Hammerhead worms are an invasive species, that are also toxic, and have been found in Hamilton since 2020. This worm has now been found throughout the area including Dundas Valley and Cootes Paradise. It was first spotted in Ontario in 2017.
Learn all about these invasive worms here, plus check out a video of one recently found in Dundas Valley.
What are Hammerhead worms?
Hammerhead worm is a general term for several different species of flatworms. The species recently found in Hamilton is invasive and commonly known as the Wandering Broadhead Planarian – scientific name Bipalium adventitium.
Are they toxic?
Yes. These worms produce a toxin they use as a defense mechanism. Simply touching them can irritate skin and eyes. Do not touch Hammerhead worms.
While there are no documented cases of humans becoming ill from handling these worms, they should be avoided and if accidentally handled, wash hands immediately.
How to identify Hammerhead worms?
These worms grow to 5 to 10 centimeters long. They have flattened yellow to tan coloured body with a long dark stripe down the centre of their back. Their heads are fan shaped, rounded, and may have a brown-grey band at the tip.
Additional Facts
Where did they come from?
Invasive in Ontario, they are likely native to Asia and arrived in soil or potted plants from the horticulture trade (University of Georgia Centre for Invasive Species and Ecosystem Health, 2020).
What habitat do they like?
The worms prefer moist soil habitats like many locations within the Dundas Valley and surrounding area, including in leaf litter, under rocks, and in gardens.
What do they eat?
They feed on earthworms, slugs, snails, and insects. Though these broadhead worms are invasive, they do primarily feed on invasive European earthworms, which negatively impact our forests in their own right (Skvarla, 2022).
How do they reproduce?
Hammerhead worms can reproduce quickly and easily, either through mating or “binary fission”, a process where the worm splits in half and regrows into two full new worms in one week (Skvarla, 2022).
What are their ecological impact?
Ecological impacts of wandering broadhead planarians in Ontario, and even more broadly in North America, have yet to be documented.
How to report sightings and contribute to HCA’s Natural Areas Inventory:
If you spot a Wandering Broadhead Planarian (hammerhead worm), please report the sighting through the community science platforms iNaturalist or EDDMapS.
HCA, in partnership with many local organizations, is currently completing an assessment of plants and wildlife in Hamilton. This work is called a Natural Areas Inventory (NAI), and has been conducted approximately every 10 years since 1993. The current NAI has been titled Nature Counts 3. You can contribute to this project by contributing plant and wildlife observations. More information can be found here.
Photo and Video Credit:
James Lees
References
Skvarla, M. J. (2022, May 2). Hammerhead flatworms and other land Planaria of eastern North America. Penn State Extension | The Pennsylvania State University.
University of Georgia Centre for Invasive Species and Ecosystem Health. (2020, December 16). Hammerhead worms.
