It’s episode 18 so it’s about time we go underground, delving well below the surface to unearth the life cycle of a rather brilliant ecosystem engineer: the earthworm. We join a survey session at Knepp with four brilliant scientists: Emma Sherlock from the Natural History Museum, Inez Januszczak and Chris Fletcher from the Darwin Tree of Life Project, and Keiron Brown from the Field Studies Council. They teach us about the different groups, or eco-types, of worms; how they recover in rewilded landscapes; and how they are quite picky when on the look-out for a mate.