances ranging from optical computing chips and solar panels to self-filling water bottles and chainsaw teeth. Biomimicry is a process where nature is modeled to inspire a version to solve a human problem. For example, the iridescent wing scales of the Morpho butterfly inspired energy-efficient digital displays used to develop interferometric modulator display (IMOD) technologies implemented in portable electronic screens.
The goal of this project is to provide a database of cuticular structural color mechanisms in insects, with a focus on iridescence. Colors of insects result from the interaction of their cuticle with light. Pigmentary colors, such as the red of a ladybug, is due to the absorption of visible light by chemicals within the cuticle. In contrast, structural iridescent color in insects is the result of a wide variety of mechanisms including quasi-ordered scattering, chirped broadband reflectors, birefractive bowls, opalescent photonic crystals, and Tyndall scattering.
The silver of a Jewel beetle is a result of refraction of light by cuticular layers of varying reflective indexes stacked in the exoskeleton. Color is also imparted by diffraction of light by regularly spaced structures on the exoskeleton of the insect. These can be microscopic grooves or parallel gratings that scatter light into various wavelengths. For example many butterflies have wing scales with regularly repeated microscale ridges on them that are responsible for their metallic color. Color depends on the spacing and shape of the ridges, and the angle at which the surface is viewed. For an excellent review of iridescent colors of beetles, refer to Gold bugs and beyond: a review of iridescence and structural colour mechanisms in beetles (Coleoptera) by Seago et al. (2009).
This database combines scanning electron micrographs, visible light photographs, UV-VIS color reflectance spectra, and structural measurements of specimens from the Virginia Tech Insect Collection (VTEC). It also includes citations of previous research on the insect's cuticular color. The database is available under a Creative Commons Attribution - NonCommercial - ShareAlike 4.0 International License.
Scanning electron micrographs of platinum-palladium coated insect cuticle samples were taken using a FEI Quanta 600F ESEM located at the Institute for Critical Technology and Applied Science's Nanoscale Characterization and Fabrication Laboratory at Virginia Tech (ICTAS NCFL). Light photographs were taken using a Canon 6D digital camera with 50 and 65 mm lenses, Visionary Digital software and Canon EOS Utilities. Color reflectance spectra was obtained using a DH-2000-BAL light source, Ocean Optics SpectraSuite software and a USB4000 Spectrometer calibrated with a Labsphere Reflectance Standard AS-01158-060 USRS-99-010 BZ37A. Orientation of visible light photographs and specimen color reflectance spectra are described with spherical coordinates. A brief explanation of spherical coordinates is given here.
Raw color reflectance spectral data is provided as TXT files and displayed as graphs of bivariate fit of percent reflectance by nanometer wavelength. Graphs were made in JMP Pro 12 with a y-axis (reflectance) from 0-100% and an x-axis (wavelength) from 230-850 nm. The x-axis is bounded in its lower range by the light source and in the upper range by the spectrometer. Use of alternative hardware could provide a wider range of detected wavelengths, but for this database we have focused primarily on colors within the UV-VIS spectrum.
This project is supported by a NSF Collections in Support Biological Research (CSBR) award, DBI #1458045.
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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.