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5 Invasive Species That Might Conquer the World

Kudzu smothers homes and cars and is a general nuisance. See more green science pictures.
©iStockphoto.com/ MichaelGMeyer

We humans think we're so smart. But boy, do we do some not-so-smart things. Case in point: kudzu. The Japanese introduced it to the United States at the 1876 Centennial Exposition. Americans thought the leafy, sweet-smelling plant was so lovely, they began using it for ornamentation. Then as forage for livestock. The government even got into the act, instructing the Civilian Conservation Corps to plant kudzu for erosion control. Yet no one spent a millisecond pondering how this non-native plant might react in its new environment. Big mistake.

Kudzu loved the climate in the Southern U.S., and took off like wildfire there, growing up to 60 feet (18.3 meters) per year. It began climbing up buildings and telephone poles, smothering cars and homes and becoming a general nuisance. And it's still around today.

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Unfortunately, that's hardly an isolated incident. For years, people have brought non-native species into their countries because they're pretty, or because they may be able to solve a problem. For instance, some might have imported amphibians or birds to eat insects that were destroying local crops. Except things didn't exactly work out as planned. Lacking natural predators, the non-native species often thrived in their new surroundings to the point where they became problems -- sometimes, rather big ones.

Today, such invasive species are found around the globe, and their presence outside of their native areas is damaging the world's ecosystems and threatening biodiversity, costing people billions of dollars in reparations, eradication efforts and preventive measures [source: EarthTrends]. Although many governments have wised up and enacted tight controls on travelers, imported goods, plant nurseries and more, plenty of non-native species continue to be tracked around the globe unintentionally, by hiding in people's shoes and luggage or hitchhiking on boat hulls, for example. Some -- like the five on this list -- seem almost unstoppable.

There you are, puttering serenely down the river or across a lake, when suddenly the water around you erupts in a frenzy as immense, prehistoric-looking fish begin jumping and thrashing about. One flies right at you, smacking you in the face and leaving you with a real shiner. Sound idyllic? Hardly. Such "attacks" are one of the many problems posed by Asian carp.

Native to China and parts of Southeast Asia, Asian carp were introduced into the southeastern United States more than 20 years ago to clear algae from catfish ponds. Since then, the fish -- known for their ravenous appetites -- have worked their way up the Mississippi and Illinois Rivers, devouring so much plankton and other organisms that there's little left for the native species. Add to that an insanely high reproductive rate and few natural predators, and you can see why they're quickly decimating all the native fish species in their path. Now they're poised to enter the Great Lakes -- an area already compromised by non-native sea lampreys, plus zebra and quagga mussels -- where many fear they'll ruin the lakes' $7 billion fishing and tourism industries [source: Harrison].

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But it's not just the Great Lakes that are endangered. The fish are also in the Kansas River and threatening to swim into the Arkansas. Plus, they're causing similar problems in Eastern Europe [source: Pearce]. And who knows where these giant fish -- some top 100 pounds (45.4 kilograms) -- will swim from there [source: WebEcoist]?

One bright spot: Asian carp are a delicacy in China, where they're increasingly rare, due to overfishing. Some Midwestern fishermen are now catching these fish and selling them back to China [source: WebEcoist].

Golden bamboo can destroy native plants and the habitats they provide for wildlife.
Golden bamboo can destroy native plants and the habitats they provide for wildlife.
©iStockphoto.com/ bayuharsa

Who doesn't appreciate the beauty of bamboo? Tall and strong, with delicate green leaves and an exotic, calming look, its appeal is apparent in the fact that several hundred species have been imported to the U.S. by the horticultural industry for use as ornamental plants. But bamboo can be a bit, well, nasty, especially the 24 varieties within the genus Phyllostachys [source: Brown]. And Phyllostachys aurea, or golden bamboo, is the nastiest of them all.

Golden bamboo was brought to Alabama from China in 1882 to create visual and sound barriers for privacy. An aggressive, fast-growing plant that can reach heights of 30 to 40 feet (9 to 12 meters), it quickly overtook everything in its path, destroying native plants and the habitats they provide for wildlife, and offering nothing in return. In the U.S. today, golden bamboo is a problem mainly in the Southeast, from Maryland to Arkansas, although it's also causing problems in Oregon and other Western states. The cost to U.S. taxpayers to fight its spread is an astonishing $138 billion per year [source: Brown].

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But it's not just America that's fighting golden bamboo. The plant is cultivated worldwide as an ornamental in tropical to temperate areas, and other countries -- such as Australia -- have problems controlling it, too [source: U.S. Forest Service, Bamboo Wholesale].

Ah, bunnies. They're so adorable, aren't they? Unless you're a homeowner or farmer, that is. Those cute, fuzzy little critters are ruining land all over the world, causing soil erosion through their overgrazing and burrowing. They also nibble on people's landscaping and flowers, and negatively impact native species by damaging fragile ecosystems.

European rabbits are native only to Southern Europe and Northern Africa. But over time, they've been introduced to almost every continent. And wherever they've been introduced, they quickly proceeded to, well, breed like rabbits. For example, a mere 24 were released in Australia in 1859 by an English farmer who thought they'd provide "a touch of home, in addition to a spot of hunting" [source: WebEcoist]. Today, rabbits have contributed to the extinction of nearly an eighth of Australia's mammal species, ruined the country's soil and caused millions of dollars annually in agricultural damage [source: Environmental Graffiti].

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Australians did try to eradicate their rabbit population in 1950 by introducing the Myxoma virus to their mainland. A biological control agent, this virus causes Myxomatosis, a disease fatal in nearly every rabbit that contracts it. Five hundred million rabbits died, but the 100 million that remained developed a resistance to the disease [source: WebEcoist]. And now, the bunnies' numbers are again on the rise [source: Zukerman].

Starlings congregate in flocks of up to 1 million or more.
Starlings congregate in flocks of up to 1 million or more.
©iStockphoto.com/ lleerogers

A noisy, aggressive bird, the European starling has been introduced into almost every corner of the world, generally because of its good looks [source: Columbia]. In the U.S., this introduction took place in about 1890, when Shakespeare lovers released 100 European starlings into Central Park so that North America would be home to every bird mentioned in the Bard's plays. Now, more than 200 million European starlings call the continent home [source: OMAFRA].

In addition to their comely looks -- which include glossy black feathers sprinkled with iridescent green and purple flecks -- starlings are omnivores, and congregate in flocks of up to 1 million or more. That's not a typo. These massive hordes devastate agricultural lands, and especially love to eat grapes, olives, cherries and grains. The birds will even settle over a field when crops are just beginning to poke their heads above ground, plucking up the tender, young plants to feast on the seeds. Starlings also chase out local bird species as they compete for food and nesting grounds, and can harm livestock and poultry facilities by swooping in to gobble up the food in feed troughs, contaminating the livestock's food and water as they eat. Their sizeable flocks are also believed to have caused a number of deadly crashes by colliding with planes [source: WebEcoist, Columbia].

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Some people defend European starlings, as they do eat a lot of insects -- which is why certain countries, such as New Zealand, introduced them to their homeland in the first place. But most feel the damage the birds do far outstrips the benefits of their bug-eating [source: Columbia].

Another creature many countries eagerly introduced to their homelands is the cane toad, a native of Venezuela and Guyana [source: Butler]. Like the European starlings, cane toads chow down on a lot of insects that can ruin sugarcane and other valuable crops. But these gigantic amphibians -- which can grow up to 15 inches (38.1 centimeters) long -- will eat almost any terrestrial animal, and fight with native amphibians for food and breeding grounds. Even worse, cane toads excrete a strong toxin from their skin that can sicken or kill domestic animals and wildlife, and even humans. People have died from eating the toads and their eggs, too [source: ISSG, WebEcoist].

Cane toads are especially problematic in the U.S. and Australia. In the latter country, some feel eradication is impossible because the toads' numbers are so great. One Queensland researcher is working on developing a strain of cane toad that can only give birth to males, ensuring the creatures' eventual demise, once the genetically engineered toads mate with regular ones [source: IMB - Institute for Molecular Bioscience]. However, only time will tell whether the cane toad or man is more resourceful -- and if we've finally learned our lesson about introducing non-native species into our homelands.

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Author's Note: 5 Invasive Species That Might Conquer the World

When I was a kid, there was a popular sketch on "Saturday Night Live" about the killer bees that were coming to invade North America from the Southern Hemisphere. They reached America some 12 years after the sketch ran, and are entrenched in several southern states today, where they're causing agricultural turmoil -- although not mass murder, as some feared. Unfortunately, invasive species are a problem worldwide. I'm sure you all can quickly cite some of the problem plants, insects, birds or mammals in your own backyard. Just keep that in mind if you're ever tempted to buy an exotic pet, or plant a pretty -- but non-native -- plant in your backyard that's known to quickly spread. If we're all more watchful, we can help combat this problem.

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Sources

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