On the day before our 200-passenger ship was set to arrive in Antarctica’s Marguerite Bay, the onboard Discovery Team performed a mandatory clothing check of everything we’d be wearing outdoors. One by one, we brought our gloves, hats, socks, and pants to one of these crew members, who then scanned each item for the tiniest crumb or seed. This quarantine-like procedure was all in accordance with protocol put forth by the International Association of Antarctica Tour Operators (IAATO), which recommends that tour operators take every precautionary measure to prevent alien pests and diseases from hitching a ride to the continent. 

So far, only about a dozen non-native invertebrate species, including mites, springtails, and an earthworm, have found their way onto the greater Antarctic continent, and the Antarctic Treaty nations (nations dedicated to regulating the peaceful use of Antarctica) are working in unison to keep this number from growing. That’s because such invasive species, as they’re known, can wreak havoc on an ecosystem where they don’t naturally live. In many cases, they prey on native species, compete with them for food, and even spread diseases. Such ill effects are often irreversible

What are Invasive Species? 

Invasive or alien species can be any type of living organism—plant seeds, zebra mussels, parasites—that is non-indigenous to a particular area. Not all invasive species are destructive, but those that are can hurt an entire ecosystem. 

Wild flower seed balls which are about to be planted in a garden, UK.

Wild seeds in the UK. © Lauren Simmonds / WWF-UK

According to a September 2023 report by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), an international organization committed to strengthening the role of science in public decision-making, “more than 37,000 alien species have been introduced by many human activities to regions and biomes around the world.” Over 3,5000 of these are harmful alien species, seriously threatening nature and the local quality of life as a whole. 

Where Do They Come From?

While many invasive species (such as those in Antarctica) arrive unintentionally in a new place, others are brought over deliberately. 

For example, the Galapagos Islands off the coast of Ecuador are remarkable for their unique flora and fauna, including many endemic species—like marine iguana and Galapagos tortoise—that have developed in isolation. However, throughout the years humans have also introduced plenty of alien species (everything from blackberry bushes to domesticated pigs and goats) to the archipelago. Mostly intended for agricultural and aesthetic purposes, several of these invasive species have unfortunately had a chaotic effect on the local ecosystem, putting native wildlife such as Darwin flycatchers—particularly on the island of Santa Cruz—in peril. 

Galápagos giant tortoise (Chelonoidis nigra) in Reserva el Chato on Santa Cruz Island, Galapagos, Ecuador

Galápagos giant tortoise on Santa Cruz Island, Galapagos, Ecuador. © Antonio Busiello / WWF-US

There are also those invasive species purposely introduced by wildlife traders or buyers, such as the American mink, a semiaquatic mammal that landed in Europe as part of the fur trade. In some cases, people deliberately released these minks from fur farms, while others inadvertently escaped. Red-eared sliders are another example. An extremely popular ‘pet trade’ turtle during the 20th century, this reptile is known as one of the most invasive species on the planet. After being released in the wild by their owners, these prolific reproducers have taken over the globe, competing with native turtles for both food and habitat and carrying diseases like Salmonella. 

Climate change also influences the advance of invasive species through rising temps and melting ice, which creates new pathways for these non-native creatures to spread. 

Examples of Harmful Invasive Species 

Here are four examples of harmful invasive species, and how they can upend an ecosystem. 

Lionfish 

Although easily recognizable with their distinctive stripes and long fan-like fins, lionfish are by no means a beloved sight in Atlantic waters. That’s because they’re instead native to coral reefs found in the South Pacific and Indian oceans. While no one really knows how they made their way east, most experts agree they came from aquariums, dumped into southeastern U.S. waters beginning sometime in the mid-1980s or early ‘90s. They’ve since spread down through Mexico and into Central America, and most recently to Brazil. 

Lionfish / Pterois in the Bahamas

© Alexis Rosenfeld

With their venomous dorsal spines, they glide through Atlantic waters relatively unperturbed, loading up on herbivores that typically eat the algae off coral. This results in algae growth left unchecked, and the survival of reefs in increased danger. 

Small Indian Mongoose

Although native to a stretch of Asia, from Iraq to Myanmar, small Indian mongooses found their way to islands such as Hawaii, Puerto Rico, and St. Croix in the late 19th/early 20th century as a means of pest control. But while these carnivorous mammals helped keep rats and snakes in check among sugarcane fields, they’ve taken it upon themselves to fast on other small creatures as well. These include avians like Hawaiian crow and goose, as well as endangered hawksbill turtles and the eggs and hatchlings of native ground-nesting birds. They’re even believed to have caused the possible extinction of Jamaican petrels. 

European Starlings

Watching a murmuration of thousands of starlings dip, whirl, dive, and soar is mesmerizing, but these small black birds are actually a U.S. invasive species. Native to Europe and parts of Asia and Africa, starlings first arrived in America in 1890, when amateur ornithologist Eugene Schieffelin decided it would be a great idea to infiltrate the country with every bird mentioned in Shakespeare plays. With about 100 starlings to start, their U.S. numbers have since multiplied to approximately 200 million. And while impressive to see, their huge flocks can cause serious damage to crops. These alien avians also fight with native birds over food, steal other birds’ nests, and simply act as bullies, driving out competitors and upturning local ecosystems in the process. 

European starling (Sturnus vulgaris) singing from a perch. Cheshire, UK

© naturepl.com / Alan Williams / WWF

Cane Toads 

Another species introduced as a form of pest control, cane toads were brought to Australia in 1935 as a way to combat damaging cane beetles in North Queensland’s sugar cane fields. From the approximate 2,400 toads released that year, there are an estimated 200 million of them today. Their skin contains a toxic venom that can kill native predators like goannas and freshwater crocs, which try to feed on them. Their poison is harmful to dogs and cats that come in contact with them, as well. 

Cane toad (Rhinella marina) in the tropic forest.

© Shutterstock / Ondrej Prosicky / WWF

What We Can Do 

Eradicating an invasive species is nearly impossible once it’s established itself in a place, but there are things we do to help control its spread. 

  • In April 2023, WWF released a list of 60 Actions you Can Take for the Planet, which includes tips for stopping the spread of invasive species. These include consciously thinking about your decisions, from “cleaning your hiking boots before exploring a new area,” to “only buying firewood where you plan to burn it.”
  • Stick to hiking trails and walking paths when you’re out in nature, and take those fruit inspections between some states and dozens of countries seriously.
  • Help support efforts like WWF-Australia’s partnership program, which works directly with native species in AU’s Kimberley region to combat the impact of cane toads. 
  • Consider making invasive species your latest culinary obsession, like locals in a small Mediterranean village are doing with lionfish. Or get your animals in on the action, with sustainable pet food made from invasive Asian carp.