Parnassius apollo L. is a widespread species that inhabits various regions of Europe, and in Italy, it can be found in the Alps, in the Apennines, and in the isolated mountain ranges of Sicily. Its Alpine populations are abundant and not currently threatened, whilst Apennine populations are strongly fragmented and in decline. The reasons for the decline of this butterfly may be different, such as anthropic disturbances and climate change, but reforestation, which has considerably reduced the open environments suitable for its survival in several areas within its European range, could also play a major role. Its larvae feed on few genera from the Crassulaceae family (e.g., Sedum, Jovibarba, Rhodiola, and Sempervivum), but Sedum is recognised as its main larval foodplant. The adults feed on nectar obtained from a variety of plants depending on their geographic range. With the aim of understanding the trophic network of one of the most isolated Italian populations of Parnassius apollo, field surveys were performed in the Aspromonte National Park, South Italy. Observations were carried out weekly in two areas where the presence of adults was abundant. In detail, the botanical species visited by the adults, the duration of their trophic activity, the number of other pollinators present on flowers, and the abundance classes of flowering species were recorded. The results highlighted that P. apollo adults foraged on a limited number of species, the most abundant of which belonged to the families Asteraceae and Campanulaceae. In addition, the observations showed that P. apollo adults preferred flowers from the same plants as those visited by several other pollinators (i.e., bees and other butterflies). This study highlighted the feeding preferences and floral resource use of P. apollo in an isolated southern Italian population and provided insights into its trophic interactions and potential conservation needs.