When we talk about conservation and biodiversity, one phrase that pops up repeatedly is "invasive species." But what is an invasive species, and why do they pose such a significant threat to native wildlife and ecosystems?

Invasive species are one of the most significant threats to biodiversity around the world. They disrupt ecosystems, outcompete native species, alter habitats, and can cause lasting economic and environmental damage. But what exactly qualifies as an invasive species, and why are they so problematic?

In this deep dive, we’ll unravel the science, history, and real-world impact of invasive species, and explore what we can do about them. we’ll break down the definition of invasive species, look at both plant and animal examples, explore case studies from various countries, and examine their impact on ecosystems, economies, and communities.

Infographic showing some of the common invasive species found in the world

What Is an Invasive Species?

An invasive species is any organism, it could be plants, animals, insects, or even pathogens, that is not native to a specific location and has a tendency to spread, causing damage to the environment, human health, or the economy. These species are often introduced intentionally or through accidental release via global trade, travel, and agriculture. Once established, they can outcompete native species for resources, alter habitats, and lead to ecological imbalance.

Why Are Invasive Species a Problem?

Invasive species are a global issue because they disrupt the delicate balance of ecosystems and cause significant environmental harm. They compete with native species for resources like food, water, and space, often leading to declines or even extinctions of local wildlife. The Smithsonian National Museum of Natural History highlights that invasive species can also introduce diseases, alter food webs, and change the physical environment, making it harder for native species to survive.

The economic impact is staggering too. According to the U.S. Environmental Protection Agency (EPA), damages from invasive species cost billions annually, up to $138 billion per year in the U.S. alone. That includes losses in agriculture, forestry, and fisheries, as well as the cost of managing these invaders.

The Key Difference Between Native, Non-Native, and Invasive

Native species evolved in a particular area and form part of the natural ecosystem.
Non-native (or exotic) species are those introduced to an area outside their natural range, where they do not naturally exist.
Invasive species are a subset of non-native species that cause harm.

Not all non-native species are invasive, but those that are can wreak havoc.

Key Traits of Invasive Species

Invasive species often share some common characteristics:

Rapid reproduction and growth: Many invasive species, like the cane toad, can reproduce quickly, leading to population booms.
High adaptability to different environments: They can survive in a variety of conditions, from urban areas to remote forests.
Lack of natural predators in the new habitat: Without natural enemies, their numbers grow unchecked.
Efficient dispersal mechanisms
Ability to outcompete native species for resources: They often outcompete native species for resources, as seen with plants like kudzu.
Highly invasive nature: These species exploit environmental changes such as wildfires or human activity, causing significant ecological disturbances.

This makes them ecological bullies. Their success often comes at the expense of native biodiversity.

close up op Golden bamboo plants — Rapid growth of Golden bamboo | Via Getty Images

Examples of Invasive Species: Animals That Cause Chaos

Let’s look at some examples of an invasive species that have made headlines for their impact on native populations and their rapid spreading.

Burmese Pythons in the United States

In the Florida Everglades, Burmese pythons are a notorious example of invasive animals in the United States, originating from their native country of Myanmar. Originally introduced through the pet trade, these snakes have established a breeding population in South Florida. The U.S. Geological Survey reports that they compete with native wildlife for food, leading to severe declines in mammal populations, such as raccoons and opossums, in Everglades National Park.

a Burmese Python rolled around a tree trunk — Burmese Python are invasive in United States | Photo by Taneth Photo

Cane Toads in Australia

Cane toads, native to South and Central America and Southeast Asia, were introduced to Australia in 1935 to control sugar cane pests. However, they’ve since become a major problem. The Smithsonian notes that these toxic toads kill predators that try to eat them, like native Australian frogs, and compete with local species for food. Today, they’ve spread across northern Australia, disrupting ecosystems.

a cane toad near the edge of a small pond laying on the grass — Cae Toads were introduced to Australia in 1935 to control sugar cane pests.

Lionfish in the Caribbean

Lionfish, native to the Indo-Pacific, have invaded the Caribbean and the southeastern U.S. coast. These animals living in non-native areas prey on native fish, reducing biodiversity in coral reef ecosystems, according to NOAA. With few natural predators, their population has exploded, threatening the balance of marine environments.

a lion fish swimming in the ocean with crystal blue waters — Lionfish are invasive in the Caribbean | Photo by Hobli via Getty Images

Examples of Invasive Species: Plants That Take Over

Kudzu in the United States

Known as “the vine that ate the South,” kudzu was introduced to the U.S. in the 1870s as an ornamental plant and later promoted for erosion control. Invasive species like kudzu can also spread through human activities, such as the use of shipping palettes, which inadvertently transport insects and other organisms globally. National Geographic reports that it grows up to a foot a day, smothering native plants and trees by blocking sunlight. It’s now a major problem across the southeastern U.S.

kudzu plant ocertaking an area of vegetation, covering most of other trees and grass present — Kudzu | Photo by Martha Snider

Japanese Knotweed in the United Kingdom

Japanese knotweed, originally brought to the UK as an ornamental plant in the 19th century, is now a widespread invasive species. The Natural History Museum explains that it outcompetes native plants, damages infrastructure, and is notoriously hard to eradicate. It’s a prime example of how introduced species can spiral out of control, causing significant economic or environmental harm.

a Japanese Knotweed — Japanese Knotweed | Photo by Michel Viard

Water Hyacinth in Africa

Water hyacinth, a floating plant native to South America, has invaded waterways in Africa, including Lake Victoria. WWF notes that it forms dense mats, blocking sunlight and oxygen, which harms aquatic life and disrupts fishing communities. These dense mats can also facilitate the spread of various aquatic organisms, further impacting native species and local ecosystems.

a pond surrounded by plants of the species Water Hyacinth — Water Hyacinth | Via Getty Images

Invasive Species Around the World: A Global Perspective

Uninvited species are a global problem, often spread by human activities such as the transport of goods and unintended introductions. Let’s explore a few examples.

United States: Zebra Mussels

Zebra mussels, originally from the Caspian Sea, were introduced to the Great Lakes via ballast water in the 1980s. The U.S. Department of the Interior reports that they’ve spread across the U.S., clogging water systems and outcompeting native mussels, leading to declines in aquatic biodiversity.

a group of zebra mussels — Zebra Mussels were introduced to the Great Lakes via ballast water in the 1980s | Getty Images

Australia: European Rabbits

European rabbits were introduced to Australia in the 18th century for hunting. Unlike domestic cows, which were introduced to North America for agricultural purposes and are beneficial in farming, European rabbits have caused massive ecological damage by overgrazing native vegetation, leading to soil erosion and the decline of native species like the bilby. BBC Earth highlights that they’ve caused massive ecological damage by overgrazing native vegetation, leading to soil erosion and the decline of native species like the bilby.

an european rabbit running in a grass field — European rabbits were introduced to Australia in the 18th century for hunting

New Zealand: Stoats

In New Zealand, stoats were introduced in the 1880s to control rabbits but ended up preying on native birds, like the kiwi. The New Zealand Department of Conservation estimates that stoats contribute to the decline of many endangered bird species, making them a top conservation concern. Understanding the risks associated with non native plants and other non-native species is crucial for making informed decisions about their introduction and management in new environments.

stoat looking at the camera standing over a grass field — Stoat | Photo by Tracy Williams

Invasive Species List in the US

The United States has a long list of invasive species, including:

Asian carp: Disrupt freshwater ecosystems
Kudzu vine: Nicknamed “the vine that ate the South”
European starling: Competes with native birds for nesting sites
Zebra mussels: Clog water infrastructure and devastate aquatic ecosystems
Burmese python: Consumes a wide range of native mammals and birds in the Florida Everglades
Invasive carp: Outcompete native fish for resources, disrupt the food web, and threaten native species in U.S. waterways, including the Mississippi River

carp swimming on the bottom of a river — Carps are common invasive species ion the world | Photo Mih tiander

Invasive Animals in the United States

One of the most well-known invasive animals in the U.S. is the feral hog, which causes billions in agricultural damage annually. Another is the northern snakehead, a fish native to Asia that threatens freshwater ecosystems by preying on native fish species.

Invasive Plants That People Love

It might surprise you that some beloved plants are actually invasive non native plants. Take the jacaranda tree, for example. Loved for its purple blossoms, it’s considered invasive in parts of South Africa and Australia, where it outcompetes native flora. Similarly, English ivy, often used in landscaping, can choke out native plants and trees in forests.

a street full of jacarandas tree on each side of the road — Jacarandas are considered invasive in parts of South Africa and Australia | Getty Images

How Are They Introduced?

Humans are the primary culprits behind the spread of introduced species. The National Geographic explains that invasive species often hitch a ride through human activities and carry uninvited species with them, such as:

Shipping: Aquatic invaders like zebra mussels travel in ballast water of ships.
Pet Trade: Burmese pythons in the Everglades were originally released or escaped pets.
Ornamental Plants: Many invasive plants, like Japanese knotweed, were introduced as garden plants.
Accidental Transport: Insects like the Asian long-horned beetle arrive in wooden shipping pallets.
Agriculture and aquaculture: Species introduced for food production escape containment

Global trade and travel have accelerated the spread, making it easier for species to cross borders.

aerial photo of a cargo ship carrying hundredths of cargo containers stacked on top of each other — Trading ship | Cloud Ship

How They Impact Native Populations

Invasive species impact native populations in several ways:

Predation: Preying directly on native species (e.g., cats on islands)
Competition: Invasive species often outcompete natives for resources. For example, lionfish in the Caribbean eat the same food as native fish, leaving less for them
Disease: Invasive species can introduce diseases, like the West Nile virus spread by the Asian tiger mosquito, which harms native wildlife and humans.
Habitat alteration: Changing fire regimes, nutrient cycles, or water availability, which can affect the conditions and survival of other species within the same environment

The Ripple Effect: Indirect Impacts on Ecosystems

The effects of invasive species go beyond direct competition or predation. They can cause a ripple effect across entire ecosystems by introducing various aquatic organisms through human activities, such as ballast water in ships. For example, the emerald ash borer, an invasive beetle in the U.S., kills ash trees that act as a sink for air pollutants. A study in Environmental Research Letters (2018) linked the loss of ash trees to increased air pollution, which in turn led to higher rates of cardiovascular and respiratory issues in humans.

Invasive species can also disrupt food webs. When lionfish reduce native fish populations in the Caribbean, it affects predators that rely on those fish, creating a cascading effect.

The Role of Climate Change

Climate change is making it easier for many invasive species to establish in new areas. The mountain pine beetle, for example, thrives as rising temperatures and altered precipitation patterns weaken plants, exacerbating the problem of invasive species. Warmer temperatures and shifting weather patterns expand the range of these species, allowing them to move into habitats that were previously too cold or inhospitable.

Ecological, Cultural and Economic Costs

Invasive species are not just a conservation issue—they’re an economic one. The U.S. alone spends an estimated $120 billion annually dealing with invasive species damage. This includes:

Infrastructure damage
Agricultural losses
Water system maintenance
Forest and wildlife management

Beyond ecology, invasive species hit hard economically and culturally. In the UK, Japanese knotweed costs millions annually in property damage and removal efforts. In Canada, the Invasive Species Centre estimates that invasive species cost billions in losses to forestry, agriculture, and fisheries.

Culturally, invasive species can disrupt traditions. In Hawaii, invasive species like the coqui frog outcompete native species, affecting cultural practices tied to the land, as noted by the University of Hawaii. The U.S. Fish and Wildlife Service encourages individuals to participate in control measures, including hunting and consuming specific invasive animals, highlighting both environmental benefits and culinary opportunities.

Human Health Impacts

Invasive species can have profound impacts on human health, often in unexpected ways. For instance, invasive plants like poison ivy and poison oak are notorious for causing skin irritation and allergic reactions. These plants can spread rapidly, increasing the likelihood of human contact and subsequent health issues.

Invasive animals also pose significant health risks. Rodents and bats, for example, can carry diseases such as hantavirus and histoplasmosis, which can be transmitted to humans. The introduction of non-native species often disrupts native ecosystems, leading to a cascade of effects that can impact human health. For instance, the spread of invasive species can increase the prevalence of disease-carrying insects like mosquitoes and ticks, which thrive in altered habitats.

Water contamination is another serious concern. Invasive species can degrade water quality, making it unsafe for human consumption. This poses a direct risk to human health and can lead to significant economic costs associated with medical treatment, lost productivity, and infrastructure damage.

The social impacts of invasive species on human health are also noteworthy. The displacement of communities and the loss of traditional ways of life can have profound psychological and cultural effects. Climate change exacerbates these issues by facilitating the spread of invasive species, leading to increased disease transmission and heat stress.

Human activities, such as global trade and travel, play a significant role in the spread of invasive species. This underscores the importance of controlling and eradicating invasive species to mitigate their impacts on human health and protect native ecosystems.

Common Misconceptions

“Invasive means bad everywhere”: Not always true—some species are only invasive in specific ecosystems.
“They were here first”: Historical records often show otherwise.
“They’ll eventually balance out”: Many invasive species do not reach equilibrium and continue expanding unchecked.
“All non-native species are harmful”: This is a misconception. Some non-native species can be a beneficial organism in certain contexts, such as domestic cows in agriculture, providing valuable benefits despite being classified as non-native.

Conservation Strategies

Combatting invasive species requires multi-faceted strategies:

Early detection and rapid response
Biological control (introducing natural predators)
Mechanical removal
Public education and citizen science
Legislation and trade restrictions
- Invasive species can be spread through human activities, such as the use of shipping palettes, which inadvertently transport insects and other organisms globally.

close up to a pair of hand using gloves removing a weed from the soil with a tool — Physical removal of weeds | Lucentius via Getty Images

Control and Eradication Methods

Effective control and eradication of invasive species require a multi-faceted approach. Biological control methods, such as introducing natural predators or parasites, can be highly effective. For example, the use of specific insects to control invasive plant species has shown promising results. However, this method must be carefully managed to avoid unintended consequences on non-target species.

Chemical control methods, including herbicides and pesticides, are commonly used but come with their own set of challenges. While they can be effective in reducing invasive species populations, they can also harm native species and the environment. Therefore, their use must be judicious and targeted.

Physical control methods, such as hand-pulling or mechanical removal, are labor-intensive but can be effective for small-scale invasions. These methods are often used in combination with other strategies to maximize their effectiveness.

Cultural control methods involve changing land-use practices or promoting native species to prevent the spread of invasive species. For instance, planting native species in landscaping can reduce the likelihood of invasive species taking hold.

Early detection and rapid response are critical to preventing the establishment and spread of invasive species. Monitoring and surveillance programs play a key role in this effort, allowing for quick action when new invasions are detected.

Education and outreach programs are also essential. By raising public awareness and promoting best management practices, these programs can help prevent the spread of invasive species. The use of technology, such as drones and satellite imaging, enhances the ability to detect and monitor invasive species populations.

Reestablishing Native Species

Reestablishing native species is a vital step in restoring ecosystems that have been disrupted by invasive species. This process often involves reintroducing native plants and animals through methods such as seed dispersal, plantings, and animal releases. The selection of species for reintroduction should consider their ecological roles, adaptability, and potential for success.

The benefits of reintroducing native species are manifold. It helps restore ecosystem functions, promotes biodiversity, and enhances ecosystem resilience. However, this process is not without challenges. Careful planning and management are required to ensure the success of reintroduction efforts.

Before native species can be reintroduced, it is often necessary to control and eradicate invasive species that may outcompete them for resources and habitat. This step is crucial to creating a conducive environment for native species to thrive.

Using native species in restoration efforts also promotes ecosystem services such as pollination, pest control, and nutrient cycling. Additionally, reintroducing native species can have cultural and social benefits, including the promotion of traditional ecological knowledge and increased community engagement.

Monitoring and evaluating reintroduction efforts are essential to ensure their success and identify areas for improvement. Developing comprehensive restoration plans that outline strategies and tactics for native species reintroduction can help coordinate and guide these efforts effectively.

By focusing on reestablishing native species, we can work towards restoring the health and balance of ecosystems that have been impacted by invasive species.

close up to the seed of a banksia tree — Banksia species are endangered in Australia | Photo by Christina Morgan

What Can You Do?

Everyone has a role in preventing the spread of invasive species:

Don’t release pets into the wild
Use native plants in landscaping
Clean boats and gear before moving between water bodies
Report unusual sightings to local conservation authorities
Prevent the spread of invasive plant species by avoiding the transport of seeds, which can propagate and outcompete native species, altering ecosystem dynamics

Can Invasive Species Ever Be Beneficial?

Surprisingly, yes! While most invasive species have negative impacts, some provide benefits. For example, in Hawaii, non-native birds have taken over seed dispersal roles for native plants after the extinction of native birds, according to a 2021 study in Scientific American. These birds also serve as a food source for other native species, highlighting the complex interplay between invasives and ecosystem dynamics. However, this comes with a catch—these birds also disperse invasive plants, which can worsen the problem.

Invasive plants like autumn olive in the U.S. produce fruit that feeds birds, but they still outcompete native species, reducing overall biodiversity. The key is to weigh the pros and cons on a case-by-case basis.

A Delicate Balance

Invasive species are a human problem with ecological consequences. They highlight how interconnected our world is. and how important it is to think ahead when moving species from one place to another.

By staying informed and making mindful choices, we can all play a role in preserving biodiversity and protecting native ecosystems. However, promoting the consumption of these invasive species could inadvertently lead to their further spreading.

What Is an Invasive Species? Understanding Their Impact on Native Populations