One species of peacock spiders – the rainbow peacock spider (Maratus robinsoni) – is particularly impressive, because it showcases an intense rainbow iridescent signal in males’ courtship displays to the females. This is the first known instance in nature of males using an entire rainbow of colors to entice females to mate. But how do males make their rainbows?
The team investigated the spider’s photonic structures using techniques that included light and electron microscopy, hyperspectral imaging, imaging scatterometry and optical modeling to generate hypotheses about how the spider’s scale generate such intense rainbows. The team then used cutting edge nano 3D printing to fabricate different prototypes to test and validate their hypotheses. In the end, the team found that the intense rainbow iridescence emerged from specialized abdominal scales on the spiders. These scales combine an airfoil-like microscopic 3D contour with nanoscale diffraction grating structures on the surface. It is the interaction between the surface nano-diffraction grating and the microscopic curvature of the scales that enables separation and isolation of light into its component wavelengths at finer angles and smaller distances than are possible with current engineering technologies.
“Who knew that such a small critter would create such an intense iridescence using extremely sophisticated mechanisms that will inspire optical engineers,” said Dr. Dimitri Deheyn with excitement during an interview. Deheyn is the postdoc mentor for Hsiung at Scripps Oceanography and a coauthor of this research.
For Hsiung, the finding wasn’t quite so unexpected. “One of the main questions that I wanted to address in my Ph.D. dissertation was ‘how does nature modulate iridescence?’ From a biomimicry perspective, to fully understand and address a question, one has to take extremes from both ends into consideration. Hence, I purposefully chose to study these tiny spiders with intense iridescence after having investigated the non-iridescent blue tarantulas,” said Hsiung.
“As an engineer, what I found fascinating about these spider structural colors is how these long evolved complex structures can still outperform human engineering,” added Dr. Radwanul Hasan Siddique, a postdoctoral scholar at Caltech and coauthor of this research. “Even with high-end fabrication techniques, we could not replicate the exact structures. I wonder how the spiders assemble these fancy structural patterns in the first place!”
In the end, peacock spiders don’t just produce nature’s smallest rainbows, they could also have implications for a wide array of fields ranging from life sciences and biotechnologies to material sciences and engineering.
More information: Bor-Kai Hsiung et al, Rainbow peacock spiders inspire miniature super-iridescent optics, Nature Communications (2017). DOI: 10.1038/s41467-017-02451-x