The Peacock Butterfly: More than meets the eye

Although seldom mentioned in the news, peacock butterflies – like many other butterflies ­– provide important pollination services for flowers often neglected by bees.

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Aglais io, the European peacock caterpillar, or the peacock butterfly caterpillar is found in Europe. Two butterflies on a flower.

Peacock butterflies can have a wingspan of more than 5 centimeters. When seen from a distance, the spots on their wings resemble eyes. The underside of the wings of adult peacock butterflies resembles the bark of trees. Image: Adobe Stock


  • Aglais io, the peacock butterfly belongs to the family of Nymphalidae.
  • Peacock butterflies can be found across most of the European continent as well as temperate Asia and even in Japan. 
  • Woods, meadows, gardens, and parks are only a few of the locations where these butterflies can be spotted.
  • Their presence has been reported from lowlands up to over 2 500 meters of elevation. 
  • Thanks to this high diversity in possible habitats, the peacock butterfly is currently not facing the decline reported for other insect species caused for example by destruction and fragmentation of natural habitats due to land use intensification.


A. io

Life cycle

Depending on the geographic location, peacock butterflies can go through one (monovoltine) or two (bivoltine) generations in a single year. While in the past in the northern parts of Europe the life cycle of the butterfly generally occurred only once a year, there are now an increasing number of countries such as Germany or Belgium, where a second late summer generation has been reported1,2. Researchers attribute this change in the life cycle of the peacock butterfly to the consequences of climate change. The monovoltine yearly cycle of this butterfly looks as follows:

Adult butterflies commonly mate soon after emerging from hibernation and lay their eggs in clusters of 30 to 80 on the underside of leaves, mostly of nettles (Urtica dioica) and sometimes of hops (Humulus lupulus).

After one to three weeks, the eggs hatch and the caterpillars start to feed on the nettle plants, usually living in communities. Freshly hatched caterpillars are only 1.5 mm long. Over the course of five instar stages and approximately one month, they will grow to a size of over 5 cm. The caterpillars are at this point ready to build their chrysalides. To do so, the caterpillars disperse and start looking for a protected site (usually the underside of a leaf or bush) to build their cocoon. The chrysalides of peacock butterflies can range in color from yellow to dark grey, depending on the site and are usually 2 to 3 cm long. 

Adult butterflies will emerge from their cocoons after two to four weeks and will spend the rest of the season feeding on the nectar of a wide range of flowers and preparing for the overwintering phase. This way the cycle repeats year after year.

Aglais io, the European peacock caterpillar, or the peacock butterfly caterpillar is found in Europe

The caterpillar of the peacock butterfly. Image: Adobe Stock

On the lookout

Males of peacock butterflies are highly territorial. They often spend the mornings feeding on nectar and the rest of the day on a high vantage point like a branch from which they can overlook their territory. When spotted, possible competitors are chased off whereas potential mates are chased in a sort of tag game that can last for hours.

How to frighten your enemies

One of the most interesting characteristics of the peacock butterfly is the different strategies against predators it has developed over the course of evolution. When not in flight, butterflies typically close their wings, as the undersides of their wings enable them to blend in with tree bark, providing excellent camouflage and a strong defense mechanism through mimicry*. When butterflies feel threatened, for example by a rapidly approaching sparrow, they quickly open their wings and display the bright-colored eye patterns on the upper side of their wings. This has been shown to be a surprisingly effective measure to deter avian predator attacks. Scientists believe that the eye patterns closely resemble the eyes of natural enemies of these birds as their sight triggers similar antipredation behaviors.

Aglais io, the European peacock, or the peacock butterfly, is a colourful butterfly, found in Europe

Choosing the right background, the peacock butterfly is almost invisible when it closes its wings. Image: Adobe Stock

Peacock butterflies usually overwinter in dark places such as tree cavities, cellars, or barns. If they are attacked in these places by small mammalians such as mice, their visual defense mechanisms are ineffective due to low visibility. To counter these threats, the peacock butterfly has developed a remarkable mechanism: by rubbing the upper wings against the lower wings, the butterfly produces a surprisingly loud hissing sound (see video below). 

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This multi-level defense mechanism with different traits targeting different predator groups is known as multimodal defense.

Did you know?

The role of butterflies in pollination is often overlooked, as they are usually much less efficient than bees or bumblebees. This is mostly because of the absence of specialized structures on their body to collect and carry around pollen. Nevertheless, a recent study demonstrated that butterflies often complement the work of more popular pollinators such as bees or bumblebees by visiting flowers the latter neglect, both in terms of different species as well as different flower locations on the same plant3

Butterflies indeed are less agile fliers than for example honeybees and because of that they tend to visit mostly flowers located on the outer edges of a plant, while bees prefer flowers towards the center of a plant. This phenomenon, in which flowers located on different locations of a plant are visited by different pollinator species, is called pollination complementarity. In the study mentioned above, it was estimated that this interplay among pollinators ensures that up to 50% more flowers are visited. The role of butterflies for the stability of our natural ecosystems is, therefore, invaluable. 


Mimicry: is a widespread phenomenon in nature. Certain animals and plants have specialized in mimicking visual, auditory or olfactory signals of other species, thus sending a "false message". The imitator profits by deceiving the receiver of the signal. 


Ein Gewinner des Klimawandels. NABU 2008.  https://www.nabu.de/tiere-und-pflanzen/insekten-und-spinnen/schmetterlinge/tagfalter/10425.html Accessed May 2023.

Herremans M et al. 2021. Abundant citizen science data reveal that the peacock butterfly Aglais io recently became bivoltine in Belgium. Insects, 12(8): 683. https://doi.org/10.3390/insects12080683

Cusser S et al. 2021. Unexpected functional complementarity from non-bee pollinators enhances cotton yield. Agriculture, ecosystems & environment, 314: 107415. https://doi.org/10.1016/j.agee.2021.107415 

The author

Portrait Ferrari Federico

Federico Ferrari

ETH Zurich - The Biocommunication Group

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