An 8.5mm striped beetle. A 4mm mosquito. A 25mm hornet. These critters are tiny, but they pack a mighty punch when it comes to economic costs. The damage these organisms and their ilk are inflicting on regions around the world puts invasive alien species — non-native flora and fauna that harm the environments they are introduced to — in the same league as extreme weather.
A paper published earlier this week in the journal Nature found that the economic burden of invasive species is 1,646 percent higher than previously recorded.
Invacost, a database that compiles all economic cost estimates associated with invasive species worldwide, is the most up-to-date and comprehensive record of the crisis, but it is heavily skewed toward Europe and North America, two well-analyzed regions that publish studies in English, meaning that it only represents a subset of the true cost. The authors of the new analysis attempted to rectify that gap by combining Invacost’s data with species distribution modeling, which predicted where non-native plants and animals might live using real-world observations.
Illustration: Kevin Sheu
When new scientific reviews come up with such large figures, they are bound to raise eyebrows, but in this instance, it is likely that the calculations — covering 162 species in 172 countries — are an underestimate. An alien species is a non-native plant, animal or other organism that is introduced into places outside of its natural range. They are considered invasive if they negatively impact native biodiversity, ecosystem services, the economy or human well-being. There are about 37,000 aliens recorded worldwide, and more than 3,500 are considered harmful invasive species.
For an underestimate, the scale is still eye-watering. Between 1960 and 2022, the Nature study suggests invasive species have cost humanity US$2.2 trillion — an annual average of US$35 billion. Compare that to a 2023 study putting the economic damages of extreme weather attributable to climate change at an average of US$53 billion a year between 2000 and 2019.
The expenses fall into two categories: Management costs refer to efforts to mitigate the impact of invasive species or keep them at bay. Take, for example, the costs of applying targeted herbicide to Japanese knotweed — every homeowner’s nightmare — or eradicating rat populations from tropical islands.
Those outlays pale in comparison to the damages inflicted on economies. The authors found that damages have a time lag — meaning costs do not peak for about 46 years after an alien has been introduced — but exceed management expenditure by a factor of 29. They also leave no industry truly untouched. Some invasive species such as the yellow fever mosquito threaten humans’ health by transmitting diseases such as dengue. Others endanger our food security. The British government has raised the alarm about the Colorado beetle, which has an “insatiable appetite” for potato foliage. The adult beetles and their larvae can strip plants bare within days, posing a huge threat to the UK’s ￡1 billion (US$1.35 billion) potato industry. Larvae were found in a grower’s field in 2023 — the first time the pest has been confirmed in a UK potato crop since 1977.
Even the most harmless-seeming animals can wreak havoc. In the mid-19th century, European rabbits were released in Australia for hunting, and their population subsequently exploded with devastating impacts. The fluffy menaces gorge on native plants and crops, killing small shrubs and young trees — leading to soil erosion and huge financial losses for farmers.
Elsewhere, invasive species have been shown to clog water treatment plants (zebra mussels), cause flooding (water primrose and signal crayfish), damage infrastructure (Japanese knotweed) and force out native wildlife (too many to list). The rate of introductions is only accelerating, thanks to increased global trade and travel, land-use change and the climate crisis.
In some ways, this is a more entrenched problem than global warming. Humans can, with money and effort, solve climate change. Clean energy, electrification and dietary shifts would get us most of the way there. However, these alien invasions feel more like wars of attrition that we are destined to lose eventually. The UK has been monitoring the influx of the yellow-legged hornet since 2016. After a few years of spotting the odd straggler, 2023 welcomed an onslaught of the bee-killers.
There has since been evidence that they have started overwintering on British shores.
There are success stories. Australia managed to eradicate five species — wekas (a type of flightless bird), cats, black rats, house mice and rabbits — from Macquarie Island. The subantarctic UNESCO World Heritage Site has since made a dramatic recovery, with more native animals thriving than at any time in the past 150 years. Islands do have a particular advantage: A 2022 study found that efforts to remove invasive vertebrates between 1872 and 2020 had an 88 percent success rate. It likely helps that, by virtue of being an island, they have natural moats and smaller land masses, and thus greater control over what sets foot on land.
Other places are having a harder time. Florida has twice managed to eradicate giant African land snails, most recently in 2021. However, these plant-munching, disease-transmitting mollusks are already back, with several counties placed under active quarantine to prevent the spread.
Still, there are some reasons to be positive. Management of invasive species seems to be cheaper than their damages, particularly if you are taking preventative measures or intervening early. A study last year showed that the UK’s efforts to hold off the yellow-legged hornet have been successful in holding off their incursion. As the insects further establish themselves in Europe, every year Europeans fend them off is another in which damages to apiaries and pollinators are avoided.
International regulations such as the Ballast Water Management Convention, which entered into force in 2017, are also helping combat the spread. Ballast water taken on board by ships for stability contain thousands of marine microbes, plants and animals which are then transported and released at a ship’s destination. Ships now have to treat that water. It is a great step forward, but a compliance assessment found that 29 percent to 44 percent of systems were failing to remove invasive species. There is clearly room for improvement.
As long as humans are trading and traveling, plants and animals would be hitching lifts. That means we would constantly need to be vigilant and invest in ways to counter the harms. Perhaps most importantly, the Nature study shows that we truly do not know the problem’s full extent. It is a best guess at addressing the scope, but when some countries — typically developing ones — and thousands of species have no data to work off, the picture is going to be blurry.
It is also worth saying that the threats and damage to ecosystems also extend well beyond invasive organisms. Humans have torn out keystone species from their environments, poured chemicals onto fields and into waterways and altered landscapes beyond recognition. If there is one invasive species that has cost humanity the most, it would have to be ... us.
Lara Williams is a Bloomberg Opinion columnist covering climate change. This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.
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