Aglais io

(Linnaeus, 1758)

European peacock butterfly, peacock butterfly

A colorful found across Europe and temperate Asia to Japan. overwinter and emerge in spring to reproduce. Recent studies in Belgium demonstrate a shift from to , with three peaks now observed: spring ( adults), early summer (first ), and autumn (second generation). The is known for prominent on its that function in anti- defense.

Aglais io by (c) S. Rae, some rights reserved (CC BY). Used under a CC-BY license.

Aglais io by (c) Céline, some rights reserved (CC BY), uploaded by Céline. Used under a CC-BY license.

Inachis io on Salix caprea by Richard Bartz. Used under a CC BY-SA 2.5 license.

Pronunciation

How to pronounce Aglais io: /ˈæɡlaɪəs ˈiːoʊ/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Distinguished from similar Aglais (A. urticae, A. caschmirensis) by the four large, colorful on the upper surface—A. urticae lacks such prominent eyespots and has more angular wing margins. The rusty red base color and eyespot pattern separate it from other European nymphalids. Underside leaf- is shared with other hibernating but the specific dark /black coloration with irregular margins aids identification. Formerly placed in Inachis, now synonymized with Aglais.

Images

Habitat

Woods, fields, meadows, pastures, parks, and gardens. Occurs from lowlands to 2,500 m elevation. Often found in anthropogenic including urban parks and gardens where larval plants occur.

Distribution

Europe (widespread and abundant), temperate Asia east to Japan. Two recognized: A. io caucasica (Azerbaijan) and A. io geisha (Japan and Russian Far East). Expanding range in some areas.

Seasonality

active from March/April following , with peaks varying by region. In Belgium and parts of western Europe: three peaks—spring (overwintering adults), early summer (late June–early July, first ), and late summer/autumn (August–October, second generation). Overwinters as adult in buildings, trees, or other sheltered locations.

Diet

feed on stinging nettle (Urtica dioica), small nettle (Urtica urens), and hop (Humulus lupulus). take nectar from diverse flowering plants including davidii, willows (Salix), dandelions (Taraxacum), wild marjoram (Origanum vulgare), danewort (Sambucus ebulus), hemp agrimony (Eupatorium cannabinum), and clover (Trifolium); also feed on tree sap and rotting fruit.

Host Associations

Urtica dioica - larval primary
Urtica urens - larval primary
Humulus lupulus - larval commonly used
Buddleja davidii - nectar sourcefrequently visited; also site of risk

Life Cycle

olive green, ribbed, laid in batches up to 400 on upper and lower surfaces of leaves. hatch after approximately one week, feed gregariously early . occurs after larval development; variable in color. emerges, mates, and may enter reproductive or continue breeding. Historically throughout most of range: single with summer-born adults entering diapause to overwinter. Recently shifted to in parts of western Europe (e.g., Belgium since ~2009): adults reproduce in spring, first generation emerges early summer, second generation emerges late summer/autumn and constitutes majority of overwintering . Occasional third generation attempts observed in autumn.

Behavior

overwinter in sheltered locations including buildings and tree hollows, often appearing early in spring. Males establish and defend territories in clearings and forest edges, perching on prominent features to intercept passing females; territorial defense involves aerial pursuits and spiraling against rival males. Territories typically located along routes to sites. Non-territorial males adopt alternative strategies including or perching in non-territorial areas. When disturbed, adults may open to display in threat posture; can also produce audible hissing sound. feed gregariously in early .

Ecological Role

as ; larval on nettles and hops. for avian including great tits (Parus major), tits (Cyanistes caeruleus), and pied flycatchers (Ficedula hypoleuca). parasitized by Telenomus kolbei. Anti-predator defenses (, hissing, ) have been extensively studied as model for predator-prey interactions.

Human Relevance

Popular and familiar in Europe, frequently observed in gardens and parks. Subject of extensive research on function and anti- defense. Citizen science data from observation platforms has documented recent changes. Occasionally enters buildings to overwinter. No significant agricultural impact; feed on common weeds rather than .

Similar Taxa

Aglais urticaeOverlapping range and ; lacks prominent , has more angular margins and orange- coloration with black spots rather than rusty red with eyespots.
Nymphalis antiopaSimilar and underside leaf-; distinguished by marbled upperwing pattern of -rimmed spots on dark , lacking the distinctive of A. io.
Anartia spp.Called ' peacocks' but not closely related; occur in Americas rather than Eurasia, with different patterns and arrangements.

Misconceptions

Formerly classified in separate Inachis; now recognized as congeneric with Aglais. Previously believed to be strictly throughout range; recent evidence demonstrates bivoltinism in parts of western Europe. Autumn peak was once hypothesized to represent aestivating re-emerging rather than a true second — wear analysis has disproven this.

More Details

Voltinism shift

Citizen science data from Belgium (2009–2020) demonstrate a recent, rapid shift from to , likely climate-driven. The second now contributes most individuals to the , contrasting with historical patterns where summer generation entered .

Anti-predator research

have been experimentally demonstrated to deter avian through intimidation rather than concealment; predator hesitation and increase when eyespots are visible. Auditory hissing is more effective against rodent predators in dark sites where visual displays are ineffective.