Rapid increase in knowledge about the distribution of introduced predatory Testacella species (Gastropoda: Stylommatophora) in North America by community scientists

Testacellidae are a group of carnivorous semislugs with a vestigial ear-shaped shell near the posterior end of their elongate bodies. The single genus Testacella is native to the western Mediterranean and western Europe, but some species have been introduced into temperate countries worldwide. The species are subterranean and feed on earthworms. Due to their predominantly subterranean lifestyle, Testacella species are difficult to observe. Here, I review of the distribution of introduced Testacella species in North America and compare the knowledge based on literature references and museum specimens collected over more than a century with that observed by community scientists on the web platform iNaturalist in less than 10 years. Literature references and museum specimens indicate scattered occurrences of the introduced Testacella haliotidea in the eastern USA and a few more occurrences in the Pacific states of the USA and in British Columbia. Community scientists have nearly replicated a century of knowledge about the distribution of Testacella in North America. Their records even show a more continuous distribution of T. haliotidea in the Pacific states and confirm its presence in Tennessee, but not yet in Pennsylvania. They also provided the first records of T. haliotidea in Georgia and Mexico, and discovered a second introduced Testacella species, Testacella maugei, in California. The most distant occurrences of T. maugei in California are about 100 km apart, indicating that the species was probably introduced several years ago.

Automated summary

Testacellidae is a type of carnivorous semislugs with a tiny shell on their elongate bodies. Testacella species are native to the western Mediterranean and western Europe and some have been introduced to temperate countries worldwide. They are subterranean and mainly feed on earthworms, making them difficult to observe. This study compares the knowledge of introduced Testacella species in North America based on literature references and museum specimens collected over more than a century with observations from community scientists on the web platform iNaturalist in less than 10 years. The records from community scientists provide valuable information, including a more continuous distribution of T. haliotidea in the Pacific states and the discovery of T. maugei in California, indicating its introduction in recent years.