The large, unmistakeable eye-spots on each of the hind-wings, which resemble those on a peacock’s tail, are what give this striking butterfly its name. It is one of the largest and most colourful butterflies in Ireland, and is a welcome visitor to our gardens in early spring and late summer.
The colourful, striking pattern on the wings is part of the adult butterfly’s defence mechanism. When threatened the butterfly flashes its wings, exposing the eye-pattern to startle would-be predators. Persistent individuals are further dissuaded by a loud grating noise that the butterfly can produce by rasping its forewings. While the upper surface of the wings is very bold and striking, the underside is dull and cryptically marked, serving as excellent camouflage when the wings are closed and the butterfly is at rest.
Peacock butterflies emerge from hibernation during the first warm days of spring, usually sometime in early March. Males will secure a vantage point near a sunny nettle patch around mid-day and will defend it vigorously against other males. This territorial instinct is so compelling that males have been known to chase birds that stray into their patch, and will even fly up to investigate a twig or stone thrown above them. Any passing female will be chased by the territorial male and hounded for several hours until mating takes place.
The female starts to lay eggs in May, and is very particular about the plant and location. She will invariably choose the tip of a healthy stinging nettle (Urtica dioica) in full sunshine, and will deposit large clusters of 300-400 eggs on the underside of the young leaves.
The adults, their role in life fulfilled, will die soon afterwards. Peacock butterflies disappear for a time during June and July when one generation dies off and the next is developing in the nettle patch.
Eggs hatch 7-21 days after laying and the caterpillars create a communal tent at the top of the nettle by drawing leaves together and binding them with silk. Safe inside the caterpillars feed voraciously on the leaves that make up their refuge until they have consumed them completely. They then move on to fresh leaves, create a new retreat and begin feeding again.
Mature caterpillars are velvety black with finely speckled white dots and are covered in black spines. The caterpillars’ spines are thought to deter larger predators, but offer little defence against spiders and parasitic wasps which kill a large number of them. Peacock caterpillars stay together in the nettle patch for about a month, at which point they are fully grown and disperse to pupate.
The pupa is usually suspended from vegetation up to a metre above the ground and is well camouflaged. During the 2-4 weeks spent in the pupae phase the remarkable transformation into an adult butterfly takes place.
Adult butterflies emerge from mid July onwards and begin seeking out nectar rich plants like buddleia and thistle to feed. This feeding continues until mid-September when the onset of cooler, shorter days prompts adults to take refuge in hollow trees, dark buildings and sometimes houses to wait out the rigours of winter.