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National Invasive Species Information Center
U.S. Department of Agriculture
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What are Invasive Species?

Invasive species the basics

Provides the official definition for what are invasive species and related information.

Invasive species can be plants, animals, and other living organisms (e.g., microbes). To learn more, see our Species Profiles which provides general information about species considered to be invasive.

View related information: Resource Search - Invasive Species 101

What Defines an Invasive Species?

As per Executive Order 13112 (Section 1. Definitions) an "invasive species" is a species that is:

1) non-native (or alien) to the ecosystem under consideration and,

2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

See also:

  • Invasive Species Definition Clarification and Guidance White Paper
    This white paper provides a non-regulatory policy interpretation of the term "invasive species." Submitted by the Definitions Subcommittee of the Invasive Species Advisory Committee (ISAC) and approved by ISAC on April 27, 2006.
  • Invasive Species Terminology: Standardizing for Stakeholder Education
    Iannone, B. V., Carnevale, S., Main, M. B., Hill, J. E., McConnell, J. B., Johnson, S. A., Enloe, S. F., Andreu, M., Bell, E. C., Cuda, J. P., & Baker, S. M. (2021). Invasive Species Terminology: Standardizing for Stakeholder Education. The Journal of Extension, 58(3), Article 27.
    This paper from the Journal of Extension has practical applications for any firewood and forest pest-related communicators.

How do Invasive Species Spread?

Invasive species can be introduced to an area by ship ballast water, firewood, accidental release, and by people. Human actions are the primary means of invasive species introductions. See our pathways information to learn more about how invasive species are introduced to new areas.

What are the Impacts of Invasive Species?

Invasive species can lead to the extinction of native plants and animals, destroy biodiversity, and permanently alter habitats. See our impacts section to learn more about the various impacts of invasive species -- economic and social, environmental and ecological, and human health.