A new hammerhead worm is threatening our gardens

• A new species of "flat" worm found in France and could potentially invade our gardens, according to our partner The Conversation.

• Other flatworms have invaded French gardens over the past decade: the New Guinea flatworm, the giant hammer-headed worms and the oddly named Obama nungara, which alone has invaded more than 70 metropolitan departments.

• The analysis of this phenomenon was carried out by Jean-Lou Justine, professor at the Institute of Systematics, Evolution, Biodiversity of the National Museum of Natural History and Leigh Winsor, research fellow at James Cook University (Australia).

A hundred new species, animal or plant, are described each year in metropolitan France.

In most cases, these are autochthonous species, present here for a long time, but which had so far escaped the attention of scientists.

In a very different way, we are now reporting the existence of a new species found in France, but which has been introduced, and which is even potentially capable of invading our gardens.

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This species is a flatworm, the size of a knuckle on your little finger.

The species is elongated, with a broader head, like all hammer-headed flatworms.

While other flatworms generally tend towards brown or yellow, its color is quite extraordinary: totally black, it is reminiscent of “liquid metal”.

Its name: 

– we will come back to this name later.

​How to tell the species apart?

For about ten years, we have known that flatworms have invaded the gardens of France.

Our team thus reported and mapped the invasion by several species: the New Guinea flatworm (

), the giant hammerhead worms (especially

) and the oddly named

, which alone has invaded more than 70 metropolitan departments.

We have also reported recent invasions overseas.

To give a name to a species, scientists must convince that it is new, and therefore explain how it is different from species already known.

In all cases, the shapes and colors must be accurately described.

Very often, it is also necessary to describe with great precision the sexual organs of the species, which are different and characteristic.

This is where a problem arises for tapeworms: some species only reproduce asexually, and therefore simply do not have sex organs.

We imagine the problem to differentiate them.

Humbertium Covidum specimen © MNHN – Pierre Gros, CC BY-SA

​The mitochondrial genome

The mitochondrial genome, abbreviated as mitogenomes, is the genetic code that operates the mitochondria, small organelles present in all cells and which ensure their energy functioning.

This mitochondrial genome is distinct from the genome of the nucleus.

As this mitochondrial genome is present in thousands of copies in each cell, it is therefore technically easier – and less expensive – to obtain it than the genome of the nucleus.

The mitochondrial genome is circular DNA, about 15,000 nucleotide base pairs long: long enough to give a lot of information, and short enough to be easily obtained.

We therefore obtained the mitochondrial genome of several species of invasive flatworms, such as that of the New Guinea flatworm and hammerhead worms.

We used the characteristics of these genomes to differentiate the species found, even if they had no visible sex characteristics.

The mitochondrial genome of the new species Humbertium covidum © Justine et al., 2022 (via The Conversation) The mitochondrial genome of the new species Humbertium covidum © Justine et al., 2022 (via The Conversation)

The new species in France

Thanks to participatory science, that is to say individuals who help us by listing the species that are at home, we found the new "metallic black" species in two gardens in France, both in the department of Pyrénées-Atlantiques, in municipalities separated by a hundred kilometers.

It is now well known that the department of Pyrénées-Atlantiques is a small paradise for flatworms introduced from all over the world, mainly because of its mild and always somewhat humid climate.

In both cases, there were only a few individuals of the black species.

At the beginning of our study, we even wondered if they were not simple black variants of a larger species,

, also found in these gardens.

But seeing the specimens up close, and comparing the genomes, no doubt the species was different.

We then looked in the scientific literature if the species had been described elsewhere, and especially in tropical Asia, which is the main continent of origin of these hammerhead worms.

We have found a few mentions of animals that look like it, but nothing more.

Also in Italy

Towards the end of 2019, we were warned that a black species was proliferating in a field in Veneto.

Hundreds of black worms, very active early in the morning, and very mobile.

Further reports were subsequently made of this black worm near Rome.

We compared the mitochondrial genome of individuals found in France with that of individuals found in Italy: they were very little different, which shows that they are the same species, which was therefore already present in two countries in Europe.

And so, it was necessary to describe the species, that is to say, to give it a Latin name.

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The name of the new species

Assigning a name to a species is an essential and essential key step for any subsequent study.

When dealing with potentially invasive species, and which therefore may attract the attention of the legislator, it is even more essential to be able to name them: the laws and decrees use Latin names, because these names guarantee that we designate well the right species.

Each Latin species name is binomial, with a genus name and a species name.

For the genus name, it is "Humbertium", simply because the animal has the characters of this genus described in 2001. For the name of the new species, we have chosen "covidum", a name obviously based on “COVID”.

Why ?

First, because we started this work in 2020, when our laboratories were closed due to confinement.

Then, as the pandemic progressed, we wanted to name the species in honor of all the victims.

And finally, it seemed to us that "covidum" was an appropriate name for an organism capable of invading the world and coming from Asia, like the Covid-19 pandemic itself.

​Invasive species

Apart from the description of this single species, what does this discovery of a new species of flatworm in Europe tell us?

Above all, that foreign species are constantly invading our regions (the same thing exists elsewhere in the world, with European species invading other continents).

Should we blame them and hold them responsible?

These species have nothing to do with it, of course.

It is humanity that is responsible, and in particular the modern phenomenon of globalization, whereby goods circulate at breakneck speed in all directions.

Humbertium Covidum specimen © MNHN – Pierre Gros, CC BY-SA

A few individuals of a flatworm, who do not realize anything, find themselves crossing the whole world in a few days, probably in the soil of a lot of plants.

They arrive in a new environment where their natural enemies are absent, find abundant food, and proliferate.

In the case of

, by analyzing the DNA of their prey, we were able to show that the species eats small snails, but it may also consume other prey.

How is this arrival of

a problem?

Because the animal species that live on the ground and in the ground have been in balance with their European environment for a long time, and the arrival of an opportunistic predator can change this balance, and therefore alter the biodiversity of our soils.

Altering biodiversity has an ecological cost, and even an economic cost.

For example, we can calculate that invasive species reduce agricultural production.

The cost of invasive alien species in France is enormous, in the order of hundreds of millions of euros per year.

Our “ANIMALS” file

Humbertium covidum

is therefore one more example of an introduced alien species, which ultimately threatens biodiversity.

Hopefully, unlike the virus that gave it its name, it doesn't take over the world.

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This analysis was written by Jean-Lou Justine, professor at the Institute of Systematics, Evolution, Biodiversity of the National Museum of Natural History (MNHN) and Leigh Winsor, research fellow at James Cook University (Australia).

The original article was published on The Conversation website.

Declaration of interests

Jean-Lou Justine has received funding from the National Museum of Natural History.

He is one of the "Academic Editor" (volunteer) of the scientific journal PeerJ (www.peerj.com) in which this research is published.

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