One of our readers recently asked us, “Do flies carry horsehair worms?” In short, the answer to her question is yes, flies could potentially carry horsehair worms. However, we will provide a more in depth explanation below.

Horsehair worms, or Nematomorpha, are a phylum of parasitoid organisms that resemble a long strand of hair or thread (hence their nickname.) So, what is the difference between a parasite and a parasitoid? A parasite is an organism that lives in or on the surface of another organism, known as its host, and steals nutrients at the host’s expense. A parasitoid is very similar to a parasite, however a parasitoid always kills its host, wheres a parasite does not always kill its host.

Horsehair worm larvae develop in the bodies of their hosts, which are always arthropods. Some common hosts for horsehair worm larvae are beetles, crickets, cockroaches, and grasshoppers. Once the horsehair worm larvae has matured enough to lay eggs, it will be ready to leave its host’s body. Adult horsehair worms are free living, and therefore don’t need a host to survive. The larvae must wait for the host to go near a body of water, then it will eject itself from the host’s body, killing the host in the process. Adult horsehair worms are usually discovered in areas with lots of moisture such as a watering trough, swimming pool, ponds, cisterns, and puddles.

As we mentioned above, horsehair worms always choose Arthropod hosts. Arthropods belong to the phylum Arthropoda. They are a diverse group of animals including insects, crustaceans, spider, scorpions, and centipedes. These animals all have an exoskeleton, segmented bodies, jointed appendages, bilateral symmetry, and an open circulatory system. So, to refer back to our reader’s question: Do flies carry horsehair worms? Since flies are arthropods, they could be hosts for horsehair worms.

To wrap up, one of our readers asked us if flies carry horsehair worms. Since flies are arthropods, and horsehair worms always choose hosts that are arthropods, flies could potentially carry horsehair worms.

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