🐛 How dogs and cats lend a paw to an invasive worm

How can we explain the new and simultaneous presence of worms, notoriously slow animals, in gardens distant from each other and without the introduction of new plants? An original answer is emerging today, pointing to an involuntary vector: pets.

This work, published in the journal PeerJ, is based on the analysis of over ten years of data from citizen science programs in France. Thanks to observations from amateur observers, worms were seen firmly attached to the hair of dogs and cats. This discovery indicates that our domestic companions can, unwittingly, transport these organisms during their wanderings, which tends to explain a rapid spread that had remained enigmatic until now.


Among the dozen or so species of exotic flatworms recorded in France, only one seems to use this method of locomotion. It is Caenoplana variegata. This worm produces an unusually adhesive sticky substance, probably linked to its diet based on capturing arthropods. This physical peculiarity gives it the ability to cling firmly to fur.

This worm's ability to reproduce on its own represents an additional advantage for its colonization. A single displaced individual can therefore initiate a new colony where it is deposited. The combination of these biological characteristics gives the species remarkable efficiency in establishing itself in new territories.

The usual movements of domestic animals, whether daily walks or longer journeys, form a vast transportation network. This process, which has remained invisible until now, could facilitate the dispersal of these worms beyond expected geographical limits, thus contributing to their local expansion and, step by step, even global spread.

Flatworms, discreet invaders

Flatworms, or planarians, belong to the group Platyhelminthes. Unlike their parasitic cousins, these species live freely in the soil and under dead leaves. Their flat, elongated, often colorful bodies allow them to slip into the narrowest gaps in humus.

These organisms feed mainly on small invertebrates such as snails, slugs, or ordinary earthworms. They hunt by secreting a mucus that immobilizes their prey before ingesting it. Their role in ecosystems is that of predators, regulating populations of other soil species.

Their introduction outside their region of origin is problematic because they can disrupt local balances. Having no natural predators in new environments, their populations can grow rapidly. Their impact on soil biodiversity is an important subject of study in ecology.