Luka Šturm, Jure Zaman, Nika Kogovšek, Rudi Verovnik

Distribution of the large blue butterflies Phengaris (Lepidoptera: Lycaenidae) in the Koroška Region, northern Slovenia

Introduction

Distribution of the large blue butterflies phengaris (lepidoptera: lycaenidae) in the koroška region, northern slovenia. Explore the distribution of endangered large blue butterflies (Phengaris) in Slovenia's Koroška Region. This study revises known localities and reports new findings vital for conservation.

Abstract

Large blues are among the most threatened species of butterflies in Europe, known for their unique brood-parasitic life cycles, which include a specific host plant and a host ant. All four species found in Europe (Phengaris arion, Phengaris alcon, Phengaris teleius and Phengaris nausithous) have been recorded in the Koroška Region. However, only a handful of localities had previously been reported for these species in the region. Furthermore, with rapid decline of their habitats in the last decades, many of the historical localities may now be unsuitable. In this article, a revision of the previously known localities of all four Phengaris species found in Koroška region was made, with a report on new findings of P. alcon, P. nausithous and P. arion, as well as a confirmation of P. teleius and P. nausithous from one of the known localities. The reported findings are especially relevant from the conservation standpoint for the species in Slovenia, as they are isolated from their respective known ranges.

Review

This manuscript presents a crucial update on the distribution of *Phengaris* butterflies within the Koroška Region of northern Slovenia, a group recognized as highly threatened across Europe due to their complex brood-parasitic life cycles. Given the acknowledged rapid decline of their specialized habitats and the scarcity of previously reported localities, this study addresses a significant knowledge gap. The authors undertake a much-needed revision of historical data and integrate new fieldwork to provide a current status report, which is essential for effective conservation planning for these vulnerable species within the region. The paper details an investigation into all four European *Phengaris* species known to occur in Koroška: *P. arion, P. alcon, P. teleius*, and *P. nausithous*. Through a systematic approach that revisited known sites and conducted new surveys, the authors successfully report novel localities for *P. alcon, P. nausithous*, and *P. arion*. Furthermore, the study confirms the continued presence of *P. teleius* and *P. nausithous* at previously documented sites. These findings are particularly noteworthy given the context of habitat degradation and the stated isolation of these Slovenian populations from their wider known ranges, underscoring their unique genetic and ecological importance. In conclusion, this study offers a valuable and timely contribution to the conservation biology of *Phengaris* butterflies, not only for Slovenia but also within a broader European context. By consolidating existing knowledge and presenting new empirical data, the authors provide a robust baseline for future monitoring efforts and targeted conservation interventions in the Koroška Region. The emphasis on the isolated nature of these populations further highlights the urgency and strategic importance of these findings, making the manuscript an indispensable resource for policymakers and conservation practitioners engaged in the protection of these charismatic and ecologically significant insects.

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