I t's said that a weed is a plant that grows where you don't want it.
Most invasive species live in balance in their native environments.
But imported into a locale where they have no natural controls, their populations can explode. Through competition for food, light or shelter, or by bringing new diseases, they can destroy the ecological balance of their new home, wiping out native populations. And viral and microbial invasions are common human health problems. Invasive Species Program of the U.S. Fish and Wildlife Service. Basic information and links to national strategy for management, impact on public lands, education, outreach, control.