10 Invasive Species That Changed the World Forever

Invasive species have a bad reputation — from plant-choking vines to nest-usurping birds, they're often rightly blamed for crowding out native flora and fauna and altering the environment they invade. But that's nothing compared to the 10 species on this list: they are so aggressive, they've actually changed the world as we know it.

1
of 10

Earthworms

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These pink creepy-crawlies might not seem like much to the casual eye, but earthworms just may be the most important invasive species in history. History scholar Christopher Lloyd points out that Charles Darwin considered the earthworm the most influential creature on the planet. As earthworms expanded to land after descending from sea worms, they provided essential soil services like ventilation and fertilization. "Wherever earthworms plow, people thrive," Lloyd told National Geographic. "Wherever worms perish, societies collapse." However, considering our influence on habitats, this might not actually be a good thing. Photo: goosmurf/Creative Commons

2
of 10

Cane Toad

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Setting cane toads loose in Australia seemed like a good idea at the time: The amphibians were supposed to help combat pests in sugarcane fields, and they did. But they didn't stop there: They became a threat to all of the native species in their paths, affecting the entire country's biodiversity as they moved west toward the national parks region. The country is now working on a $7 million, 15-year plan to reign them in. Photo: Sam Fraser-Smith/Creative Commons

3
of 10

Zebra Mussels

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Zebra mussels made their debut in North America in 1988, after they hitched a ride on ships from their native Russia. A mussel may sound like the most non-threatening creature in the ocean, but the zebras are an exception: They've spread from Lake St. Clair (near Detroit) to the Mississippi River and the Great Lakes, edging out native clams and mussels, clogging industrial intake valves, changing the migratory patterns of local ducks, and bloodying feet of beach goers (they are really sharp). And while edible, they store toxins and therefore are not recommended for eating. Photo: andres musta/Creative Commons

4
of 10

Rats

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Ah, rats: The original stowaway. These rodents have been hiding in ships for generations, and changing the ecosystems where they land. For example: They were the first invasive species to arrive on Macquarie Island, and efforts to rebuff them -- which included introducing cats -- only made things worse; the cats -- and the rabbits later introduced for food -- have since "resulted in the annihilation of two native bird species and the stripping of Macquarie Island's vegetation." Estimated cost of fixing this "ecosystem meltdown": $16 million. Photo: Wikimedia Commons

5
of 10

Gypsy Moths

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Caterpillars turning into moths sounds like the stuff of sweet children's books, but when they're Gypsy Moths, it's a very different story. The species, brought to the United States in 1869, can decimate entire trees, stripping them of their leaves and affecting forests and native wildlife. Photo: Wikimedia Commons

6
of 10

Starlings

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According to the USDA, starlings were brought to America from Europe as "part of a plan to introduce to the U.S. all birds mentioned in the works of Shakespeare," which just proves that the Bard's followers aren't perfect. A population that started out small in New York City at the end of the 1800s is now a massive group that spreads disease to other animals, "usurps nesting sites," and causes $800 million in crop damage each year. "Out, dammed bird," indeed. Photo: Walter Baxter/Creative Commons

7
of 10

Kudzu

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An invasive plant is nothing you can't handle with a pair of garden shears, right? When it comes to kudzu, wrong. This Japanese vine, originally planted as a way of preventing soil erosion, does its job a little too well. According to The Nature Conservancy, it also "grows out of control, smothers native plants, and even uproots native trees by the sheer force of its weight." If you're able to get rid of it -- by getting rid of the entire root system -- try planting passionflower, honeysuckle, or trumpet creeper instead. Photo: Donna *deestea*/Creative Commons

8
of 10

Brown Tree Snake

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As one of the most expensive invasive species ever, according to Daily Finance, the brown tree snake is a lot more imposing than it looks. In the 1950s, the reptiles stowed away on military planes to end up in Guam where they took over the previously snake-free island. Now Guam is believed to be home to 13,000 of the snakes -- which were also the culprits behind the demise of the now extinct-in-the-wild Micronesian kingfisher bird. Photo: Wikimedia Commons

9
of 10

Mountain Pine Beetles

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Mountain pine beetles usually only grow to about 1/3 of an inch, but these tiny pests can have a huge impact with their tree-killing capabilities. They already cover 3.6 million acres of forest in Northern Colorado and Southern Wyoming alone, and also live throughout Canada. They're even a threat to massive grizzlies, since the beetles eat whitebark pine -- which is also a main source of pre-hibernation food for the bears in Yellowstone. Photo: Wikimedia Commons

10
of 10

Humans

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If you're looking for the worst invasive species of them all, it's us. We move from one region to another; affect the flora and fauna with our activities; endanger native species; and change the environment wherever we end up. Migrations and human activities throughout history have affected every part of the natural world: plants, animals, water, soil, and even the atmosphere. In fact, most of the species on this list became invasive because of us. Something to think about for 2011.