This is its defense mechanism to scare off potential predators.
The Peacock butterfly’s main anti-predator defense mechanism comes from the four large eyespots that it has on its wings. These eyespots are brilliantly colored concentric circles. Like many other butterflies that hibernate, the Peacock butterfly exhibits many lines of defense against would-be predators. Avian predators of the butterfly include blue tits, pied flycatchers and other small passerine birds. The first line of defense against these predators for many hibernating butterflies is crypsis, a process in which the butterflies blend into their environment by mimicking a leaf and staying immobile. Some hibernating butterflies such as the Peacock have a second line of defense: when attacked, they open their wings, expose their eyespots and perform an intimidating display of threat. The intimidating visual display shown by the Peacock butterfly gives it a much better chance at escaping predators than butterflies that rely solely on leaf mimicry. While the main targets of these anti-predation measures are small passerine birds, even larger birds such as chickens have been shown to react to the stimuli and avoid the butterfly when exposed to eyespots.Via A London Salmagundi.