Horsehair (Gordian) Worm
September 18, 2012
By Matt Marine
You're probably wondering why I've created a page for the horsehair worm. True, it's not an Arizona iconic creature (you won't see one of these on a billboard for Arizona), but since I recently encountered one, I thought I would share my experience and knowledge with you.
One September morning, my sister, Cat-dog and I were hiking along the Canyon Loop Trail in Catalina State Park and we stopped at one of the frequent wash crossings. Water is usually here and we were in luck: cool, clear water trickled through the sandy wash.
Then we noticed something in the water. It looked like a weed or piece of algae. But this didn't float with the current. It was "swimming"!
The creature was about 8-10 inches long and very thin (maybe an 1/8" in diameter).
At first I thought it must be some kind of eel or snake. But it was too thin. It also had what looked like a square breathing tube at each end. What the heck was it? Maybe I had found the Arizona version of the Loch Ness Monster!
After much discussion with my friends at Offroad Passport with guesses ranging from a western blind snake to tapeworm, we finally found out it was a horsehair worm (belonging to the group Nematomorpha).
So what is a horsehair worm? It's a long, slender worm that got its name from the old belief that they were the long strands of hair that fell off a horse's main into a horse trough and then came to life. Also, when they are found in large masses or knots, some called these Gordian worms.
The specimen I saw in the water was a free-living adult. When they are immature, they are parasites living on insects and arthropods. As young larvae they infect insects, but it is not known exactly how. I'm thinking it's sort of like the movie Alien, at least from the insect's point of view.
The larvae then parasitize the insect (which is like eating it from the inside out), then when the insect is near water, the now mature horsehair worm emerges, killing the host. Again, I'm thinking the movie Alien here. The only difference is that the adult horsehair worms don't feed on anything (all they are looking to do is mate), which is vastly different than the creature from Alien. Oh, and they don't have acid for blood.
Adult horsehair worms can be a wide variety of colors, white/tan like the one we saw, or brown, green or blackish. They can grow up to 14 inches long and are usually found in or near water. They are often seen in puddles, pools, troughs or tanks of water especially after a rainfall.
Horsehair worms mate during all seasons except winter with males coiling around females. It isn't uncommon to find numerous worms all entwined making a big ball of horsehair worms. Eggs are long and gelatinous and found in fresh water.
If you're getting a little grossed out, you're not alone. But the good news is that they are harmless to humans and pets in all stages of their lives. Whew!
For more information, visit:
University of Kentucky Entomology
University of Minnesota Yard and Garden Brief
Here is the video I took of this creature swimming in the water.