Photo: AP Photo/J Pat Carter

The Western Governors’ Association published its first-ever list of the 50 worst invasive species inhabiting that region of the country on Thursday, and some of the culprits may surprise you.

Meant to help better address regional risks and aid people recognizing and eradicating invaders early on, the list includes 25 terrestrial and 25 aquatic species. Some are more familiar like feral hogs and fire ants, while others like the rusty crayfish and New Zealand mudsnail have less notoriety. Then there’s a few surprises, like feral cats and the American bullfrog (doesn’t sound very invasive).

Kierán Suckling, Executive Director of the Center for Biological Diversity, told Earther the report should help galvanize coordinated cross-state efforts and funding to keep them under control.

Suckling, who wasn’t involved in the release, said invasive species are definitely increasing in number, which he attributed primarily to four factors: habitat degradation, human population growth, globalization, and climate change.

According to The Nature Conservancy, invasive species have contributed directly to the decline of over 40 percent of the United States’ threatened and endangered species, with invasive plants inhabiting an area around the size of California. In the U.S. alone they cause an estimated $120 billion a year in damage to the economy.

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To arrive at these 50 offenders, the WGA worked with invasive species coordinators in states across the West, which already typically have their eye on harmful invasive species in their home states.

“Western governors have said the spread of invasive species is one of the greatest risks to the Western environment,” Bill Whitacre, the association’s policy adviser for public lands and agriculture, told Earther.

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For instance, Whitacre said, feral cats—the descendants of house cats that have now adapted to life in the wild—have a huge impact on bird species. A 2016 analysis found that worldwide, feral cats have driven over 60 species to extinction over the past 500 years—only rodents have caused more mayhem. It’s estimated that cats kill over a billion birds a year nowadays.

“Species that have the greatest potential range, and can thrive in the largest variety of ecosystems, are a high concern at a regional level,” said Whitacre. “These include cheatgrass, invasive carp, and the emerald ash borer.”

A number of invasive species arrived as a result of international trade, according to the Nature Conservancy. For instance, the emerald ash borer beetle and Dutch elm disease, both devastating tree killers, are invaders from abroad. The former from China and the latter from Europe.

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Quagga and zebra mussels are an especially taxing issue for many conservationists these days as they spread across the country, clogging machinery and pipes, throwing food chains out of balance, and creating costly cleanup sites. The problem has gotten so severe that the U.S. government is currently offering a $100,000 prize for the best idea of how to stop their spread.

Announced in February, Sherri Pucherelli, a biologist with the U.S. Bureau of Reclamation, told the AP that “we might as well give it a try...nothing has been developed right now that causes complete eradication in a large water body.”

According to U.S. News & World Report, “the species are native to Russia and Ukraine, and are believed to have arrived in the U.S. in the 1980s aboard ships that released ballast water into the Great Lakes.”

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“Quagga and zebra mussels have become established in the lower Colorado River, causing major ecological and environmental impacts to the states with infested waters,” said Whitacre. “It is a high priority of the Western Governors to keep these invaders out of the Columbia River basin—the last major un-infested water system in the West.”

These mussels are increasingly threatening treasured outdoors areas, including Glacier National Park and Yellowstone National Park. Yellowstone National Park recently banned felt-soled wading boots to help stave off any contamination.

Zebra mussels
Image: USFWS

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Suckling said he wasn’t surprised that the report was tilted towards impacts to ranching, farming, and water infrastructure.

“This is not surprising as 90 percent of all money to fight invasive species is done for economic reasons, not environmental reasons...control efforts target less than five percent of all nonnative species and the vast majority of the work and funding is for economic, not ecological reasons,” he said.

Suckling said the biggest-problem endangered species on the list are the white nose fungus, the American bull frog, the Western mosquito fish, and the rusty crayfish. He also said he was surprised that bufflegrass, cowbirds, and chytrid fungus didn’t make the list.

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“Bufflegrass is devastating large swaths of the Sonoran Desert,” he said. “Cowbirds kill many endangered birds.”

And then there’s chytrid fungus—the greatest single cause of invasive-driven extinctions globally, according to Suckling. “It is wiping out amphibians all over the world, especially North and South America,” he said.

Suckling suggested making international shippers, the livestock industry, agribusiness, and the pet trade contribute more financially to the cause of dealing with invasive species. He also supports much tighter controls on the legal importation of invasive species, especially reptiles and amphibians.

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But the most important thing to do is to prioritize keeping ecosystems intact and restoring degraded areas. “This is the cheapest, most effective way to blunt invasive species and keep native species at healthy numbers,” he said.

Many of the invasive species have been around for decades, if not centuries. For instance, the tamarisk, also known as the salt cedar, was introduced from Russia and China around 200 years ago in part as a good tree to protect against strong winds. In the early part of the 20th century it was used to fight soil erosion across the Great Plains. Now, in the early 21st century, it’s best known for having a voracious appetite for water, for increasing soil salinity, and for posing a fire danger. Today, it may cover close to one million acres of the western United States.

In California’s Los Padres National Forest the U.S. Forest Service is working on a removal project for the tree that involves a tamarisk-eating beetle also native to China and Russia.

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Sometimes it takes one to know one.

Update: A previous version of this post included a statement from an outside source that was not properly attributed. The text has been updated to clarify the source of the language and properly attribute it.