An unusual creature with a distinctive head shape might be lurking in your garden, prompting curiosity and perhaps a bit of unease. Hammerhead worms, named for their spade-like or half-moon-shaped heads, are predatory land planarians that have gained attention due to their strange shape and non-native status in many regions. We get some emails every year reporting their presence, because their presence can be a cause for concern among gardeners due to their potential impact on the local ecosystem.

Recognizing Hammerhead Worms

Identifying a hammerhead worm begins with recognizing its key physical traits. The most prominent feature is the head, which distinctly resembles a hammerhead shark or a half-moon. Their bodies are long, flattened, and unsegmented, often described as ribbon-like or snake-like; and can range in size from a few inches to over a foot in length.

Coloration varies, but they are commonly light brown or honey-colored, frequently adorned with dark longitudinal stripes that can range from one to five depending on the species. One notable species, Bipalium kewense, often exhibits an incomplete dark collar around its neck.

The surface of these worms is typically slimy due to a mucus covering that aids in their movement and prevents them from drying out, allowing them to thrive in the moist environments gardens often provide. They move using a “creeping sole,” a ciliated area on their underside that helps them glide along a film of mucus.

Invasive Species in North America

The world is home to a diverse array of terrestrial flatworms, with over 900 species known to science and many more yet to be formally described. Within the genus Bipalium, to which many hammerhead worms belong, there are more than 60 identified species.

Hammerhead worms are not native to North America and are considered invasive. In North America, around five species of hammerhead worms are considered invasive, highlighting the global reach of these creatures and the importance of understanding their presence in local ecosystems. They are believed to have been introduced from tropical regions, particularly Southeast Asia, likely through the movement of potted plants and soil in the horticulture trade. While some flatworm species are native to North Carolina, the hammerhead worms, particularly those in the genus Bipalium, are considered exotic. Specifically for the region around Sanford, North Carolina, these worms have been present for many years, with Bipalium kewense being documented in the state since at least 1951.

What Do They Do In the Garden

In the garden, hammerhead worms primarily act as predators, with a particular fondness for earthworms. Earthworms play a vital role in maintaining healthy soil structure and fertility, so their predation by hammerhead worms can be a concern for gardeners. They also feed on other soil invertebrates like slugs, snails, and insect larvae, potentially impacting the garden’s biodiversity. These flatworms also produce a neurotoxin called tetrodotoxin in their mucus, which they use to subdue prey and which can cause skin irritation in humans and be harmful to pets if ingested.

What Should You Do If You Find One?

There are certain actions recommended if you encounter a hammerhead worms. It is crucial to avoid touching them with bare hands due to the neurotoxin in their mucus, which can cause skin irritation. Furthermore, cutting or chopping the worm is not advisable as it can regenerate into multiple new worms.

The most effective method for eliminating them is to collect them using gloves or a tool and place them in a sealed bag or container with salt or vinegar, which will cause them to dehydrate and die. Freezing the sealed container overnight is another effective disposal method. Some experts also suggest using citrus oil or soapy water. It is generally advised to avoid using salt or vinegar directly on the soil as it can harm plants and other beneficial organisms.

In conclusion, while hammerhead worms might seem like a bizarre addition to your garden, understanding their identification, ecological role, and non-native status is key to managing them effectively. By taking appropriate precautions and following recommended removal methods, gardeners can mitigate any potential negative impacts these uninvited guests might have on their garden ecosystem.

Amanda Bratcher is the Horticulture Agent for North Carolina Cooperative Extension in Lee County.