In water, transparency seems an ideal concealment strategy, as testified by the variety of transparent aquatic organisms. By contrast, transparency is nearly absent on land, with the exception of insect wings, and knowledge is scarce about its functions and evolution, with fragmentary studies and no comparative perspective. Lepidoptera (butterflies and moths) represent an outstanding group to investigate transparency on land, as species typically harbor opaque wings covered with colored scales, a key multifunctional innovation. Yet, many Lepidoptera species have evolved partially or fully transparent wings. At the interface between physics and biology, the present study investigates wing transparency in 123 Lepidoptera species (from 31 families) for its structural basis, optical properties, and biological relevance in relation to visual detection (concealment), thermoregulation, and protection against UV. Our results suggest that transparency has likely evolved multiple times independently. Efficiency at transmitting light is largely determined by clearwing microstructure (scale shape, insertion, coloration, dimensions, and density) and macrostructure (clearwing area, species size, or wing area). Microstructural traits, scale density and dimensions, are tightly linked in their evolution, with different constraints according to scale shape, insertion, and coloration. Transparency appears highly relevant for concealment, with size-dependent variations. Links between transparency and latitude are consistent with an ecological relevance of transparency in thermoregulation, and not so for protection against UV radiation. Altogether, our results shed new light on the physical and ecological processes driving the evolution of transparency on land and underline that transparency is a more complex coloration strategy than previously thought.

中文翻译：

---

蝴蝶和飞蛾的翅膀透明度：结构多样性、光学特性和生态相关性

在水中，透明似乎是一种理想的隐藏策略，各种透明的水生生物就证明了这一点。相比之下，除昆虫翅膀外，陆地上几乎没有透明度，关于其功能和进化的知识很少，研究零散，没有比较的视角。鳞翅目（蝴蝶和飞蛾）是研究陆地透明度的杰出群体，因为物种通常拥有覆盖着彩色鳞片的不透明翅膀，这是一项关键的多功能创新。然而，许多鳞翅目物种已经进化出部分或完全透明的翅膀。在物理学和生物学的交界处，本研究调查了 123 种鳞翅目物种（来自 31 个科）的翅膀透明度，以了解其结构基础、光学特性、与视觉检测（隐藏）、体温调节和紫外线防护相关的生物学相关性。我们的结果表明，透明度可能已经独立发展了多次。透光效率在很大程度上取决于透明翅的微观结构（鳞片形状、插入、着色、尺寸和密度）和宏观结构（透明翅面积、物种大小或翅膀面积）。微观结构特征、鳞片密度和尺寸在其进化过程中紧密相连，根据鳞片形状、插入和着色具有不同的限制。透明度似乎与隐蔽高度相关，具有与尺寸相关的变化。透明度和纬度之间的联系与体温调节中透明度的生态相关性一致，而在防止紫外线辐射方面则不然。共，