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?