An invasive and toxic worm that can grow up to three feet long has made its way to Ontario, and with sightings across the GTA becoming more prevalent, gardeners and pet owners are being warned about its presence.
Since 2019, the broadhead planarian, more commonly known as the hammerhead worm, has continued to be spotted in the province. The invasive species from Asia that has been spotted plenty in the U.S. and Quebec looks a lot like an earthworm but gets its nickname from the flat shape of its head.
But perhaps more notable is the worm’s toxicity, a paralyzing toxin similar to that of a puffer fish—one of the most poisonous in the world.
“It isn’t really harmful to adults. It might create a rash and reaction in really young children, but they can be a bit of a problem,” said John Reynolds, a laboratory biologist. “But they certainly aren’t fatal.”
How did hammerhead worms get here?
While they might be intriguing from a biological standpoint, hammerhead worms are considered invasive in certain regions where they’ve been introduced. They can disrupt local ecosystems by preying on native earthworms and altering soil composition.
Cathy Kavassalis, a member of the Halton Region group Master Gardeners of Ontario (MGOI), says the worms are likely coming into the province from the nursery trade. As for the possibility of the hammerhead worm showing up in your garden?
“Potentially. Particularly if you have moist soil that is really rich in earthworms,” Kavassalis said. “Don’t touch it with bare hands. Wear gloves. We give this advice to many things in the garden. I’d be more concerned with the damage they’d cause to ecosystems than people.”
Hammerhead worms are predators that primarily feed on earthworms and other soil invertebrates. They have a unique hunting method in which they extend their pharynx out of their mouth to engulf prey. Hammerhead worms are also hermaphrodites, possessing both male and female reproductive organs.
“Earthworms are an invasive species themselves, so the ones that you see in your garden are actually problematic,” Kavassalis said. “They harm fields of Trillium.”
Kavassalis noted that there is more than one species of hammerhead worm, and depending on which version takes hold in Ontario, their diets will be an important factor. Some prefer earthworms, snails, and slugs, while others feed on the larvae of grounding pollinators.
“That will be a problem,” she said. “We don’t have in place a system to look at how things are spread, like the worms in these soils.”
If a person or a pet ingests one of the invasive worms, seek emergency attention immediately.
