Each kind of plant or animal (each species) has a place of origin, although its range (where it is found) may be more extensive. A species is considered native or indigenous in the place where it has lived the longest. There are two ways that species can move to new areas, and when they do that they are considered adventive (new to a place). A species becomes adventive by immigrating of its own accord or by being deliberately introduced (moved) by people.

Immigration is a natural process, and it allows plants and animals to colonize new areas. Some immigrant species extend their range slowly. For example, the love bug, which is erroneously thought by many to have been deliberately introduced into Florida, naturally extended its range from Central America and Mexico, arriving in Florida of its own accord in 1949. Others may be moved to a new place during one event, such as by being blown in on a hurricane or by hitchhiking on cargo moved by people.

Either adventive or native species may be invasive if they extend their range. Exotic species are those that are not native to an area, whether they are actually found there or not. Many exotic species, both plants and animals, have become invasive in the U.S. by becoming permanently established in new areas (in which case they are then considered adventive). Increasing commerce and transportation have provided opportunities for exotic species to enter the country in a number of ways, including being imported (ornamental plants and pets, especially reptiles and amphibians) and coming in on imported plants or on food items smuggled through airports (insects). Movement of people and goods has aided the spread of many of our worst pests, both plants and insects. Even if only a small percentage of the entering exotic species later become pests, the economic impact is heavy.

Florida is particularly susceptible to the establishment of invasive, exotic species, given the state's mild climate and the large number of plants that are shipped through the port of Miami annually. Each year, more than 300 million plants are shipped into Florida, which receives about 80% of U.S. plant imports. USDA -APHIS plant inspectors have intercepted over 18,000 immigrant insects on the plants they inspected in a single year. Less than 2% of imported shipments are inspected, providing a great opportunity for insect stowaways.