Hammerhead Worm, Spotted Locally, No Cause for Concern, Says Scientist

A wandering broadhead planarian (Credit: Sanjay Acharya/ Creative Commons)


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A number of hammerhead worms found in Old Saybrook are not a cause for concern, and may actually be helpful in managing a damaging invasive earthworm in the area, according to a scientist from the Connecticut Agricultural Experiment Station.

Dr. Gale Ridge, an entomologist in the CAES insect inquiry office, said she was still waiting to see one of the worms captured in Old Saybrook. But from what she has seen, she thinks it’s a species called the wandering broadhead planarian that is found in Pennsylvania, and has been seen in Canada.

Hammerhead worms – a term that applies to a group of predatory worms with a distinctive flat, hammer-shaped head – are often reviled by farmers and gardeners for eating earthworms commonly thought to be good for soil.  But despite that reputation, Ridge said the hammerhead worms aren’t a concern, and could even be good news for Guilford, which has a population of a damaging and very active earthworm called the crazy snake worm, which originated in Japan. 

Ridge said she has seen examples of hammerhead worms in Connecticut before, suggesting that they have an established population in the state, but in very low numbers. She noted that the more beloved earthworm is also invasive, largely brought over by European colonists.

“They are in a prey-predator cycle, so they’re managing earthworm populations,” Ridge said. “The earthworms are perfectly capable of maintaining their populations with these plenaria [hammerhead worms] around, and they are in many respects beneficial.”

The hammerhead worms are also a predator of the crazy snake worm, which Ridge said are the serious issue. The crazy snake worm can deplete the soil of nutrients to the point where plants can’t germinate. It’s possible the hammerhead worms could help push back on those.