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Because horsehair worms are parasites of invertebrates, especially certain insects, they are commonly encountered in agricultural areas, particularly those having water-impoundment and irrigation facilities. An old and still common misconception is that these long, thin, brown to blackish worms develop from horsehairs that fall into water. Adult worms measure 1/25 inch in diameter and may reach 1 foot or more in length. Horsehair worms occur in knotted masses or as single worms in water sources such as ponds, rain puddles, swimming pools, animal drinking troughs, and even domestic water supplies. They are also called Gordian worms, because they will often twist into a loose ball-shaped knot resembling the baffling one Gordius created in the Greek myth and that is referred to as the Gordian knot (Figure 2).
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Horsehair worms belong to the phylum Nematomorpha, from the Greek word meaning thread-shaped, class Gordioida (Figure 1).
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Horsehair Worms Integrated Pest Management
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