Aglais io

Distinguished from similar Aglais species (A. urticae, A. caschmirensis) by the four large, colorful eyespots on the upper wing 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-mimicry is shared with other hibernating butterflies but the specific dark brown/black coloration with irregular margins aids identification. Formerly placed in genus Inachis, now synonymized with Aglais.

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

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

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

Larvae feed on stinging nettle (Urtica dioica), small nettle (Urtica urens), and hop (Humulus lupulus). Adults take nectar from diverse flowering plants including Buddleja 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.

• Urtica dioica - larval food plantprimary host
• Urtica urens - larval food plantprimary host
• Humulus lupulus - larval food plantcommonly used
• Buddleja davidii - adult nectar sourcefrequently visited; also site of predation risk

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

Adults 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 flights against rival males. Territories typically located along routes to oviposition sites. Non-territorial males adopt alternative strategies including patrolling or perching in non-territorial areas. When disturbed, adults may open wings to display eyespots in threat posture; can also produce audible hissing sound. Larvae feed gregariously in early instars.

Pollinator as adult; larval herbivore on nettles and hops. Prey for avian predators including great tits (Parus major), blue tits (Cyanistes caeruleus), and pied flycatchers (Ficedula hypoleuca). Eggs parasitized by scelionid wasp Telenomus kolbei. Anti-predator defenses (eyespots, hissing, crypsis) have been extensively studied as model for predator-prey interactions.

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

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

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

• butterfly
• Nymphalidae
• Europe
• eyespots
• hibernation
• territoriality
• citizen science
• climate change response

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• Catalogue of Life
• Provisional checklist of European butterfly larval foodplants
• Look but do not touch: puss caterpillar, Megalopyge opercularis; White flannel moth, Norape ovina; Io moth, Automeris io; buck moth Hemileuca spp.; and hag moth, Phobetron pithecium — Bug of the Week
• Bug Eric: Scientific Illustration
• How Beekeepers Can Foster Propolis Production for Better Hive Health
• Platystomatidae | Beetles In The Bush
• From the mailbag: Fig-eating Kudzu bugs come to college, Megacopta cribraria — Bug of the Week
• Specialiserad predation av talgoxe Parus major på påfågelöga Aglais io och nässelfjäril Aglais urticae
• Territorial Behaviour of the Nymphalid Butterflies, Aglais urticae (L.) and Inachis io (L.)
• Abundant Citizen Science Data Reveal That the Peacock Butterfly Aglais io Recently Became Bivoltine in Belgium
• First record of Telenomus kolbei (Hymenoptera, Scelionidae) in France, parasitizing the eggs of Nymphalis antiopa and Aglais io (Lepidoptera, Nymphalidae)
• New distribution record of Indian Tortoiseshell Aglais caschmirensis aesis (Fruhstorfer, 1912) (Lepidoptera: Nymphalidae) from the state of Assam, India