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What's the difference?: Non-native vs. invasive species

Two clusters of zebra mussels on a rock in the water.
Zebra mussels. (Photo by Anthony Schalk)

We learn at a young age that all living things in our ecosystems are connected and that harming or removing even a single species can affect all the other living things in the ecosystem. But some species don't naturally belong in our ecosystems, and their presence can have negative effects on the species that do belong there and the ecosystem as a whole.

Within our ecosystems are plants and animals that belong and those that do not. The species that belong, those that naturally occur in a region, are referred to as native species. Those that don't belong are non-native species. And among non-native species are some that are harmful or destructive to the ecosystem, and these are known as invasive species.

Not all non-native species are invasive. Take the fruits and vegetables we grow in our gardens and some of the flowers we grow in our yards, or the animals we raise as livestock. Many of these plants and animals are not native to our area or even North America, but they have been raised or cultivated in the United States for many years — centuries even —without causing any harm to the ecosystem, according to the National Park Service.

But many non-native species are not harmless in these new, introduced environments. Instead, they begin to invade and upset the balance of the ecosystem, making them invasive. The federal government officially defines an invasive species as a plant, animal or other living organism "whose introduction does or is likely to cause economic or environmental harm or harm to human health," according to the National Invasive Species Information Center

Invasive species are able to become problematic in their new environs because they adapt and reproduce quickly, according to National Geographic. They often become a threat to native species in the same ecosystem because they compete for the same resources and also change the composition of the habitat. In addition, many invasive species have no natural predators in their non-natural environments, allowing their populations to grow unchecked. 

How did non-native and invasive species get here? Mostly because of human activity, both intentional and unintentional. Some invasive species arrived in the United States aboard ships from other parts of the world, according to the Invasive Species Information Center. Invasive species can also be introduced when firewood is moved from one location to another or when plants are imported or transported to different regions. Even releasing unwanted pets or dumping unused bait can introduce invasive species into environments where they can cause harm.  

One of the most well-known invasive species in the United States is the Burmese python. These large snakes, which are native to southeast Asia, can now be found in the Florida Everglades and other parts of Florida. They can grow to be more than 23 feet long and have had devastating effects on the ecosystems they have invaded in Florida, according to the National Park Service. It is believed that the pythons were introduced in Florida either by people releasing them when they could no longer keep them as pets or they possibly escaped from the damage and destruction caused by Hurricane Andrew in 1992.

Today, the pythons are such as threat to the ecosystem in the Everglades that Florida residents are allowed — and even encouraged — to capture and humanely kill them. Some agencies, like the South Florida Water Management District, even incentivize people to capture them by paying bounties for the snakes, with bigger bounties paid for bigger snakes.

Another invasive species getting a lot of attention of late is the spotted lanternfly, which is a threat to many trees and fruit crops. Spotted lanternflies are native to China and were first reported in the United States in Pennsylvania in 2014, according to the U.S. Department of Agriculture. Since then, have been reported in many states in the eastern United States, as far as west as Indiana. Because of how destructive they can be to U.S. ecosystems, officials in many states are encouraging people to kill them when they see them.

Closer to home, invasive species are wreaking havoc in our local ecosystems. One of the most well-known invasive species in Illinois is the Asian carp. Asian carp were introduced in the United States as part of an effort to reduce nuisance vegetation in controlled waterways such as wastewater treatment plants and aquaculture ponds without using poisons that could affect wildlife, according to the Illinois Department of Natural Resources. They escaped these controlled environments in floodwaters and then infiltrated our river system. 

In Illinois, Asian carp are present in waterways including the Mississippi and Illinois rivers, with the state and other agencies investing millions of dollars to create barriers to control their spread, IDNR reports. The goal of the efforts to stop the fish from spreading is to prevent them from reaching Lake Michigan, where they could have a devastating effect on the Great Lakes ecosystem.

Another invasive species that gets a lot of attention is the zebra mussel, which is native to the Caspian Sea region of Asia and was introduced to the Great Lakes region by way of water from ships from Europe in the 1980s, IDNR reports. These small mussels will attach to any hard surface in the water, including rocks, docks and even boats. 

Humans often inadvertently contribute to the spread of zebra mussels by moving them from place to place when transporting boats, marine equipment and even bait buckets and fishing gear, according to the National Park Service. To help prevent the spread, boaters should drain their boats, motors and livewells when leaving a lake or river, wash them thoroughly and allow them to dry for at least five days before putting them in the water again. 

Other animals in Illinois that are considered invasive species include insects such as the spongy moth, formerly known as the gypsy moth, and emerald ash borer. And even some of our most familiar birds are considered invasive. Mute swans are considered invasive, as are European starlings and house sparrows, according to the National Park Service. All three of these bird species were introduced to the United States from Europe and have seen their populations explode. 

Locally we also have many plants that are considered invasive, quickly taking over and harming even restored habitats. In the Will County preserves, natural resources and volunteer crews work year-round to remove invasive species like buckthorn and honeysuckle. Other invasive plants that can be destructive to our habitats include teasel, poison hemlock and autumn olive, according to the University of Illinois Extension


The damage caused by invasive species is costly, totaling as much as $138 billion a year, according to the U.S. Environmental Protection Agency. These damages aren't limited to certain areas or habitats. Our oceans and waterways are harmed, as are farmland, forests, prairies and even our own yards. Invasive species also interfere with our ability to enjoy the outdoors and partake in our favorite recreational activities. 

Eliminating and preventing the spread of invasive species will require large-scale global efforts, but you can do your part too. A few simple steps you can take include cleaning your shoes before hiking a trail, avoiding dumping unused bait in waterways and following all local rules and restrictions about the transport of watercraft and firewood.

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