An invasive species is a species that is capable of surviving without human aid and of existing in natural areas. Although most introduced species are not invasive, and only a fraction of these are ecological pests, biological invasion is the second leading threat to the preservation of global biodiversity. Only habitat loss and destruction have a larger impact on our native flora and fauna. Some notorious invasive species in the United States are zebra mussel, sea lamprey, cheatgrass, purple loosestrife, melaleuca, kudzu, hydrilla, diffuse knapweed, and water hyacinth. Exotic species can outcompete, parasitize, and prey upon native species.
Some invasive species pose threats to human health, agriculture, industry, and recreation.
The economic loss in the United States due to invasive species exceeds hundreds of millions of dollars annually. Because of the economic and ecological impact of invasive species, considerable efforts have been undertaken to control these species. Research to understand the ecology of these species and to manage for them is ongoing. With the continuation towards a world trade market and without a change in strategy to regulate the importation of species, it is probable that the ecological and economic impacts of invasive species will continue to rise. Biological Control Classic biological control is the use of natural enemies to reduce the spread or impact of an invasive species.