A number of scientists are warning that the spread of invasive species could become the next big environmental crisis. Some of the invasives are brought into non-native areas deliberately, but most are imported accidentally, particularly as global trade increases. Once the species get established in places where they have no natural predators, they can spread like wildfire and wreak havoc on native ecosystems. Harvard biologist E. O. Wilson believes that invasives will lead to more extinctions than pollution. One recent study estimated that invasive species, including diseases, cost the U.S. more than $130 billion a year. A few examples: The Asian longhorn beetle has lead to the deaths of more than 5,000 maple trees in New York and Chicago. The sagebrush of the Western U.S. is being wiped out by cheat grass, an extremely flammable invader from Europe. And lygodium, or Old World climbing fern, is now smothering 100,000 acres in south Florida.