Destructive Invasive Species That Could Take Over the World

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You might be familiar with the term “invasive species,” but you probably don’t know just how much damage these invaders can cause. According to the National Wildlife Federation, roughly 42% of endangered or threatened species are imperiled because of invasive species.

Without any natural predators or counterbalances to keep them in check, most interlopers thrive, destroying trees, reefs and native animal populations. Read on to learn about the most shocking invasive species that are continuing to plague our ecosystems.      

Cane Toads

The world’s largest toad was introduced to Australia in 1935 to combat the growing cane beetle population. Initially, 3,000 toads were released, but, without any natural threats to curb their growth, that number now exceeds 200 million.

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Cane toads have harmed native species by poisoning them, consuming a lion’s share of the food sources and depleting fauna. Although some Aussies keep them as “pets,” most consider them pests. Community-based “toad-busting” groups have cropped up to kill cane toads by any means possible.

Feral Pigs

Brought to the Americas in the 1500s, feral swine are descended from run-of-the-mill farm pigs. Found in roughly 35 states, these 5 million pigs cause $1.5 billion in damages annually. Even if you don’t have 30 to 50 feral hogs in your yard, these pigs can still cause a lot of destruction.

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Responsible for transmitting diseases and parasites to livestock and humans, they can also easily eat and trample an entire field of crops. For $4,000, Texas-based Helibacon lets customers gun down feral pigs from a chopper.

Burmese Pythons

Among the largest snakes on Earth, Burmese pythons can reach lengths of 23 feet and weigh in at 200 pounds. In 1992, Hurricane Andrew ripped through a python-breeding facility and zoo, allowing Burmese pythons to escape into the Florida Everglades.

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Known for constricting their prey and then swallowing it whole, these pythons have decimated raccoon, opossum, deer and coyote populations. Even the rare Florida panther and the American alligator aren’t safe.

European Rabbit

In 1859, a wealthy estate owner released 24 specimens in Victoria, Australia, so he could hunt them for sport. With ample food sources and no natural predators, these fast-breeding rabbits quickly took over the eastern part of the country.

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In addition to devastating crops, the rabbits also pushed out the native rabbit-like bilby, which remains endangered. In the early 1900s, Australia built a “Rabbit-Proof Fence” to keep the pests out of Western Australia — of course, they just burrowed under it. And, in the 1950s, the government released a deadly virus, temporarily curbing the population growth.

Nile Crocodile

Native to East Africa, the Nile crocodile hasn’t been seen in the U.S. before — well, until now. Researchers have spotted at least four of these crocs in Florida. Unlike American crocodiles and alligators, these crocs can grow up to 16 feet long and weigh up to 1,600 pounds.

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It’s easy to imagine how an established population of these massive predators could pose a huge problem. To make matters more difficult, the Nile crocodile is protected by the Endangered Species Act, meaning you can’t move them, even if they are invasive.

Asian Carp

The silver, bighead, grass and black carp are collectively called Asian carp. These fish were imported to the United States in the 1970s to filter pond water in Arkansas. However, flooding enabled the carp to spread to the Illinois River and other waterways.

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Without any natural predators, these fish are free to lay their half a million eggs. Despite the introduction of electric fences, toxins and the predatory alligator gar, nothing has curbed the carp population. Fed up, Kentucky declared an official “War on Carp” in 2019.

Monk Parakeet

The monk parakeet was popular in the “exotic” pet trade of the 1960s, which is how this species arrived in Florida. By 1968, 16,000 birds had been imported to the U.S., with escapees traveling as far north as New York and as far west as Oregon.

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Now some 35,00 parakeets build huge (sometimes 100-pound) nests from twigs and grasses on utility poles, leading to fires and power outages. Florida’s utility companies routinely knock down nests — only to see them rebuilt.

Brown Marmorated Stink Bug

The brown marmorated stink bug (BMSB) is native to Japan, China, South Korea and several other Asian countries. In the mid-1990s, the BMSBs appeared in Pennsylvania, though it is unclear exactly how they ended up in the U.S.

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Although the bugs can be a nuisance for homeowners in the mid-Atlantic and New England states, they aren’t at all as devastating as termites or cockroaches. In fact, BMSBs do the most damage to the agricultural industry, decimating peaches, apples, corn and other crops.

Green Iguana

Native to Brazil, Portugal, Mexico and several surrounding islands, the green (or American) iguana is one of Florida’s most destructive invasive species. Surprisingly, iguanas don’t really compete with other native lizards for food. Instead, they wreak havoc on lawns and gardens.

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These strict vegetarians chow down on everything from fruit-bearing plants to ornamental shrubs. Once an iguana finds a yard it likes, consider it eaten. These creatures are also great burrowers, leading to damaged sidewalks, wells and house foundations.


About 50 species are part of the genus Ligustrum, so “privet” refers to quite a few different shrubs and trees. Able to adapt with ease, privet often outcompetes and displaces native vegetation. The ornamental plant was first brought to the United States from Asia in the 1700s.

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Privet was also introduced to New Zealand and Australia, where its pollen has been linked to asthma and eczema, leading to New Zealand’s ban on cultivating and selling it. Controlled burning, herbicides and mechanical removal are all ineffective.

Feral Cats

Cats may not come to mind when you think of an invasive species. However, homeless cats lead rough lives. Abandoned and abused, they form colonies in cities and on islands, where the adept hunters have a huge impact on the place’s biodiversity.

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According to Smithsonian Magazine, cats kill between 1.4 to 3.7 billion birds each year in the United States alone, and feral cats account for upwards of 70% of those deaths. Studies have shown that feral cats on islands are “responsible for at least 14% of global bird, mammal and reptile extinctions.”

Zebra Mussels

These bivalves were transported across the Atlantic Ocean in the ballast water of ships. In the 1980s, they started to cause huge problems in the Great Lakes. Now, by hitching rides on the bottoms of boats, zebra mussels have spread to at least 29 states.

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When they eat, these mussels filter the lake water. Although the water has never been clearer, it has also never been so devoid of plankton, which means less food for declining native fish species. An estimated 10 trillion zebra mussels fill the Great Lakes today.

Little Fire Ants

Not to be confused with Hawaii’s native tropical fire ant, little fire ants have infested the state’s Big Island. Due to their habit of building nests in potted plants, trees and shippable produce — instead of building mounds — they were accidentally imported.

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Although the Department of Agriculture attempted to contain a 1999 infestation, the ants spread quickly by infiltrating plant nurseries. With more than 50 little fire ant infestations in East Hawaii alone, the Hawaii Ant Lab (HAL) has been established to monitor invasive ant species.

European Green Crab

Native to — you guessed it — Europe, these crustaceans were first introduced to the East Coast of the United States in 1817, possibly through ballast water. By 1989, European green crabs were spotted in San Francisco Bay, and the creatures have since spread both north and south.

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These crabs are known for being skilled predators, able to crack open shells with such ease that they’ve been blamed for the collapse of Maine’s robust clam industry. Additionally, the European green crab takes food sources away from native fish, birds and fellow crustaceans.

Burma Reed

Burma reed is a tall grass native to subtropical Asia, but it has become a huge issue in southern Florida. In the Everglades, this fast-growing plant heavily shades the understory, killing the sunless flora.

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Wildfires also pose a threat: With large, feathery plumes and dense leaf litter, these reeds make great kindling, spreading flames upwards of 30 feet into the air. Pair that with strong winds and you’re looking at detached, fiery plumes flying around.

Mozambique Tilapia

Native to its namesake in southern Africa, the Mozambique tilapia is popular in the aquaculture industry. In many parts of the world, it escaped from fish farms into native water sources; in other instances, the tilapia was purposely released to temper mosquito populations.

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By competing for nesting areas and food, the Mozambique tilapia is the direct cause of the decline of several (now threatened) fish, including Hawaii’s striped mullet and the desert pupfish, which was found in California’s Salton Sea.


Mongooses are native to India and parts of Southeast Asia, but they were introduced to Hawaii, Jamaica and other nations in the 1800s, during the rise of the sugar cane industry. The goal was simple: Mongooses would feed on the rats that were gobbling up the sugar cane.

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However, their impact is questionable. Unlike mongooses, rats are nocturnal creatures — so this poses a bit of a problem. Furthermore, the mongoose hunts birds and eggs, threatening native species. Shockingly, mongoose have even preyed on the fawns of white-tailed deer.

Hybrid Tumbleweed (Salsola Ryanii)

A tumbleweed is the above-ground part of a plant that has matured, dried and detached from its roots, tumbling to disperse seeds. Hybrid tumbleweeds — formed by plants native to Australia, Africa and Europe — have invaded California’s Central Valley since the early 2000s.

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This hybrid species not only competes with farmers’ crops for nutrients and water, it also causes huge issues for road maintenance. Without any naturally-occuring insects around to chow down on hybrid tumbleweeds, they have to be pulled apart by hand.


Native to the Indo-Pacific, the carnivorous lionfish is now an invasive species that has infiltrated the Atlantic Ocean. Lionfish are a top predator, and their introduction to a whole new ocean has had lasting effects on the delicate ecosystems of coral reefs.

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Those venomous spines make potential predators wary of lionfish, and that leaves these creatures free to eat the lion’s share of food. They feed on animals that help support the reef’s stability, which has allowed seaweed to overtake some reefs in the Caribbean and Atlantic.

Brown Tree Snake

Native to Australia, Indonesia and Papua New Guinea, the brown tree snake — probably a cargo stowaway — was accidentally introduced to Guam in the 1950s. With an abundance of prey and few natural predators (save the occasional feral pig or mangrove monitor), the snakes have taken over.

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Brown tree snakes have killed off small forest-dwelling animals and native birds, preyed on pets and small children and caused an untold number of power outages by nesting on electrical lines. Now, trained dogs are used to search outbound military and commercial cargo for brown snakes.

Multiflora Rose

This multi-stemmed, thorny shrub can grow up to 15 feet. As you might imagine, that means multiflora rose plants form impenetrable thickets in forests and fields. First introduced to North America in 1866 as rootstock for ornamental roses, the multiflora rose is native to parts of Asia.

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On its own, multiflora rose is responsible for displacing native plant species and restricting where wildlife might move or live. In fact, the plant is so hardy and dense that it was used as a “living fence” to corral livestock.


Weighing upwards of 100 pounds, the capybara is the world’s largest rodent. Native to South America, it has set up shop in Florida for at least the last 15 years. It’s estimated that roughly 50 of these rodents call the Sunshine State home, but that number is expected to climb rapidly.

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In addition to reproducing quickly, the capybara has little to fear from predators, as few native carnivores hunt prey of that size. Researchers believe the capybara will soon decimate native herbivore species by chowing down on food sources.

Africanized Bee

Known commonly as the killer bee, the Africanized bee is a hybrid species first introduced to Brazil in 1956 to increase honey production. In 1957, however, 26 swarms escaped quarantine, and the bee has spread throughout the Americas, arriving in Texas in 1990.

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Reportedly, these murderous bees have killed horses, livestock and an estimated 1,000 humans. Although they are often more defensive than aggressive, these bees have been known to usurp native European bee colonies by killing and replacing their queen.

Spiny Waterflea

The spiny waterflea is a microscopic animal — or zooplankton — that thrives in open water. Originally, this zooplankton called the waters off Europe and Asia home, but it was accidentally carried over to the Great Lakes in the United States through ships’ ballast water.

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Spiny waterfleas munch on other zooplankton, which means they take away from the natural food source fishes in Lake Ontario and Lake Superior rely on for survival. To make matters worse, they aren’t good food replacements: The flea’s spines and long tail make it difficult to eat.

European Starlings

Known as the European or common starling, this bird seems harmless, but it has been labeled a pest in some countries. The starling was introduced to places like Australia and New Zealand to feed on insects devastating local crops, but their journey to North America was a bit different.

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In 1890, the president of the American Acclimatization Society released 60 common starlings in New York City’s Central Park. Allegedly, the goal was to bring every bird species mentioned in Shakespeare’s works to the States. Since then, the bird’s numbers have swelled to 150 million.

Snakehead Fish

This freshwater predatory fish became known as a popular food fish. Because of that tie to aquaculture, the fish accidentally escaped into non-native waters. And it has become your standard food hog.

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In 2002, northern snakeheads were spotted in a pond in Crofton, Maryland, and then became a permanently established fish in the Potomac River just a few years later. Along a 120-mile stretch of the river, you can expect to see more than 21,000 snakeheads.

Emerald Ash Borer

Native to northeastern Asia, these beetles have come to devastate North America. As the name implies, the insects bore into ash trees to lay their eggs. The ash trees have no defense against the beetles and, once chosen, are destroyed.

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Because the emerald ash borer can fly, these bugs can spread rapidly. They have also been known to hitch rides on lumber and commercial firewood. To fight the infestation, researchers have tried to diversify ash tree species to make them more resilient.


Kudzu, derived from the Japanese name for the East Asian arrowroot plant, is a vine native to eastern Asia, Southeast Asia and various Pacific islands. Known for climbing and coiling, these vines often kill trees and shrubs through shade — heavy amounts of shade.

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This invasive species was first brought to the United States in 1876 to decorate the Japanese pavilion for the Centennial Exposition in Philadelphia, Pennsylvania. Later, it was sold to farmers as a way to combat erosion. The U.S. Forest Service estimates that kudzu claims 2,500 acres a year.

Giant African Snail

These large land snails are considered pests on many continents due to the ways they attack agriculture and spread disease. Not only do these snails transmit diseases to crops, they can also spread the parasitic nematode that causes meningitis to humans.

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The snails also have an appetite for the stucco used in buildings, giving a whole new meaning to the phrase “household pest.” In an effort to control the population of giant snails, some communities have tried to promote them as a food source.

Rusty Crayfish

These invasive crustaceans are native to the Ohio River but have spread to several other states and into Canada. Because a female crayfish can carry fertilized eggs, the release of just one crayfish can be devastating.

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It is believed that either aquarium owners introduced them, or fishermen carried them to new waterways via bait buckets. Unlike other crustaceans, rusty crayfish are aggressive and good at fending off predators. Moreover, they have no problem devouring fish eggs and aquatic plants.