6 of the most invasive species on the planet

Invasive species are a danger to ecosystems all over the world

Spotted lanternfly on leaf.
The spotted lanternfly has been seen all over the American Northeast, and experts want them killed.
(Image credit: Catherine McQueen / Getty Images)

An invasive species is an organism that is "non-native (or alien) to the ecosystem under consideration," and whose introduction "causes or is likely to cause economic or environmental harm or harm to human health," according to the U.S. Department of Agriculture. The species can be introduced to a new area through "ship ballast water, firewood, accidental release, and by people."

Invasive species can cause a great deal of harm to an ecosystem, even causing the extinction of native species. They also tend to grow in population rapidly as the non-native environment doesn't have natural predators to manage numbers.

1. Spotted lanternfly

Spotted lanternflies are native to China but have run rampant all across the northeastern U.S., prompting experts to advise people to kill them. While they are harmless to humans and animals, they are a danger to over a hundred plant species. It feeds "on a wide range of fruit, ornamental and woody trees, with tree-of-heaven being one of the preferred hosts," according to the U.S. Department of Agriculture. In addition, they cause "serious damage including oozing sap, wilting, leaf curling and dieback in trees, vines, crops and many other types of plants," according to the Pennsylvania Department of Agriculture. "The expansion of this pest has been fueled by its ability to hitch rides undetected on cargo and passenger vehicles," explained Earth.com.

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2. Feral cat

While we view cats as beloved furry friends, they are actually classified as an invasive species. Feral cats have been "incredibly devastating" to native animals in Australia, according to West Australia Environment Minister Reece Whitby, adding that the country is "trying to give native species a fighting chance against this incredible, voracious predator," Newsweek reported.

A 2013 study published in the journal Nature Communications found that free-ranging domestic cats, mostly strays and feral cats, "kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually." To combat populations, experts have adopted the TNR method (trap, neuter, return) which aims "to limit cat population growth by eliminating reproduction," according to the U.S. Department of Agriculture, or in some cases poisoning them.

3. Burmese python

Burmese pythons are one of the largest snake species and are native to India, lower China, the Malay Peninsula and some islands of the East Indies, according to the Florida Fish and Wildlife Conservation Commission. The snake has preyed on a number of mammals, birds, and reptiles in Florida to the point where the state has allowed for the species to "be captured and humanely killed year-round and without a permit or hunting license."

The pythons have caused "severe mammal declines in Everglades National Park," per the U.S. Geological Survey (USGS). They eat both native and non-native species, including endangered species. "Populations of raccoons had dropped 99.3 percent, opossums 98.9 percent, and bobcats 87.5 percent since 1997," wrote the USGS. "Marsh rabbits, cottontail rabbits, and foxes effectively disappeared."

4. Guinea grass

Guinea grass is a highly flammable invasive plant species, which greatly contributed to the Maui wildfires. The species is native to Africa but was planted in Hawaii by 18th-century European ranchers. "Today, almost a quarter of Hawaii's land cover consists of these invasive shrubs," wrote the Smithsonian.

"Those fire-prone invasive species fill in any gaps anywhere else—roadsides, in between communities, in between people's homes, all over the place," Elizabeth Pickett, co-executive director of the Hawaii Wildfire Management Organization, told Wired. Along with flammability, the grass "uses a combination of crowding that blocks out light from growing seedlings and what amounts to a chemical warfare in soil that is toxic to native plants," according to a 2023 study by researchers at The University of Texas at Austin.

5. European starling

These starlings are birds native to Europe, southwest Asia, and northern Africa. They were first introduced in the U.S. in the 1890s. They are now "one of the most abundant birds in North America," according to New York Invasive Species Information. The birds "compete with native species as well as destroy crops," and are "prolific breeders."

The birds have caused problems for agriculture at an estimated $800 million per year. Also, starlings "eat cattle rations and destroy fruit and grain crops, "carry various diseases which may be transmissible to humans, other birds (including poultry), and livestock." The birds are adaptable in many environments and forage for a variety of food.

6. Red fire ant

Red fire ants were found in Italy and could cause “devastating and costly impacts on biodiversity, crops and human health,” all over Europe, Euronews explained. The species is also rapidly spreading throughout the continent because “the climate in half of Europe’s urban areas is already suitable for the species.”

The species is native to South America and has a painful sting that could cause burning and, in more severe cases, chest pains, nausea and dizziness. Climate change is also increasing the suitable range for these insects. “This is especially concerning because many of the cities, including London, Amsterdam, and Rome, have large seaports, which could allow the ants to spread rapidly to more countries and continents,” author of a 2023 study discussing the insects, Roger Vila, told The Independent.

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Devika Rao

Devika Rao is a staff writer for The Week. She graduated from Cornell University with a degree in Environment and Sustainability and a minor in Climate Change. Previously, she worked as a Policy and Advocacy associate in the nonprofit space advocating for environmental action from the business perspective. She is passionate about the environment, books, and music.