Invasive species are the second greatest threat to biodiversity
after habitat loss. Plants and animal species are introduced
into new environments through many different pathways, but human
actions (both intentional and unintentional) are often the
cause. Some plant species, such as kudzu, are considered
ornamental, and are brought in new areas and planted by humans.
Other species, such as fish, are often transported as sources of
food or to be kept as pets. Some species "hitch a ride" from
their native lands as human-created transportation systems move
cargo from one geographic location to another. People who
intentionally release non-native species into new ecosystems are
often unaware of the consequences that could result, but
introduced species can be a grave threat to ecosystem stability.
One of the newest "foreign invaders" in the United States is the
northern snakehead fish (channa argus). Native to China, Russia,
and Korea, the northern snakehead was first reported in the
United States in 1977, when i