In 1906, a University of Miami forestry professor named John Gifford thought that planting thirsty trees at the borders of the Everglades would help dry up land on the periphery for development. He chose the melaleuca, a hardy Australian tree that had been imported to Florida for the first time 20 years earlier, says Allen Dray, an ecologist at the United States Department of Agriculture's invasive plant research lab in Fort Lauderdale, Fla.

With no natural enemies, however, the melaleuca took over more than half a million acres. It became such an environmental nightmare that some cities required its eradication on a lot before issuing a building permit. That was no small feat: The tree is virtually indestructible.

A century after its widespread introduction, the melaleuca has met its match in the form of two bugs from back home—the melaleuca snout beetle, which eats only young melaleuca leaves, and the sap-sucking psyllid.

After nearly a decade in quarantine to make sure they didn't eat anything else, the insects were released into infested areas in the 1990s. And they're working, Dray says. In heavily infested areas, researchers have recorded up to a 75 percent reduction in the growth of the trees.

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