Even if eradication fails, several technologies often can control invasive species at acceptably low levels. No method is a magic bullet, each can have drawbacks if misused, and each has failed when used against certain invaders, but each also has successes to its credit. Biological control entails introducing a natural enemy usually from the native range of the introduced pest. For example, prickly pear cactus from the Americas is well controlled on hundreds of thousands of square miles of Australian rangeland by caterpillars of a moth introduced from South America. A disadvantage of biological control is that some agents attack nontarget species, and it is very difficult to remove a troublesome introduced natural enemy once it is established.
Chemical control involves using a pesticide, such as an herbicide or insecticide.
In mechanical control, hand-pulling or various kinds of machinery are employed. For example, volunteer convict labor is used in Florida to cut paperbark trees and in Kentucky to rip out Eurasian musk thistle. Because it is so new, the specific ways in which ecosystem management can be employed must be determined in each type of habitat. International cooperation and management is the best solution. The numbers of introduced species are growing in the United States and elsewhere because of increased trade and travel, but the situation is not hopeless.