Even the most pernicious invasive species have a native home range where they usually do not cause harm. Often species are held in balance in their native range by their relationships with other species, such as predators, competition for food, diseases, or limited habitat. Some species, when moved to a new location outside their native ecosystem, can take advantage of their new environment to quickly spread and become invasive.

Sometimes, a species can be native in one part of a state and invasive in another part, as is the case for several species tracked by the Pennsylvania iMapInvasives program. Invasiveness is also a subjective term, and some species may be considered invasive by some organizations and not by others.