Black rat (Rattus rattus). Slightly smaller and more slender than the brown rat (Rattus norvegicus), it also has a longer tail, a pointier nose and larger ears. It was spread around the world by Europeans, but has now largely been replaced (at least in colder and more urban areas) by the heavier, more aggressive brown rat who also tends to have more babies. Brown rats are also burrowing animals while black rats are arboreal. They are still considered of least concern in the wild.