Q&A: Worms are showing up in Ontario with hammerheads. What exactly are they?

Have you noticed a worm in your garden that's much longer than most, and has a hammerhead? You're not alone.

There have been reports of hammerhead worms showing up in Ontario, but although they've recently been noticed in the province, Jonathan Witt, an invertebrate biologist from the University of Waterloo, said that they've been in North America much longer.

CBC Kitchener-Waterloo's The Morning Edition host, Craig Norris spoke to Witt about what these animals are and how they got here.

This interview has been edited for length and clarity. 

Host Craig Norris: Let's talk first about why this is called a Hammerhead worm.

Witt: If you look at the worm from above, its head sort of spans out in a sort of a disc shape and it looks superficially like that of a hammerhead shark. It's a member of a group of animals called the Platyhelminthes, which are the flatworms.

It has a very flattened profile unlike the typical earthworms that you see in your garden which have a cylindrical profile and are segmented. These are non segmented worms.

Norris: So where do they come from and how did they get here?

Witt: There are about five species in this group that have invaded North America ...The one that we've been seeing popping up around Ontario, its scientific name is Bipalium Advantium, which is commonly known as the the wandering broadhead planarian, and so this particular species is thought to have originated from possibly Japan or South Korea, but we don't know exactly where it came from.

Norris: We've been hearing just anecdotally that there are more around our region this year. Is that true?

Witt: They have been popping up a little bit more. There's more reports of them on the website [iNaturalist.org], which is a website where biologically inclined individuals can report sightings of various organisms, and so we are seeing more reports of it on there.

It was actually first reported in Quebec in 2018, but it arrived in North America probably prior to 1943. It was first discovered in California and then subsequently in New York in 1947, so it's probably been here for quite some time in North America.

In Ontario, we're not sure how long it's been here, but it's probably been here for at least 10 years, I would guess.

Norris: So let's get into why it's a problem. What damage can they do to an ecosystem?

Witt: We don't actually know what impact they're actually having on ecosystems, but what we do know is this: They feed on earthworms, and what we want to note here is that earthworms themselves are not native species in Ontario.

Earthworms themselves are invasive species within Ontario and are doing quite a lot of damage in forest ecosystems. Earthworms are real ecosystem engineers.

What they do in forests is they consume leaf litter and detritus on the forest floors, but they do so at a rate which is a lot greater than what our native invertebrate species would do, such as millipedes, insects, things like that and it reduces the depth of leaf litter on the forest floor and reduces biodiversity.

If these new invasive hammerhead flatworms are feeding on earthworms, then maybe, just maybe, that might not be a bad thing. But we don't know that for sure.

Norris: What happens, say, if you come across one of these in your garden and you touch it?

Witt: This is a species that produces a neurotoxin called tetrodotoxin, and that name is derived from a group of fishes called the tetraodontiformes.

That group includes the puffer fish, which as you might know also has this very same toxin and so you don't want to touch these worms because they can potentially give you a skin irritation or a bit of a rash and you certainly don't want to ingest them.

But having said that, these worms have been in North America for over 80 years now, and there isn't a single credible record of anyone ever being hurt by one, so it's not something that you really need to be particularly worried about.