Far field scattering pattern of differently structured butterfly scales

Area of Science:

• Biophysics
• Materials Science
• Zoology

Background:

• Butterfly wing coloration is crucial for species recognition, thermoregulation, and predator avoidance.
• The structural basis of butterfly scale optical properties is complex and varies across species.

Purpose of the Study:

• To investigate the relationship between the anatomical structure of butterfly scales and their measured angular and spectral reflectance.
• To elucidate the physical mechanisms underlying different types of light scattering and iridescence in butterfly wings.

Main Methods:

• Measurement of angular and spectral reflectance of single scales from five butterfly species.
• Analysis of scale anatomy using microscopy to correlate structure with optical properties.

Main Results:

• Pierid scales (Pieris rapae, Delias nigrina) scatter white light randomly, consistent with Lambert's cosine law, due to randomly organized beads.
• Morpho aega scales exhibit iridescent blue via multilayer structures in ridges, causing planar diffraction.
• Colotis regina purple scales use multilayers for blue iridescence, but red scattering relies on pigment-containing beads, similar to pierids.
• Urania fulgens scales display green-yellow coloration with narrow-angle backscattering due to multilayer structures in the scale body.

Conclusions:

• Butterfly scale nanostructure dictates optical performance, leading to diverse visual effects.
• Randomly organized beads and multilayer interference are key mechanisms for generating color and reflectance patterns.
• Understanding these structures provides insights into natural photonic materials and evolutionary adaptations.