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Invasive and toxic hammerhead worms spotted in Ontario

Meet your new nightmare...

It appears our province is facing an uptick of an unwanted intruder – the invasive and toxic hammerhead worm.

According to multiple media reports, these creatures, native to Southeast Asia, have recently made their presence known in areas like Newmarket, Hamilton, and the Kitchener region, sparking concerns about their potential impact on local ecosystems and wildlife.

Measuring up to three feet long, these hammerhead worms, also known as broadhead planarians, pose a threat to small animals and pets due to their toxic nature.

Their flat-shaped heads and distinct appearance make them easily identifiable, but their real danger lies in the neurotoxin they carry – tetrodotoxin, the same toxin found in deadly pufferfish.

Stock image of a hammerhead worm. Photo via Canva

It's believed that these worms found their way into Ontario inadvertently, possibly hitching a ride on nursery stock materials. Despite their small size, they pack a powerful punch with their potent toxin. While tetrodotoxin can be lethal to small creatures, humans may only experience a rash upon contact.

Reports of hammerhead worm sightings have been pouring in, with concerned citizens using platforms like to document their encounters. The most recent reports date back to the end of March, but records show sightings dating as far back as 2017, indicating a persistent presence of these invasive worms in the province.

If you come across these worms in your garden, there's no need for immediate action. However, it's recommended to document your observation. You can report sightings to the Invasive Species Centre through their online reporting tool or use a community science app like iNaturalist for reporting purposes.