Southern festoon (Zerynthia polyxena): range, host plants and life cycle

The Southern festoon, Zerynthia polyxena, is a small, scallop-winged butterfly of the family Papilionidae, first described by Denis and Schiffermüller in 1775, patterned in pale yellow, black and red. It ranges across southern and southeastern Europe and western Asia, from France and Italy through the Balkans and Slovakia to Greece, and east through Kazakhstan to the Urals.

Identification

The Southern festoon has a wingspan of 46 to 52 mm. Its wings carry the festoon pattern typical of the genus: pale yellow ground colour crossed by black bands and markings, with a row of red spots near the scalloped wing margins. The hindwing edge is distinctly toothed rather than smooth, which separates the festoons from most other European swallowtail-family butterflies at a glance. The sexes differ slightly: females have somewhat longer wings than males and are usually lighter coloured, while males tend to show the deeper, more contrasting yellow-and-black pattern. The dark brown body carries red patches on the sides of the abdomen, and the hindwing edges show a black, sinuous line with a row of blue and red warning spots that likely deter predators.

Range and habitat

The species favours warm, sunny, open places such as herb-rich meadows, vineyards, river banks, wetlands, brushy and waste ground, and rocky karst terrain, from sea level to about 1,700 m but usually below 900 m. This mix of open, flower-rich ground reflects the needs of its caterpillars, which depend on a single group of host plants that itself favours disturbed, sunny sites.

Life cycle and host plants

Females lay their eggs singly or in small groups at the base of the host plants, favouring plants that already carry more leaves, which give a hatching caterpillar more food within easy reach. The caterpillars grow up to 35 mm long, starting out black before turning yellowish with six rows of fleshy orange-and-black spikes. Because birthworts are toxic, the caterpillars sequester the plants’ compounds and become unpalatable to predators, a defence that carries through to the adult butterfly. Caterpillars feed on birthworts (Aristolochia), mainly Aristolochia clematitis, A. rotunda, A. pistolochia and A. pallida. The species overwinters as a chrysalis, with the pupae attached to supports by silk belts. It completes one generation a year, with adults on the wing in spring before the summer heat sets in across its Mediterranean and continental range.

Behaviour and flight period

Adults fly from April to June, in a single brood, across its European and western Asian range, though individual adults are on the wing for no more than about three weeks within that window. This early, compressed flight period lets the butterfly complete its life cycle while its birthwort host plants are still fresh, before the open, sun-baked habitats it favours dry out later in the season. Though populations occur only locally across the range, rather than continuously, wherever its host plants and open ground coincide the Southern festoon can be a dependable spring sight.

Conservation

The facts box gives the IUCN category for this species, sourced from its Wikidata record rather than the Red List directly.

Similar species

• Eastern festoon (Zerynthia cerisy): a close relative with the same scalloped wing shape and festoon pattern, replacing the Southern festoon in Greece, the Aegean and Turkey.
• Spanish festoon (Zerynthia rumina): the western counterpart of the genus, found across Iberia and southern France, with similar red-spotted markings but a more angular wing shape. The two overlap in southeastern France, where the Southern festoon is told apart by the blue spots on its hindwings and a comparatively smaller amount of red on the forewings.
• Clouded Apollo (Parnassius mnemosyne): another early-flying, pale-winged butterfly of the same family found across much of the Southern festoon’s European range, though it lacks the red spots and toothed wing margin.