The white 'comma' as a distractive mark on the wings of comma butterflies

Distractive marks have been suggested to prevent predator detection or recognition of a prey, by drawing the attention away from recognizable traits of the bearer. The white 'comma' on the wings of comma butterflies, Polygonia c-album, has been suggested to represent such a distractive mark. In a laboratory experiment using blue tits, Cyanistes caeruleus, as predators, we show that the comma increased survival, since the blue tits attacked butterflies with overpainted commas more often than sham-painted butterflies with intact commas. In a field experiment we placed hibernating, similarly manipulated, comma butterflies on tree trunks of two different species and noted their survival. Although survival was higher on birch trees than on oak trees, there was no effect of treatment, probably because the butterflies were preyed on by both diurnal and nocturnal predators and the latter are unlikely to attend to small conspicuous markings.