Chopping up Invasive Worms Makes New Individuals, California Officials Warn

Wildlife officials in California have warned residents not to chop up two invasive worms, as doing so will create new individuals from the severed parts.

Hammerhead worms (Bipalium kewense) and jumping worms (Amynthas agrestis) are damaging to gardens, forests and wildlife.

The California Department of Fish and Wildlife (CDFW) has said hammerhead worms will eat earthworms, a crucial organism to soil regeneration and essential member of the forest food chain, and jumping worms will eat protective layers of leaf litter and topsoil, excreting pellets that make the soil structure poor, killing plants.

In the case of hammerhead worms, which are native to Southeast Asia, they can attack and kill prey that are many times larger than themselves.

"Despite being formidable predators, we don't yet have information on how much impact this group of planarians may have on local populations of earthworms," Peter Ducey, a hammerhead worm researcher at the State University of New York College at Cortland, told Newsweek.

"The mouth of Bipalium is found on the lower side of the middle of their bodies—it's not on the head. When a planarian crawls up onto an earthworm, a thin small sheet-like pharynx extends out of its mouth onto the earthworm. Enzymes are released from the pharynx that cause the earthworm to turn to a liquid outside the planarian. This liquid is then drawn into the gut of the planarian."

Hammerhead worms have a mucus coating that if handled can be a skin irritant to humans. According to Ducey, a team of researchers recently found that B. kewense and their cousins B. adventitium have the potent neurotoxin tetrodotoxin found in their bodies.

"At this point it is uncertain whether the toxin is serving mainly as a defensive molecule against predators of Bipalium or as a venom used by Bipalium to subdue its own prey," Ducey said.

The CDFW has issued advice on how not to kill them if encountered: "Attempts to kill either type of worm should NOT include cutting them up as each of the individual parts will create a new worm," it said in a Facebook post.

Ducey said: "This ability to regenerate body parts and organs reflects the large numbers of stem cells (called neoblasts) found throughout the bodies of many planarians. That is also the reason why cutting up a single Bipalium into multiple pieces may result in each of the pieces regenerating all the parts needed to become a separate individual."

Jumping worms, originally from Japan, have also become an issue across California.

"These earthworms are extremely active, aggressive, and have voracious appetites," said a report from California Department of Food and Agriculture: "Jumping worms are considered aggressive as they out-compete common European earthworms."

Jumping worms can grow and reproduce faster, and consume more nutrients than native earthworms. Not only does that mean that other species can't access as much food, jumping worms turn the soil into granular pellets which makes it harder for native plants to grow in.

As reported by ScienceNews, the layer of topsoil containing decomposing plant matter covering the forest floor could be over 10 cm thick, but after an invasion of jumping worms, the soil is barren and has a different structure and mineral content.

"Worms can reduce leaf litter by 95 percent in a single season," Sam Chan, an invasive species specialist with Oregon Sea Grant at Oregon State University in Corvallis, told ScienceNews.

Studies have also shown that the longer these jumping worms had lived in an area of soil, the higher the basal metabolic rate of the soil was, and the more the nitrogen and carbon levels of the soil changed.

In essence, soils invaded by jumping worms may end up emitting more carbon dioxide into the atmosphere, and may not be hospitable to native plants that are adapted to growing in soils with a specific carbon/nitrogen balance.

Experts say you can easily kill hammerhead flatworms using salt or citrus oil, and kill jumping worms by pouring a mustard-water mix onto the soil, which will irritate the worms and bring them to the surface, where you can pick them out, bag them and leave them in the sun before throwing them away.