Gordian worms, also known as horse hair worms, are worms in the phylum Nematophora that parasitize various arthropods. While they are not human parasites, they may be incidentally discovered in the toilet bowl and mistakenly thought to have come from the human body. Therefore, they are not uncommonly submitted to the clinical parasitology for identification. They are long slender worms, usually measuring 50 to 100 mm, with a diameter of only 1 to 3 mm.