A reader wrote to us recently about a hammerhead worm, or what is believed to be a hammerhead worm, that she found on her kitten. The worm was found on the side of the kitten, and before the reader could remove the hammerhead, the kitten licked it. The reader was concerned that this might hurt the kitten, and was wondering if the kitten would become sick from licking the hammerhead worm. Unfortunately, this question falls outside of our purview. We are not veterinarians, so all we can ever say is that if something is questionable about your pet, you should go to the vet’s office. We can, however, take this opportunity to talk a little about hammerhead worms, explaining what hammerhead worms are and what they do.
To begin, we should note that finding a hammerhead worm on your pet (kitten or otherwise) is coincidental. In other words, hammerhead worms are not known to afflict pets or other mammals, making them distinct from creatures like hookworms and tapeworms. The kitten perhaps rolled over on the hammerhead worm, which is why it happened to be found on the kitten’s body. It is not as if the hammerhead worm was attacking the reader’s kitten or anything like that.
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That said, hammerhead worms are a type of flatworm (i.e., the members of the phylum Platyhelminthes) that live on land. More precisely, hammerhead worms are part of the family Geoplanidae, which are also called “land planarians,” and the worms that are specifically labeled “hammerhead worms” compose the genus Bipalium. There are several different species in this genus, so a hammerhead worm is not a specific species of worm, but rather a loose term that ranges over several types of worms that have a distinctly shaped head (one that roughly resembles a hammer head, naturally.)
Hammerhead worms are carnivorous, with many of the species preying on earthworms specifically. A hammerhead worm will track an earthworm by following the earthworm’s trail, and then the hammerhead will capture and hold the earthworm using its muscles and a sticky secretion. How the hammerhead worm actually eats the earthworm is a little brutal. It’s a complicated process, but this is what happens in a nutshell: the hammerhead will push its pharynx out of its mouth to secrete enzymes on the captured earthworm. These enzymes will begin to dissolve the earthworm, meaning that the hammerhead’s digestion process is actually occurring outside its body. Once the earthworm is sufficiently dissolves, the hammerhead sucks the liquefied earthworm tissue into its body. So, hammerhead worms are predatory, but they prey on creatures like earthworms (and certainly not kittens!). This is true even when hammerhead worms grow to be quite large; some species can actually grow to be 20 inches (50 centimeters) long.
Hammerhead worms are nocturnal, meaning it is easiest to see them at night. However, they are commonly seen in the early morning hours too. Like a lot of other types of worms, they enjoy, and in fact need to live in, moist places. This means that they are often beneath the soil, but if it rains hard, they may emerge from underneath the ground. Thanks to the global shipping of horticulture plants, hammerhead worms could technically be found anywhere. They are a common invasive species, disrupting ecosystems all over the place, including the United States.
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Those are some basics about hammerhead worms. Unfortunately, we weren’t able to address the reader’s concern about her cat, but perhaps she will take some comfort in the fact that the hammerhead worm wasn’t going after her kitten specifically. We would urge our reader to keep an eye on her kitten and take it to the vet if it has any problems or if she has any concerns.