Experimental assessment of the predation pressure by the exotic flatworm Obama nungara in its introduced range

Land planarians are carnivorous predators that feed mainly on soil macrofauna such as earthworms, gastropods, and other land planarians. Several land planarian species have become invasive worldwide and pose a threat to soil biodiversity. Among them, Obama nungara is one of the most abundant invasive species found in France. The aim of this study was to investigate the predation frequency, growth rate, and preferential predation of O. nungara using an experimental approach. O. nungara's predation was tested on 8 prey species found in its French-introduced area. Two types of experiments were carried out: single experiments, where one O. nungara was offered 3 prey items of the same species and mixed experiments, where one O. nungara was offered 3 prey items of different species at the same time. We showed that O. nungara feeds equally on earthworms, snails, and slugs and that they can also prey on another introduced land flatworm, native to Australia: Caenoplana variegata. This ability to prey on a wide variety of native prey and to thrive on a mixed or single diet demonstrates its opportunistic feeding behavior, a likely predominant factor in O. nungara's invasiveness. In addition, long-term observations of O. nungara specimens revealed that they can live up to 10 months, are able to shrink to survive starvation, and can produce egg capsules after several weeks in isolation, which may also positively influence their invasion success.