Worm Found in Colorado is a Horsehair Worm

We just heard from one of our followers in Littleton, Colorado. He discovered a worm-like organism in his garden after some heavy rain. He is curious if we know what this creature is, and also wonders if it could cause harm to his pets or family members.

We are quite pleased that he has included a photograph. While descriptions are useful, photographs are often crucial when making an identification on an unknown species. The photo our reader sent shows a long worm that fades from a blackish dark green to a very pale light green that is almost white. The worm is positioned next to a piece of human hair, so it is obvious that it is much thicker than a strand of hair, and is probably closer to the thickness of a piece of spaghetti.

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We believe this is a Nematomorpha, which is commonly known as a horsehair worm or a Gordian worm. Horsehair worms are 1-3 mm thick and can grow up to 50-100 centimeters long. People find horsehair worms in damp places containing freshwater such as watering troughs, swimming pools, ponds, and streams. Adult horsehair worms are free-living (which means living independently and unattached to a substrate), but at the larval stage they are parasitic to arthropods, like beetles and cockroaches. The parasitic larvae enter an arthropod host and then eject themselves out of the host when they can sense they are close to water. However, they are not harmful to mammals. So, unless our reader’s pets are insects, it is safe to say that this worm is not harmful to his pets of family members.

To conclude, a reader found a long, thin worm in his garden after a downpour. Based on the photograph, we determined this to be horsehair worm. This horsehair worm likely appeared due to the heavy rain!

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We just heard from one of our followers in Littleton, Colorado. He discovered a worm-like organism in his garden after some heavy rain. He is curious if we know what this creature is, and also wonders if it could cause harm to his pets or family members.
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