Invasive flatworms are spreading via global trade

A flatworm specimen collected in France.
A flatworm specimen collected in France. Photo credit: PeerJ

Invasive, predatory flatworms are spreading around the world and popping up in unlikely places because of global trade, a new report says. 

Several species of flatworm - including the hammerhead flatworm native to Asia - have been showing up in French cities for the better part of two decades, according to a report published Tuesday in the journal PeerJ. 

People in France have reported 111 sightings of large hammerhead flatworms between 1999 and 2017, co-authors of the French study Pierre Gros and Jean-Lou Justine said. This particular species of flatworm can grow to a foot or more in length. 

There are also concerns in northwest Europe (including the UK) regarding the spread of the New Zealand and Australian flatworms that prey on earthworms, a study by the Ecological Society of America says. 

A New Zealand flatworm is thought to have reached Europe in containers of plants imported by botanical gardens. 

According to entomologist Archie Murchie of Britain's Agri-Food and Biosciences Institute, invasive flatworms can "have a major impact on other soil fauna". 

Flatworm preying on a common snail.
Flatworm preying on a common snail. Photo credit: PeerJ

New Zealand flatworms that have made a home in Ireland and Scotland have devoured the local earthworms, according to Mr Murchie. The New Zealand flatworms have eaten so many earthworms that grass in the affected areas has shrank about six percent, he says. 

Biologists have warned the soil-dwelling species will continue spreading around the world through increased global trade. The worms, which can feed on snails, earthworms and mollusks, can often be overlooked in cargo, which explains their unintended shipment around the world. 

Hammerhead flatworms have been sighted in French territories, alongside other newly discovered species, according to the French study, which could support the theory that these worms are spreading through trade. 

Bipalium, more commonly known as 'hammerhead worms' because of the distinctive shape of their head region, are considered large predatory land planarians (flatworms). 

It has been shown that these flatworms can track their prey. 

When captured, earthworms will begin to react to the attack, but a flatworm uses the muscles in its body as well as sticky secretions to attach itself to the earthworm to prevent escape, according to a paper published by the University of Notre Dame. 

Mr Murchie told The Washington Post the authors of the new French study are "rightly cautious about the potential impact of the hammerhead flatworms" that have settled in France. 

There are concerns about flatworms continuously infesting areas where the local animal and plant life have no natural defence against them.