A Head-Turning Invader

Found a hammerhead worm in your yard? Here’s what to know about the predator and the safest way to remove it.

2:45 p.m. July 18, 2026

DUANE CROSS
MCO Publisher•Editor

They look like something from a horror movie, but the primary concern surrounding hammerhead worms is not what they might do to people. It is what they eat.

More Tennesseans are reporting the invasive flatworms in gardens, flower beds and landscaped areas. The worms prey on earthworms and other soil-dwelling organisms, raising concerns about their potential effect on gardens, agricultural soil and surrounding ecosystems.

They are also difficult to kill. Cutting one apart may only create more worms.

What is a hammerhead worm?

Hammerhead worms are terrestrial flatworms, also known as land planarians. They are native to Southeast Asia and are believed to have reached the United States through the movement of infested plants and soil.

The U.S. Department of Agriculture’s National Invasive Species Information Center lists 1891 as the earliest U.S. record of Bipalium kewense, one of the most commonly reported hammerhead worm species.

The worms are generally easy to recognize by their:
• Long, flat, ribbon-like bodies
• Brown, tan or gray coloring, often with dark stripes
• Broad, crescent- or shovel-shaped heads
• Slippery coating of mucus

Some may grow longer than a foot, although size varies by species and age.

Why are they a concern?

Hammerhead worms are predators that primarily feed on earthworms, although they may also consume slugs, snails and other small organisms.

In gardens and agricultural soils, earthworms can help break down organic material, move nutrients and improve soil structure. The USDA says hammerhead worms could potentially affect agricultural, horticultural and natural ecosystems by reducing earthworm populations.

The full ecological effect of hammerhead worms is still being studied, and finding one does not mean a garden or yard has been seriously damaged.

However, because the worms are invasive and can be spread through soil and nursery plants, officials encourage residents to avoid moving them to new locations.

Are they dangerous to people?

Hammerhead worms do not bite or sting, but they should not be handled with bare hands.

Some species produce tetrodotoxin, a neurotoxin found in the mucus covering their bodies. Contact is more likely to cause skin irritation than serious illness, but the slime should be kept away from the eyes, mouth and broken skin.

Children and pets should also be kept from touching, licking or eating the worms.

Anyone who handles one should wear gloves and wash their hands afterward.

Do not cut them apart

Do not try to kill a hammerhead worm by chopping, crushing or cutting it into pieces.

Hammerhead worms can reproduce through fragmentation. A separated section of the body may regenerate into another worm.

That means cutting one apart could leave multiple living pieces instead of eliminating the original worm.

What should you do if you find one?

Wear gloves or use tongs, a stick, or a small shovel to pick up the worm.

Place it in a sealable plastic bag or container. Penn State Extension recommends killing individual flatworms by placing them in alcohol or sealing them in a bag and freezing them. Salt may also be applied directly to an individual worm.

Keep the worm contained during treatment, then place the sealed bag in the trash.

Do not place a live hammerhead worm in compost, loose soil or another section of the yard.

Where are they found?

Hammerhead worms prefer moist, shaded areas and are often easier to spot after rainfall.

They may be found:
• Beneath rocks, logs or landscape timbers
• Under mulch
• In flower beds
• Around compost piles
• Inside or beneath potted plants
• On patios, sidewalks or driveways after rain

They are commonly transported in nursery plants, potting soil, mulch and other landscaping materials.

Are hammerhead worms established in Tennessee?

Yes. Hammerhead worms have been documented in Tennessee, and the state’s Protect Tennessee Forests program says it is receiving additional reports of the invasive species.

An increase in reports does not necessarily prove that the population has suddenly surged. More public awareness may also be helping residents recognize and report worms that previously went unnoticed.

Tennessee’s warm, humid weather and the widespread movement of nursery plants and landscaping soil can create favorable conditions for worms and help them reach new areas.

How can you prevent their spread?

Inspect new plants before placing them in a garden or landscaped area.

Check the container, root ball, and surrounding soil, as well as the underside of the pot and its drainage holes. Hammerhead worms may hide in cool, damp spaces during the day.

Do not move plants, mulch, or soil from an area where worms have been found without carefully inspecting the material.

Residents can also photograph and report suspected invasive pests through the Tennessee Department of Agriculture’s Report a Pest program.

Hammerhead worm fast facts

• Native to Southeast Asia
• Invasive in Tennessee
• Preys primarily on earthworms
• Does not bite or sting
• Should not be handled with bare hands
• Can regenerate from body fragments
• Should never be cut apart
• Should be treated inside a sealed bag or container

Hammerhead worms are not a reason to panic, but they should not be ignored.

Recognizing them, properly containing them, and checking newly purchased plants and soil can help limit their spread. Most importantly, do not touch one with bare hands—and do not cut it apart.

More information about invasive species and reporting suspected pests is available at ProtectTNForests.org.