The impact of free-roaming pigs on arthropod diversity: a field survey in four European countries

The diversity and composition of arthropod communities are influenced by a broad range of environmental factors, including local livestock management practices. Free-roaming domestic pigs, through activities such as, wallowing, exploration, foraging at and below the soil surface, and defaecation can substantially alter arthropod habitats. While these behaviours may reduce populations of soil-associated arthropods, they can also create novel microhabitats that support other species. In this study, arthropods were sampled using Malaise traps positioned both in proximity to free-roaming pigs and at distances from them across five locations in four European countries—Norway, Denmark, Italy, and Slovenia—during 2022 and 2023. DNA metabarcoding of the Cytochrome Oxidase I (COI) gene was used to identify the collected bulk samples. The results revealed significant differences in arthropod order composition between areas with or without pigs at sites in Norway and Italy in 2022. Moreover, free-roaming pigs significantly modified the relative distribution of arthropod orders across all investigated locations. The analysis further demonstrated a strong positive relationship between α- and β-diversity and the total site γ-diversity across all sites and study years. Implications for insect conservation: These findings indicate that free-roaming domestic pigs enhance arthropod diversity. Accordingly, agricultural management practices that integrate free-roaming pigs may contribute to strengthening arthropod biodiversity within managed ecosystems.