Wiklund, C. 2005: Hornet predation on peacock butterflies and ecological aspects on the evolution of complex eyespots on butterfly wings. - Entomol. Fennica 16: 266-272.
Sixteen peacocks Inachis io (L.) and one red admiral Vanessa atalanta (L.) were killed by hornets Vespa crabro during a four day observation period in August 2002 on butterflies feeding on fermenting plums. Four successful attacks on peacocks were directly observed, and were invariably preceded by the butterfly opening its wings when attacked. When feeding, peacocks usually kept their wings closed and only flicked their wings open to prevent another approaching insect from alighting on the plum. Wing-flicking behaviour by peacocks is effective when thwarting attacks from birds, but was fatal when practised against hornets. A hypothesis for the evolution of intimidating eyespots on butterfly wings is advanced, suggesting that it is preceded by, and associated with, wing-flicking behaviour which in turn is associated with fruit- or sap-feeding.