In water, transparency seems an ideal concealment strategy. By contrast, transparency is nearly absent on land, except for insect wings. 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. 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 are tightly linked in their evolution, leading to differential investment in transparency according to scale shape, insertion, and coloration. Physical transparency translates into visually effective concealment with interesting interactions with species size and ecology (activity rhythm). Links between transparency and latitude are consistent with an ecological relevance of transparency in thermoregulation, not for protection against UV radiation. It is obvious that transparency is more complex than previously thought.