Anoplophora graafi Longhorn Beetle Coloration is due to Disordered Diamond-like Packed Spheres

TL;DR

This study reveals that the coloration in Anoplophora graafi beetles results from a disordered diamond-like packed sphere structure, providing insights into natural photonic materials and inspiring new colloid-based photonic designs.

Contribution

The paper uncovers the disordered diamond-like packing of chitin spheres in beetle scales, linking natural photonic structures to potential new material development.

Findings

Disordered diamond lattice best describes the sphere assembly.

Low volume fraction and neighbor count incompatible with close packing.

Natural photonic structures can inspire new colloid-based materials.

Abstract

While artificially photonic materials are typically highly ordered, photonic structures in many species of birds and insects do not possess a long-range order. Studying their order-disorder interplay sheds light on the origin of the photonic band gap. Here, we investigated the scale morphology of the Anoplophora graafi longhorn beetle. Combining small-angle X-ray scattering and slice-and-view FIB-SEM tomography with molecular dynamics and optical simulations, we characterised the chitin sphere assemblies within blue and green. A. graafi scales. The low volume fraction of spheres and the number of their nearest neighbours are incompatible with any known close-packed sphere morphology. A short-range diamond lattice with long-range disorder best describes the sphere assembly, which will inspire the development of new colloid-based photonic materials.