The Southern Swallowtail Papilio alexanor Esper, 1800 is a butterfly inhabiting the southern portion of the western Palaearctic region. Its range extends from western Europe (southern France) eastward to Kyrgyzstan and northern Afghanistan (Bollino and Sala 2004; Balletto et al. 2023). The distribution is highly fragmented, comprising widely disjunct populations of varying size.

In Europe, the range includes a wide area of south-eastern France, from the coast up to the Alps, the westernmost part of Liguria, and some valleys in south-western and north-western Piedmont, Italy (Lafranchis et al. 2015; Anselmo 2021; Balletto et al. 2023; Anselmo et al. 2025) and the Valais in Switzerland as an anthropogenically introduced population (Gerber 2015). Historical records from Calabria and Sicily, spanning from 1918 to 1985, have never been followed by confirmation of a stable population (Table 1). The species is broadly distributed in the southern Balkan Peninsula, particularly in Greece, where it is well established both on the mainland and on several Ionian and Aegean islands (Bollino and Sala 2004). A small population is known from the Croatian coast (Verovnik and Švara 2016), and a single individual was recently recorded from Serbia (Vukajlović et al. 2025). Beyond Europe, the species occurs in Anatolia, the Caucasus region, Syria, Lebanon, Israel, Iran, Turkmenistan, Uzbekistan, Kazakhstan, and Kyrgyzstan (Bollino and Sala 2004; Kudrna et al. 2011). European populations are only slightly differentiated, showing a few characteristic mutations between the Franco-Italian and Balkan lineages. Greater differentiation is observed when comparing them with Middle Eastern populations (Dapporto et al. 2022; Nazari et al. 2025).

The last documented evidence of a female ovipositing in southern Italy dates to 1985, near Morano Calabro, and was not confirmed by subsequent surveys at the same locality (Bollino and Sala 2004). More recently, two unpublished observations retrieved from the citizen science platforms iNaturalist.org and Observations.org have come to the authors’ attention: the first one of an individual apparently engaged in oviposition behaviour on a yellow-flowered umbellifer in Basilicata (2023, observer: Luigi Campagna), the second one a female individual resting on a Valeriana rubra L. in Campania (2024, observer: LennartH) and a third-instar larva in Sicily (2024, observer: gius8890). None of these records were accompanied by confirmed host plant identification, and the Sicilian locality could not be confirmed during a field visit by the authors in June 2025.

P. alexanor is a strongly heliophilous species, occurring from sea level to approximately 1800 m, with a marked preference for open habitats with sparse woody vegetation. It favours steep terrain characterised by cliffs or rocky outcrops, where adults exploit thermal updrafts in flight. At least in Europe, the species appears confined to calcareous substrates (Baruzzi et al. 2016; Balletto et al. 2023; Anselmo et al. 2025).

Throughout its range, P. alexanor is univoltine and oligophagous, with larvae feeding exclusively on Apiaceae. Univoltinism is a direct consequence of the larval diet: caterpillars feed solely on the flowers and developing seeds of the host plant; however, should these edible parts of the floral scape be completely consumed, larvae will also feed on leaves, closely linking adult emergence to its phenology in each area. The flight period may therefore vary considerably among populations, depending on the local host plant used (Balletto et al. 2023; Anselmo et al. 2025). The host plants of north-western Italian populations are Ptychotis saxifraga (L.) Loret & Barrandon and Opopanax chironius (L.) W.D.J.Koch, as confirmed by recent and extensive field observations (Anselmo et al. 2025). Some authors have also reported Trinia glauca (L.) Dumort and Seseli montanum L. as additional host plants (Bollino and Sala 2004; Balletto et al. 2023), but these records most likely reflect misidentification, given the strong morphological similarity between these taxa and the confirmed hosts (Descimon 1991; David and Sanetra 1994; Anselmo et al. 2025). Balkan and Central Asian populations also use several Ferula Tourn. ex L. species (Bollino and Sala 2004; Balletto et al. 2023).

P. alexanor is strictly protected in Europe under Annex IV of the Habitats Directive (Council Directive 92/43/EEC) and Appendix II of the Bern Convention. According to the most recent Article 17 reporting cycle (2019–2024), the conservation status of P. alexanor in Italy is U1 (inadequate) in the Alpine biogeographical region, while it is still not considered present in the Mediterranean Region, although, during the fifth reporting cycle, the presence of two Ligurian populations prompted a request for evaluation in the next reporting round. According to the European Red List of Butterflies, the species is assessed as Near Threatened (NT; Van Swaay et al. 2025), while in Italy it is listed as Endangered (EN; Balletto et al. 2016; Bonelli et al. 2018).

the study area spans the border between the Provinces of Salerno (Campania Region) and Potenza (Basilicata Region), both in southern Italy. The area was selected on the basis of a single iNaturalist record from Basilicata and subsequent prospecting of sites presenting habitat characteristics consistent with the known ecology of P. alexanor. Precise locality data are withheld in this publication to protect the populations from disturbance and illegal collection; locality information is available to conservation authorities and qualified researchers upon request. Field surveys were coordinated by the authors in collaboration with the University of Turin (Department of Life Sciences and Systems Biology) and the Italian Lepidopterological Association (Associazione Lepidotterologica Italiana, ALI), in April and May 2025 and in April and May 2026. Host plant identification was carried out following Pignatti et al. (2017). Plant nomenclature follows the World Flora Online (2026) database (https://wfoplantlist.org). All observations are supported by photographic documentation.

The discovery of a reproducing population of P. alexanor in southern Italy, approximately 790 km of linear distance from the nearest previously known Italian population, constitutes a significant finding for the biogeography and conservation of this protected species. Both main presence sites support active reproduction, confirmed through direct observation of ovipositing females, larvae at multiple developmental stages, and — at the first site — the presence of a pupa at the base of a F. glauca plant. This plant species is hereby confirmed as the larval host plant of P. alexanor for this population. While the use of Ferula species is well established for Balkan and Central Asian populations (Balletto et al. 2023), it had not previously been recorded in Italy or France, where the species relies on P. saxifraga and O. chironius (Anselmo et al. 2025). The use of F. glauca specifically has been documented only recently in the Peloponnese, Greece (Sanetra 2026). Within the monitored areas, F. glauca is clearly the most widespread Ferula species; although F. communis is also present, its distribution is more scattered and primarily restricted to highly anthropised zones. Nonetheless, all observed ovipositions and larvae were exclusively found on F. glauca. Its broad distribution across central and southern Italy (Pignatti et al. 2017) might suggest that additional populations of P. alexanor could potentially occur in currently unsurveyed areas.

V. rubra is documented as an important nectar source for adults at both sites. Its abundant presence in the frequented biotopes is likely a key resource for adult maintenance throughout the flight period.

The flight period recorded at both sites (early April to the end of May) is earlier than that of known northern Italian populations, which are more tightly coupled to the later phenology of their respective host plants. This early phenology is broadly consistent with the Peloponnesian Greek populations, recently observed laying on F. glauca (Sanetra 2026). The early and relatively brief flight window, combined with the difficult access to rocky cliff habitats, may explain why these southern Italian populations remained undetected for decades.

The presence of larvae at multiple developmental stages simultaneously on the same flowering stem, together with the discovery of a pupa at the base of the same plant, suggests that multiple females may select the same floral scape for oviposition during the flight period. This behavioural pattern warrants further investigation.

The populations discovered have been confirmed as reproducing for at least two years (2025–2026); the 2023 iNaturalist record of a female apparently engaged in oviposition behaviour suggests that a reproducing population may have been present for at least four years. The extent of occupied habitat (0.6 km² and 0.4 km² at the two sites respectively) suggests that conditions may be sufficient to support viable reproducing populations, though dedicated demographic surveys will be needed to confirm this. Historical records from southern Italy had always been interpreted as vagrant individuals or ephemeral occurrences (Bollino and Sala 2004; Balletto et al. 2023); the present data suggest that this interpretation should be reconsidered, at least for this part of the peninsula. However, the origin of these populations — whether long-established, the result of recent natural range expansion, or anthropogenic introduction — cannot be determined from the available data and warrants further investigation.

Being listed under Annex IV of the Habitats Directive (92/43/EEC), P. alexanor is afforded strict protection throughout its range. One of the two sites falls within a Natura 2000 area; as the species is not currently listed among its protected elements, the associated conservation measures do not yet apply to it — a gap that should be urgently addressed. Both the national Red List assessment and the Habitats Directive conservation status should be revised in light of the data reported here. The high desirability of P. alexanor among collectors makes both adults and larvae particularly vulnerable to poaching.

The present findings call for a number of urgent research and conservation actions. Long-term population monitoring at both sites should be initiated in compliance with Habitats Directive requirements. Systematic surveys of adjacent areas in Campania, Basilicata, and Calabria are needed to assess the true extent of the species’ presence in southern Italy, guided by the distribution of calcareous cliff habitats and F. glauca. Historical localities should be re-surveyed during the phenological window documented here (early April–end of May), which differs substantially from that of northern Italian populations. The possibility of additional larval host plants at higher elevations, where F. glauca may be replaced by other Apiaceae, also warrants investigation. The genetic characterisation of these populations, in relation to other European populations of P. alexanor, would be essential to clarify their origin and phylogeographic affinities. Finally, the assessment of ecological connectivity between the newly discovered sites and known populations, building on analyses already conducted for the Maritime and Ligurian Alps (Anselmo et al. 2025), would contribute to understanding the broader metapopulation structure of this species in Italy.