LAUSR

The radiative cooling of butterfly wing scales hierarchy has great value in understanding how poikilotherms adapt to the environment and developing bionic materials. Yet, it remained unclear what the cooling system is like and how the variation of hierarchy affects the cooling efficiency. Therefore, the correlation between the variations of the structure and emissivity of scale hierarchy is thoroughly investigated in Tirumala limniace (Cramer, 1775), whose thermal properties are highly heterogeneous among different wings and regions but similar between males and females. Patterns were deduced from the biological and model simulation experiments. The scale hierarchy variates at the micro to nano-level on both surface and section, corresponding to the variating emissivity. Scales on wing veins and margins have large nanostructured units with small lumens and are distinctly thickened, which bring extraordinarily high emissivity. The variations of light and dark scales, respectively, lead to the high emissivity of the middle region of wings and the front wings. Generally, the elevation of the inner surface area and the thickness of the chitin is the key to enhancing the cooling efficiency. For the first time, the effects of the variation of hierarchy towards emissivity of the mid-infrared spectrum are systematically clarified. It is demonstrated that wing scales integrally differentiate in coping with the heterogeneous cooling needs, which may benefit in balancing multi-functions and the development towards the adaptation to the abiotic environment. The study provides insights into the comprehensive thermoregulation system of butterflies and the further development of radiative cooling materials. Scale hierarchies of a single individual butterfly variate significantly at the micro to nano level in both surface and sectional views. These variations all contributed to the heterogeneous cooling efficiency. For the first time, the effects of the variation of hierarchy in three dimensions towards the emissivity of the mid-infrared spectrum are systematically clarified by both biological measurements and model simulations. Scale structures integrally differentiate in coping with the heterogeneous cooling needs of the wings, which possibly involves considerations for multifunctions and the benefit of development towards the adaptation to the abiotic environment. This article is protected by copyright. All rights reserved.