Abstract
The role of transparency in camouflage is understudied, particularly in terrestrial animals. What level of protection can intermediate levels of transparency offer? Does this protection depend on light conditions or background characteristics? Does transparency more protective than backgroundmatching uniform coloration? Can transparency free animals from background dependency? Using a computer-based predation experiment, we asked human subjects to locate a butterfly (with uniformly opaque, semi-opaque, or transparent wings) hidden against different background (vegetation, soil or trunk). Our results confirm for the first time experimentally that intermediate transparency levels offer better protection in dimmer light conditions. Butterflies appearing smaller (either smaller in size or seen from a greater distance) or with more edge-disruption markings were more protected, especially when transparent. Butterflies closer to the predator's focal point or on poorly-contrasted background were less protected, unless more transparent. As the game went through, participants learned to find butterflies more frequently and quickly, with more significant progress for more transparent butterflies. Brighter light facilitated learning. Younger participants improved their reaction times while older participants increased their likelihood of finding the butterflies. Overall, transparency outperforms uniform coloration, whether generalist across several backgrounds or specialist of one background. This suggests that transparency, due to its high fidelity to the background, helps free prey from background dependency. The limited prevalence of transparency in Lepidoptera might be due to potential trade-offs that require further investigation.