Lizards as Predators of Butterflies: Shape of Wing Damage and Effects of Eyespots

In warm climates, lizards may be important as predators of butterflies and thus exert selection pressure on butterfly colour patterns, including eyespots. However, this has received little attention. Two studies reported no evidence that butterfly eyespots deflect lizard attacks, while possible intimidating effects of butterfly eyespots on lizards have not been investigated. We exposed common evening brown butterflies (Melanitis leda) with a wide range of eyespot sizes (dry season forms with very small and faint eyespots, intermediate phenotypes with small eyespots, and wet season forms with large or very large eyespots) to house geckos, and recorded the location and shape of wing surface loss. We supplemented these data with direct observations of attacks of house geckos (Hemidactylus frenatus) and bronze skinks (Eutropis macularia) on common evening brown butterflies. We found that about three quarters of symmetrical wing surface loss, and about half of the non-symmetrical wing surface loss was rounded like the mouth of a gecko. Symmetrical as well as non-symmetrical wing surface loss was significantly more common in hindwings. We surmise that rounded wing surface loss and a bias in symmetrical wing surface loss to hindwings can be taken as evidence for failed lizard attacks. Rounded wing surface loss was more common in butterflies with small eyespots than in those with very small eyespots or with large eyespots. This suggests that small eyespots can deflect lizard attacks away from the head towards the wing margins, and that large eyespots can thwart lizard attacks. In four cases, skinks appeared to explore rather than attack butterfly eyespots. In contrast to earlier studies, our data provide evidence that butterfly eyespots can be an effective defence against lizards, and thus that predation by lizards can select for eyespots in butterflies.