Look around the English countryside and you'll find animals and plants that shouldn't be there - from Muntjac deer to Mitten crabs, Harlequin ladybirds to Tree of Heaven.So-called invasive species are reckoned to be one of the world's greatest threats to native wildlife. And when you factor in a changing climate, the situation gets even more complicated.Richard Hollingham meets an invasive species expert from the Centre for Ecology Hydrology who tells us not only what we can expect, but also what you can do to help.We also hear from a climate expert at the UK Met Office to find out why he believes climate scientists should take responsibility for communicating their science to the world.Finally, we hear how researchers figured out that a pit full of decapitated bodies in Dorset were Vikings and why small honeybees don't do as well as their normal-sized peers when it comes to mating.