Large Arion Slugs—Conservation Concerns of Invasion, Hybridization, and Pest Genesis

The vast majority of animals on Earth are invertebrates, however they receive proportionately little conservation interest. One of the most diverse and imperilled animal groups is the mollusks, which hold the greatest number of recorded animal extinctions. A particularly pertinent threat to the persistence of mollusk species is the threat of invasive species. Many mollusks are highly susceptible to impacts of invasive species, whereas others have become notorious invasive pests. Arion vulgaris and A. flagellus are highly invasive terrestrial slugs, which have become major pests of agriculture and horticulture. The arrival of these highly fecund Spanish slugs coincides with declines in the native slug species A. ater and A. rufus. It is suggested that a key mechanism resulting in the displacement of native slugs is hybridization. Over time, successive hybridization and introgression could result in biotic homogenization of slug species, with eventual genetic assimilation and possible extinction of A. ater and A. rufus. The impacts of invasive arionids should be a major conservation concern. To mitigate the damage to agriculture, there is a pressing need to develop effective chemical or biological control agents against large arionids. In order to protect native biodiversity, management priorities should focus on biosecurity measures to prevent the spread of invasive slugs.