It doesn’t take much to throw an otherwise orderly ecosystem off balance. Sometimes, the arrival of a single species is enough to bring about a slew of less-than-desirable effects.

The Environmental Protection Agency (EPA) defines an invasive species as one “whose presence in the environment causes economic or environmental harm or harm to human health.” To clarify, all invasive species are nonnative, but not all nonnative species are invasive. (This goes for plants, animals, and insects.)

More than 6,500 nonindigenous species have been identified in the U.S. alone; add Mexico and Canada into the mix, and you’ll find that North America is home to many, many transplants, their rapid spread fueling endangerment and even extinction of other native species. So, what exactly are these species doing that’s causing such substantial harm? And why are they sticking around despite the arduous work of environmental scientists?

Here, a look at the invasive species that have found new habitats in North America, and the effect that their arrival is having on a nonnative ecosystem.

8 Most Invasive Species in North America

1. Canadian “Super Pigs”

Canadian “super pigs” are a mix between domestic pigs and feral boars. Originally created by farmers in the 1980s, they’ve since gotten smarter and stronger—and now they’re about to cross the U.S. border, where they could cause major ecological damage.

The prime problem with these super pigs (and why experts consider them the “worst invasive large mammal on the planet”) is that they’re incredibly hard to find and catch. Once they know they’re in danger, they go almost completely nocturnal and are really good at hiding.

These qualities allow them to wreak havoc on the environment. Existing feral pigs contribute to the spread and creation of disease, which kills off vital species, destroy crops, and cause other environmental harm.

2. Asian Carp

Asian carp—including bighead, silver, black, and grass carp—were brought stateside in the 1970s as a means of cleaning up the country’s wastewater treatment plants and aquaculture ponds. Originally from China, they can now be found along the Mississippi River as well as many other spots in the U.S.

The large (as in, up to 31 pounds) freshwater fish is incredibly resilient, which is great for them, but an issue for the native species of fish that occupy shared spaces. Asian carp out-complete their neighbors, consuming much of the resources (think: plankton, plants, snails, and mussels) in a given ecosystem. The carp are also high jumpers, allowing them to leap out of the water which, given their size, can result in injury to boaters and anglers.

3. Purple Loosestrife

Invasive plants have been imported for centuries, usually for the sake of beautifying landscapes that, let’s face it, were likely beautiful to begin with. Purple loosestrife is one such plant. Originally native to Eurasia, the plant was purposefully relocated in the 1800s for use in landscaping and its desirable herbal properties, though the seeds also arrived as accidental stowaways on ships.

Now, the perennial bloom can be found in every Canadian province and every contiguous U.S. state with the exception of Florida. Purple loosestrife’s resilience and rapid rate of reproduction eliminate ecological diversity in the wet-soiled habitats in which it thrives, posing a threat to any native plants nearby.

4. Lionfish

Lionfish are undeniably cool-looking, which is likely why and how their journey in North American waters began: Some suspect that aquariums and pet owners released them into the Atlantic Ocean in the 80s, unaware of the potential and lasting effects. Originally hailing from the South Pacific and Indian Oceans, the fish continue to spread rampantly in the Caribbean, the Gulf of Mexico, and along the southern coastline of the United States.

Lionfish prey on many species of fish and invertebrates, threatening the already endangered coral reefs by throwing their habitat off-balance. Humans should also be wary: these fish may be eye-catching, but their sting can result in painful injury.

5. English Ivy

Did you know that good old English ivy is an invasive offender? The highly recognizable plant is naturally found in Europe, Western Asia, and North Africa, but can now exists in excess across the U.S. The climbing plant is commonly sold at garden stores despite the USDA and U.S. Forest Service having included it in a list of invasive plants that pose significant threat to our forests.

As with other invasive species, ivy is both tough and adaptable—but keep it out of your next landscaping project. Though pretty, the evergreen has the potential to escape your garden and propagate, threatening overstory and understory alike.

6. Emerald Ash-Borer

The emerald ash borer may be small, but it is to blame for the destruction of tens of millions of ash trees. The beetle likely made its way to the U.S. from its native Asia hidden within the wood that it commonly boroughs into. Initially identified in Michigan in 2022, the bug can now be found in as many as 35 states as well as throughout Canada.

As the emerald ash borer favors firewood or other ash wood products, many suggest opting for options that are locally-sourced, the better to avoid introducing this species to new environs.

7. Spotted Lanternfly

Native to Asia, the spotted lanternfly has been making itself at home in the United States—specifically Pennsylvania—since 2014. The eye-catching insect poses a threat to crops and trees alike: In addition to swarming, prolific procreation, and general annoyance, the spotted lanternfly secretes a substance known as honeydew that leads to mold and plant damage.

Though the spotted lanternfly is not a long-distance flyer, it’s a hitchhiker, laying egg masses on any available outdoor surface. Areas in which the bug has been spotted are quarantined, with those passing through advised to check their vehicles and clothes to cull the spread.

8. European Starling

The European starling has called the United States home since the 1890s. Rumor has it that Shakespeare fan Eugene Schieffelin was the first to intentionally import and release these starlings in New York City as an ode to the author. Now, there are 150 million and counting starlings in the States—quite the homage.

These birds cause significant agricultural damage through the consumption of various crops. Starlings love to feast on fruits, grains, and even cattle feed. These birds also produce E.coli and Salmonella through fecal matter which can contaminate water and feed in livestock agriculture.