Earthworms are fascinating organisms that play an important role in ensuring the soil in your yard and garden remains fertile. These segmented creatures may breathe oxygen and release carbon dioxide just like humans do, but they don't have a nose and lungs. Instead, they breathe through their skin.
How Earthworms Breathe
Earthworms have the same need for oxygen that other animals do, but they don't have lungs that allow them to inhale and exhale in the way that we commonly think of breathing. Earthworms breathe through their skin using a process called diffusion. Diffusion is the way that molecules move to an area of lower concentration.
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In the earthworm, the concentration of oxygen is lower in their body than it is in the soil or air around them, which means that oxygen moves through the skin to directly enter the earthworm's bloodstream. The concentration of carbon dioxide is higher in the earthworm's body than outside, which ensures that the carbon dioxide moves out of the earthworm through the skin.
Earthworms have not one, but five heart-like structures that help to pump the oxygenated blood to their head. Movement is important as this is what pushes the blood away from the head area and back through the earthworm's body.
Earthworms Environmental Requirements
Earthworms are able to breathe through their skin because the skin is thin and covered in slimy mucus. The gases cannot diffuse through the skin without this moist surface. This is why it is so important that earthworms stay in a moist environment, such as the damp soil in your garden.
It is common to see earthworms on the surface after a rainstorm, but if they get stuck in the sun, their skin dries out and they can no longer breathe. Researchers don't fully understand why earthworms leave the soil during a rainstorm but theorize it is because it is easier to move on the wet ground than through wet soil. In addition, while earthworms can survive underwater for short periods as long as there is sufficient oxygen in the water, they will eventually drown.
Other Earthworm Senses and Organs
Earthworms navigate the world in a way that is foreign to people. They are not only different from people in not having a nose and lungs, but they also lack eyes and ears. They do have light receptors in their body and can sense vibrations in the ground. This allows them to sense animals nearby and know whether there is daylight if they are near enough to the surface of the soil.
Worms do have mouths so that they can eat, but they don't have teeth to chew their food. They consume dirt and decaying plant material. This food is moved down to the worm's stomach, or gizzard. The gizzard grinds the food before passing food on to the intestines. Similar to a human's intestinal system, the needed nutrients are absorbed through the intestines into the worm's body and the waste continues on and is expelled.
Worm waste is called castings. Castings are nutrient-rich and help keep the soil fertile to nourish your plants. In addition, as the worm moves through the soil, it helps to mix and aerate the soil.
- University of Wisconsin Madison, "Journey North": Life of an Earthworm
- Woodland Trust: Do Worms Have Eyes? And Other Worm Facts
- University of Pennsylvania: Wow! The Wonders of an Earthworm, How Diffusion Allows an Earthworm to Breathe
- University of Illinois Extension: The Adventures of Herman, My Anatomy, How I Breathe