Rats that are the size of sheep might be a good horror movie story. However, scientists from the University of Leicester in England say that in the future, there could really be giant rats on the Earth. They could be as big as sheep and weigh up to 80kg. Rats are spreading all over the Earth. They are now the strongest animals on many small islands. One of the reasons for this is that they travel on ships and relocate to areas that never had rats before. Another reason is that many larger animals are becoming extinct, so there are fewer animals that might kill rats. Researcher Dr Jan Zalasiewicz said: "Given enough time, rats could probably grow to be…the world's largest rodent."
Dr Zalasiewicz said rats are one of the best examples of a species that we have spread around the world, and have successfully adapted to many of the new environments. He said: "There will be future thin rats, future fat rats, slow and heavy rats, fast and ferocious rats, probably future aquatic rats - the list goes on." After the dinosaurs died out, many small animals slowly grew bigger and bigger. The same thing could happen with rats if there are no animals left that hunt and kill them. Dr Zalasiewicz also believes that "super-rats" will start killing other species to make them extinct. This will have a big impact on food chains. He did not say what humans would do about giant rats running around everywhere.