How to get rid of toxic hammerhead worms

The invasive – and toxic – hammerhead worm has been spotted in Ontario.

Also known as a broadhead planarian, the worm can grow up to three feet (or a little more than 91 centimetres) long and has a neurotoxin, called tetrodotoxin, which is also found in pufferfish. The extremely potent poison can cause tingling or a rash when touched by humans, and nausea if swallowed.

But John Reynolds, a laboratory biologist and worm expert, said they’re not dangerous.

"They don't really do a lot of damage to crops or anything. They aren't fatal to people.”

Reynolds said the worm poses more of a threat to small animals and pets, but he doesn't know of any fatal cases.

“It's not going to kill them. But they can get upset, vomit or whatever, and they'll get a stinging sensation or numbing of their tongue," Reynolds explained. "I've heard rumours about pets, but I've never had any actual person, give me any useable data or information."

He added that the hammerhead worm doesn’t really have a predator.

"If you break a piece off or cut it, every piece that breaks off can become a new individual. So it's almost like they're here forever if you're not careful.”

A hammerhead flatworm is seen in this photo, spotted in Newmarket, Ont. on Sept. 23, 2021. (David Rudkin)

The worms have been spotted around Guelph and Hamilton over the past several years and reported to the invasive species platform iNaturalist.ca. The latest sighting was recorded in Newmarket in March.

"They're different than anything that's ever been here before. All of a sudden the change in the climate, things are moving up that you're finding here," Reynolds said.

He explained that the hammerhead worm originated in Southeast Asia and were likely brought over accidently through plant deliveries to nurseries.

"If they came up, not in bare root, but in ball and burlap, then it's quite conceivable that either small members of these flat worms or their cocoons were in the soil," he said.

Reynolds recommends gardeners purchase plants without any soil around their roots.

"When you go to the plant nursery, get bare root, because then you can really see, because the cocoons are quite small, they're really hard to see.”

If you do come across a hammerhead worm in your garden, Reynolds said the best thing to do is pick it up with gloves or a shovel and put it into a plastic bag, then leave the bag out in the sun until the worm dies. The bag and worm can be thrown into your garbage.

"Even if they were still slightly alive when in the garbage, they're going to a landfill, they're not going to bother anything in a landfill," he said.

According to Reynolds, the worms will likely move on from a garden if there isn’t any other insects or worms to eat.

"Their main focus is eating slugs, snails and my beloved earthworms,” he said. “If they can't find any of those, they're cannibalistic. They'll eat other members of their own species."

Composting concerns

Amanda Hunter, the owner of Worm Wrangler in Kitchener, provides red worms to customers who compost. While hammerhead worms are not an issue for those who do it indoors, Hunter said anyone using worms to help with outdoor composting could experience challenges.

"I would suspect that these hammerhead worms would potentially inhibit their ability to compost. They would probably decimate their worm population that they've invested to inoculate their compost with, that sort of thing," Hunter explained. "I'm not interested in seeing these guys flourish.”

Reporting sightings

Ontario’s Ministry of Natural Resources and Forestry encourages people to report sightings online through the Early Detection and Distribution Mapping System to assist in tracking the hammerhead worm.

The Invasive Species Centre also encourages people to report any hammerhead worms, or any other invasive species, on iNaturalist.ca.