What does it mean to talk about ‘invasive’ species?

Analysis: As people trade more, animals and plants are getting picked up en route, writes Phoebe Weston

A wild parakeet in Kensington Gardens, London (Getty/iStock)

Footloose species are cruising around the planet and setting up homes in new and distant lands. Parakeets now soar over British cities, grass carp swim in our rivers and grey squirrels have taken over our forests.

Animals have always travelled great distances – and many of our species, such as snowdrops, horse chestnuts and rabbits were “alien species” in the past – but they are spreading faster than ever.

As people trade more, animals and plants are getting picked up en route. These “hitchhikers” travel in the ballast water of ships, escape from people’s gardens, or hide as “stowaways” in fishing equipment.