If you notice a strange, flat worm with a broad, hammer-shaped head in your garden, you may have encountered a hammerhead worm. Unlike familiar earthworms, these unusual creatures are predators that typically live in damp soil, gardens, and other moist environments. Their distinctive shape makes them easy to recognize once you know what to look for.

Hammerhead worms are native to Southeast Asia, but some species have spread to other regions through the movement of soil, plants, and landscaping materials. Their ability to survive in new environments can make them difficult to control. Some species can also reproduce from separated body sections, which is one reason cutting them apart is not recommended.

Their presence can be particularly concerning for gardens because hammerhead worms prey on earthworms. Earthworms are important for soil health because they help break down organic material and contribute to soil structure. A large population of predatory worms could therefore affect the balance of a local garden ecosystem.

Although hammerhead worms may look frightening, they generally are not considered a major threat to people or pets. However, some species contain substances that can irritate or potentially harm if handled improperly, and tetrodotoxin has been detected in certain hammerhead worms. For that reason, it is best to avoid handling them with bare hands and keep children and pets away.

If you find one, take a photograph first so you can help identify the species, and follow local guidance for invasive-species removal. Avoid cutting the worm into pieces, since some species may regenerate from fragments. These unusual creatures may look harmless or even fascinating, but their impact on earthworms and soil ecosystems makes them worth taking seriously.