Rheas stomp over snow-covered fields of Northern Germany. Flocks of bright green parrots fly screeching over the Cologne Cathedral. And beaver-like nutrias with orange teeth gnaw at French and Dutch canal dams. What do they have in common? They are all non-native and are suspected of causing ecological and economic damage. Although the EU wants to combat such “invasive animals”, the fight against them is proving difficult. A cumbersome and sometimes unprepared bureaucracy, quarrelling scientists and uninformed citizen facilitate the spread of these animals. Must the intruders be fought? When is an animal species actually “native”? Or is constant change in nature not the rule? The series gets to the bottom of the accusations against animal aliens by picking out three relevant and also visually interesting species as examples