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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.

Non-native species are plants and animals living in areas where they do not naturally exist. "Non-native species" and "invasive species" can not be used interchangeably. Many commonly grown fruits and vegetables are not native to the U.S. For example, tomatoes and hot peppers originated from South America, while lettuce was first grown by the Egyptians. Domestic cows are non-native to North America and were introduced as a food source, and considered to be a beneficial organism in an agricultural setting.

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 are spread primarily by human activities, often unintended. People, and goods transported, travel quickly around the world, and often carry uninvited species with them. Invasive species can be introduced to an area by ship ballast water, firewood, accidental release, and by people. Insects can be transported easily in wood, shipping palettes, and crates shipped across the globe. Ornamental plants can become invasive after escaping in the wild. Released unwanted pets are another way invasive species are spread. See our pathways information to learn more about how invasive species are introduced to new areas.

What are the Impacts of Invasive Species?

The introduction and establishment of invasive species to the U.S. (intentional or unintentional) can pose a significant threat to native and plant communities. 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.