Neurotoxic worms growing up to 3ft long are in Ontario and you should kill them on sight

Spring has sprung in Ontario, and with temperatures soaring into the high teens this week, there are some warm-weather creepy-crawlies now emerging that people may want to familiarize themselves with.

The wandering broadhead planarian (Bipalium adventitium), or hammerhead worm, was first sighted in Ontario in 2017, and the potentially dangerous invasive species of large carnivorous landworm has been regularly spotted in the years since.

And pet owners with gardens should take special note of this threat that could be lurking closer than expected.

What is a hammerhead worm?

Native to Asia and deemed invasive in North America, hammerhead worms get their nickname from their distinctive T-shaped heads and dark red stripe running down the length of their squirming, slimy bodies. 

And, like the similarly named hammerhead shark, these worms are efficient predators with voracious appetites.

Oh, and they can grow to be three feet long.

Hammerhead worms are capable of ecological destruction by preying on native earthworm species, which are totally defenseless against these wriggling carnivores and can easily be killed off in great numbers by just a small population of these invaders. 

B. adventitium will stalk its victims using chemoreceptors that can detect faint chemical trails left by native worm species. Once these predators catch up with their victims, they will immobilize prey by coiling around their bodies, similar to a constricting snake. But, unlike constrictors, these worms deliver a fatal blow with a stabbing appendage called an everted pharynx that looks like it came straight from the Alien movie franchise.

And these critters can harm animals several hundred times their size, including unwitting pets.

How dangerous can a worm be?

The species of B. adventitium that has been confirmed as present in Ontario packs a potent punch for any animals that mistake them for a slimy snack. Tetrodotoxin, a neurotoxin found in some of the world's most deadly animals, like the pufferfish and blue-ringed octopus, poses serious danger to pets and even humans.

Scientists aren't aligned on the evolutionary function of this toxin for the worms, but there is no doubt about just how harmful tetrodotoxin is. Its oral median lethal dose (LD50) of 334 micrograms per kilogram in mice is orders of magnitude more toxic than even potassium cyanide at 8,500 micrograms per kilogram.

Ingesting these worms can cause illness and even death, while merely handling them can cause symptoms like skin irritation. Gloves are recommended for anyone attempting to remove and dispose of these harmful garden invaders to avoid contact with their toxic mucus.

When and where are they most active?

Sightings of these worms tend to spike in the damp spring and fall months, and the first hammerheads of the year were spotted in late March as the post-winter thaw arrived.

The first suspected hammerhead worms of the year were reported (but remain unconfirmed) using online observation platform iNaturalist out of Windsor, and several more sightings are expected to pop up as weather conditions become more favourable for worms to surface.

You're most likely to see these worms in the typical worm-friendly places, like a garden or a park on a rainy day, or even crawling in your potted plants.

How to get rid of them

Hammerhead worms, being an invasive but also potentially deadly species, should be exterminated with the utmost ruthlessness, but exercise extreme caution while doing so.

When reports of hammerheads first started stirring up attention in Ontario back in 2022, Rebecca Morton of Toronto-based Armour Pest Control told blogTO that there are some easy and environmentally-friendly methods of dispatching these invaders.

 "If seen, it's critical to catch them without contacting bare skin and kill them with salt, vinegar, or neem oil, then dispose of them in a sealed container," said Morton.

Experts also suggest avoiding any method that involves cutting the worms, as these segmented creatures can regenerate into two separate worms if split in two.

So, keep those pets safe, and happy hunting, Ontario!