Thousands of invaders could qualify for listing. Narrowing it down to 100 is difficult and the Oregon Invasive Species Council updates the list yearly. To be added to Oregon’s 100 Worst list of invasive species, the invader must be non-native to Oregon and absent from the state or limited to a small, contained range within the state; and pose a greater threat than something already listed.

In creating this list, the Oregon Invasive Species Council weighs factors such as:

  • the risk to human health 
  • the impact of the species in habitats similar to those found in Oregon
  • the likeliness of the species to cause significant economic loss
  • the difficulty other regions have had eradicating the invader
  • the capacity for the species to spread in Oregon

2014 Oregon Invasive Species Council's 100 Worst List  (pdf)