Have you seen any of these? It is a non-native invasive species, the Australian flatworm (Australplana sanguinea). This year I have found a dozen in my backyard at Warton, often climbing up the wall when it is raining. Prior to this they have been recorded on tennis courts in Lancaster in 2019. They mainly eat earthworms and it is said they can seriously deplete the soil of them.
Words and Photograph Linda Renshaw