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Invasive and toxic hammerhead worms make themselves at home in Ontario

A hammerhead flatworm is seen in this photo, spotted in Newmarket, Ont. on Sept. 23, 2021. (David Rudkin) A hammerhead flatworm is seen in this photo, spotted in Newmarket, Ont. on Sept. 23, 2021. (David Rudkin)
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Ontario is now home to an invasive and toxic worm species that can grow up to three feet long and can be dangerous to small animals and pets.

Numerous reports have been made that hammerhead worms, also known as the broadhead planarian, have been recently spotted in Newmarket, Hamilton, and the Kitchener area.

“They are here,” John Reynolds, a laboratory biologist and worm expert told CTV News Toronto on Friday. “People are surprised to see them because they’re just so unusual. People are not used to seeing them. They are a semi-tropical organism originally.”

The worms, originally from Southeast Asia, were likely brought into the province accidently through nursery stock material possibly from the U.S., Reynolds said. For years, the worms have been spotted across America and in Quebec.

“They don’t go very far on their own. They need to be transported,” Reynolds said. “They can spread quickly because if you cut them up, each piece becomes a new individual.”

The hammerhead worm, which gets its name due to the flat shape of its head, has a very dangerous neurotoxin called tetrodotoxin which is also found in pufferfish, Reynolds said. While the toxin can be lethal for small animals, it will only produce a rash for people.

“They are not seriously harmful to people,” he said. “They may make an awful rash and make your hands tingly for a bit. If you ingest one by mistake, it will just make you nauseous. It certainly won’t be fatal.”

The Kitchener-based worm expert advised people to not pick up the worms with their bare hands, and to always use gloves or a shovel to pick them up.

People have made reports and posted photos of the hammerhead worms they have found in Ontario on iNaturalist.ca, an invasive and native species reporting platform. The most recent reports are from the end of March but there are reports of the worms in the province dating back to 2019.

“These worms have been here, but in such low numbers that they were originally overlooked, but they just become more visible recently,” Reynolds said, adding that as the number of these worms increase, the more sightings and more awareness there will be.

Emily Posteraro from the Invasive Species Centre told CTV News Toronto on Friday that she encourages people to report any sightings of the worms or any invasive species to the centre or on iNaturalist.ca. In some cases, she added, it would be important to report an invasive species to the Canadian Food Inspection Agency.

“Ideally get the precise location information, an address,” she said. “And get some photos because that’s really the only way the detection can be verified.”

Ontario’s Ministry of Natural Resources and Forestry told CTV News Toronto that they are encouraging people to report sightings via the Early Detection and Distribution Mapping System, which is an online tracking system. 

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