F@stSheet Ent-1011

Horsehair Worms IN THIS F@STSHEET BIOLOGY IMPORTANCE FOR MORE INFORMATION

Horsehair worms are parasites of certain insects, especially crickets and grasshoppers. They are commonly found in puddles of water, on damp sidewalks and patios, or as they emerge from bodies of their insect hosts. Despite their sometime frightening appearance, these creatures are not harmful and have no economic importance.

The long, thin structure of these worms is so similar to that of a hair that it was formerly thought that they were transformed from horse's tail hair. Horse hairs frequently drop into watering troughs where they can accumulate. Coincidentially, insects (including those parasitized by horsehair worms) also frequently fall into the water of horse troughs and die. Horsehair worms which emerge from parasitized insects were seen swimming in water troughs and supposed to have spontaneously transformed from the long horse hairs; hence the term "horsehair worm".

BIOLOGY
Horsehair worms are insect parasites that belong to the phylum Nematomorpha. One of the most common species in the United States in Gordius robustus.

The body of the horsehair worms is extremely long and thread-like. Lengths of a foot or more are not common. The body diameter is about the width of a pencils's lead. They are creamy to blackish in color, and frequently are twisted and coiled like a discared thread.

Not much is known about the life of horsehair worms. Adults, the stage most commonly seen, live in water or very moist soil. Immature stages are parasitic, living in the bodies of insects and crustaceans. Adults live in all types of fresh-water habitats and can be found in both temperate and tropical regions. They commonly swim or crawl about by a whip-like motion. Immature stages are parasites on insects living in or near water, or in moist soil. Beetles, cockroaches, crickets or grasshoppers are the most common hosts. One species lives in salt water and parasitizes crabs. Emergence from the host occurs only when the host is near water. Occasionally, they are found after a cricket of cockroach is crushed, or when the host hops into a container of water, when the worm begins to wiggle out of the insect's body.

IMPORTANCE
Since horsehair worms are parasitic, they are assumed to be beneficial in the control of certain insects. Its true value as a parasite, however, is questionable because the worm does not kill its host until it matures. Horsehair worms are not parasites of humans or pets. Therefore, these creatures are primarily of interest as one of nature's oddities. If their presence in a swimming poll is bothersome, they can be safely removed by hand or with a net.

Horsehair worms can be confused with other parasitic worms of the phylum Nematoda. Parasitic nematodes are usually microscopic and can further be distinguished by the structure of the posterior (tail) of the body. The tail of parasitic nematodes is hooked and the anoal opening occurs before the body's end. In contrast, the end of Gordius horsehair worms have a cleft (see figure).

FOR MORE INFORMATION
For more information about crickets and cricket control, see the fact sheet Cricket Control in the Fall. For more information about grassshoppers, see Grasshoppers and Their Control. Information in this fastsheet was based, in part, on Pennak, R.W. 1978. Chapter 10: Nematomorpha (Horsehair worms, Gordian worms) pp. 231-238. in Freshwater Invertebrates of the United States. 2nd Ed. John Wiley and Sons, New York. 803 pp.

Authors:
Michael Merchant, Ph.D., Urban Entomologist, Texas Agricultural Extension Service
James Robinson, PhD. Extension Entomologist, Texas Cooperative Extension.
Mary Wicksten, Professor of Biology, Texas A&M University.

Publication information:
This publication is part of the House & Landscape Pest Series produced by the Department of Entomology, Texas A&M University, College Station, TX 77843-2475. The most recent update can be found at: [FrontPage Substitution Component] . Series Editor: M. Merchant. For more information about arthropods, check out the Texas A&M Entomology Website at http://insects.tamu.edu
Last Revised: 5/12/03