In addition to these, many animals were introduced to new habitats on the other side of the world either accidentally or incidentally. These include such animals as brown rats, earthworms (apparently absent from parts of the pre-Columbian New World), and zebra mussels, which arrived on ships. Escaped and feral populations of non-indigenous animals have thrived in both the Old and New Worlds, often negatively impacting or displacing native species. In the New World, populations of feral European cats, pigs, horses, and cattle are common, and the Burmese python and green iguana are considered problematic in Florida. In the Old World, the Eastern gray squirrel has been particularly successful in colonising Great Britain, and populations of raccoons can now be found in some regions of Germany, the Caucasus, and Japan. Fur farm escapees such as coypu and American mink have extensive populations.