What is an Invasive Species

On February 3, 1999, President Bill Clinton signed Executive Order 13112, on Invasive Species. The order defines an invasive species as an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.

There are hundreds of invasive species that have found their way into the United States since Colonial times, affecting every region of the country, and both aquatic and terrestrial ecosystems. Invasive species can be plants, animals, or disease organisms.  A species that can be relatively benign in one environment, typically in its native habitat, can go wildly out of control exhibiting invasive characteristics in an environment where it is not native. Not every alien species turns out to be invasive, so risk assessment is an important tool in anticipating and getting out ahead of potential invasive species introductions.  Photos and short narratives about some of the higher profile invasive species are featured here.