Can it endanger your house and garden?

Hammerhead flatworms are no ordinary garden worms. These slippery, slimy flatworms have a hammerhead-like head (hence the name) and are known for destroying their victims, releasing a neurotoxin to stun them and an enzyme to liquefy them so they can be eaten.

OK, we’ll let you catch your breath now.

“These worms are very long, and if they’re present in your yard or backyard, you probably won’t miss one,” he says Katelyn Kesheimer, an entomologist at Auburn University and the Alabama Cooperative Extension System. “Similar to other worms, they are more active after a rain event, so you might see them crawling around after a downpour.”

While hammerhead flatworms aren’t dangerous to humans, they can cause a disturbance in your garden, so here’s what you need to know if you come across one of these creepy pests.

What are hammerhead flatworms?

Hammerhead flatworms are distantly related to earthworms.

(photo courtesy of patrickpartyof2 via Instagram)

Hammerhead flatworms originated in parts of Asia and Madagascar, but are now entering the United States through the transport of exotic plants.

They are a type of terrestrial planarian that can range in length from 10 to 15 inches. Distantly related to earthworms, they are slimy and flat in profile with a crescent or crescent-shaped head. They are usually light brown or honey colored with dark lines running down their backs.

How hammerhead flatworms affect your garden

Because hammerhead flatworms love to prey on snails, earthworms, and snails, they can threaten your garden’s native ecosystem.

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Worms, in general, are not usually dangerous to humans. However, these hammerhead flatworms carry a venom that can cause skin irritation, so you should always wear gloves when digging in your garden, especially after it has rained. Also, you should keep dogs and other pets out of your yard in case a hammerhead flatworm is present.


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Because hammerhead flatworms love to prey on snails, earthworms, and snails, they can threaten your garden’s native ecosystem. Earthworms are vital to the well-being of your garden as they help loosen compacted soil and convert organic matter into nutrients for plants.

“Earthworms contribute to soil health, so we don’t want them removed from our lawns or gardens,” says Kesheimer.

signs of infestation

Hammerhead flatworms require moisture to survive.

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While hammerhead flatworms may be present in your garden and backyard, there are no obvious signs of an infestation other than seeing a specimen. So keep your eyes peeled and always wear gloves when working in your garden.

Typically, this type of worm likes hot, humid environments and is active at any time of the year when the temperature is just right.

How to get rid of hammerhead flatworms

Spraying them with vinegar or citrus oil also works.

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It can be alarming to see a hammerhead flatworm prowling around your garden, and your first inclination might be to smash it with a garden tool. But remember that they reproduce asexually.

“Don’t cut them open! Fragments can regenerate into new worms,” he says Sydney Crawley, Assistant Professor of Urban and Structural Entomology at North Carolina State University. “Instead, soak them in salt water, rubbing alcohol, soapy water, or some other abrasive solution. You can also wrap and freeze them.”

Crawley says you shouldn’t spray a solution — like salt water — on the hammerhead flatworm in your lawn or garden because the solution will also kill earthworms. Instead, you should lift the flatworm out of the garden to kill it.

“Use a stick or other tool to lift the hammerhead worm into a Ziploc bag where you can contain and apply the salt water to kill it,” he says Jonathan Larson, Entomologist and Assistant Professor in the Extension Program at the University of Kentucky. “Spraying them with vinegar or citrus oil also works.”

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