Wildlife Species

Keep reading to learn more about the pros and cons of invasive wildlife, the names and stories of some well-known invasive species, and what you can do to help.

Most people agree that wildlife should be protected, but there are some caveats to this, including invasive species. Invasive species commonly pose problems for their new ecosystems, requiring control measures. At the same time, not all non-native species are bad and there are some situations in which these species can become an integral and helpful part of the local ecosystem.

Take a look at invasive species, including the problems that they can potentially cause.

What Is an Invasive Species?

The average person likely thinks of an invasive species as any species that is not naturally from the area. However, the technical definition is actually slightly different. To be an invasive species, the plant or animal has to have a negative consequence of some sort on its new habitat. This can be an impact that is harmful to human health, the economy, or the environment. 

If an introduced species does not have negative consequences on the new area, then it is considered an alien or exotic species. This is a very important distinction as it means that anything that is technically an invasive species is harmful in some way. 

While not all non-native species are harmful, all invasive species will be. Those non-harmful ones would be alien or exotic species, which we will also touch on briefly. 

Why Do Species Become Invasive?

Since not all non-native species introduced to an area become invasive, it is common to wonder what causes them to become invasive, or to cause harm. 

Lack of Predators 

In many cases, the lack of predators in the new area is a strong contributing factor in which species become invasive. 

Keep in mind that predators and prey typically evolve together in what experts call the co-evolutionary arms race. Essentially, the prey evolve to have better defenses, which results in the predators evolving to overcome those new defenses or better hunt the prey. For example, the fastest antelopes survived because they could escape cheetahs better, which led to only the fastest cheetahs surviving and that species evolving to become fast as well. 

By contrast, if a new species gets introduced into an ecosystem, it has not co-evolved with any local predators. This can result in a lack of predators in the area that can successfully prey on the new species. In many cases, the original ecosystem of the non-native species has at least one predator that co-evolved with it, but this is not the case in the new area. 

Exploiting Natural Resources

It is also common for invasive species to become invasive due to their ability to take advantage of some native resources that the local species do not use. One example is barbed goatgrass in the Western United States. Native plants do not usually grow in serpentine soils but this type of grass does well there, providing the species with almost no competition for resources. 

Altering the Environment

In other cases, invasive species become invasive by changing the environment in a process known as ecological facilitation. This process makes the environment favorable to them while making it less favorable for native species. An example is the yellow starthistle on the West Coast. It secretes a chemical from its roots that harms native plants and as the starthistle has less competition, it can spread more. 

Common Features of Most Invasive Species

Because of the above factors that tend to make species become invasive, invasive species tend to share some of the same characteristics. 

They tend to reproduce quickly, have fewer natural predators, and be able to thrive in varying environments.

How Invasive Species Arrive

There are multiple ways that invasive species can arrive in new environments, with humans being the culprit in many cases. In many cases, humans simply want to spread a plant or animal species that they find useful or pretty, and quickly discover that there are unintended consequences of their actions.

Other times, invasive species sneak along when humans travel, such as rats on ships or pollen on clothes. An example would be the 16th century Spanish galleons that were loaded with ballast soil, but there were fire ants in the soil. 

There are also situations where humans intentionally bring non-native species but intend to keep them contained, such as in zoos or aquariums, but then they escape or somehow get introduced to the ecosystem. For example, experts believe that lionfish first entered the Caribbean when Hurricane Andrew broke a beachfront aquarium in 1992. 

It is also common for invasive species to start off as exotic pets. In this case, the animal in question grows too large or becomes too hard to care for and the person simply releases them into the environment. That is how Burmese pythons originally entered the Florida everglades. 

How They Spread

In addition to the previously mentioned reasons that the species become invasive, their spread is frequently facilitated by humans or other aspects of the habitat. For example, fire ants found it easy to spread along human roads because of the lack of vegetation next to them. Other species also get a boost from areas by roads, since native species there have been removed to clear a path.

Invasive Species Kill Native Species

When most people think of the problems caused by invasive species, they picture invasive predators killing prey, or invasive herbivores eating too many plants and stealing food sources. 

Not only can invasive species kill the native ones, but they have been connected to numerous extinctions. Experts predict that invasive species had a significant contribution in half of the species that have gone extinct since 1600, and are solely responsible for the extinction of 20% of those. 

Additionally, around 42% of the species listed on the Endangered Species Act are in danger because of invasive species, either alone or in combination with other factors. There are also almost 40 more species being considered for inclusion on this list for which invasive species bear at least some of the blame in the reduced numbers. 

Burmese Pythons

Burmese pythons are one of the best examples of invasive species that cause harm by killing native species. In the Everglades, they are the top predators and have contributed to the decimation of local populations of birds and mammals. Burmese pythons are known to eat nearly any animal they come across when hungry, including alligators and deer. They have also eaten endangered species. 


In the Great Lakes, lampreys infect native fish with parasites. The native fish did not evolve to have defenses against these parasites, so even if a native fish does not die from the wounds caused by lampreys, they may die from the infection.

Invasive Species Compete for Resources

Another significant problem with invasive species is that they compete with native species resources, from shelter to food. 

Asian Carp

For example, when humans introduced Asian carp to the United States, the carp started to outcompete native fish for both of these. This has led to vast declines in the populations of native fish.

Invasive Species Cause Habitat Loss

One of the many ways in which invasive species negatively affect their new home is by causing habitat loss. In fact, experts estimate that over 90% of San Francisco Bay’s biomass comes from non-native species. 

Habitat loss is a significant problem because not only do the invasive species affect the native plants that make up that habitat, but they then also indirectly harm the native wildlife by removing their habitat. 

In extreme cases, species that rely on the habitat may go extinct.

Beavers in Tierra del Fuego

In 1946, humans brought 50 Canadian beavers to Tierra del Fuego, with is an archipelago that sits at South America’s southern tip. The idea was to hunt the beavers for their pelts, but the beavers quickly multiplied beyond control. Today, there are hundreds of thousands of them. 

While North American trees have adapted to deal with beavers by healing after being gnawed on, this is not the case for the South American trees. In addition to destroying the native trees, the beavers create ponds, which flood the forest. 

Those pools of stagnant water change the nutrient cycles in the forest, affecting the plants themselves as well as all the wildlife that rely on them. There are also direct impacts on livestock when beavers build dams in the drainage ditches. Livestock can fall in these ditches and then get stuck and die. 

Hemlock Woolly Adelgids 

One example of this is the hemlock woolly adelgid, an invasive insect that came to the United States from Asia. Its name comes from the fact that it targets hemlock trees, which it rapidly infests and kills. Experts estimate that this insect has caused as many as 80% of the hemlock trees in some eastern areas of the country to die. 

Kudzu Vines

A plant example of habitat loss is kudzu vines, which originally came to the United States in the 19th century from Japan. People spread the plant throughout the southeastern region of the country to provide food for grazing animals and control erosion. 

However, the vine quickly showed its invasive tendencies and is able to overgrow full forests quickly. As it overgrows the forests, it blocks sunlight, preventing the trees from getting this key nourishment and causing them to die. The vines can also be heavy enough when they form mats to break trees and make them fall over. 

Other Ways Invasive Species Can Impact the Habitat

It is also possible for invasive species to have a negative impact on the biodiversity of an area. This tends to come from a combination of the above effects, including killing animals, competing for resources, and potentially reshaping the ecological landscape. 

Invasive species can also lead to erosion or soil degradation or change fire cycles.

Invasive Species Can Also Hurt Human Health

In addition to their negative effects on native species, invasive species can also have negative consequences for human health. 

Zebra Mussels

Zebra mussels are invasive and they accumulate PAHs, PCBs, and other toxins in their tissues. Other animals prey on the mussels, bringing the toxins up the food chain until they can eventually reach humans. 

Other Human Health Impacts

There is also the issue of invasive species potentially transmitting diseases, with feral swine carrying 30 disease organisms and 37 parasites that can affect people and fire ant bites potentially leading to hospitalization. Giant African land snails can also carry meningitis.

Invasive Species Can Have Economic Costs

Invasive species can even have a negative impact on the economy. Experts estimate that just within the United States, between environmental resource loss and control methods, invasive species cost about $120 billion each year. 

Kudzu Vines

Looking back at the kudzu vines that destroy trees and forests, estimates indicate that power companies spend $1.5 million annually to control these vines on their power lines. 

Zebra Mussels

Going back to the zebra mussels, they can quickly cover surfaces that are submerged. This means that they clog the water intakes at power plants or water treatment facilities. Estimates indicate that just within the Great Lakes, remove zebra mussels costs about $500 million each year. 

Other Estimates

Various experts have created estimates outlining the impact of invasive species on the economy, including the following estimates. 

The California Academy of Sciences’ Molly Michelson estimates that invasive species cause $1.4 trillion of global economic damage. 

Cornell University Professor David Pimentel estimates that in the United States alone, this figure is $127 billion. This estimate includes $21 billion spent because of invasive agriculture crop weeds, $18 billion on crop plant pathogens, $9 billion on livestock disease, $6 billion on pasture weeds, $4 billion on forest pests, and $3 billion on landscaping pests. 

In terms of animals and insects, zebra mussels have an estimated impact of $2 billion across the country while pigeons, Asian clams, Formosan termites, fire ants, and feral pigs are each responsible for around $1 billion. Other invasive species have annual costs of between $10 and $100 million. 

Recreational Impacts

There are also economic impacts via the loss of recreational activities, some of which contribute significantly to the economy. For example, the Asian carp threatens the recreational boating industry on the Great Lakes. Or Burmese pythons in Florida kill native species that are commonly part of recreational hunting, reducing the opportunities for local hunters.

How to Prevent and Control Invasive Species

Controlling invasive species needs to come from a combination of control and preventative methods. 

Educating about Invasive Species and the Risks

Any strategy must include education on the matter, since many people are not aware of the extent to which invasive species can negatively impact their local ecosystems. This education should focus on the dangers and consequences associated with bringing wildlife into new areas. 

Regulating Importation of Invasive Species

Many areas have begun creating laws or other regulations to completely ban or severely restrict the importation of species that are known to be invasive. One example is that it is now illegal to import Burmese pythons into the United States. 

Promoting Harvest or Killing of Species – But It Is Controversial

Some areas have tried to help control invasive species populations by encouraging people to harvest or kill them. Examples would be the rattlesnake roundups in Florida and other states. Or in Argentina where officials have encouraged people to hunt beavers and tried to create a market for their pelts. Or in areas where people harvest the kudzu vine and turn it into craft baskets. 

As mentioned, this is a controversial method, as it is not without its negatives. For one, this type of effort is almost never enough to make a significant impact on the population. There is simply not enough demand for the products or interest in the activity. 

Additionally, in the case of invasive wildlife, there are concerns about humane treatment. Encouraging regular people to hunt or kill wildlife will not result in them doing so in the most humane matter, at least not without proper training. 

Analyzing the Past and Making Predictions

There is also a great deal of promise in using science to analyze the past movements of the invasive species and predict their future movements or impacts. 

For example, some scientists have conducted genetic studies to analyze how invasive species spread within an area. These studies can also let experts know if the invasive species could potentially form a hybrid with a native species. 

Research can also try to determine how the range of a given species is likely to increase in the future. This gives us time to prepare those areas. 

Other research can look to humane, effective methods of killing invasive species, especially in the case of plants.

Ethics Can Come into Play

The case is not cut and dry for all invasive species. The wattle-necked softshell turtles originally came from China but are now on Kauai, Hawaii, where they are invasive. Sugarcane farmers originally brought them during the 1850s, as they used them for soup. Now, however, they are invasive in Kauai, where they eat too many native fish. 

But experts do not want to simply return the turtles to China or worse, kill them. The species is endangered, so it requires extra care. To further complicate matters, conservationists worry that the turtles are at-risk of being hunted in their home range in China. 

The wattle-necked softshell turtle is far from the only invasive species in this situation. Just looking at wildlife, not plants, Brown University ecologist Dov Sax reported that 10 percent of birds and 15 percent of mammals introduced into non-native habitats are threatened in their home ranges. 

The red-crowned Amazon parrot is also one of these birds. It is native to northeast Mexico, where it is endangered, but it is doing well in Hawaii and California, where it is loud and invasive. 

Another example is the hippo, which is in danger of becoming extinct in sub-Saharan Africa yet doing well in Colombian lakes thanks to Pablo Escobar, the drug lord, importing them.

Some Non-Native Species Can Be Fine or Even Helpful

While it is important to be aware of the negative impacts of invasive species, it is also crucial to note that not all non-native species will be harmful. In fact, many non-native species have successfully integrated with our adapting ecosystems, such as when humans spread crops or livestock around the world. 

Others have been introduced to overcome specific challenges and have succeeded in that goal. Yet others simply have no impact on their new habitats, positive or negative. 

It Is Hard to Define Native

At this point in the history of the planet, it is hard enough to define which species are native. Over hundreds of thousands of years, animals and plants have moved around, just like humans have in more recent history. Even if you just look at recent history, would non-native species only be those moved by humans or those that moved themselves naturally? It becomes complicated to draw a line, making it hard to justify removing all non-native species. 

Spartina Grass in California

One of the many examples of non-native species helping native species is the spartina grass that now grows on California beaches. Although it is not native, it has become a key habitat of the endangered and native shorebird, the California clapper rail. 

In this case, if people were to remove the non-native spartina grass, it would have devastating consequences for the already-endangered native California clapper rail. 

Japanese White-Eye Bird

In Hawaii, many of the native flowers today are pollinated thanks to the Japanese white-eye bird. Invasive species have caused the other pollinators to go extinct, leaving this non-native species to take care of pollination. 

Tamarisk Shrubs

Tamarisk shrubs are an invasive species, yet the southwestern willow flycatcher, which is not only native but endangered, nests in the plant.


Invasive species can threaten local wildlife, plants, and the balance of the ecosystem. They can also spread disease and have economic impacts. Education, regulation, and research are all key parts of preventing and controlling invasive species. At the same time, the desire to control them is complicated by factors such as endangered invasive species or invasive species that provide benefits for local wildlife.

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