A stunning work of narrative nonfiction that asks: what is natural? Now as never before, exotic animals and plants are crossing the globe, borne on the swelling tide of human traffic to places where nature never intended them to be. Bird-eating snakes from Australia hitchhike to Hawaii in the landing gear of airliners; disruptive European zebra mussels, riding in ships' ballast water, are infiltrating aquatic ecosystems across the United States; parasitic flies from the U.S. prey on Darwin's finches in the Galapagos. Predatory American jellyfish in Russia; toxic Japanese plankton in Australia; Burmese pythons in the Everglades-biologists refer fearfully to "the homogenization of the world" as alien species jump from place to place and increasingly crowd native and endangered species out of existence. Never mind bulldozers and pesticides: the fastest-growing threat to biological diversity may be nature itself.