• Biological invasions represent the second threat (ahead of climate change) to biodiversity, according to our partner The Conversation.

  • They designate the introductions of species, whether intentionally or not, in a region other than the one in which they are native, and the proliferation of which causes multiple damage to biodiversity.

  • The analysis of this phenomenon was carried out by Franck Courchamp, CNRS research director in biodiversity dynamics and human impacts on ecosystems and species (Paris-Saclay University).

Biological invasions form a really interesting paradox.

Even if we talk about them very little in the public debate, they are not trivial.

It would even be the second threat to biodiversity, ahead of climate change.

These invasions cause a number of damages, in fields as varied as that of agriculture or health.

In Madagascar, massive deforestation leaves landscapes of desolation © Cunningchrisw / Wikimedia, CC BY-SA 4.0

And yet, we talk about it very little.

Everyone knows the risks of climate change, deforestation or pollution, but much less biological invasions, yet at least as problematic for the environment.

So why do we talk about it so little?

For researchers specializing in the issue, like those in my team, one of the explanations lies in the fact that it is a more complex process to understand and much less intuitive than those attributable to deforestation or pollution.

A mess of examples

Biological invasions refer to the introductions of species, whether intentionally or not, in a region other than the one in which they are native, and whose proliferation causes multiple damage to biodiversity.

If we often cite nutria or Louisiana crayfish, these two examples however represent only a tiny proportion of the thousands of so-called “invasive” species in the world.

It can be microbes, fungi, plants or animals ...

Nutria in a protected area of ​​Hesse (Germany) © R. Nagel / Wikimedia, CC BY-SA 3.0

Their impacts are therefore very varied and concern health, tourism, real estate, forestry, fisheries, etc.

Take agriculture, for example.

Countless species can destroy crops, stocks or infrastructure, like the now famous Colorado beetle, this pretty Colorado beetle that arrived in Europe in the 19th century;

its ravages on the potato fields caused memorable famines.

Now imagine the impact of invasive alien species attacking dozens of plants at the same time!

The evil bug spoils many fruit and vegetable crops, but also ornamental plants of trees and shrubs.

The Mediterranean fly can attack more than 300 species of fruit (wild and cultivated) ...

Even species with harmless and vulnerable profiles can become problematic, such as the American mink.

Escaped from our fur farms, it is now causing the decline of European species and can transmit certain diseases to us, such as the coronavirus.

Wild American mink in Delta, British Columbia © B. Lally / Wikimedia, CC BY-SA 2.0

On the other side of the planet, herds of majestic dromedaries from Asia are thirsty for Australia, threatening countless local species.

Evaluate the cost of invasions

Faced with such a variety of impacts, bringing them together under a common unit (the dollar or the euro) - like the degree Celsius for global warming - would make it possible to become better aware of all this damage.

It is therefore on the financial consequences of biological invasions that we looked at: evaluating this global cost in money would probably speak more than the mere mention of the number of endangered species (alas!).

For five years, my colleagues and I have built a database of thousands of costs collected in the scientific literature, totaling trillions of dollars across the globe.

In France, damage amounting to billions

Our country is not spared from biological invasions;

these are facilitated by our central geographical position (with the French overseas territories in particular) and our status as an economic power, involving exchanges of people and goods among the most important in the world.

Asian ladybug, Florida turtle, Korean squirrel, Gabon tulip tree, Argentine ant, Japanese knotweed… There is no shortage of examples of invasive species!

Tulip tree flower from Gabon © S. Kannur / Wikimedia, CC BY-SA 4.0

And the economic costs are impressive: in total, between 1.14 and 10.2 billion euros in just 25 years.

Some species are champions of loss and damage, like tiger mosquitoes, vectors of many diseases (dengue, Zika, chikungunya);

we can also cite ragweed, causing many allergies and agricultural losses.

These species alone “cost” nearly 40 million euros per year.


presenting ambrosia (eSET Bourgogne-Franche-Comté, 2016)

Little studied species, underestimated costs

In addition to being considerable, these costs have three characteristics that should alert us.

They correspond first of all, for at least 80%, to the losses and damage caused;

the share allocated to fight against these invasions is minimal.

However, scientists have shown that preventing invasions would be much less expensive than undergoing them.

This is all the more crucial since it is society as a whole that is paying the price today, while the “polluter pays” principle should apply to make those responsible for these invasions accountable.

Take the example of the Asian hornet, a species whose invasion has been particularly rapid.

Arrived in 2004 in a shipment of pottery from China, it is already colonizing almost all of France and has reached neighboring countries (Spain, Italy, Germany, England, etc.);

its progression seems to have no end!

At the same time, the magnificent and very poisonous lionfish is spreading with lightning speed in the seas of the Antilles and the Mediterranean.

Native to the Pacific, no natural predator controls it in the new areas where it thrives, to the point that in Honduras they try to train sharks to hunt them.

“Red” lionfish (Pterois volitans) from Duisburg Zoo (Germany) © R. Spekking / Wikimedia, CC BY-SA 4.0

Second point: although important, this economic assessment is only the tip of the iceberg, the damage being very underestimated because very few species have been studied - less than a hundred to date while more than 2,750 exotic species are estimated in France.

Finally, these costs are constantly increasing in France, as the report for decision-makers that we have drawn up with my colleagues underlines, as in the rest of the world;

driven by globalization - which favors the introduction of exotic species - and climate change - which favors their establishment and invasion - we already know that these costs will explode in the years to come.

Our “Environment” file

In the end, understanding that biological invasions are an economic burden could be an incentive to preserve the environment.

This would highlight another interesting paradox: for once, interest in money would help protect biodiversity.


Forest: Why the "oak tiger" could permanently modify the appearance of our green spaces


Environment: What are “nature-based solutions” and how are they implemented?

This analysis was written by Franck Courchamp, CNRS research director in dynamics of biodiversity and human impacts on ecosystems and species (Université Paris-Saclay) in collaboration with Élena Manfrini (Université Paris-Saclay, CNRS, AgroParisTech, Systematic Evolutionary Ecology, Orsay).

The original article was published on The Conversation website.

Declaration of interests

Franck Courchamp has received funding from the BNP Paribas Foundation (Climate Initiative) and the Axa Research Fund.

  • Environment

  • ecology

  • Asian hornet

  • Global warming

  • Biodiversity

  • Tiger mosquito

  • The Conversation

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