Non‐native freshwater snails: a global synthesis of invasion status, mechanisms of introduction, and interactions with natural enemies

Non‐native freshwater snails can play important roles as consumers, hosts, and prey. Despite their potential ecological importance, global patterns in non‐native snail taxonomy, geography, and ecology have not been documented. Our objectives were to use a semi‐quantitative systematic review to describe non‐native freshwater snail global diversity, distribution, mechanisms of introduction, and interactions with natural enemies, including parasites and predators. Based on 506 relevant publications, we recorded 95 non‐native freshwater snail species from 16 families. Six taxonomic families, and pulmonate snails as a group, were over‐represented relative to the number of species expected by chance. Eight snail species represented 63% of the research records. A few snail taxa (15%) were widespread global invaders, reported from four or more continents, while most invasions were limited to a single continent. Australia and the Pacific Islands were the largest ‘sink’ for non‐native snails, with the greatest difference in the number of non‐native taxa relative to native taxa that had spread to other continents. Aquarium hobby sales were implicated as the most common mechanism of introduction (41% of species), followed by “hitchhiking” on aquatic vegetation, human consumption, use for biocontrol, transportation in canals, commercial shipping, and outdoor recreation. A search of internet sales posts indicated that four of the six over‐represented snail families were readily available for purchase online. Non‐native snails hosted parasites of wildlife, livestock, and human health importance, yet on average had 80% lower parasite richness in their non‐native compared to native range. At least 65 taxa were documented as consumers of non‐native snails, including native predators of conservation concern. These findings suggest that non‐native snails often are released from parasitism, but may commonly experience biotic resistance from predators. Our synthesis emphasizes the relatively high diversity of non‐native snails, but the disproportionate role of a few taxonomic groups in driving ecological, economic, and public health challenges. Moving forward, it will be important to limit new snail introductions through policy, education, and monitoring, particularly as the effective control of established snail invasions remains challenging in most ecosystems.