Hammerhead worms invade local ecosystems

CAMBRIDGE – There’s a new worm to watch for in Ontario, and its unusual hammer-shaped head makes it hard to miss.

This spring, staff at the Rare Charitable Research Reserve found about 15 invasive hammerhead worms at one of rare’s properties in Cambridge. 

The worms were recorded between May and June, mostly on humid days.

All the worms found at Rare were wandering broadhead planarians (bipalium adventitium), one of two species of hammerhead worm identified in Canada. 

Hammerhead worms are non-native flatworms that come from warmer parts of Asia and Madagascar. 

They are often found in moist soil and humid environments. 

The first formal reports of bipalium adventitium adventitium in Canada are from 2018 in Quebec.

While their name comes from their distinct crescent or hammer-shaped head, this head shape can be more or less obvious on different individuals. 

The species found at rare is usually yellow or tan, about five to 10 centimetres long and has one dark stripe running down its back.

Because hammerhead worms are not native to Ontario, their spread could threaten native biodiversity. 

As generalist predators, hammerhead worms may pose a threat to the abundance and diversity of soil invertebrates such as snails or slugs. 

Further research is required to ascertain how hammerhead worms will affect populations of earthworms, which themselves are predominantly non-native and invasive. 

Hammerhead worms also produce a neurotoxin to protect themselves from predation and hunt prey – while the amount of toxin is not thought to be dangerous to humans, handling may induce mild skin irritation. 

The worms may be accidentally moved from place to place through plants, soil and gardening equipment.

 Following the sightings, Rare staff monitored the area to learn more about where the worms were being found. 

Rare has also reported its sightings to EDDMapS, an online tool used to track invasive species. 

Rare officials recommend anyone who spots a hammerhead worm to take a photo and report it to EDDMapS at eddmaps.org/report/. 

“By doing so, you can help Rare and other environmental organizations track their movements through Ontario,” states a press release. 

Do not touch a hammerhead worm with bare hands – wear gloves and use tweezers or forceps. 

Avoid pulling or breaking the worm. 

To safely dispose of it, place the whole worm in ethanol or in a freezer-safe bag and freeze it before disposal. 

To help prevent their spread, clean soil from footwear and gardening tools and avoid moving or sharing plants, soil or mulch from areas where hammerhead worms have been found.

“In the early days of a new biological invasion like this, the best tools we can have are widespread community awareness and early detection data,” stated Rare conservation scientist Mike McTavish in the release. 

“These initial observations of hammerhead worms will form the baseline for understanding where they are, how quickly they spread, what impacts they have on invaded ecosystems and eventually how best to manage those impacts. 

“Because hammerhead worms are closely associated with horticulture and gardens, reports from community scientists are particularly important for understanding these new non-native species,” McTavish continued.

To make identification easier, Rare created an information sheet with photos and simple tips for identifying, reporting and safely handling these unusual worms.

The Rare Charitable Research Reserve is a community-based urban land trust and environmental institute that protects more than 1,550 acres of environmentally sensitive lands across Waterloo Region and Wellington County. 

Through conservation, research, education and community engagement, Rare works to protect biodiversity and connect people with the natural world.