'Quite urgent': Spread of hammerhead flatworms in Ontario, Quebec poses concern to existing ecosystems

Although it’s been years since any official sightings of the hammerhead flatworm in either Ontario or Quebec, one organization says it’s only a matter of time before they’re reported in Canada again.

Hammerhead flatworms are an invasive species, meaning they are not native to Canada. The worms produce a neurotoxin used to paralyze prey, including earthworms, and there is the potential for harm to humans if these worms are touched.

Most recently, they have been spotted in Ohio.

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“It hasn't been recorded through us … but that doesn't mean it's not here because people don't go sifting through their soil to look for these things,” said Cathy Kavassalis, the social media administrator for Master Gardeners of Ontario Inc., in a telephone interview with CTVNews.ca on May 18. MGOI is an independent non-profit organization supporting home gardeners.

The first academic record of these worms in Canada dates back to May 2018, when the hammerhead flatworm was spotted in Montreal. A paper based on the discovery was published in 2019.

In an email to CTVNews.ca on May 17, Quebec’s Ministry of Forests, Wildlife and Parks said there have not been any other reports of these flatworms since 2018, and that little remains known about their presence in the province at the moment.

“The distribution and abundance of this exotic species are therefore unknown to date,” the ministry wrote in the email, translated from French. “Being considered predators, these flatworms could pose a risk, particularly for the soil fauna and the biodiversity of these ecosystems.”

Ontario’s Invading Species Awareness Program is designed to confront the threats posed by invasive species that enter the province. It’s the product of a collaboration between the Ontario Federation of Anglers and Hunters and the Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry. According to the program’s distribution mapping system, there have been no reports of hammerhead flatworms seen in Ontario.

Despite this, it appears as though several spottings of the hammerhead flatworm have been made since 2018 according to iNaturalist, a crowdsourced platform used to identify different species. Participants are able to log their own observations of different organisms they come across, and connect with others who may be struggling to identify them.

“From an invasion science perspective, [these platforms] are incredibly useful because they effectively increase the geographic area from which we can draw observations,” said Michael McTavish, a researcher with the S. M. Smith Forest Health Lab at the University of Toronto, in a telephone interview with CTVNews.ca on May 20. “It's very likely that the current distribution [of these worms] is more widespread than what we have records for and that we will only see more of them in time.”

David Rudkin, a retired paleobiologist and educator based in Ontario, posted about two observations he made of the worm in his garden in Newmarket, Ont., once on Sept. 22, 2019 and again on Sept. 23, 2021. Since then, there have been other research-grade observations of the worm across different parts of Ontario, according to the website, including in Toronto and Hamilton, Ont.

“In both sets of sightings, the [worms] were found in a cool, moist setting in our garden,” he wrote in an email to CTVNews.ca on May 30. “The first was under a slab of rock adjacent to a wall, and the second was on top of a tree stump beneath a clay dish we use as a bird bath.”

Kavassalis said it does not surprise her that these worms are being identified in parts of the province, despite the lack of formal reporting in the form of scientific journals. The reason for this lies in what she described as a shift in regulatory processes regarding the transportation of organisms such as worms from the United States to Canada.

“There's simply so much plant material coming up from the United States that it would be very, very simple for [the worms] to be transported here,” she said.”We get a lot of plants in the industry shipped through nurseries in the U.S. [so] the likelihood is very high that it will come through that pathway.”

Part of what makes invasive species so problematic, Kavassalis said, is the cascading impact they have on existing ecosystems. With hammerheads primarily feeding on soft-bodied creatures such as earthworms, which exist in the southern half of Ontario, for example, they have access to plenty of food, which may allow them to expand in numbers, she said. This can threaten the livelihood of other organisms existing in the same ecosystem, said Kavassalis.

“We're seeing huge declines and things like pollinators, and a lot of our bees are ground nesters,” she said. “So when you start getting things like hammerhead worms and earthworms in the soil disrupting their nesting habitat, that puts even more pressure on creatures that are already at risk.

“This kind of cascade event impacts food webs, and particularly insect populations which support bird life – it's all interconnected.”

The broader concern related to cascading events is that they could ultimately result in reduced abundance of biodiversity or the disappearance of species entirely, McTavish said. Conditions may also open the door for other organisms to be introduced, making it easier for them to arrive or increasing the impact they might have once they do.

Kavassalis said she hopes to see more people pay attention to the introduction of invasive species in Canada. She also said she hopes that government officials aim to improve regulatory protocols around screening for infestation of non-native species – such as hammerhead flatworms – in materials that are shipped to Canada. Additionally, she hopes to see more education be provided to the public, informing them of the risks of introducing invasive species to new environments.

“It's really quite urgent that we pay attention to what's happening,” Kavassalis said. “Nature will adapt to some extent, but it's the rate at which they can adapt to these changes that's the concern.”

The benefit of slowing the spread of these invasive species is that it buys some time for ecosystems to adjust to changing conditions, as opposed to being overwhelmed by multiple stressors at once, McTavish said.

“Realistically, we're not going to be able to stop this – you can't remove what's already there ... but there is a lot of value in slowing down the rate at which they do arise.

“If it's slower, we have a better chance to mitigate adverse impacts on biodiversity and ecological function.”