Foxes are enemies of all clan cats. They don't appear much but they are mentioned. Especially in the New Prophecy series when the twolegs put up fox traps in ThunderClan territory to stop them from eating their chickens. The twolegs didn't catch any foxes in them but they caught a lot of clan cats. Firestar and Berrykit were both caught in the fox traps. The clan figured out how to dig up the fox traps. Foxes were also mentioned when they said that Firestar lost a life from a fox.