Predictive Distribution Modeling of the Medicinal Leech Hirudo verbana Carena, 1820 (Hirudinea, Hirudinidae) in Sicily: Implications for Conservation

Abstract

Hirudo verbana, a medicinal leech species of conservation concern, has long been considered rare and fragmented across its distribution range due to overexploitation and habitat alteration. In this study, we present the first predictive distribution model for H. verbana in Sicily, combining field occurrence data (time: 1980–2024) with environmental variables using an ensemble species distribution modeling (SDM) framework. Unlike its typical occurrence in temperate lowland wetlands of central-eastern Europe, the species in Sicily shows a marked shift toward upper hill and montane zones. Species presence was strongly associated with high NDVI values, reflecting a preference for areas with dense and structurally complex vegetation. In contrast, presence probability declined sharply with increasing terrestrial human footprint (THF), indicating a notable sensitivity to anthropogenic disturbance. Aquatic habitat type also emerged as a key predictor: the species was most likely to occur in lentic environments such as standing water bodies, and least likely in lotic systems or areas lacking aquatic habitats. Notably, most high-suitability areas overlapped with sites in the Natura 2000 network, emphasizing the importance of existing protected areas as refugia for the species. Moreover, some previously undocumented areas of high habitat suitability were identified, providing a spatially basis for refining monitoring strategies and informing conservation planning for this ecologically sensitive freshwater invertebrate.