“What is this?” asks this reader about the long, thin, white worm pictured below slithering over some big rocks. “It is a live worm as thick as a thread of cotton. Many thanks.” She does not provide more context than this, though based on the photo alone, we would say this most resembles a horsehair worm. Unfortunately, the horsehair worm has garnered an unsavory reputation that is founded in a lot of misinformation. Also referred to as a Gordian worm, because of its tendency to tangle in on itself like the mythical Gordian knot, the horsehair worm is a parasitic worm that only takes insects and other smaller invertebrates as hosts.
Horsehair worms are technically marine worms: they start off as eggs floating in a body of water, and eventually hatch and become larvae. When an insect drinks that water and ingests the larvae, they move to the stomach of the insect and begin feeding off whatever the insect consumes. Once the worm has fully matured, it will burst forth from the insect, causing the insect to virtually explode, and then will roam freely, looking for a mate to start this whole process over again. When the mature worm is free of its host, it may want to take to bodies of water and swim around looking for other worms, though it can also move across land.
Now, the misinformation that causes a lot of people to fear, and even detest, horsehair worms is that they infect humans purposefully. The key word here is ‘purposefully’. There have indeed been instances of horsehair worms being found in people: some even have crawled their way up people’s throats and been spit out. Yet, the majority of these cases have been a product of the human ‘host’ ingesting an insect that is infected by a horsehair worm. For that reason, the worm accidentally ends up in the human. All studies point to the fact that, even when a horsehair worm finds its way into a human body, it will not successfully take the human as a host, nor will it affect their health negatively to any significant extent.
In conclusion, the worm our reader found looks like a horsehair worm, and it is possible that that is what it is, though it is difficult to say anything for sure without more context. Our reader needs not fear the worm, though we do not recommend touching it, as our identification is not 100% certain. We hope this helps and we wish our reader the very best!
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