Horsehair Worms: The World’s Thinnest Worms

If you have ever seen a super thin worm wiggling it’s way out of the body of an insect such as a cricket, out of the nose of an amphibian or out of any orifice of a reptile, chances are it was a horsehair worm. Also called the “Gordian worm,” the horsehair worm is a parasite that not only lives inside crickets, but they also live inside cockroaches, grasshoppers, and beetles. These odd threadlike creatures can grow up to 3.2 feet (one meter) and only 0.03 inches (3 millimeters) in diameter. If you have observed the horsehair worm emerging from the body of a larger animal or anything other than an insect, it was probably inside of the cricket, cockroach or beetle that was just ingested by a larger animal.

Horsehair worms belong to the roundworm family and they earned the name because they look just like the thin hair of a horse tail. Horsehair worms are typically dark brown in color, but some are tan, yellow or black. They usually peak during the late summer as well as during the fall months. Finding horsehair worms in odd places is not uncommon. They have been spotted emerging from a cricket on the kitchen floor of homes or in the toilet after a cricket has been dumped there, and they have even been spotted in pets water bowls. They can also be found swimming around in lakes, rivers, streams, and garden ponds.


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The life cycle begins when a male and female horsehair worm mate in soil or freshwater. The female can lay as many as 10 million eggs. She typically lays her eggs in water plants. Once the eggs hatch into larvae, they live inside cysts in vegetation — vegetation that is ingested by crickets, grasshoppers and other insects or bugs. Once ingested, the cysts dissolve inside of the grasshopper or cricket gut. The parasite makes its way into the body cavity of the insect where it absorbs nutrients from the insects’ food through the body wall. The horsehair worm is so thin that it can develop and grow to its maximum length inside the body cavity of small cricket. However, the usual length of time that a horsehair worm will develop inside the host is 4-20 weeks. Amazingly, once the horsehair worm reaches maturity inside of the host, it can live out the rest of its life from the nutrients and energy obtained from the host.

Another amazing thing about the horsehair worm is its ability to manipulate its body into many forms. The horsehair worm can even twist itself into a ball that resembles a Gordian knot. Hence the name, Gordian worm.

When the horsehair worm is ready to exit its host, usually when the host is near or in water, it will wiggle out of the nearest opening. This is not always the case, however. They have also been known to exit on dry land, of course. Once the parasite exits the body of an insect, this emerging actually completes the life cycle of the horsehair worm. If you dare, you can witness the horsehair worm exiting the body of a cricket here. Fair warning, its not a pretty sight.

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Author: The Top Worm

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