The last remaining habitats of amphibians and dragonflies are at risk. Calico crayfish are endangering biodiversity along the upper Rhine. These crayfish can strip entire biotopes bare. They've completely destroyed a project to reintroduce marsh turtles costing millions of Euros. We meet a frustrated research team and a fisher who says he can't simply stand by and watch - and who catches and eats as many of the crayfish as possible. But is this really a solution? Should we be using biocides in future as a way to combat invasive species? And how did the American crayfish get to Europe in the first place?
It's evident that the crayfish can no longer be completely eradicated, but as a research team from Karlsruhe has found, small biotopes can be protected. Although such measures don't come cheap, this offers a glimmer of hope for endangered amphibian species. But what lessons can be learned, and what might our future response to invasive species look like? This documentary shows how much damage a single invasive species can cause.