12 Invasive Species Deliberately Introduced into the U.S. – Plus 1 INSANE Near Miss!

Invasive Species
© VladislavStarozhilov from Getty Images/ via Canva.com

Written by Drew Wood

Published: May 21, 2024

Share on:

Advertisement


There are over 6,500 invasive species in the United States, with more gradually joining them over time. Many of them arrived as stowaways in cargo from other parts of the world, but quite a few of the most successful—and most damaging—species were introduced deliberately. Find out in our list how many of these are living in your yard or even inside your house. And don’t forget to check out at the end the absolutely bonkers near miss the United States had with the most dangerous invasive species in the world.

Pigeon

flock of pigeons

Urban people have a love-hate relationship with pigeons. Feeding them is a favorite pastime, as is complaining about their droppings and noise.

©MNStudio/Shutterstock.com

Pigeons have made themselves so much at home that most people probably assume they are native to North America. In fact, colonists introduced them as a food source in the early 1600s. People in Britain and Ireland, the home of most of the early colonists, were accustomed to eating them. Today, they have multiplied into the millions and can spread disease and damage property with their droppings.

Nutria

capybara vs nutria

Nutria are large and more hardy than rabbits, producing soft fur and tasty meat.

©Barbora Polivkova/Shutterstock.com

Myocastor coypus, or nutria, are large South American rodents that have become established in 17 U.S. states, particularly along the Gulf Coast and Chesapeake Bay. They are sometimes confused with beavers or muskrats but are a separate species. Fur ranchers brought them to the country in the early 1900s for their pelts but then released into the wild when this proved not to be profitable. They are destructive in wetland environments, eating down reedy grasses that help secure boggy soil and provide shelter for other animals. By removing grasses and burrowing into riverbanks, nutria also contribute to erosion along waterways.

Eastern Grey Squirrel

A grey squirrel with a bushy tail perching on a fence post against a defocused background.

Grey squirrels are a wildly successful invasive species in North America.

©Nigel J. Harris/Shutterstock.com

In the mid-1800’s Eastern Gray Squirrels, Sciurus carolinensis Gmelin was introduced from Europe to the United States entirely for aesthetic reasons. There is a relatively rare morph of the grey squirrel that is jet black. These were also introduced to North America in the 19th and 20th centuries. Grey squirrels outcompete indigenous red squirrels and typically completely take over habitats from them within 15 years. In urban areas, grey squirrels are now the most common tree squirrels.

English Ivy

English Ivy (Hedera helix)

English ivy is visually attractive but ultimately destructive of masonry construction.

©iStock.com/Marina Denisenko

Hedera helix, or English ivy, forms a beautiful dark green ground cover and climbs attractively on trees, brick walls, and buildings. Introduced to the U.S. in the 1870s, it was often planted along the walls of wealthy estates and by public buildings, lending its name to “Ivy League” universities. English ivy grows so densely it crowds out indigenous species and can get up into tree canopies and ultimately kill them by monopolizing sunlight. People who allow it to grow on walls often regret it, as its tenacious roots probe into small cracks and widen them, allowing moisture to penetrate and cause the masonry to crumble.

Feral Swine

large wild feral hog, pig or swine (sus scrofa) sow running in an open field in central Florida, in evening yellow light, dry grass background, nuisance animal, destructive, apparent mother

Feral hogs are especially prolific in Texas and other parts of the South.

©Chase D'animulls/Shutterstock.com

Known as feral hogs, feral pigs, wild boars, razorbacks, and many other common names, the species Sus scrofa was introduced to the New World originally by Christopher Columbus and other early explorers. Brought along as food for sea voyages, swine were released to multiply on the Caribbean islands and the North American mainland to multiply as a food source for future explorers and colonists. Today, they number in the millions and do $1.5 billion in damage every year to farmland, landscaping, and water sources as well as being a source of disease and aggressive toward people and pets.

Golden Bamboo

The beauty of the Golden bamboo With golden stems and green leaves. Popular to decorate the garden because it is a golden bamboo And beautiful yellow Look more unusual than the typical bamboo.

Golden bamboo has traditionally been a valuable building material in Asia.

©Phuwadon Phichairat/Shutterstock.com

Native to Asia, Phyllostachys aurea also goes by the names golden bamboo, fishpole bamboo, or walking stick bamboo. In its homeland, it has traditionally been a sturdy, multipurpose material for building and making tools and implements. It was introduced to the United States in 1882 as an ornamental plant. Its quick, dense growth makes it an excellent privacy screen. However, it crowds out native species and is difficult to contain, as it sends out runners underground that can pop up in unexpected places.

House Sparrow

sparrows

©fewerton/Shutterstock.com

Passer domesticus, the house sparrow or English sparrow, was introduced from Europe to New York in 1852 to eat caterpillars that were killing basswood trees. Within only 50 years, these songbirds had colonized the entire continental United States. Bird lovers bemoan how this dull brown species has displaced indigenous species, such as Eastern bluebirds, from their habitat. Morbidly, sparrows will attack and kill nesting bluebirds and other small species and build their own nests right on top of their dead bodies.

House Cat

feral cat

Undoubtedly, cats are one of the most beloved invasive species in the world.

©Brocken Inaglory | CC BY-SA - Original / License

Bet you didn’t expect to find an invasive species in your house. But yes, the ancestors of your beloved housecat (Felis catus) were indigenous to North Africa and the Middle East before being brought to Europe, North America, and the rest of the world. Today about 25% of American households have at least one cat. There are up to 62 million pet cats in the country, and another 100 million have gone feral and are multiplying in colonies in urban, suburban, and rural environments. Wild cats have a devastating effect on bird and small mammal populations, having caused the extinction of at least 60 American animal species. So, if you spot a feral cat, please don’t feed it as that contributes to increasing the population. You can catch it following these guidelines and take it to a rescue or shelter.

St. John’s Wort

Blooming St. John's wort, hypericum perforatum

St. John’s wort has ornamental and medicinal value, but can also become a pest.

©M. Schuppich/Shutterstock.com

The scientific name of this plant is Hypericum perforatum L. but it goes by numerous common names, including St. Johnswort, St. John’s wort, common St. Johnswort, Klamath weed, common goatweed, or tipton weed. It’s a pretty plant with yellow flowers and medicinal properties. Some people swear by it for help with depression, anxiety, and similar issues. Native to Eurasia and North Africa, it was introduced to North America by colonists in the 1700s and is today considered a noxious weed in some states. It kills out indigenous plant species and is toxic to some livestock.

Kudzu

Kudzu (Pueraria montana var. lobata)

Kudzu can quickly engulf trees, homes, and anything else in its path unless it is aggressively tended.

©Scott Ehardt / public domain - Original / License

Pueraria montana var. lobata is the scientific name for kudzu, an astonishingly fast-growing and tenacious vine indigenous to Asia. As railroads began cutting across the landscape in the 1800s, kudzu was introduced to provide quick ground cover to stabilize railroad embankments and prevent erosion. It adapted better than anyone could have anticipated to the humid American south. It’s almost possible to see it growing, as a vine and its tendrils can add a foot or more to their length on a rainy day. Untended property can become completely engulfed and forests can die out as kudzu covers the trees and hogs all the sunlight.

Asian Carp

Asian carp jumping

Asian carp jump aggressively and can injure boaters and swimmers.

©SandmanPhotography/Shutterstock.com

In the U.S. “Asian carp” refers to two species of fish imported from China in the 1970s: the bighead carp (Hypopthalmichthys nobilis) and the silver carp (Hypopthalmichthys molitrix). the purpose of bringing them to America was as a food source on fish farms and to clean aquaculture facilities by eating algae. Flooding enabled them to escape into the Mississippi River by 1980 and begin multiplying explosively.

Now, they are a threat to indigenous species as they use up resources, and they are an annoyance and danger to boaters as they jump up in large numbers from the water and can hit people in the face and body while moving at high speeds. The government is taking careful measures to prevent this species from making it into the Great Lakes.

Water Hyacinth

Water Hyacinth (Eichhornia crassipes)

Water hyacinths are quite beautiful when they bloom but they make a pest of themselves by clogging waterways.

©iStock.com/Shai-Halud

The water hyacinth (Eichhornia crassipes) made its first appearance in the United States in 1884 at an exposition in New Orleans. It originally came from South America and was valued for its beautiful flowers. However, it forms dense mats that clog waterways, making them useless for boating and fishing, crowding out indigenous species, and reducing oxygen levels in the water for aquatic species. Today it thrives in California, Washington state, and across the Southeast. It’s especially a problem in Florida.

Near Miss: Hippopotomus

Aggressive hippo male attacking the car. Huge hippo male intimidating the opponent. Wild animal in the nature habitat. African wildlife. This is Africa. Hippopotamus amphibius.

Hippos kill more people every year than any animal besides disease-bearing mosquitoes.

©PhotocechCZ/Shutterstock.com

So about those invasive water hyacinths. What better way to get rid of an invasive species than by introducing another invasive species? That’s what almost happened in 1910 when the U.S. Congress tried to pass a bill that would have introduced hippopotamuses into the Mississippi River. Proponents reasoned that the huge behemoths would clear the waterways by eating tons of hyacinths and would be a meat source for hungry Americans. The plan actually got a lot of traction. Theodore Roosevelt (an enthusiastic big game hunter) and the New York Times and Washington Post all endorsed the idea. Ultimately the plan failed by one vote in Congress.

If it hadn’t, what would American life look like with a Mississippi full of hippos? Check out the novel River of Teeth by Sarah Gailey for a fanciful alternative history. Or maybe you’d like to know what an actual, real-life hippo invasion looks like. Have a look at the A-Z-animals.com article: Discover the Incredible Story of Pablo Escobar’s ‘Cocaine Hippos’


Share this post on:
About the Author

Drew Wood is a writer at A-Z Animals focusing on mammals, geography, and world cultures. Drew has worked in research and writing for over 20 years and holds a Masters in Foreign Affairs (1992) and a Doctorate in Religion (2009). A resident of Nebraska, Drew enjoys Brazilian jiu-jitsu, movies, and being an emotional support human to four dogs.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.