A reader from South Africa (Durban, South Africa, more precisely) wrote to us about two hammerhead worms that he found in his home. He was wondering if hammerhead worms are harmful or dangerous to animals or babies, and he was also keen to discover what is causing them to enter his home. So, the question before us is this: are hammerhead worms harmful to humans or animals (like pets), and how do you get rid of hammerhead worms? (Technically, the reader didn’t ask how to get rid of hammerhead worms, but he was wondering how they got into his house, and in answering the latter we also answer the former.)
First, for those unfamiliar with hammerhead worms, here is a little background. Hammerhead worms are flatworms, which means they are members of the phylum Platyhelminthes. Working further down the taxonomic ladder, they belong to the family Geoplanidae (i.e., the “land planarians”). There are several species of hammerhead worms, so the term “hammerhead worm” actually ranges over multiple types of similar worms that belong to the genus Bipalium. Ok, enough taxonomy.
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Hammerhead worms can grow to be quite large, up to 20 inches (about 50 centimeters) in length, in fact. They are nocturnal, so it is easiest to find them at night, but they are commonly seen in the morning too. They are most often found on the top of soil – like in a garden or on one’s lawn – after it has rained. Like earthworms, hammerhead worms live in the soil because they need a moist environment to survive.
Now, onto our reader’s specific questions. Hammerhead worms are not harmful to humans, nor are they harmful to animals like household pets. In fact, they are only harmful to earthworms, which serve as their source of food. (Earthworms are technically animals, so we can’t make the blanket statement that hammerhead worms are harmless to all animals.) Because they feed on earthworms, hammerhead worms are carnivorous. Hammerhead worms will follow an earthworm’s trail to capture it, and then it holds its victim in place with its muscles and a sticky secretion. Hammerhead worms eat earthworms in the most gruesome of ways. A hammerhead worm will push its pharynx out of its mouth and then secrete enzymes on the worm. The enzymes will dissolve the earthworm’s body, and once this occurs, the hammerhead worm sucks the liquefied tissue into its body. Because the earthworm is dissolved before being consumed, the hammerhead worm’s digestion process largely occurs outside of its body.
Why are hammerhead worms entering our reader’s house? Of course, we can’t be sure, but they probably just ended up there by accident. Since hammerhead worms eat earthworms, there is presumably no source of food inside the house that is attracting them. Moreover, hammerhead worms depend on moist soil for survival, so they are generally only above ground after it rains. So, again, we have to assume the hammerhead worms simply entered the reader’s house by chance. Maybe there are some cracks in the foundation of the reader’s house that let them through, or perhaps they managed to get through a crack at the bottom of a door. If the reader wants to keep the hammerhead worms out, he should seal up any gaps in his house that he finds, but it seems unlikely that they will keep coming into the house. It’s not an environment they want to be in.
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So, we can tell our reader that hammerhead worms are not harmful to humans or animals that aren’t earthworms. It might have been a little starling to find hammerhead worms in his house, but the reader shouldn’t worry about them harming anyone, and if he wants to keep them out, we can recommend nothing more than sealing up any gaps or crack that may allow them into the house.