Invasive species are a problem throughout the world — but in Japan, with its fragile island ecosystems, the problem is particularly severe. The most prominent Japanese battle to protect native species is raging in Lake Biwa, the nation’s largest freshwater lake and a cultural icon frequently referenced in literature, theater, and film. There, voracious American fish, initially introduced for sport fishing, are out-competing their Japanese counterparts. Goats, mongooses, dandelions, beetles, raccoons, and other nonnative species are also wreaking havoc on Japan’s environment. Ironically, in Japan as elsewhere, some of the now-problematic invaders were brought in to solve environmental problems. The mongoose, for example, was introduced to kill rats and the venomous habu snake; instead, it’s found easier prey among native Japanese species and thrives in the tens of thousands. Until last year, Japan had no policy in place to address environmental problems stemming from nonnative species; now, the country is working to exterminate species that threaten its original ecosystems.