Though many invasive aliens are notorious for the harm they bring (pythons in Florida, cane toads in Australia, brown tree snakes in Guam), many others enhance the local nature scene.

WSJ: Ecology and Change: Nature Has No 'Balance' for Us to Keep | Mind & Matter

The U.S. Fish and Wildlife Service says brown tree snakes have wiped out most of Guam's native populations of forest birds since being accidentally introduced to the island after World War II, probably after they stowed away on a ship or plane from their native range in Australia, Papua New Guinea and the Solomon Islands.

CNN: Deadly mice to rain down on Guam snakes