Are Toxic Butterflies More Easily Detected by Human 'Predators'?

Butterfly colours often signal unprofitability due to toxicity to predators, with more conspicuous colour signals increasing predator avoidance learning. These signals can be on the dorsal and/or ventral wing surfaces, which are more visible during flight or at rest respectively. Here we are interested in the relationship between toxicity and conspicuousness in Australian butterflies. We use detectability as a proxy for conspicuousness and test whether toxic butterflies are more detectable on both the dorsal and ventral wing sides using a computer game where humans hunt butterflies against multiple backgrounds. The game was played by over 1700 players who collectively reacted to over 67,000 images of butterflies. Toxicity was assessed using Daphnia mortality assays on over 420 individuals from 61 species. Specifically, we tested (1) if the detectability of dorsal or ventral butterfly wings was related to toxicity, and (2) if butterflies that were more toxic had similar dorsal and ventral detectability. For dorsal surfaces, we found that the more toxic butterflies were detected faster than less toxic butterflies, whereas there was no relationship between toxicity and detection time for ventral surfaces. These findings are consistent with previous work that suggests aposematic signals are particularly relevant when animals are in motion, since the dorsal wing surface of butterflies-the more detectable side-is usually visible during flight rather than at rest. We also found that more toxic butterflies were more similar between dorsal and ventral detection, suggesting that greater levels of toxicity are communicated both ventrally and dorsally.