Invasive Species: Oregon’s 10 Least Wanted

Zebra Mussels

Invasive species cost the state $81 million each year, according to the Oregon Department of Agriculture (ODA). Some, like the bullfrog, were introduced intentionally. Others were accidents. These invaders displace native species and disrupt the ecosystem in unpredictable ways. Their success comes from a lack of natural predators, a prolific nature, and the ability to adapt to a wide variety of environments. Some are just plain hard to kill.


Another factor on the side of invasive species is a slow response time. States are reluctant to place money into researching the potential effects of invasive species–until the damage occurs, when it’s too late.


“It’s very poorly invested in,” said John Chapman of the Hatfield Marine Science Center and the Department of Fisheries & Wildlife at OSU. “We only react after the homicidal killer has done its thing.”


Below are 10 species that are definitely not wanted in Oregon:



Originally raised in Oregon for their fur, nutria are found today throughout the western part of the state. These 10- to 20-pound aquatic rodents displace native muskrats and damage crops such as alfalfa and corn. Nutria are also capable of destroying huge areas of marshland. They burrow into fragile root systems and devour vegetation, making marshes susceptible to erosion.


Himalayan Blackberry

It’s hard not to delight in blackberries–right? However, the Himalayan blackberry is one of the most tenacious invaders. This spiked, trailing plant can grow 20 feet in one season, displacing native plant species and dominating areas near rivers and streams. The ODA calls it “the most widespread and economically disruptive of all the noxious weeds in western Oregon.”


Worse, “Any control strategy can be considered short-lived unless projects are planned and funded for the long-term,” reports the ODA website.


American Bullfrog

It’s partly our own fault that bullfrogs are everywhere. The state introduced bullfrogs as a game species during the 1930s, when they featured on restaurant menus.

Bullfrogs breed prolifically; females can lay as many as 20,000 eggs, about four times as many eggs as our native frogs. They eat basically anything living that fits into their mouths.  They’re responsible for declines in numerous native species, including the western pond turtle and the Oregon spotted frog. Both of these species are classified as vulnerable; the latter is now locally extinct in the Willamette Valley.


Tansy Ragwort

Deemed “noxious” in Oregon for its impact on pastures, the tansy ragwort was originally introduced for its medicinal qualities. However, it’s toxic to cattle, horses, and other livestock and has caused millions of dollars in damages. Today, it’s an example of successful biological control. Cinnabar moths and ragwort flea beetles were released to control the tansy’s spread; no further livestock poisonings have been reported since the 90s.


Snapping Turtle

Found in muddy ponds and lakes throughout the Willamette Valley, the snapping turtle is a large, aggressive turtle named for its powerful bite. Native to the eastern United States, it out-competes other species of turtles for habitat and food–plus it’s introduced them to new diseases and parasites. These turtles can reach 18 inches in length, and eat everything from other turtles to ducks and frogs.


Purple Loosestrife

The purple loosestrife has gorgeous purple flowers and is known as a garden ornamental. However, a small cluster of this noxious weed can grow to cover a marsh in a single season. This densely growing plant crowds out native marsh plants such as cattails and sedges. Worse, it provides no useful food or habitat for native wildlife, so biodiversity is reduced wherever it’s found–and no county in the Willamette Valley is free of it.


Three Invaders from Japan

The tsunami brought another host of potential invaders in the form of the 66-foot-long dock that washed ashore in Newport carrying almost 100 species. Many of these were near-shore species carried all the way from Japan. According to Chapman, this was an unprecedented event. Three of the finds right away had biologists worried: a brown algae used in miso soup, the northern Pacific sea star, and the Asian shore crab. All have the potential to spread quickly and upset the delicate balance of Oregon’s coastal ecosystem.

“We found all three of those right away on the float,” said Chapman, who likened the debris to a dirty needle in the ecosystem. “The northern sea star was introduced into Tasmania and had a huge population explosion there.”


Zebra Mussel

The freshwater zebra mussel has not yet invaded Oregon–but the state is on red alert. Zebra mussels take over entire lake bottoms and are almost impossible to eradicate. They clog intake pipes and could be potentially devastating to Oregon’s hydroelectric facilities. Initial control measures could cost as much as $24 million at the Columbia River Basin’s hydroelectric plants. Already, they have been intercepted on boats traveling into the basin.

“There’s a huge investment to stop it from spreading and it continues to spread. There’s no evidence they’re going to stop it,” said Chapman.


For more info or to report an invasive species, call the Invasive Species Hotline at 1-866-INVADER (1-866-468-2337).


By Jen Matteis