Source: The Conversation – France – By Jean-Lou Justine, Professeur, UMR ISYEB (Institut de Systématique, Évolution, Biodiversité), Muséum national d’histoire naturelle (MNHN)
What was discovered?
Domestic dogs and cats can carry invasive flatworms (Platyhelminthes) attached to their fur. Unwittingly, this is how they contribute to the spread of these invasive alien species. Our work on the subject has just been published in the scientific journal PeerJ.
Globally, invasive alien species represent one of the major threats to biodiversity. It is striking to discover that dogs and cats, our everyday companions, unwittingly contribute to the invasion of gardens by a species potentially dangerous to biodiversity.
How was the research conducted?
We were alerted by e-mails from individuals reporting the presence of worms attached to the fur of dogs and cats. We then re-examined over 6,000 messages received over 12 years and found that these observations were far from anecdotal: they represented approximately 7% of the reports. Remarkably, among the dozen or so species of exotic flatworms introduced into France, only one was affected: the yellow-striped flatworm, or Caenoplana variegata, a species from Australia whose diet consists of arthropods (woodlice, insects, spiders).
by Jean-Lou Justine, CC BY
Why is this discovery important?
It has long been known that exotic flatworms are transported from their countries of origin to Europe through means linked to human activities: containers of plants shipped by boat, trucks then delivering them to garden centres, and finally transported by car to gardens. It was not well understood how flatworms, which move very slowly, could then infest surrounding gardens. The mechanism identified is quite simple: a dog (or cat) rolls in the grass, a worm sticks to its fur, and the animal then deposits it a short distance away. In some cases, it even takes it home, bringing it to owners’ attention.
Furthermore, it is surprising to note that only one species is affected in France, even though it is not the most abundant. Obama nungara is the most widespread species, both in terms of the number of districts affected and the number of worms found in gardens, but there were no reports of animal transport for this species. This difference is explained by their diet. Obama nungara feeds on earthworms and snails, while Caenoplana variegata eats arthropods, producing a very abundant and sticky mucus that traps its prey. This mucus can adhere to animal fur (or to shoes or trousers, for that matter). On top of that, Caenoplana variegata reproduces asexually by cloning itself: just one single, transported worm can infest an entire garden.
We then attempted to estimate the distances travelled by the ten million cats and sixteen million dogs in France each year. Based on existing data, we arrived at a spectacular estimate: several billion kilometres in total, which is many times the distance from the Earth to the Sun! Even if only a small fraction of domestic animals carry worms, this represents an enormous number of opportunities to spread these invasive species.
It is important to clarify that this is not parasitism, but a phenomenon called “phoresy”. This is a well-known mechanism in nature, particularly in plants with sticky or spiny seeds, which cling to animal fur and fall a short distance away. But here, it is a sticky animal that accidentally becomes attached to a domestic pet and is dislodged some distance away.
What’s next?
We hope this discovery will stimulate further observations, and we expect more reports of the same kind. Furthermore, our published results concern France, for which citizen science has provided a wealth of information, but some observations suggest that the same phenomenon exists in other countries, albeit with different species of flatworms. It is now necessary to expand this research internationally to better understand the extent of this dispersal method and the species involved.
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Les auteurs ne travaillent pas, ne conseillent pas, ne possèdent pas de parts, ne reçoivent pas de fonds d’une organisation qui pourrait tirer profit de cet article, et n’ont déclaré aucune autre affiliation que leur organisme de recherche.
– ref. Dogs and cats carry invasive land flatworms from garden to garden – https://theconversation.com/dogs-and-cats-carry-invasive-land-flatworms-from-garden-to-garden-274999