We recently received several photos of a fairly long, skinny worm that a reader found in his backyard. We have received many questions about long, skinny worms, and every time we do our first thought is that the reader has found a horsehair worm (sometimes incorrectly written “horse hair worms”), as horsehair worms are indeed long and skinny. With respect to our present reader’s question, we also think there is a good chance he found a horsehair worm. However, the reader specifically asked about tapeworms (which is also incorrectly spelled frequently – as “tape worms”) and was wondering if the creature he found could “burrow” into a body. So, we’ll address the reader’s concerns concurrently, explaining why we think he found a horsehair worm (and not a tapeworm), and in so explaining it will be clear why there is no need to worry about this worm burrowing into a body.

First, let’s take a look at a couple of the best photos the reader submitted along with his question.

The nail in the picture is one and half inches long (about four centimeters), indicating that the worm in the picture is probably a little over two inches (about six centimeters) in length. In the first picture, you can see that the worm is coiled up, and this is the first reason we think the reader found a horsehair worm.

Horsehair worms can coil up extremely tightly; in fact, because they are known to coil up, horsehair worms are often called “Gordian worms” because they resemble Gordian knots. They are able to coil up in this manner because of their parasitic way of life. Horsehair worms start off as larvae (well, they are technically eggs first) that hide in small cysts on certain types of plants. These types of vegetation, along with the cysts on them, are consumed by various insects, like crickets, grasshoppers, and beetles. Once the cysts are consumed, the horsehair worm starts to mature, absorbing the nutrients that the host insect eats. So, horsehair worms grow inside the bodies of small insects, forcing them to coil into a very small space. Their coiling efforts are even more impressive considering how long horsehair worms can grow before exiting an insect’s body. They can be up to three feet (or nearly a meter) in length, although they are much more commonly around a foot long. They are also extremely thin – no larger than the width of mechanical pencil led – and this helps them compress into small spaces too.

Obviously, the worm our reader found isn’t a foot long, but not all horsehair worms are this long. Their size depends on how long they mature inside an insect’s body, which is generally in the range of four to twenty weeks. Horsehair worms only exit an insect’s body if it is near water, so perhaps the worm our reader found exited an insect’s body when it was by water, and maybe this occurred before the horsehair worm could reach a substantial length (relative to other horsehair worms).

The reader mentioned that he picked up the worm he found and it wiggled around. If he found a tapeworm, he very likely wouldn’t have picked it up, considering that tapeworms are most frequently found in the stool of an infected person or animal. Also, tapeworms found in this way are generally in segments and not as full worms. (However, interestingly, these segments can still move in some cases.) Moreover, tapeworms are often a lot larger than horsehair worms, which look like no more than discarded threads of dental floss.

Neither of these worms “burrow” into bodies. They enter a body when they are consumed, often in the larval form. Tapeworms frequently enter animals when they consume infected meat, much like horsehair worms enter insects when they eat infected vegetation.

To conclude, we think there is a good chance our reader found a horsehair worm, and we don’t think he found tapeworms, or a type of worm that can burrow into a body. Horsehair worms are not harmful at all to humans or pets, so the reader shouldn’t be concerned that he found one; they pose no threat. Our one hesitation in suggesting our reader found a horsehair worm is that he didn’t mention any body of water near where the creature was found, but perhaps there was, and in any case horsehair worms seem to come out after it rains on occasion. And with that we conclude yet another article about horsehair worms.