Some 20 hammerhead flatworms have been spotted in Westmount. The invasive species from Asia secretes a dangerous paralyzing toxin and is increasingly present in North America.

Lisa Osterland, a retired teacher, discovered about 20 hammerhead flatworms (bipalium) in her garden in Westmount, a municipality on the Island of Montreal.

Earlier this week, while removing slugs that were eating the flowers in her garden, she noticed a type of invertebrate she had never seen before.

A few days later, she came across a report on CNN that hammerhead flatworms were now spreading across New York State.

"The shape of the worm was the same as what I'd seen" in the garden, so "I knew right away what it was", the woman told The Canadian Press.

The retiree explained that she had spent a lot of time collecting the worms at night, as they seem to be more active at night than during the day, and then handed them over to a team of entomologists from the Université de Montréal.

"There's a rule among biologists that when you find a specimen of an invasive species, you can multiply it by 100 to estimate the population, so we're up to around 40 specimens observed in recent years in Quebec, if not more," said entomologist Étienne Normandin.

"So we can estimate that the hammerhead flat glass population is in good health."

In recent years, a few occurrences of hammerhead flatworms have been reported in Gatineau and Montreal, but this is the first time that this many have been reported in Quebec.

A PARALYZING TOXIN

Their proliferation is a cause for concern, not least because this worm secretes a paralyzing toxin, tetrodotoxin.

"It's one of the most powerful molecules in the biological world, the same molecule that is produced by puffer-fish," Normandin said.

"If a young child puts soil in his mouth and ingests a flatworm or two or more, there's a real risk of damage. If ingested, it's a toxin that will first attack the perioral region — the face, the tongue and everything in the esophagus," and "in such a case, the child needs to be hospitalized very quickly," the expert added.

Hammerhead flatworms are also a danger to birds, dogs and other animals that frequent gardens.

The arrival of a predator like the hammerhead flatworm also threatens soil biodiversity.

Normandin explained that the invasive species — because it is new to the area — has no predator, and preys on "slugs, snails and millipedes, which provide a very important service, which is the recycling of organic matter". The worm can therefore change this balance and alter ecosystems.

"In France, this type of worm has had a negative impact on soil invertebrate communities. We're slowly seeing the long-term effects of this, so we can expect similar damage to our soil fauna over the years," he added.

SPECIES FROM ASIA

The invasive worm originated in Asia and was probably transported to North America on cargo ships.

"The most likely hypothesis is the transport of plants from abroad," says Normandin.

"Often, it's found in affluent neighbourhoods like Westmount, "because in these neighbourhoods, we often have a lot of landscaping, we have exotic species of plants that are beautiful" and that are imported from faraway countries.

The hammerhead flatworm was first observed in Montreal in 2018, by a member of the Université de Montréal entomology team, "but it was probably already established in the neighbourhoods around Mount Royal", according to Normandin.

According to Environment and Climate Change Canada, invasive foreign species can cost the global economy billions of dollars every year, due to negative repercussions on forest productivity, agriculture, fishing and the costs of control measures, among other things.

Invasive species "represent a new threat to Canada's northern ecosystems as the climate warms and species normally intolerant of current northern climatic conditions expand their range."

This report by The Canadian Press was first published in French on Aug. 18, 2023.