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Horsehair Worms
by Barb Ogg, PhD, Extension Educator

Horsehair Worm Emerged from this Cricket

Horsehair Worms are parasites of some insects

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A couple years ago in late September, I was in the middle of preparing a salad for dinner, I noticed a very large female field cricket sitting in the middle of my kitchen floor. It seemed a bit sluggish so I stepped on it lightly. A few minutes later after finishing my salad preparation, I turned to dispose of the cricket. To my surprise, I noticed a long, black threadlike "worm" emerging from the cricket's body. As I watched, it continued to emerge. I was fascinated to see how long it was—fully extended it was at least 8-10 inches long. This was a horsehair worm—an internal parasite of crickets and other insects like grasshoppers, cockroaches and beetles.

Horsehair worms are threadlike roundworms that get their name because they resemble the hair of a horse's tail or mane. In fact, people once thought that they arose spontaneously from the hairs of a horse's tail. Horsehair worms are about the width of dental floss and very long (four to 14 inches). Color usually ranges from tan to dark brown, although yellow and black worms also occur.

Horsehair worms are active and often observed during late summer or fall months. People sometimes find them like I did, after stepping on a cricket. We've received calls from people reporting horsehair worms "swimming" in the toilet bowl after emerging from a cricket that had been tossed into the toilet. Horsehair worms are also found in streams and ponds and in domestic water containers such as bird baths, swimming pools, backyard ponds and pet dishes. They may also be found on damp garden soil after a rain.

The adult horsehair worms are free-living in fresh water and damp soil. Parasitized crickets seek water because they are thirsty. This behavior allows the horsehair worm to emerge from the insect's body and swim away in the water—an essential step in completing its life cycle.

Male and female horsehair worms mate in freshwater or damp soil. The female lays millions of eggs in long strings that wrap around water plants. Eggs hatch into 0.01-inch larvae that do not resemble the adults. Shortly after they hatch, it is thought that the larvae encyst on vegetation near the water's edge and later the vegetation is eaten by a grasshopper or cricket. The cyst covering dissolves inside the insect gut which allows the juvenile worm to bore through the gut wall and into the body cavity of the host. The worm absorbs nutrients directly through the body wall. Amazingly enough, the long horsehair worm that I watched on my kitchen floor, grew and developed inside the body cavity of this cricket.

Horsehair worms may 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.

These internal parasites of insects do not parasitize other animals or plants and are completely harmless. Because they are beneficial organisms, no control measures are needed when this interesting worm is found.

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