3. Harlequin Ladybird

In the years since the harlequin ladybird first hopped across the English Channel, its spread has been scrutinised by an army of scientists and amateur naturalists.

Its rapid colonisation has given it the unfortunate title of the world's fastest invader.

Derek Mooney talks to ladybird expert Dr Helen Roy to find out how this little beetle came to be a great invader.

Telling the stories of non-native invasive species and our complicated attitudes to them and with an uncertain political future, how do we police our ecological borders?

Producer: Ellie Sans

First broadcast on BBC Radio 4 in August 2016.