Many fare poorly when introduced to a new environment, but some thrive when freed from native competitors, predators, and diseases. Left unchecked, they can transform entire ecosystems and out-compete or consume native species to the point of extinction.

Invasive species are a harmful subset of so-called exotic, alien, non-native, or introduced species, and are one of the most serious global environmental challenges we face.

An ever-increasing number of new invasions

They are not a new phenomenon, but the increasing globalization of our economy, with its extensive travel and shipment of goods, brings an ever-increasing number of new invasions. In the United States alone, scientists estimate that about 7,000 invasive species of plants, mammals, birds, amphibians, reptiles, fish, arthropods, and mollusks are established. Consider this:

• The northern snakehead fish (Channa argus), an Asian native, was discovered in a lake in Maryland in 2002. Some species of snakeheads, including the northern, can move short distances across land and live out of water for three days. Officials feared this predator could move into other waterways and decimate a host of other species.

• A series of aquatic invaders in the Great Lakes -- including the sea lamprey, rusty crayfish, and zebra mussel -- has caused catastrophic declines in populations of native species; introduced new parasites and diseases; and changed the way ecosystems function in this, the world's largest freshwater resource.

More progress needed

Invasive species cost billions of dollars annually in damage and control measures. Zebra mussels alone were estimated to have cost the United States $750 million to $1 billion from 1989 to 2000. Current US laws and government programs are insufficient to guard against further introductions or control invasives that are already here. Whole categories of organisms are imported without regard for their potential invasiveness.

There has, however, been progress. Invasive species have gained new prominence in federal and state policy, and there is more cooperation among government agencies, trade organizations, and environmental groups. Thanks to scientists' lobbying, the United States now has an interagency National Invasive Species Council (NISC), a National Management Plan, a Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW), and a federal Aquatic Nuisance Species Task Force. Moreover, some states are strengthening their own invasives laws, regulations, or policies instead of awaiting stronger federal action.

Work with us to preserve native ecosystems and species

At UCS, we are striving to substantially reduce the introduction and spread of harmful invasive species in the US and to decrease their impacts on native ecosystems and biodiversity. Specifically, we are working to:

• Ensure reauthorization of the National Invasive Species Act (NISA) as the National Aquatic Invasive Species Act (NAISA), with stronger and broader provisions than in the 1996 version of the law.

• Draw more attention to the need to screen intentionally imported species and to the most egregious pathways of introduction for those species that we bring here unintentionally.

• Help environmental groups -- including our own -- to "Do No Harm" by pledging not to distribute or promote invasive species through institutional practices, such as fundraising, membership work, publications, or promotional items.

We collaborate with some of the world's most prominent scientists and several other environmental groups to achieve our goals. A key resource is our Sound Science Initiative (SSI), a quick-response electronic network of ~3,000 scientists, including more than 300 with expertise in invasive species. Working with UCS, SSI scientists have opportunities to provide the media, policymakers, and the public with timely, authoritative input on invasive species and related biological diversity issues.

We look forward to significant policy gains, and invite you to join us in our efforts: browse our site, learn what you can do, visit the UCS Action Center, and, if you are a scientist, visit the Sound Science Initiative page.