Don’t Kill That Bug Yet. Some Scientists Want to Rethink the War on Invasive Species

Each year, approximately $34 billion dollars are spent in the global war on invasive species.

Those billions fund a range of control measures, including publicity campaigns that urge residents to stomp on spotted lantern flies, inspection at airports or waterways that catch non-native species being transported by humans, and herbicides, fungicides, insecticides and other chemical means of eradicating unwanted species from ecosystems.

To most biologists, these costs are largely worth it. Apart from control measures, invasive species cost the global economy more than $389 billion by harming food security, human health and contributing to 60% of global extinctions, according to a recent report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, or IPBES. The 86 authors of that report argue the world needs to do more to combat the growing toll these newcomers exact on ecosystems.

But a small yet vocal minority of biologists contend this war on invasive species is misguided, inconsistent and even immoral. They question the scientific merits of “nativeness,” and argue that many introduced species have positive benefits that are often overlooked. Some say that the whole enterprise is unethical, as it grants the imprimatur of science to the mass killing of creatures whose only fault is living in the increasingly interconnected world we’ve built.

Perspectives within this minority vary, but most agree that we need to rethink our approach to invasive species, and cool down the often militaristic rhetoric, even as the number of disruptive new introductions accelerates.

“I think it's a much more complex, complicated, and difficult problem than it's commonly made out to be,” said Matthew Chew, a biologist at Arizona State University. “These things are here because of everything we do. Just trying to stomp on them all when you encounter them... strikes me as absurd.”

Others disagree, arguing that current approaches acknowledge that complexity, and that the obvious negative impacts of many invasive species largely outweigh potential benefits. 

“Different values and perspectives are phenomenally important to account for when making decisions, as is ensuring that people are using the best available evidence,” said Helen Roy, an ecologist at the UK Centre for Ecology and Hydrology and co-author of the IPBES report. “There’s no doubt that invasive alien species are a major threat to biodiversity and ecosystems. We need to all be working together to address these environmental challenges.”

The debate highlights growing tensions over what counts as native and worthy of preservation in a rapidly changing world. Most agree that many introduced species are very harmful and we should try to mitigate their impact, but disagreement arises over just how far humans should go to undo the changes we’ve made.

The often blurry line between native and non-native

Critics of mainstream invasion biology argue that it fosters black and white thinking: species are either good (native) or bad (invasive). Which side they fall on depends on their "nativeness" to an area, a concept that isn’t always clear-cut.

The IPBES defines native species as “Indigenous species of animals or plants that naturally occur in a given region or ecosystem.” Throw a new species into the mix and it can disrupt how things have come, over centuries or millennia, to work in that particular place.

Invasion biologists generally work to keep the status quo intact by removing alien species that throw things off.

But the history of life is all about change. “Unless you happened to evolve in that particular place, everything arrived there at some point,” said Mark Davis, an ecologist at Macalester College. “It’s just that some arrived a lot longer ago than others.”

Biological invasions are typically defined as facilitated by humans, not animals naturally arriving to a new place. But our increasingly interconnected world of travel and trade has accelerated this mixing, introducing about 200 new species each year. 

Drawing the line for immediate newcomers is conceptually straightforward. Last month, Georgia officials were on alert after the yellow-legged hornet —an insect native to Asia that can kill honey bees in midair— was spotted for the first time in the United States. Given that it has never been here before, the alien designation seems warranted. 

But it becomes less clear for species that have been around for a while. 

“Once upon a time, non-natives were viewed by the Western world as the best thing since sliced bread,” said Dov Sax, an ecologist at Brown University. “Organizations all around the British Empire and the United States were trying their level best to introduce as many useful non-natives as they could.”

In the United States, these species include crops that have become American fixtures, ranging from apples and peaches to soybean and barley. Other creatures introduced within the last couple centuries include starlings and horses. Before that, Indigenous people moved crops to new areas across North America.

“The world is dynamic, it’s really unclear where you should go back and draw a line between what’s native and what’s not,” said Chew. He sees the concept of nativeness more as a social metaphor than grounded in biological reality. “The term is loaded with ideas about belonging and rights of prior occupation,” he said.

Those ideas are fine to have, critics say, but shouldn’t be confused with scientific facts. 

“A lot of invasion biologists have a worldview that things should be the way they were, that it’s important for ecosystems to be pristine or historical,” said Sax. “I’m not saying they should or shouldn’t be, but that’s a world view, not a scientific view,” he said. An alternate view might be to value ecosystems that are more productive or beneficial to humans.

Ideas about what sort of nature should be valued can shape thinking on introduced species, and influence the sorts of questions that scientists ask when evaluating our changing world.

“Science can tell you what changes occur,” said Sax. “But whether that change is good or bad is really in the eye of the beholder.”

Costs and benefits of invasives

A central focus of invasion biology is to study how invasive species impact an ecosystem. Since invasive species are defined as newcomers with negative effects, some scientists argue that potential benefits of introduced species —like providing food, boosting soil health or controlling pests — are often ignored or underemphasized.

“Some non-natives are incredibly harmful, and I think we should try to prevent those harms,” said Sax. “But I think most non-natives have various benefits and various costs, and it’s not at all clear to me that on average, the net effects are negative.” 

Take wild horses and donkeys, which arrived in North America within the last 500 years. These species are often vilified in the west for trampling vegetation, eroding creek beds and competing with native elk and antelope. Decades of data demonstrate these real harms, but more recent research suggests the equids can benefit ecosystems too, for example by digging wells that can act as desert oases used by other critters. 

Invasive species can come to be culturally valued, too. The dingo, Australia’s wild dog, was introduced to the continent around 4,000 years ago, likely via human boats. Over time, dingoes became enmeshed in Aboriginal mythology and cultural practices. Some research suggests they help control feral cats, more recent arrivals that threaten Australia’s unique marsupial species. Efforts to remove dingoes in the name of conservation could end up doing more harm than good, some researchers argue.

Newcomers can benefit humans as well. Earthworms native to northern North America were wiped out by glaciers during the last Ice Age. Since then, humans have reintroduced the worms to many regions, significantly boosting soil health by recycling and mixing nutrients.

“They pump up productivity for organic agriculture by close to 30 percent,” said Sax, “but conservation biologists view them as invasive species because of their impact on forests.” Those ecosystems evolved without earthworms after the glaciers receded, and throwing them back into the mix can harm native insects and other invertebrates.

To Sax, these potential benefits — to people or ecosystems — aren’t given proper weight or study in evaluating non-native species. That lopsided data colors both scientists and the public’s thinking on invasive species.

The recent IPBES report does assess the positive impacts of invasive species, but found that only 15% of quantified impacts were positive. 

“Invasion biologists have acknowledged from the very beginning that there can be some benefits to invasive species,” said Laura Meyerson, an ecologist at the University of Rhode Island and IPBES report co-author. “But those benefits don’t offset or mitigate those negative impacts.” 

Sax and other critics suggest that invasion biologists are often predisposed to studying the negative effects over positive effects, resulting in biased data. But Meyerson, whose own work has documented how an invasive plant called phragmites removes heavy metals from marshes, disagrees with that analysis. “The data are incomplete across the board,” she said, suggesting many harms likely go undocumented too.

Better data on both sides of the ledger would still force conservationists to make tough choices. For many species, the harms would likely still outweigh benefits, said Sax. But for others, he thinks a more nuanced picture could lead to gentler approaches to dealing with new species. For example, if an invasive plant happens to do a better job at storing climate-warming carbon or boosting ecosystem productivity, perhaps managers should take a more relaxed approach, rather than spraying the plants with herbicides. 

“There’s a lot of money being spent on controlling invasive species,” said Sax. Given eradication or control efforts often fail, “some of that money might be better spent conserving more land or bolstering endangered species,” he said.

A problem of framing

Critics of invasion biology argue that the militaristic language of the field itself is problematic. The centrality of terms like “invasion” and “alien” put biologists and the public in a warlike, us-versus-them mindset, critics told The Messenger.

“The coverage reminds me of how an outlet like Fox News might cover human immigrants coming from South America to the U.S.,” said Sax. “They talk about ‘invasions’ and the real harm being caused by these people, but they don’t mention the benefits,” he said. 

When invasive species are talked about in a similar way, “it’s really powerful framing that can elicit an emotional reaction,” said Sax. Describe a species as an invader and “your reaction is going to be, well we’d better do something about that,” he said.

That something often involves killing. 

“I think a major flaw of this approach is that it tends to make people cruel and ruthless,” said Arian Wallach, an ecologist at the Queensland University of Technology. In the name of protecting native species, the U.S. government poisoned over one million invasive starlings in 2022. Invasive rats, which are driving many island birds towards extinction, get killed by the millions in countries including New Zealand. 

Wallach is a proponent of “compassionate conservation,” a field which seeks to treat all wildlife with respect and compassion, native or not. “In my view, life is life, right in its various forms and I am unconvinced by the arguments made by invasion biologists that I should only value or care about some forms,” she said. 

Compassionate conservationists try to save species in ways that don’t involve humans killing animals. One approach Wallach herself studies involves managing top-predator populations, like dingoes in Australia or coyotes in the U.S., to act as natural checks on invasive species.

Such an approach is controversial among many conservation biologists, who argue tough choices have to be made to save species on the brink of extinction. 

“I don’t know a single invasion biologist who would ever take pleasure in killing anything,” said Meyerson, who also agrees that the militaristic language of the field could be toned down. 

To Meyerson and many other biologists, the enormity of the problem necessitates valuing different species differently. Invasive species are among the top five drivers of biodiversity loss, and were solely responsible for the demise of 16% of recorded extinctions, the IPBES report found, often on islands.

“We’re working really hard to find alternative ways to manage species ethically,” said Meyerson. “But if you’re watching ground-nesting bird chicks being eaten alive by rats, wiping out a species that could be gone forever, you have to make a difficult choice,” she said. “It’s sad and it’s hard, but that’s where we are.”