Investigating the Financial Costs of Invasive Species

Economic costs of biological invasions in the United Kingdom (2021) Cuthbert et al., NeoBiota,

The Crux

I write near constantly about non-native species on Ecology for the Masses, but I mainly focus on the negative impacts that many of them have on native ecosystems. Yet often if we want to really kick off initiatives to manage invasive non-native species, we need to point out the financial burden that many of them bring.

Yet obtaining a simple monetary estimate for invasive species is not easy. A few particularly notorious invasives tend to take up a lot of research focus, which mean that there are many species out there for which our cost estimates could be unreliable. Likewise, we’re likely to have a better picture of the impact of non-native species which have been established longer than ones who have just arrived, and haven’t been sufficiently studied or haven’t spread far enough to have had a measurable impact.

But non-native species aren’t slowing down in their spread anytime soon, so it’s important to figure out what the costs of invasive non-native have been and will be, as well as where there are holes in our knowledge that need to be filled. That’s what today’s study set out to do, by looking at invasive species in the United Kingdom.

What They Did

The researchers used InvaCost, an online tool which records cost analyses for invasive species-related projects. The cost analysis had to be exclusively attributed to an invasive species, which in this case was defined as a non-native species that caused some economic cost. The costs were calculated on a yearly basis from 1976 (first year with a record) to 2019, so if a project took £100,000 over ten years, £10,000 was attributed to each year.

The researchers also broke the costs up into separate categories, including which taxa the relevant species belonged to, which sector the species impacted, and where in the UK the invasion took place. They also investigated the relationship between the length of time a species had bee established in the UK and the total costs that species had racked up.

Did You Know: Invasive Minority

While non-native species are often thought of in a negative light, most newcomers have very little impact on their surroundings. Many ecologists use the term ‘invasive’ to indicate a negative effect, although both terms carry their own implications and complications. I was fortunate enough to speak to Professor Helen Roy at the end of 2019, who pointed out that of the UK’s invasive species, only about 15% are causing any kind of problems. Knowing which ones helps put resources in the right place.

What They Found

The UK incurred between 6.9 and 17.6 billion USD worth of damage (maybe mention why there is such a large range in that estimate?) between 1976 and 2019. The vast majority of these costs were a product of animals species (~65%) was caused by animals, mostly mammals and insects. Plants made up almost all of the rest, with fungi making up a small portion of the total costs. The agricultural sector took up 4.9 billion USD.

While there are over 520 non-native species in the UK listed as invasive in 4 separate databases, only 56 of these turned up in any capacity in InvaCost. Together, mammals, insects, birds and magnolias make up 60% of the total. The actual costs as attributed to species were heavily lopsided, with Japanese knotweed making up 62% of the money spent on species management, and the European rabbit making up 82% of the money lost to environmental damage.

Lastly, there was a fairly linear relationship between time since establishment and total costs. The longer a species is established, the more expensive it turns out to be.

Plant from the magnolia family make up 16% of the invasive species with reported costs in the UK (Image Credit: elPadawan, CC BY-SA 2.0)


Early on in this study’s results, they give their ‘confidence interval’ for the economic costs – the numbers between which they are confident the actual cost lies. They then go on to use the most conservative estimate for the rest of the figures. While I understand the desire to play it safe, giving the upper limit would have been a good idea as well, seeing as the policy makers who may read this paper could easily only take away the lower estimate, and vastly underestimate how damaging hese species could be.

So What?

There is a stark, simple message to this paper – invasive species cost the UK a lot of money. These costs rise every year, as invasive species establish themselves further, and as more turn up. This is a trend that is obviously not limited to the UK, with many other countries publishing similar research recently.

Unfortunately once a species is established it is VERY difficult to completely eradicate. And while an ounce of prevention is still better than a pound of cure, globalisation means that species continue to flow around the globe at ever-increasing rates.

As defeatist as that may see, studies like this are very effective in pointing out areas where we need to focus research in the future. The fact that only around 10% of the UK’s invasive species turn up in InvaCost should be setting off alarm bells.

Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology and would gladly see Norway’s oil fund dedicated solely to the elimination of the common ragweed (it triggers his hayfever). You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.

Title Image Credit: Waldemar Zielinski, Pixabay licence, Image Cropped

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