Peacock butterflies

Every year we find nests of peacock (Aglais io) caterpillars among the reserve’s nettle beds. Those caterpillars will be pupating soon and we will begin to see the new adults this month.

Peacock butterflies are large and colourful with striking and beautiful eyespots, which are believed to be a defence mechanism against predators. There are two theories to explain how this works, not necessarily mutually exclusive.

One theory suggests that the sudden flash of the colourful eyespots produces an automatic startle response in birds, which gives the butterfly time to escape. The second theory holds that the eyespots mimic the eyes of creatures that birds recognise as enemies.

a nest of peacock caterpillars and an adult feeding on spear thistle

Research has shown that birds attacking a peacock butterfly, hesitate for a much longer time if the butterfly displays its eyespots. If the eyespots are covered the birds hesitated for measurably less time before attacking. Sometimes, faced with the flashing eyespots, predators flee even before they attack. The butterfly, when it is able to intimidate a bird so that it delays or gives up its attack, obviously has created a much better chance of surviving.

In one experiment, birds responded to the eyespots, not only with increased vigilance and a delay in their return to the attack, but also with alarm calls usually associated with ground-based predators. This suggests that the eyespots do, in fact, mimic the eyes of creatures that birds usually fear.

DKG’s photographs of a peacock butterfly on bramble

Hibernation is a necessary evil for butterflies: a period of great danger undertaken to ensure the species is ready to breed in the next spring. More than 50% of peacock butterflies are predated in the first few weeks of their hibernation. They choose dark places: cracks in trees, holes in the ground, sheds or spare bedroom wardrobes. These are places where they encounter all kinds of rodents; against these predators, in the dark, the display of eyespots doesn’t work. Instead, the butterfly hisses, which also seems to act as a deterrent.

A newly hatched peacock butterfly is a brilliant flash of colour among the lush greenery of the reserve in July.

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