An assessment of the habitats and trophic level of the introduced slug Limax maximus in Japan

Abstract Limax maximus is one of the most widely introduced terrestrial gastropods in the world. The first record of the species in Japan was published in 2009, and its distribution range has rapidly expanded. Our aims were to estimate the habitat characteristics and diet of introduced L. maximus in Japan. We conducted field surveys at 21 sites in Ibaraki Prefecture, where L. maximus is frequently reported by citizens. We found that the habitat range of L. maximus is broad, occurring from rural to urbanized areas; this is distinctively different from the case of native slugs and non-native slugs previously introduced to Japan. To characterize L. maximus diets, we performed stable isotope analyses on individuals and the species’ potential food sources. Limax maximus consistently showed high δ 13 C and δ 15 N, meaning that it occupies a similar trophic position as predatory invertebrates such as spiders and ground beetles. Analyses of the stable isotope data by using a Bayesian mixing model (MixSIAR) suggested that L. maximus feeds on various food sources but mainly mushrooms. Our findings imply that L. maximus is a generalist with regard to habitat preference and has a flexible diet; these are likely factors in its rapid population increase. Currently, the Japanese government designates L. maximus as an introduced species that requires comprehensive countermeasures. We recommend sharing the species’ occurrence information with the public and cautioning farmers to be aware of this slug and its detrimental effects, so that they may take measures against its potential agricultural damage.