Specialized scales in Atlides polybe butterfly thermally insulate pheromones

Many Lepidoptera scales possess micro-to-nano structures that have evolved to fulfill specific functions, ranging from optical signaling to thermal management to self-cleaning. Certain specialized scales exhibit enhanced emissivity due to their structural features and are co-located with volatile pheromones, which are produced and stored in the wings of male butterflies until evaporation. While these exhibit structure-derived radiative cooling, here, we report that in Atlides polybe, the specialized scales have a previously unreported structure that promotes heat retention. X-ray characterization shows a tortuous, fibrillar internal structure combined with a regular, windowed exterior. The interior structure reduces heating and cooling rates, as indicated by an elevated time constant. Thermal simulations confirm that this insulating behavior is only achievable with the combination of increased thickness and porosity unique to these specialized scales, and that the tortuosity of the fibers decreases the heat transfer rate. The reduced heat transfer may promote steady, consistent pheromone release. Although past works have focused on structure-based emissivity, this case expands our understanding of the relationship between scale structure and thermal management in Lepidoptera. This work illuminates another facet of butterfly thermoregulation and provides a more accurate foundation when deriving bioinspiration from natural structures for the fabrication of materials for thermal management.