Invasion of the redback spider Latrodectus hasseltii (Araneae: Theridiidae) into human-modified sand dune ecosystems in Japan.
Invasions of some areas of Japan by the exotic redback spider Latrodectus hasseltii Thorell (Araneae: Theridiidae) have been reported. While most of these invasions have occurred in urban areas, anthropogenic habitat modifications may provide an opportunity for L. hasseltii to invade semi-natural ecosystems, but the ecological impacts of L. hasseltii have only rarely been studied. We therefore examined the distribution of L. hasseltii in sand dune ecosystems and its potential impacts on other animals. In addition, we surveyed the occurrence of spiders on the exotic yucca Yucca gloriosa L. (Asparagaceae), another invader of sand dune ecosystems. Latrodectus hasseltii was observed in six of 18 sand dunes in the Chita Peninsula, central Japan, and was the dominant web-building spider at one site. The web contents of L. hasseltii consisted of various arthropod species, including the threatened ground beetle Scarites sulcatus Olivier (Carabidae). In all, 24 of 172 patches of exotic yucca were occupied by L. hasseltii, suggesting that colonization by exotic plants may facilitate the invasion of L. hasseltii into sand dunes. This is the first report of the invasion of L. hasseltii into semi-natural habitats in Japan, and these results suggest that L. hasseltii poses a threat to the conservation of coastal insects inhabiting human-modified sand dune ecosystems.