For a species (plan, animal or microbe) to be considered invasive, it must be non-native to the region and capable of causing harm to the environment economy or human health.
When an organism is transported (whether accidentally, intentionally or naturally) outside of its native range it can experience less predation and disease pressure.
Disturbed areas such as right-of-ways, croplands and developments create opportunities for non-native species to rapidly populate areas without competition from native organisms.
Several species from Northern Europe began arriving into North America with the first settlers in the mid-1500s. Worldwide trade, travel and immigration create pathways for intentional and accidental introductions.
Invasive species and habitat destruction are the leading causes of animal/plant endangerment and extinction. The cost of invasive species control can exceed land values in many areas.