Fabio Pupin / Red swamp crayfish (Procambarus clarcki), invasive species, captive, Italy, July.

Nigel Cattlin / Harlequin ladybird (Harmonia axyridis) larvae still with a raft of empty egg cases, June Berkshire, England, UK.

Nick Hawkins / European green crab (Carcinus maenas), an invasive species in North America, Kejimkujik Seaside National Park, Nova Scotia, Canada. July.

Shane Gross / Invasive Lionfish (Pterois volitans) which have taken over and are wiping out native fish in the Atlantic ocean. The highest densities are in the northern gulf of Mexico. Destin, Florida, USA.

Shane Gross / Invasive Lionfish (Pterois volitans) which have taken over and are wiping out native fish in the Atlantic ocean. The highest densities are in the northern gulf of Mexico. Destin, Florida, USA.

Emanuele Biggi / Great Fen / Raft spider (Dolomedes plantarius), adult female eating an invasive species of fish, Western mosquitofish, (Gambusia affinis), Alessandria, Italy, August.

Franco Banfi / Freshwater jellyfish (Craspedacusta sowerbii) Lake Lugano, Ticino, Switzerland. August. Invasive species.

Franco Banfi / Freshwater jellyfish (Craspedacusta sowerbii) Lake Lugano, Ticino, Switzerland. August. Invasive species.

Sven Zacek / American mink (Mustela vison) on ice with Common frog (Rana temporaria) prey, Tartumaa, Estonia, January. Introduced species.

Sven Zacek / American mink (Mustela vison) shaking off fur on ice with Common frog (Rana temporaria) prey, Tartumaa, Estonia, January. Introduced species.

Sven Zacek / American mink (Mustela vison) running on ice with Common frog (Rana temporaria) prey, Tartumaa, Estonia, January. Introduced species.

Stephen Dalton / Harlequin ladybird (Harmonia axiridis) on end of leaf, invasive species. Sussex, England, UK. March.