Hammerhead worms: what to know about the toxic worm that could be in Illinois gardens

The hammerhead worm has been inching its way through news headlines, but is it dangerous and what should you do if you see one in Illinois?

The hammerhead worm - also known as a “flatworm” - is a worm species seen across North America. Not only does the worm stand out from your typical earth worm with its hammerhead-like appearance, but also because it contains toxins that can be dangerous to humans.

In Chicago, it’s something you could see in your own backyard.

SUNY Cortland Professor Dr. Peter Ducey specializes in the study of these worms and said there are about five species that have invaded the U.S. While southern species of worms can get up to a foot long, worms in Chicago and northern regions are usually smaller.

“It’s about two to three inches long, kind of a tan color with a dark stripe down the middle of its back,” Ducey said.

If spotted, it’s not safe to touch. This is because the worm contains a neurotoxin called tetrodotoxin, also known as “TTX”. This neurotoxin prevents neurons and certain muscle cells from working and is the same toxin found in pufferfish. Although served as a delicacy in Japan, the pufferfish can be deadly if prepared incorrectly. The hammerhead worm contains some of this same toxin, though in a seemingly lower amount.

“We’re not sure whether they’re using it against their prey when they go to eat something, or if they just use it as a defense so nobody else can eat them,” Ducey said.

Ducey also noted that these toxins do not enter your body through your skin, but rather through the circulatory system. Touching a hammerhead worm and then rubbing your eye or biting your nail could be incredibly harmful.

“By itself, just touching one shouldn’t be a deadly thing,” Ducey said. “In my lab, though, everyone wears gloves when they handle them.”

There’s another thing most people may not know about the worm: it has the power to regenerate. This means crushing it, cutting it in half or even into even smaller pieces won’t kill the planarian.

So, what should you do if you find one in your backyard?

Ducey said the best thing to do is to pick it up with gloves or another object and place it in a bag.

“They are sensitive to vinegar, boiling water, drying out. Just Ziploc them in a Ziploc bag and putting them in the sun will take care [of the worm]”.

Ducey also said the worms can be thrown out to avoid disrupting their habitat.

Although the worm’s regeneration abilities may appear creepy to some, Ducey said people are already studying the regenerative abilities among animals and planarians across the world.

“[They are] studying how those guys regenerate missing body parts, and then trying to apply that to human medical issues, like fixing spinal cord injuries,” Ducey said.

While we do not know the exact origin of the Chicago species, all hammerhead worm species are from Southeast Asia and now span from the East to West Coast in North America. Although the worms have been here for nearly 100 years, numbers are continuing to grow.

“You probably have a lot more in everybody’s backyard than they expect and in all the city parks and botanical gardens probably have plenty of them already,” Ducey said.

The worms cause harm to our environment because they eat earthworms, which are needed for gardens and agriculture.

"We don't want to just let them be and let them take over and remove our earthworms. So it is important that we take care in our area and remove them as quick as possible. Just because they're here and they're widespread doesn't mean we should give up the fight," Ashley Morgan-Olvera, the director of research and education at the Texas Invasive Species Institute said.

If you suspect you or a child may have ingested these worms or their toxins, Ducey advises to call Poison Control or 911 and ask for medical advice.

While Ducey said he knows no records of any person getting ill from interacting with these terrestrial planarians, but that people should stay cautious and treat the animals with care.

“In general, they’re not an animal that should be feared that much, but they just should be respected,” Ducey said.