Significance of butterfly eyespots as an anti-predator device in ground-based and aerial attacks

Many butterfly genera are characterised by the presence of marginal eyespots on their wings. One hypothesis to account for an occurrence of eyespots is that these wing pattern elements are partly the outcome of visual selection by predators. Bicyclus anynana (Satyrinae) has underside spotting on its wings but there is also a seasonal form in which the eyespots are reduced in size or totally absent. This natural variation gives us a useful tool to test the hypothesis that marginal eyespot patterns can decoy the attacking predator by, at least sometimes, diverting attack from vital body parts to the edges of the wings. We used lizards, Anolis carolinensis, and pied flycatchers, Ficedula hypoleuca, as predators for living spotted and spotless B. anynana. The presence of eyespots did not increase the escape probability of resting butterflies once captured (even a form with enlarged eyespots did not add to effective deflection of attacks). There was also no evidence that eyespots influenced the location of strikes by the predators. This study thus provides no support that marginal eyespot patterns can act as an effective deflection mechanism to avoid lizard or avian predation.