Horsehair Worm

Image of a horsehair wormDescription of horsehair worms

The horsehair worms are interesting threadlike roundworms that resemble the "hair of a horse's tail or mane." These long, active worms may be observed during late summer or fall in streams and ponds, but are more commonly noticed in domestic water containers such as bird baths, swimming pools, water troughs, pet dishes, sinks, bathtubs and toilets. They may also be found on damp garden soil or vegetable plants after a rain.

Horsehair worms are no bigger around than kite string (1/25 to 1/16 inch wide) and very long (4 to 14 inches). Amazingly, the entire horsehair worm grew and developed as a parasite inside the body cavity of crickets and other large insects such as grasshoppers, katydids, beetles and cockroaches. This internal parasite of insects does not harm humans, animals or plants.

Life cycle of horsehair worms

Parasitized crickets are thirsty and go to water to drink. While there the horsehair worm emerges from the insect's body and swims away in the water, an essential step in the life cycle of this internal parasite. Insects infected with horsehair worms die as a result of the parasite.

Horsehair worms are white when they first emerge from the host's body. They turn yellowish-tan to brownish-black after a short period of time. The worms often squirm and twist in the water, knotting themselves into a loose, ball-like shape, resembling the "Gordian Knot." Another name for horsehair worm is Gordian worm.

Horsehair worms resemble hairs from horses actively moving in the water. A superstition once surrounding this species held that the worms in water troughs and puddles had miraculously come to life from the long, thin hairs of a horse's mane or tail that had fallen into the water.

Damage caused by horsehair worms 

Horsehair worms are completely harmless. They do not infest people, livestock, pets or plants. They are beneficial because of the small percentage of crickets that they kill. No control measures are needed when this interesting worm is found.

 

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.  

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