The list of 100 of the world's worst invasive alien species, compiled by the International Union for Conservation of Nature (IUCN), aims to help biodiversity conservation efforts worldwide (see After a position on the list fell vacant as a result of the global eradication of the rinderpest virus (see, for example, Nature 474, 10–11; 2011), we coordinated the community of invasion biologists in a unique initiative to vote for a replacement.

We assessed more than 10,000 invasive species from the world's largest databases for their capacity to spread and for their potential ecological or economic impact. More than 650 experts from 63 countries then voted on the ten candidate species we shortlisted, and selected the giant salvinia (Salvinia molesta), an aquatic fern.

Native to Brazil, this fern has spread throughout the tropics and subtropics. It doubles in abundance within days, forming thick, floating mats that block light from expanses of water, reduce its oxygen content and degrade water quality. They also impede water-based transport, clog irrigation and power-generation systems, and harm local fisheries.

Now in the global spotlight, this new entrant to the IUCN list is set to increase public awareness of the harm caused by invasive species and to stimulate more discussion in science and policy circles.