8 Exotic Pets That Became an Invasive Species

A school of goldfish swim in a tank.

Justin Sullivan / Getty Images

Have you never considered the wider consequences of releasing an exotic pet into the wild? Then you might not be surprised that many people haven't, either. Whether intentional or not, non-native species entering a foreign ecosystem can lead to serious systemic problems and even disaster. Just ask state officials across America, who have discovered that some former pets have turned into problematic invasive species under their jurisdiction, displacing and out-competing native flora and fauna for resources and living space.

The following are just eight of the invasive species that were released by humans into the wild. Read on to find out about the disastrous ramifications to native species, local ecosystems, and even expertly manicured residential front yards that these invaders bring.

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A swimming goldfish looks up.

Justin Sullivan / Getty Images

Goldfish, those innocent pets of childhood once relegated to the fish bowl, are now taking over fresh waterways around the world. A member of the carp family, the species can grow to between 16 to 19 inches and weigh more than two pounds in the wild.

Due to a high rate of reproduction and a lack of natural predators, goldfish easily disrupt ecosystems by consuming resources, eating eggs of native species, and spreading diseases. Impact examples include the recent drainage of an artificial stream in Utah to remove thousands of illegally dumped goldfish, a lake under threat from a booming population in Colorado, and the previously domestic fish running amok in Australia.

The species is so prevalent in the warm, shallow waters of western Lake Erie that it's now a commercial catch with over 113,800 pounds of goldfish netted in 2015.

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Argentine Tegu

An Argentine tegu walks with its tongue stuck out.

Allan Hopkins / Flickr / CC BY-NC-ND 2.0

In 2009, as part of campaign to trap invasive species in South Florida, biologists captured 13 Argentine tegus. Just six years later, they caught more than 700.

The black and white lizard, native to South America, is commonly found in pet stores throughout the United States. Because they can grow in excess of five feet, owners sometimes release them into Florida's copious swamps and waterways.

In the wild, they can survive for 15 to 20 years, gorging themselves on a diet of fruits, eggs, and small mammals, sometimes even attacking humans too. A tough species, they can survive temperatures as low as 35 degrees and can reproduce extremely quickly; just one nest can contain around 35 eggs.

"There is no debate about tegus," biologist Frank Mazzotti told the Orlando Sentinel. "All of Florida is at risk."

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A snakehead glides through the water.

Mohd Fazlin Mohd Effendy Ooi / Flickr / CC BY 2.0

Snakehead, native to parts of Asia and Africa, are quickly making themselves at home in North America.

Discovered in a Maryland pond in 2002, the species has since been spotted in states such as Virginia, California, New York, and Maine.

Not only can they grow over three feet long and weigh more than 12 pounds, but they also have the unique ability to migrate short distances over land thanks to specialized gills. By almost flopping over the wet land, snakeheads make it to neighboring bodies of water. The species's population is difficult to control as it lacks natural predators, not to mention the fact that its females are capable of releasing up to 100,000 eggs each year.

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Burmese Python

A Burmese python coiled up on green grass.

U.S. Fish and Wildlife Service / Flickr / CC BY 2.0

With population estimates as high as 300,000 in southern Florida, the Burmese python has gone from exotic pet to established apex predator in just three decades.

With an average length of 12 to 13 feet, pythons have few predators besides alligators and humans. In regions with established populations, sightings of raccoons, foxes, bobcats, and other mammals declined between 88 and 100 percent. Even birds and deer have been found inside pythons killed by park officials.

Burmese pythons are not only surviving in their nonnative habitat but breeding and becoming a more numerous threat to American ecosystems. In response, measures are being taken to combat this invasive population: Ordinary citizens can apply to become "removal agents" and be paid an hourly rate to euthanize Burmese pythons in South Florida, with an extra reward for removing larger ones.

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A group of migratory starlings sit perched on a wire.

 Tim Graham / Getty Images

In 1890, a New Yorker named Eugene Schieffelin acted on a plan to introduce every bird mentioned in the works of the playwright William Shakespeare to North America. After importing 60 starlings from Europe, he subsequently released them in Central Park.

Those original 60 have since turned into a population of more than 200 million.

While they may have hypnotic murmuration displays, starlings have become a major invasive pest. Besides sometimes devouring entire fields of wheat, they're also prone to kicking other birds out of their nests, killing fledglings and destroying eggs in the process.

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Red-Eared Slider

A red-eared slider sits perched on a rock.

 Rhododendrites / Wikimedia Commons / CC BY-SA 4.0

Originating from the warmer climates of the southeastern U.S., red-eared sliders have since proliferated around the world due to their popularity as pets. Feral populations now exist in areas such as Israel, Guam, Australia, and the Caribbean Islands.

In Japan, the Ministry of Environment says that red-eared sliders now outnumber native turtle species eight to one, consuming up to 320 tons of water weeds each week in a single region of the country.

Because of their larger body sizes (growing up to one foot in the wild) and higher reproductive rates, red-eared sliders quickly dominate native species, out-competing them for food and basking spots.

Red-eared sliders clock it at number 98 on the list of the 100 worst invasive species in the world, and it's no wonder; their omnivorous diet and ability to adapt to different types of habitats make these turtles especially good at surviving in new ecosystems.

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A pacu swims underwater with its mouth visible.

Ginkgo100 / Wikimedia Commons / Public Domain

Notable for its uncanny mouth of humanlike teeth, the pacu is a popular pet store fish that has made its way into the lakes, ponds, and creeks of at least 27 U.S. states.

While popular as juveniles, this South American native can grow aggressively, prompting owners to free them into local waterways. In the wild, the pacu can grow up to three and a half feet long and weigh up to 97 pounds. Their teeth, while humanoid in appearance, are used for grinding down tree nuts that fall into local waters.

While most pacu do not survive winter conditions in the U.S., there's a fear that a sizable population could take hold in warmer regions, leading to even more displacement and disruption of native species and their habitats.

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Green Iguana

A green iguana sits on a table.

 Chris Weeks / Getty Images

If this mighty reptile feels familiar, it's because the population of this noninvasive species has exploded over the the last half century. Hailing from Central and South America, these green lizards account for 46 percent of the trade for reptiles across the United States after being bought up by the millions as pets since the 1960s and '70s.

With males typically reaching over five feet in length and weighing in at up to 19 pounds, these beloved creatures have become a real ecological nuisance in states like Florida and Texas.

Luckily, green iguanas are intolerant to cold weather, and the booming population is reigned in by unexpected cold snaps. But these large layabouts still pose a threat to certain endangered snails, as well as homeowners' laboriously manicured greenery.