Invasive species are plants or animals that live where they don't belong, most often as a result of human tampering (or neglect). We brought cane toads to Australia so they would eat the cane beetle. Cane toads have now completely overrun the country, killing native species and generally being a giant pain in the arse (that's Australian for beer).
We brought kudzu over from Japan because it was pretty to look at, and it has now grown out of control and can be found choking native plants all across the Southern United States.
It was the same deal with Eurasian Watermilfoil in midwestern lakes, the rabbit in Australia, or any other time a plant or animal is put into an environment where it has no natural predators to keep its numbers in check.
In the south, the State Botanical Garden of Georgia isn't taking invasive species lightly. They've started a new program that trains volunteers to identify and kill invasive species like privet, English ivy, honeysuckle and bamboo. The program's founders hope to get enough people out in the fields killing invasive species to slow the advance of the non-native plants, which are even now threatening Georgia's barrier islands.
AJC has the full rundown, swing over and give it a read.
If you live in the Athens, Ga., area and want to lend your arm to the war against invasive species, click over to the Botantical Garden of Georgia site and sign up for a Native Plants class.
May you have good hunting.