Horse Hair Worms Facts: What Are These Hair-Like Worms in My Bathtub?

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Horsehair worms are neither pests nor are they dangerous to us. Here is a collection of horse hair worms facts to cover everything you need to know about them.

If you ever happen to see a tangled mass of black or brown, writhing strands in a stream – beware!

While it might look like horse hair fell into the stream and came to life, these strands are actually horsehair worms.

Despite how their imaginative name came to be, the worm has little relation to horses.

They neither infect them nor live amongst them. Let’s take a deeper look at these interesting-looking worms.

Horse Hair Worms Facts

What Are Horse Hair Worms?

Horsehair worms are a type of aquatic, parasitic worms. They have thin, unsegmented bodies with a cylindrical cross-section that remains uniform.

One end is unpigmented and has the “mouth” of the worm.

According to scientists, there are as many as 2,000 species of horsehair worms, though we have only found around 350.

While mating, opposite sexes twist themselves into a knot. This is why they are also called Gordian worms. The name comes from the Gordian Knot – a type of knot from Greek mythology.

Where Do They Live?

They are found worldwide but mostly occur in places close to a water source. The US alone has 11 species of them.

Larvae are parasitic in nature. The worm larvae prey on an arthropod or insect host, living within their bodies and absorbing their fluids through the skin.

The adult lays eggs in freshwater sources like lakes, streams, and sometimes even in a swimming pool or pet water trough.

In general, horse hair worms dwell in any water source, ranging from lakes and puddles streams to water collected on cabbage leaves!

Their appearance in farm troughs and similarity to long strands of hair gave them the name “horsehair” worms.

What Do They Eat?

During the larval stage, the worms survive on the bodily fluids of host insects. Some common terrestrial hosts include grasshoppers, crickets, beetles, and cockroaches.

The microscopic larvae are born in the water and move freely until an insect host drinks them.

They then absorb the fluids of the insect from within its body cavity. After emerging as adults, the worms do not eat.

This is because they do not have a digestive tract. The sole purpose of the adult is to find a mate.

What is the Lifecycle of A Horse Hair Worm?

Adult worms lay eggs in any source of water. These eggs hatch within a time of 3 months. Newly hatched larvae protect themselves using a cyst and move around freely in the water.

They wait for an insect host they mistakenly eat them. Once inside the body walls of their host, they survive on its fluid and grow until the host dies.

Adults can only survive in water. Their life cycle depends on the host they find.

If a larva finds an aquatic host, then they keep growing within. On becoming an adult, they kill the host and navigate out of its husk.

If the aquatic host is one that completes its lifecycle on land (eg: midges) – then the larvae enter a dormant stage.

It remains so until another suitable host comes along and consumes the earlier host. In such a process, the earlier insect was simply an intermediate host.

Sometimes, larvae within a terrestrial host can drive them toward the water. We do not understand this process entirely.

But once the host dives into the water, the adult emerges by making holes in its exoskeleton.

If you next see a dead cricket in a water body, one of its death causes could be these worms.

This is also how sometimes horsehair worms get into indoor spaces like animal water troughs and swimming pools.

Do They Bite or Sting Humans?

Horsehair worms do not bite, sting, or infect humans. They are also not dangerous to pet dogs, cats or plants.

They are parasites of insects and only infect them. If you happen to ingest a horsehair worm by mistake, visit a doctor immediately.

They cannot cause an infection, but you might experience some discomfort and pain in your digestive tract. A common treatment medication used is diethylcarbamazine (DEC).

Are They Poisonous or Venomous?

These worms are not poisonous or venomous but are parasitic. This means that they burrow within their host insect and slowly suck in their fluids.

Eventually, they kill their hosts either by drilling holes in their bodies or by forcing them to drown themselves.

Are They Harmful to Humans as Pests?

Horsehair worms are not considered pests as they cannot infect humans, dogs, cats, livestock, or plants. They do not pose any danger if touched or ingested.

Generally, one need not control measures of their population in freshwater bodies.

However, if they make their way into your animal’s drink or any domestic water supply – you can install a mesh or use chemicals to get rid of them.

Are They Beneficial?

Yes, they are actually beneficial for us! This is because these worms help to control populations of other insects like millipedes, grasshoppers, beetles, cockroaches, and crickets.

They prey on arthropods and small and large invertebrates alike.

However, they only kill their hosts after they mature fully inside. This process takes around three months.

And they are only parasitic towards a set species of insects – making them only mildly beneficial.

Can They Come Inside Homes?

It is quite likely for horsehair worms to grow within water storage areas inside a home.

If a common host, such as a cricket, drowns itself in the water, it can release the adults into the water.

You might see them in flushes, bathtubs, or water supply tanks.

What Are They Attracted To?

Horsehair worms are attracted to host insects such as beetles, snails, slugs, mantises, cockroaches, grasshoppers, and crickets.

Eventually, their hosts are attracted to water to drown themselves and release the worms.

Horsehair Worm

How To Get Rid of Them?

Seeing horseworm hairs in your home does not mean you need to vacate and call a pest control company.

They are quite harmless, and you can dispose of any visible tangles you see. However, to prevent continuous growth, you have to discourage their hosts as well.

To prevent the entry of any common host, you can spray a barrier of insecticide around your house. A mesh can prevent insects from getting into water tanks.

Regularly flush out any animal’s water trough to remove cysts and eggs. You can also seal any small crevices in your home to prevent the hosts from growing in there.

Interesting Facts About Horse Hair Worms

  • The diameter is a single horsehair worm is around 1/25th of an inch.
  • After a host consumes a cyst, the shell of the cyst dissolves, the larvae emerge from it and bore a hole in the digestive tract to reach the body cavity. It resides there until it is ready to emerge as an adult.
  • Initially, a new adult is whitish in color. Eventually, they turn yellowish, then tan, and finally brownish-black.
  • During mating, many worms coil around together to form a large tangle. You might see them more often after a bout of rain.

Frequently Asked Questions

Can a human get a horsehair worm?

If a human happens to eat a cyst or infested host, they can end up with a worm in their gut. However, they cannot infect a human.
If this happens, you will experience some intestinal discomfort. It’s best to visit a doctor who will prescribe the right medication.

Can horsehair worms hurt humans?

Horsehair worms cannot hurt or bite humans. It is safe to remove them manually from any domestic water source using a mesh!
An adult female worm lays millions of eggs at the same time. Since the larvae are microscopic, it’s best to treat the water source with chemicals.

What does a horsehair worm do?

One thing the horsehair worm is famous for is driving its host mad. Since adults only thrive in water, they charge infected hosts to find water bodies.
Crickets and grasshoppers infected with the worm develop suicidal tendencies and drown themselves, allowing the worm to escape.

Are horsehair worms in the US?

The US alone hosts 11 species of horsehair worms. They’re a pretty common species in and around water bodies.
The most common species is Gordius robustus, which belongs to the phylum Nematomorpha. They also look very similar to mermithid nematodes.

Wrap Up

How horsehair worms control their host’s behavior is a mystery. The nervous systems of infected insects produce different proteins than regular insects.

It’s interesting seeing these long worms wriggle in the water. But despite their non-toxicity, it’s best to leave them alone. Thank you for reading.

Reader Emails

Over the years, many of our readers have been confused, interested or even terrified after observing these worms in their midst. Read up on the experiences of our readers in the emails below.

Reader Emails


Letter 1 – Horsehair Worm or Gordian Worm


Unknown critter
I am not sure what I found. After a recent rain, I found the wormlike creature on my sidewalk. It was very flexible and even tied itself into a knot and was able to untangle itself. My first thought was a centipede or millipede, but I could discern no feet or antennas on it. Nor did I see any segmentation. The diameter of it was so small, that I could not tell through my fingers what it felt like, although it seems to have a hard skin (exoskeleton). It wasn’t soft like a worm. In the picture, I believe the head is in the lower right corner, away from the penny. It wasn’t easy trying to get it in focus. I let the guy (gal?) go. Most likely I will never see another one again. (If it helps to identify it, I live in La Crescent, MN)
Greg Watson

Hi Greg,
Your is one of two letters that arrived the same day with images of a Horsehair Worm or Gordian Worm. The other letter is from Nebraska. We found a great site with more information.

Letter 2 – Horsehair Worm or Gordian Worm Worm


Its Raining Horse Hair
I found this creature in a puddle in a park in Kentucky. I was checking out a frog and this thing started moving. I happen to have a baggy so I scooped it up and brought it home. I remember an old saying that said "It would rain horse hair in the dog days of summer." Anyway, Any idea what it is?

Sorry about the tremendous delay here. We have thought about your letter from time to time, though we didn’t have time to do any research. As we are cleaning out our mailbox since we are canceling our old web host, we wanted to post your letter despite not having an answer. We are going to make it a priority to get to the bottom of this interesting example of local lore and the falling Horse Hair.

Update (04/02/2006) We finally found a site that identifies the Horsehair Worm or Gordian Worm.

Letter 3 – Horsehair Worm


Subject:  Horsehair or Gordian Worm Geographic location of the bug:  Washington, Texas Date: 02/09/2018 Time: 09:33 PM EDT Your letter to the bugman:  Here is another example of a Gordian worm. It was observed following a rain Jan 27, 2018. How you want your letter signed:  A Texas Master Naturalist
Horsehair Worm
Dear Texas Master Naturalist, Thank you for sending in your awesome image.  We are quite fond of both descriptive common names for this parasite.  Horsehair Worm is the name we are using to describe the image you submitted because the creature is stretched out and really does resemble a hair from a horse’s tail or mane, and we suspect the illusion might even be more startling given the opportunity to view the worm submerged in water.  The other common name, Gordian Worm, refers to the Gordian Knot of mythology that could not be untangled, and it is a perfect visual metaphor for a Horsetail Worm when it is contracted into a ball.  How long was your Horsehair Worm? It was about 15 inches or maybe more if it had been straight. The stick to the right of it is my walking stick, which is about 1 in diameter.  

Reader Emails

Over the years, our website, has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Horsehair Worm


At least 24″ long Horsehair Worm??? Hi, Found this worm in the driveway. Looking at your site, we thought maybe this is a horsehair worm but didn’t see any nearly this long. In the photo, the ruler is 12″ and the worm is more than twice that length. Otherwise, matches descriptions from others: smooth, no sections, very thin, slightly stiff – not floppy like an earthworm. Michelle & Pete Redding, CA Hi Michelle and Pete, Thanks for sending us your amazing photo of an enormous Horsehair Worm, an internal parasite of the Potato Bug.


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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Tags: Horse Hair Worms

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1 Comment. Leave new

  • I have a heavy rain today. I have found something that looks like this angil hair spaghetti size ,looks like snake or worm on my patio and driveway. some look plae and one of the ones on driveway was black. very hard couldn’t crush it.


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