10 Incredibly Destructive Invasive Species

By: Wes Walcott
An introduced pest, a cane toad feeds on insects under a street light.
Originally introduced as a way for farmers to quell the problem of insect pests in their sugar cane fields, cane toads quickly grew into a massive problem for Australia. Jason Edwards / Getty Images

Bullying isn’t just something that happens on school playgrounds, it’s a daily occurrence in nature all over the world. Invasive species are plants and animals that, once introduced to a new habitat, start bullying the native species to the point where they can no longer survive there. They’re generally hardier, consume more resources, and reproduce much faster than the species they compete with. And, since they are new to the environment, they have very few, if any, natural predators to keep them in check.

The introduction of non-native plants and animals to a new ecosystem will almost always results in environmental stress, degradation and sometimes even disaster for native populations. These are 10 of the most destructive invasive species the world has ever known.


10. Cane Toads

Originally introduced as a way for farmers to quell the problem of insect pests in their sugar cane fields, cane toads quickly grew into a massive problem for Australia. Especially since the over 60,000 toads initially released didn’t save the crops they were meant to protect because they didn’t like to venture into the farmers sugar cane fields.

After the cane toad population exploded, there was no easy way to stop it due to the toads amazing defence mechanism — they secrete toxic ooze that’s poisonous enough to kill just about any animal that would try to eat it. While predators in their native habitat are very much immune to this toxic ooze, unfortunately, the Australian predators have yet to build up a resistance to it. Many animals that attempt to eat a cane toad die instead. With nothing around to keep their numbers in check, populations of cane toads in non-native habitats like Australia have grown out of control and, because they’ll eat pretty much anything they can fit into their huge, gaping mouths, its taking a serious toll on native animal and plant species.


9. Common Rabbits

In 1859, English farmer Thomas Austin released 24 common European rabbits to the Australian wilderness thinking they “could do little harm and might provide a touch of home, in addition to a sport of hunting.” Less than 40 years later the rabbit population had mushroomed to the point where many native Australian plants and animals were on the brink of being wiped out. The problem was the European rabbits started inter-breeding with the local rabbits on such a profuse scale that even after trapping or killing two million of them annually, there was barely an impact at all to the overall population.

Perhaps Austin was unaware that female rabbits can have more than 30 babies a year and that their methods of burrowing and overgrazing can lead to irreparable soil erosion. Thankfully, Australia now has some of the most strict customs laws in the world.


8. Kudzu

The fact that it sounds like a fabled Japanese monster is pretty fitting considering this ornamental vine species originated in Japan and has caused extensive destruction to buildings and habitats.

Kudzu was first brought to the United States at the Philadelphia Centennial Expo in 1876. There, it was exalted as a hardy, fast-growing plant that could quickly cover a lot of ground and help prevent soil erosion. The problem was it grew too fast — as much as a foot a day under the right conditions. It was soon known as the “mile-a-minute” vine and, today, it runs rampant throughout southern U.S. states and as far north as New Jersey. Recently, small pockets of wild kudzu have even been spotted near the coast of Oregon, which could mean big trouble for American and Canadian farmers in the west.


7. Burmese Pythons

Authorities in Florida estimate that over 30,000 Burmese pythons now infest the Everglades National Park and that the number will likely only continue to rise since the formidable intruders have very few predators. Even five-foot-long alligators are getting swallowed up by scaly beasts, along with a wide variety of other native wildlife, some of which are fragile endangered species.

It turns out that global warming has provided a larger habitable zone for the snakes, allowing them to spread throughout the southeastern states. A fully grown Burmese python can get up to 20 feet in length and will eat pretty much any living thing that gets close enough to it.


6. Snakehead Fish

National Geographic has dubbed the Northern Snakehead “Fishzilla” for it’s monsterous appearance and propensity to devour anything in its path. Once these sharp-toothed fish invest a pond or lake, they eat up everything they find until they’re forced to move on to another source. Amazingly, snakeheads have a primitive oxygen utilizing organ that lets them breathe air for up to four days as they slowly crawl across land to find a new body of water.

While they were originally only found in East Asian waters, a number of snakehead species have decimated food chains in the U.S. ranging from California to Maine. Officials have even gone so far as to poison entire reservoirs purely in an attempt to annihilate these ravenous fish.


5. Asian Carp

These massive carp can weigh over 100 pounds and, while fishermen might be jump at the chance to land one, they’re presence is shattering the ecosystems they inhabit. Asian carp take food and habitats away from native fish and have been known to eat the eggs of other fish species. When carp feed, they stir up sediments and organisms from the lake and river beds, transforming a crystal clear lake into murky muddled one where some species can no longer survive.

Asian carp were first imported to help clear algae from catfish ponds in the southern United States. But, as a result of flooding, some carp were able to escape into the Mississippi River and its tributaries where they quickly multiplied and became a force that couldn’t be ignored.


4. Zebra Mussels

Ballast water is water carried by large ships that can be pumped out or taken in from the surrounding liquid to help balance a ship during its voyage. It’s also believed to be the method by which Zebra muscles where first carried to Europe, North America, and Russia.

Zebra mussels have rapidly growing populations that make them one of the most aggressive freshwater invaders. Since they feed by filtering the water that passes over them, massive zebra populations can deplete the food sources of species like plankton, which are linchpins in the global food chain. Without enough plankton to go around, fish species start declining and it can eventually lead to a decline in other animal populations that rely on the fish as a primary food source.


3. Starlings

Eugene Schieffelin was a rich New York drug manufacturer. Between 1890 and 1891, he brought in 100 European starlings and released them all over Central Park. The reason for this being, Schieffelin was a huge Shakespeare fan, and he wanted to make sure that the United States was home to every single one of the birds mentioned in the famous writer’s plays.

Starlings are extremely social birds with flocks that can amass up to a million or more. From a distance, airborne flocks can move in intricate swirling patterns that are mesmerizing to watch. Unfortunately the same can’t be said from up close. Not only are these abundant birds noisy and aggressive, they’re blamed for causing plane crashes and costing the United States roughly 800 million dollars annually in crop losses.


2. Asian Long-Horned Beetles

Asian longhorn beetles aren’t too picky about where they lay their eggs. They’ll make almost any deciduous tree a home for their larvae. But as the larvae eat the soft, sappy bark, it makes it difficult for nutrients to get to other parts of the tree. The growing larvae then burrow into the middle of the tree leaving tunnels that weaken the tree even further. Once fully grown, Asian long-horn beetles emerge from the tree, breaking through the bark leaving large holes. Many trees find it impossible to recover once they are infested with Asian longhorn beetles. To prevent their spread, a growing number of officials have resorted to cutting down and burning infested trees.

In 1996, Asian long-horn beetles were discovered in New York and they quickly spread until they covered most of the U.S. East coast, where they now pose a threat to 35 percent of the trees in surrounding urban areas. The level of destruction caused by the beetles in terms of the economic value of the trees they’ve destroyed is thought to be estimated in the hundreds of billions of dollars.


1. Black Rats

Perhaps the first species to ever be recklessly distributed by humans, black rats are believed to have been spread throughout Europe and the rest of the world by stowing away on European ships that had visited the tropical Asian countries where they originate. Black rats are extremely resourceful and resilient, managing to survive and thrive in just about any environment, be it urban or rural. Unfortunately, it’s runaway success as an adaptable species has meant the dramatic decline and even extinction of countless bird and reptile populations across the world.