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About Invasive Species

What are Invasive Species?

Countless species have been brought intentionally to the United States for food, garden plants and as pets. Many of our important crops, landscape plants and aquarium fish are native to other parts of the world.

Most introduced animals and plants do not survive outside of captivity or cultivation in their new environment. However, a minority of non-native species may reproduce successfully and become invasive, causing adverse impacts.

Although few introduced species cause significant problems, the ones that do cause substantial damage. Americans spend billions of dollars annually trying to control and manage aquatic and terrestrial weeds; crop, forest and wetland pests, feral animals, and escaped or released pets.

Invasive species are defined as species that are not native to a region and result in adverse environmental, economic or social impacts. The federal government defines invasive species as ” a non-native organism whose introduction causes or is likely to cause economic or environmental harm, or harm to human, animal or plant health” (Executive Order 13751).

Different terms are used occasionally when referring to invasive species, including:

  • Alien a foreign species
  • Exotic typically a species from a different country
  • Introduced released, intentionally or unintentionally, by humans
  • Non-native not native to a particular ecosystem or region
  • Nonindigenous not originating from a particular area
  • Nuisance -an introduced species that causes ecological or economic harm

Other than nuisance species, these terms do not necessarily mean a species is invasive. The key is whether these species lead to impacts described below. Species that migrate (or are transported) to a new area without human assistance, directly or indirectly, often are not considered invasive.

Risks of Invasive Species

Most often, non-native species are not invasive throughout the U.S. because of a different climate. Many aquarium fish are from the tropics and will not survive harsh winters in much of the country. Species adapted to humid conditions are not suited for dry climates in the western states. Risk analysis is used by scientists to assess the chance that a non-native species will be able to survive and cause harm in various regions of the U.S.

Categories of harm caused by invasive species: 

Environmental – Invasive species have the potential to harm native species or their habitats in the following ways:

  • By preying on native species, particularly imperiled species
  • Through competing with native species for food, habitat or breeding area
  • By degrading native habitat
  • By interbreeding with native species (genetic contamination)
  • Through introducing new parasites or diseases of native wildlife and plants

Economic – Invasive species also may cause increased expenditures in a variety of ways:

  • Agricultural damage
  • Forest damage
  • Recreation loss
  • Infrastructure damage
  • Weed and nuisance animal control costs

Harm to humans – Invasive species also may threaten human health and safety by:

  • Serving as a vector for transmitting non-native parasites and diseases
  • Creating safety hazards
  • Increasing exposure to organic pollutants

Pathways

Non-native species travel through different routes and by different means. Many species enter the United States through planned shipments of plants and animals for agriculture, horticulture, forestry, fisheries and aquaculture and other purposes. Occasionally, otherwise beneficial species have become invasive, leading to unintended adverse impacts.

Many invasive species were introduced unintentionally, hidden in shipments of cargo, burrowed into wood imported from other countries, hitchhiking on and in boats and ocean-going ships, transported with ornamental plants, and as parasites and diseases of other species. 

Preventing Invasive Species

In some cases, people are not aware of the risks when non-native companion animals and water garden plants are not properly contained. Taking steps to prevent the release or escape is important to reduce the potential risks posed by non-native  plants and companion animals.

  • Research your pet’s size and behavior to determine the appropriate enclosure.
  • Invest in a habitat that is secure and sturdy to minimize the chance of escape.
  • Feature native or non-invasive plants in your water garden.
  • Plan your water garden to prevent flooding into natural lakes, streams, and wetlands.

A key step is learning about invasive species in your area. Some species are invasive in parts of the United States but cannot survive in other areas. State fish and wildlife agencies, natural resource agencies and agriculture departments have websites with information about invasive or nuisance species; many of these sites list non-native species that may be restricted or prohibited.

An important invasive species pathway is the intentional release of non-native plants or animals by a well-meaning pet owner or gardener. Every so often pet owners find themselves unable to continue caring for their animal, despite their best intentions. Fortunately, there are others who share your commitment to caring for pets and the environment. Check the Finding a New Home for Your Pet page for possibilities.

For more information about collaborative efforts to prevent invasive species:

Examples of Invasive Species

For examples of  different invasive species, click here.