One of the consequences of globalization is the introduction of invasive species. Giant hammerhead flatworms, or land planarians, up to 40 cm (over 1 foot) in length, are reported from France and overseas French territories by an international team led by Jean-Lou Justine of ISYEB (Muséum National d’Histoire Naturelle, Paris, France). This is the first study of this invasion, reported in an article to be published in the open-access journal PeerJ.