Invasive, alien, exotic, and non-native species. No matter what you call them, invasive species are bad news. They are "plants, animals, or other organisms that are introduced to a given area outside their original range and cause harm in their new home. Because they have no natural enemies to limit their reproduction, they usually spread rampantly. Invasive alien species are recognized as one of the leading threats to biodiversity and impose enormous costs to agriculture, forestry, fisheries, and other human enterprises, as well as to human health."(*1)
I sometimes wonder though, whether or not dedicated naturalists and environmentalists take the issue a bit too far. To anyone who is moderately educated about ecological issues, the spread of alien invasives is of far more concern than the immigration of illegal aliens. Usually in order to be considered an invasive species, the organisms would have to be spread or transplanted by humans (either accidentally or on purpose). But in order to subscribe to that idea, I believe you would also have to subscribe to the idea that man is apart from nature, or not a part of the natural ecosystem. Just because a certain species of ape developed a sentience and got a big ego about it doesn't mean we ever became anything more than just animals surviving in our environment. Sure, there's something different about being man-made, artificial, or synthetic, but that doesn't mean that man himself is different. Therefore if man's actions spread certain other plant and animal species into new ecosystems, is that not natural development? Sure, it will kill off some biodiversity in the short term, but new plants and animals will evolve and keep balance, and every necessary niche will eventually be refilled. Not in our lifetimes probably, but earth has been around a while, and she knows what she's doing. I mean, no plants and animals were here in the beginning, so they all had to have come from somewhere.
Still, I can't argue that invasive species are a good thing. Especially not if you're trying to preserve a "natural" habitat the way that it is or the way that is used to be, however short a time it may have actually remained that way on the geologic time scale. Nature isn't necessarily meant to be preserved, in the way many people think of the term. It's meant to grow, adapt, and evolve. Protected, yes. But not preserved.
The idea of invasive species is based on the idea that native organisms have more value than non-natives. Humans have struggled with this idea from the beginning. Since the inception of western society, humans have thought of themselves as more important than all other species on earth, and as such have assigned a value to others. The term "vermin" (or "varmit" around here), refers to species that are considered pests or nuisances. At one time, and still probably in many areas of the country, predators of big game animals were all considered to be pest species. Before westerners had time to learn about the concept of ecosystems and the idea that all organisms are dependent on each other, they had nearly wiped out all the game predators in the US. Wolves, coyotes, mountain lions, bobcats, bears... Now in states like Kentucky deer hunting season is crucial, because white tailed deer are ridiculously over-populated and humans are their only natural predators left. I only mention all of this because ecology is still a very young science, and I'm not sure that we always know best.
Regardless, exotic species cause a big headache for the relatively native species. Some of the big ones in the Bluegrass state right now are wintercreeper (a type of ivy), the Emerald Ash Borer beetle, fire ants, zebra mussels, and honeysuckle.
I had no idea honeysuckle wasn't a Kentucky native plant until I was a sophomore in college. Honeysuckle has always been (and remains) one of my favorite plants. The smell of honeysuckle bushes and fresh cut grass are the scents of summer in Kentucky. I have so many memories as a child of sitting in front of honeysuckle bushes and plucking off the flowers, one by one, to suck out the sweet juice of the blossoms. It requires a very special technique in order to get the biggest drop of the "honey". Turns out that honeysuckle actually secretes some sort of chemical into the ground "to inhibit other plant growth, effectively poisoning the soil." (*2) I never would have guessed.
So as much as I may hear friends bitching about it, and see employees at nature centers ripping it up from the roots, if I see honeysuckle growing around my yard, I'm going to let it grow. It deserves to be here every bit as much as I do.