Do Worms Have Bones? How Do Earthworms Move?

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Earthworms move in an interesting way. One side of the worm almost pulls the other side in the direction it wants to go in. It begs the question; do earthworms have bones?

The short answer is no, earthworms don’t have bones. They are invertebrates. Earthworms are considered annelids and while they don’t have bones, they do have what is known as a hydroskeleton. 

These aren’t bones in the normal sense, but as the name suggests, it’s a skeleton made of liquid with muscles surrounding it. This is what gives an earthworm its cylinder shape and stops it from being flat.

When it comes to bones and earthworms, some people may think of snakes as a comparison.

Although earthworms may look similar in shape and movement to snakes, there are a few differences. 

Snakes are vertebrates and have bones while worms are annelids and don’t. 

Bones cannot contract, but a snake’s muscles can. So you will find that snakes usually move in a serpentine S-shape, while earthworms move forward and backward in a straight line.

Since there are no bones, why can worms still drill into the ground?

This is a good question. The cylindrical body of an earthworm is composed of multiple segmented bodies. 

Of course, worms are not hollow. There are many important organs, skin and muscle layers inside the body cavity.

There is a layer of muscular pharynx throat muscles next to a worms mouth area. 

These muscles not only help them drill the soil but also grab food. 

For example, we’ve seen earthworms eat bananas before . 

In addition, the muscles of earthworms account for about 40% of the body, and there are mainly two muscle layers. 

The first layer behind the skin is the circular muscle, and the longitudinal muscle layer is next to the circular muscle. 

You can think of the ring muscles as a rubber ring set on an earthworm body. 

The ring muscles will stretch the body of the earthworm as soon as they are relaxed. 

The opposite happens with the longitudinal muscles. They will contract which results in the body of the earthworm shrinking and becoming thicker and shorter. 

Just like this, the earthworm can move forward and backward in an orderly alternating fashion.

There are other interesting characteristics of earthworms, I have written some more worm facts ← here.

Earthworms and Their Invisible bristles

earthworm bristles

The body of the earthworm is not bare. 

They have very fine protrusions of setae bristles which are mostly located under the abdomen. 

Even with the alternating tightening of muscles to help an earthworm advance, without these bristles, the earthworm would spin around in place due to a lack of proper friction. 

The number of bristles in each link of an earthworm’s body will vary from species to species, but generally they have around 10-50.

And these hairs or bristles don’t stick out all the time, otherwise friction would make it more difficult to move forward. 

When the circular muscle contracts to help the earthworm slide forward, the bristles will retract. 

Then when the longitudinal muscle layer is tightened, the body becomes shorter and thicker, and the bristles will extend.

This alternation allows the earthworm to move forward slowly.

If you can’t imagine it, this is how earthworms move from up close.

A small experiment to find the bristles of earthworms and see that they’re not smooth

If you have a friend who raises earthworms, or try to catch a few in the soil in your garden, you can do a simple experiment to see if the bristles actually exist. 

Just prepare a newspaper and a piece of glass, and then put the earthworms on it and let them crawl.

If you listen carefully, you will hear the rustle in the newspaper, but not on the glass. 

This is because of the friction between the bristles and the newspaper; and the smooth surface of the glass will not produce much friction with the bristles, and there will be no rustling sound as a result.

Speaking of sounds – do worms make noise? < – – We explain here