Waterproof and translucent wings at the same time: problems and solutions in butterflies.

Area of Science:

• * Entomology and Materials Science
• * Biomimetics and Surface Engineering

Background:

• * Butterfly wings exhibit super-hydrophobicity (contact angle > 150 degrees), crucial for waterproofing.
• * Reduced scale cover on translucent wings may compromise hydrophobicity.
• * Life history and migration demands may influence wing waterproofing requirements.

Purpose of the Study:

• * To comparatively analyze wing hydrophobicity and morphology in two translucent-winged butterfly species.
• * To investigate the relationship between reduced scale cover, wing surface morphology, and waterproofing properties.
• * To understand how translucency is maintained without sacrificing water repellency.

Main Methods:

• * Measurement of water contact angle (CA) on wings.
• * Analysis of wing surface morphology using scanning electron microscopy (SEM) and atomic force microscopy (AFM).
• * Comparative study of *Parantica sita* (long-lived, migratory) and *Parnassius glacialis* (short-lived, non-migratory).

Main Results:

• * *Parantica sita* wings demonstrated super-hydrophobicity (CA > 160 degrees) with specialized, thin, ovoid scales.
• * *Parnassius glacialis* wings showed lower hydrophobicity (CA = 100-135 degrees) with setae-like or spade-like scales.
• * Both species had over 80% of wing surface uncovered; *P. sita* featured ridges and knobs, while *P. glacialis* had a smooth wavy pattern.
• * Specialized scales on *P. sita* bend and elastically recover, maintaining apparent high CA despite incomplete coverage.

Conclusions:

• * *Parantica sita* achieves super-hydrophobicity with reduced scale cover through unique scale morphology and underlying surface structures.
• * This waterproofing mechanism allows translucency, essential for the species' long lifespan and migratory behavior.
• * The study provides novel insights into the adaptation of wing surface properties for waterproofing in translucent-winged butterflies.