Creature Feature: Wriggling Ways of the Earthworm

Our Creature Feature series is brought to you through our collaborations between education and citizen science. In this post, the Biomimicry Institute describes how earthworms get around as part of their mission to bring nature-inspired ideas to modern-day challenges.

Earthworm in Mexico. Photo by dani_etxe (CC BY-NC-3.0). Submitted to the Great Nature Project.
This lombriz (earthworm) is wriggling its way through a lawn in Mexico. Photo by dani_etxe (CC BY-NC-3.0). Submitted to the Great Nature Project

By Jeanette Lim from the Biomimcry Institute

Earthworms moving about through dirt and grass are a common sight in gardens, backyards, and parks everywhere. As they move through the soil, earthworms feed on organic matter and create networks of tunnels lined with the undigested waste they leave behind. This activity is beneficial to the soil ecosystem, as it aerates and adds nutrients to the soil.

How do earthworms create these underground tunnels? Think of the kinds of tools that we use to dig into the ground. Shovels, backhoes, and other tools all have rigid structures that can plunge through the soil. Even our hands take advantage of their bony structure to dig and push dirt around. But earthworms are invertebrates that lack a rigid bony skeleton inside their soft bodies. However—and this is the amazing part—they do have a strategy that enables them to dig and navigate through small spaces in the soil. They just use a different kind of skeleton—one filled with fluid.

Look closely at an earthworm and you’ll see that its body is lined with rings. The earthworm’s body is made up of a series of small segments, each separated by a partition, giving the worm this ringed appearance. Each segment is shaped like a cylinder and is filled with fluid that can’t flow into neighboring segments or be compressed, so the volume of the segment always stays the same.

But while the volume of the segment doesn’t change, the shape of the segment can. Body shape changes are what’s behind earthworm wriggling. The shape of each segment is controlled by two different sets of muscles: circular muscles wrap around the segment’s walls, and when they contract the segment gets skinnier and longer. Longitudinal muscles run along the length of the segment, and when they contract the segment gets shorter and fatter.

This shape-shift between long and skinny to short and fat happens because the segments are filled with fluid. Like a water balloon, squeezing the middle of the balloon pushes water to the ends, making them swell. To keep shape changes from getting too extreme in the worm body, strong connective-tissue fibers spiral around the segments. These fibers reinforce the muscular walls and keep bending movements smooth.

Muscles in this kind of structure, called a hydrostatic skeleton, don’t apply forces to bones. Instead, they apply forces to internal compartments filled with fluid under pressure. In earthworms, each segment can move independently, so that alternating contractions between the two different sets of muscles in many different segments create shape changes all along the body. This produces accordion-like body movements that help the worm push through soil and maneuver through small spaces within.

What can humans learn from this resourceful strategy?

How might we learn from the earthworm’s wriggling ways to solve human challenges? Perhaps we can apply the earthworm’s strategy to construction, medicine, or disaster management. For example, the way the earthworm moves its body could inform designs for drills, medical devices, or rescue equipment that needs to navigate through tight spaces.

Have you ever looked to nature for inspiration to solve a problem? You can see more examples of how to learn from nature by browsing the AskNature collection of Great Nature Project photos.

The Great Nature Project

Submit your photos of earthworms or any other living thing to the Great Nature Project. You can keep track of your observations and get help from other people to identify what you saw. Use our nature missions to guide your exploration. Browse or search the photo stream to see other amazing living things. Create an account to your share your photos of plants and animals.

More to learn and do:

Interested in classroom activities related to biomimicry? Find free resources on the Biomimicry Institute’s Biomimicry Education Network.

To learn more about the earthworm’s cool strategy and how we might apply it to make our human world more sustainable, check out AskNature.

Interested in contributing to AskNature? Learn more about sharing graphics, interning, and more.

Jeanette Lim is the AskNature content coordinator and gets to talk about nature’s wonders and inspiration with other nature enthusiasts. She has a newfound appreciation for the earthworms she sees in her vegetable garden.

Jeanette Lim works for the Biomimicry Institute and is a frequent guest blogger for the Great Nature Project.
Jeanette Lim

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