Why are Invasive Species Dangerous to the Environment?

Largest Wild Boar - Giant Forest Hog - Invasive Animals
© iStock.com/chingkai huang

Written by Cindy Rasmussen

Updated: October 14, 2022

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Invasive species are plants or animals that are new to an environment and harmful.

They are dangerous to the environment because they can cause an imbalance in ecosystems and can constitute a danger to native plant and animal populations.

An example is the Burmese Python in Florida. These enormous snakes are not native to Florida and are very harmful to the balance of the current environment. Because the only predators of these 26-foot 200 lb snakes are alligators and humans, they can continue to grow their population quickly. They eat all the small mammals that other animals rely on for food like raccoons, opossum, and bobcats. When these animals are depleted, the alligators and large cats have to relocate to find food.

Before we go on to find out about some other ways invasive species are dangerous to the environment, we’ll define what an invasive species is properly.

Apex predator: Burmese python

Burmese Pythons are an invasive species in the Everglades in Florida.

©Heiko Kiera/Shutterstock.com

What is an invasive species?

According to the USDA, the official definition of an invasive species is a species that is not native to the environment and whose introduction causes or is likely to cause economic or environmental harm or harm to human health. So, it is a plant or animal that is new to an ecosystem and harmful. Some invasive species harm the environment and are extremely costly. Imagine you have 100 acres of corn and a herd of wild boars comes in and tramples and consumes 20 acres in one night! That is 20% of your profits. The Department of Conservation estimates that a herd of 10 wild boars can destroy 10-20 acres in one night. An estimate of $1.5 billion dollars of damage to crops like rice, corn, and grains is caused by wild boars each year in the US!

Now that we know what an invasive species is, let’s dive into why they are dangerous to the environment.

Invasive species can destroy plants

The gypsy moth is an invasive species in the US that eats all the leaves off of trees! Large groups are responsible for the defoliation of a variety of tree and shrub species which then affects the animals that depend on those for food and shelter. It also leaves the trees vulnerable to disease and fires.

Emerald Ash Borer

The Emerald Ash Borer destroys ash trees by eating the inner bark.

©Don Bilski/Shutterstock.com

The emerald ash borer is an invasive species that has killed more than 100 million trees in the United States. They are small metallic green beetles that target ash trees and were discovered in 2002. Their larvae eat the inner bark of the tree making the trees unable to move water and required nutrients to the leaves, therefore killing the tree. The EAB has spread to many states in the Northern Eastern and Southern US.

Invasive species can kill animals

The Burmese Python in Florida as mentioned above has been killing a variety of animals in the Everglades. Researchers in 2012 found that the populations of raccoons had dropped 99.3 percent, opossums 98.9 percent, and bobcats 87.5 percent since 1997. They also found that cottontail rabbits, marsh rabbits, and foxes were almost gone altogether.

Invasive species can kill endangered species

Burmese Python in the Everglades.

Burmese Pythons could make some endangered animals, like the wood stuck and American crocodile, extinct.

©Heiko Kiera/Shutterstock.com

The National Wildlife Foundation suggests that about 42% of threatened and endangered species are affected by invasive species. The Burmese Python could make some of the endangered animals in the Everglades extinct. Although the Python doesn’t directly prey on all of these animals, if they kill off animals that the others rely on for food then they could die off too. The following animals are in danger of becoming extinct in the Everglades:

Threatened or Endangered Mammals in the Everglades:

Threatened or Endangered Birds in the Everglades:

  • Cape Sable seaside sparrow
  • Red knot
  • Ivory-billed woodpecker
  • Piping plover
  • Kirtland’s warbler
  • Wood stork
  • Red cockaded
  • woodpecker
  • Everglade snail kite
  • Roseate tern
  • Bachman’s warbler

Threatened or Endangered Reptiles in the Everglades:

Threatened or Endangered Fish in the Everglades:

Threatened or Endangered Invertebrates in the Everglades:

  • Florida leafwing butterfly
  • Miami-blue butterfly
  • Stock island tree snail
  • Bartram’s scrub hairstreak
  • Ceraunus blue butterfly
  • Cassius blue butterfly

Invasive species compete for food with native animals

The fresh water supply of the Southern United States has been invaded by the zebra mussel, which has a huge economic and environmental impact on the waters it invades.

Zebra mussels invade freshwater environments and eat all of the algae and phytoplankton, leaving other mussels and fish hungry.


The Zebra mussel has been a huge problem in the Great Lakes and waterways in Nevada, Utah, Colorado, California, and Texas. They are small, fingernail-sized mollusks (like snails, slugs, and mollusks) that live in tiny shells and attach themselves to something hard, which is frequently the shells of native mussels. Zebra mussels eat phytoplankton, zooplankton and algae. That is the same diet as the native mussels and many fish like shad and herring. There just isn’t enough food to go around! Female zebra mussels can lay a million eggs each year, so you can see why they have the upper hand in taking over an area and dominating the competition for food.

Invasive species carry harmful disease to other animals

Animals with Opposable Thumbs-possum

The Australian brushtail possum carries bovine tuberculosis which is harmful to cattle.

©Timothy Christianto/Shutterstock.com

Invasive species can introduce new parasites or diseases that have never been present in other animals. The Australian brushtail opossum aids in the spread of bovine tuberculosis. The opossum got it from the wild deer, but because they are so mobile they spread it to livestock and cattle at an increasing rate. New Zealand is trying to deal with the spread of this debilitating disease.

The raccoon dog is responsible for spreading rabies to other animals like raccoons, skunks and foxes. As more animals get rabies, the more they can spread it and there is a risk that some Eastern European countries that are currently rabies-free may have it reintroduced.

Invasive species carry harmful diseases to humans

Mosquito sucking blood on human skin.

The Asian


mosquito carries the deadly West Nile Virus.


The Asian tiger mosquito carries the West Nile Virus which is a very deadly disease. There are 65 different mosquito species that also carry this disease. In the United States between 1999-2020, there were a total of 52,532 cases and 2,456 deaths.

Feral swine (wild boar) can carry a whole list of horrible diseases including salmonella, toxoplasmosis, brucellosis, tularemia, trichinellosis, swine flu, hepatitis, and pathogenic E. coli. Humans can get these diseases by handling the pigs, using the same watering/feeding containers, and eating undercooked meat from feral swine.

Invasive species can be dangerous to humans and pets

Marine Toad in the grass

Cane toads have extremely toxic skin.

©Patrick Gijsbers / Creative Commons – Original

The Africanized honeybee is an invasive species that is more aggressive than native bees and they swarm in large numbers. They can be fatal to humans and pets. The Red imported fire ant is a nasty little ant that can have a very painful bite. Cane toads (also known as the Marine Toad) are an invasive species that has extremely toxic skin which can make humans and pets sick. When you think about an animal invading a city, the Cane toads actually do this. In a Smithsonian Magazine article, one resident described Palm Beach Gardens, Florida in the spring of 2019, “In some areas, people can’t walk outside or drive for fear of squashing the amphibians. There are so many they are even clogging pool filters.” That is a lot of toads! Definitely dangerous!

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About the Author

I'm a Wildlife Conservation Author and Journalist, raising awareness about conservation by teaching others about the amazing animals we share the planet with. I graduated from the University of Minnesota-Morris with a degree in Elementary Education and I am a former teacher. When I am not writing I love going to my kids' soccer games, watching movies, taking on DIY projects and running with our giant Labradoodle "Tango".

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