Today we will answer a reader’s question about hammerhead worms. He wrote, “I found this hammerhead worm crawling up our concrete retaining wall outside. We live in East Tennessee. How common are these worms here? This is the first one I’ve ever seen and I didn’t know what it was until I googled it!” The picture shows a light brown hammerhead worm with some faint stripes running down its back:
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Hammerhead worms, or broadhead planarians, belong to the Bipalium genus, which is made up of predatory land flatworms. As the word ‘predatory’ suggests, hammerhead worms are brutal hunters. They primarily eat earthworms, which they cleverly track and then capture. Once captured, the hammerhead worm uses a combination of its muscles and sticky secretions to attach itself to the earthworm and prevent its escape. Instead of simply eating its prey like a polite dinner guest, the hammerhead worm secrets enzymes on the earthworm that dissolves its body, which the hammerhead worm then slurps up. As you can imagine, its quite a traumatizing death for the earthworm.
Hammerhead worms aren’t dangerous towards humans or considered harmful, but they are an invasive species and some people think of them as pests because they reduce the earthworm population, and earthworms are really beneficial to the environment. There are currently four known invasive species of Bipalium in the United States, and they are believed to have arrived alongside horticultural plants.
Now, to answer our readers question: How common are these worms? They are quite common and found often in greenhouses and gardens throughout the United States. However, they are nocturnal, so it’s easiest to notice them at night. They prefer to live on top of the soil and, like earthworms, need a moist environment to survive. Maybe our reader has stepped right over a hammerhead worm in his yard before without noticing it, and now that he knows more about them, perhaps his eyes will start to see more of them around his home.
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In summary, a reader in Tennessee found a hammerhead worm in his yard. Although these broadhead planarians aren’t dangerous, they are invasive species that are sometimes considered pests.