Many times an exotic species will invade a new area by accident, however. Red fire ants arrived in Alabama on ships carrying wood. They spread throughout the southern United states and replaced many native insects. They have also killed birds and small mammals. Another recent invader, the Asian long-horned beetle, is destroying hardwood trees in parts of the U.S. Ecologists estimate that more than 6,500 exotic species have established themselves in the U.S. As a result, 315 native species are very close to extinction.