There are thousands of non-native species in the United States, many of them invasive. The National Invasive Species Council provides information on invasive plants, animals, and aquatic species, as well as state-by-state information. Below are just two examples of the more than 6000 invasive species causing harm in the United States.
While some potentially invasive species have been kept at bay, countless others have found their way into the United States where they are causing extensive ecological and environmental harm.
The Northern snakehead fish (Channa argus), native to Asia, was discovered in a lake in Maryland in 2002. Likely to have been released from fish markets, the species has been found in a number of areas from Boston to Atlanta, as well other local spots. Some species of snakeheads, including the northern, can move short distances across land and live out of water for up to three days. Officials fear this predator could move into other waterways and decimate a host of native species. Shortly thereafter (2002) it was listed as Injurious Wildlife, meaning that a permit is needed for trade and transport of this species.
West Nile virus is a mosquito-borne illness that first appeared in New York State in 1999, probably on legally or illegally imported birds. Since that time, it has spread explosively across the United States, Canada, Mexico, and Caribbean islands. In the 16 years since its introduction, over 41,000 cases of human illness have been documented, including more than 1,700 deaths. Many native bird species are highly susceptible to the virus. Infecting more than 100 bird species, actual mortality is difficult to assess. Other wildlife and horses are also affected and many species are extremely susceptible to the virus. Its long-term impact on human and animal populations is not known.
Keeping them out
Through diligence, attention, and costly efforts, a few likely invasive species are being held at bay, although it is a constant battle.
The brown tree snake (Boiga irregularis) caused an alarming number of bird extinctions when it was introduced to the once snake-free island of Guam during World War II. If brown tree snakes become established in Hawaii, many endemic birds will likely disappear. The snake is particularly adept at stowing away on planes—a number have been found hidden away in landing gear after trans-Pacific flights. Ongoing efforts to prevent snakes from leaving Guam and from entering Hawaii have so far been successful.
The citrus long-horned beetles (Anoplophora chinensis) has the potential to cause extensive damage to commercial fruit trees and native forests. The species is known to attack citrus trees, as well as pecan, peach, apple, pear, cherry, and mulberry trees. It also attacks native forest trees such as sycamore, maple, oak, ash, elm and walnut. Similar to the better-known Asian long-horned beetle, the boring larvae cause extensive damage, leading to tree decline and death.
Native to China and nearby areas, since 2001 it has been found in Georgia, Wisconsin, and Washington, thought to be brought in on live plants or in wooden packing materials. Fortunately, those introduced populations were exterminated through quick action.