Sightings of invasive, toxic hammerhead flatworm increasing in Ontario

An invasive and harmful worm capable of growing to three feet long has been discovered in Ontario, Canada. The hammerhead land planarian is toxic and, experts warn, can pose a threat to pets, small children and small animals.

“They’re here. People are surprised to see them because they are very unusual. People are not used to seeing them. They are originally a semitropical organism,” John Reynolds, a laboratory biologist and worm expert, told CTV News Toronto.

According to iNaturalist, an online platform where people can report sightings of invasive species, the initial presence of hammerhead worms in the province dates to a couple of years ago, but the number of sightings in the province have increased over the past 12 months — with reports as recent as yesterday.

A hammerhead flatworm found in Napierville, Illinois.

bg1159 / Creative Commons Attribution 4.0


The flatworms are native to southeast Asia and thrive in moist soil, and have been a longstanding issue in the United States and Quebec. Now, they are making their way to new locations, possibly via greenhouse plants.

“The predatory land planarian is no friend of earthworms. In fact, they are parasites that eat earthworms and can wipe out entire populations,” said Howard Garrett, a gardening and landscaping expert in Texas, on his website The Dirt Doctor.

“It seems that it is only a destructive pest that needs to be gotten rid of,” Garrett said.

Hammerhead worms have remarkable regenerative abilities capable of growing back from small parts of their body. When the worm is cut into pieces, such as when someone is shoveling land, each piece turns into a new, individual hammerhead worm.

“Smashing this pest is the thing to do, except for the fact that it grows back from small pieces,” Garrett wrote. “A better solution is to spray with orange oil to completely destroy it and prevent return.”

The hammerhead worms are poisonous and harmful to the ecosystem. Experts advise wearing gloves when dealing with them to avoid exposure to their mucus. Handling with bare hands can cause skin irritation.

“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 Reynolds, the biologist. “But they certainly aren’t fatal.”

This post was originally published on CBS News

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