Hammerhead Worms, Invasive and Toxic, Establish Presence in Ontario
Ontario Welcomes Invasive, Toxic Worm Species: Potential Threat to Pets and Wildlife
Recent sightings confirm the presence of hammerhead worms, also known as the broadhead planarian, in Newmarket, Hamilton, and the Kitchener area. These creatures, capable of growing up to three feet long, pose a danger to small animals and pets.
“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 origins of these worms trace back to Southeast Asia, likely introduced accidentally into the province via nursery stock, potentially originating from the U.S. This invasive species has been reported across America and in Quebec for years.
According to Reynolds, the worms rely on transportation for their spread, as they do not travel far on their own. Their ability to regenerate from cut segments facilitates rapid multiplication.
Named for their distinctive flat head shape, hammerhead worms harbor a potent neurotoxin called tetrodotoxin, also found in pufferfish. While lethal to small animals, exposure typically results in a rash for humans.
“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 expert from Kitchener strongly advises against handling the worms directly and recommends using gloves or a shovel for handling.
Numerous reports and photographic evidence of hammerhead worm sightings in Ontario have been submitted to iNaturalist.ca, an invasive species reporting platform. While the most recent reports date back to the end of March, sightings have been documented in the province since 2019.
Ontario’s Ministry of Natural Resources and Forestry has encouraged the public to report sightings through the Early Detection and Distribution Mapping System, an online tracking platform.
