Red Worm Anatomy - Eisenia fetida - the Perfect Composting Worm

The Anatomy of a Red Wiggler Composting Worm – Eisenia fetida

Live Worms, Red Worms, Vermicomposting

worm anatomyThe best type of worms for your composter is the Red Worm (Red Wiggler). Their voracious appetites, medium size, and heartiness make them ideal composting worms. Falling into the genus “anulus,” meaning “ring” in Latin, the Eisenia fetida has up to 120 circular rings.

The Red Worm Body

On the outside of the red wiggler worm is the cuticle. Below this, the epidermis is skin-like tissue that sends information to the nerve tissue. Sensory information travels from layers of nerve tissue to the nerve cord. Data is processed in the cerebral ganglion, which is the worm equivalent of a brain.

Ever notice the rings on a red worm? These rings are made from circular muscles. They expand and contract, which shortens and lengthens the worm’s body. Muscles also run the length of this worm. Together, these two types of muscles make the worm move in all directions. The bedding they live in needs to be moist to lubricate the worm’s motion.

Ever seen a bird try to pull a worm off the ground? Sometimes the worm fights back by clinging to the ground. Most of the rings on their bodies have setai sticking out. These hair-like, stiff protrusions grip the soil. They also help the worm navigate instead of just sliding around.

Worm Nervous System

Red worms are simple creatures, and this is reflected in their basic brains. The cerebral ganglion is a bundle of nerves that receives sensory data. For example, the cerebral ganglion processes data about moisture levels, vibrations, light and heat. The worm can then respond to its environment to keep itself safe, fed, warm, etc.

Red worms are not likely self-aware, but they are living creatures. As such, we should show respect whenever possible. If your indoor composting bin has too many worms, try to wait until warm weather to release some of them outside. Also, do not allow pets or children to violently play with them. And take care of your composting bin so that the worms can thrive.

Circulatory System

Red worms have a five very simple “hearts.” Each chamber has a valve that regulates the flow of blood. The blood delivers nutrients and oxygen throughout the body. The outer cuticle of the worm brings in oxygen. Liquid waste products — urine — is excreted through the skin.

Reproductive System

Worms are hermaphroditic. They reproduce by joining clitella, wide bands that are visible when they are fertile. Learn more about red worm reproduction.

Digestive System

Worm digestion starts with the mouth, technically called the buccal cavity. Food travels through the entire worm, in this order: mouth, pharynx, esophagus, crop, gizzard, intestine, and finally, anus.

The worm’s mouth has sensory cells that detect minerals and foods. They can tell the difference between edible and inedible matter. And they will seek out edibles.

Similar to a suction pump, the pharynx pulls food from the mouth into the digestive tract. Food travels down the esophagus, into the crop. You may recall that birds also have a crop, for storing food (similar to a stomach).

Next, food is ground up in the gizzard. Sandy particles, or grit, from the soil smash food into tiny pieces.

Then, the partially-digested food goes through the intestine, which is almost 2/3rd the length of the worm. The worm absorbs many nutrients during this part of the journey. Finally, the worm excretes through the anus.

Worm Excrement

Gardeners treasure worm poop, also called “castings” and “humus.” Worm castings are a dark, nutrient-rich fertilizer for plants. When concentrated in a composting bin, humus can be harvested easily. Gardeners and farmers can then apply the humus to the soil around food-producing and decorative plants. Part of its great value comes from the living microorganisms in the humus. Earth-friendly bacteria, fungi, enzymes, protozoa, and actinomycetes live in the worm’s digestive system. Some of them show up in the finished compost. Compost from worms should be used up within a short time before all the microorganisms die. Compost that has sat longer still works because it contains composted organic matter. But fresh compost from worm excrement is the most potent.


Red worms are humble creatures. Their anatomical features make them ideally suited for breaking down organic matter. People learned to harness the power of the red worm by concentrating the worms in a composting bin. The resulting worm castings make an inexpensive and 100% organic fertilizer for plants. Uncle Jim’s Worm Farm is the #1 supplier of composting worms in the United States. We ship out live red composting worms that are grown on our farm in rural Pennsylvania. We also offer Super Reds (European Night Crawlers) for aeration and mealworms for pet food and science classes.

9 thoughts on “The Anatomy of a Red Wiggler Composting Worm – Eisenia fetida

    1. We do not have a walk-in business, but if you are local and would like to come pick up your order rather than pay for shipping that is possible!

  1. Hello – I have been trying to find online any info. regarding the smell of a compost worm – I was always led to believe that they weren’t good for fishing until you “cleaned them out” by feeding them oatmeal or cornmeal or something (?) to rid the compost odor and that it also cleared up the white rings around their body . Is there any truth to this ?

  2. the largest width of the red wigglers is about 1\8 of an inch. and the largest length of the red wiggler is 3-4 inches

  3. Dave Fooks, No. Finished compost smells good — much, much better by far than plastic worms do. I don’t see how it would be much different than the compost at the bottom of a lake. When I was a child my grandmother dug up worms from around her fieldlines on the way to the pond and they caught a many a fish at the end of my cane pole. Just keep the hook in the water. My brother kept moving his around and caught none. Check your worm every once in awhile. Some perch love to nibble off but don’t bite where they need to.

  4. How big is a worm mouth? How fine does eggshell or coffee grounds, for instance, have to be for the worms to digest?

    1. Hi Guy,

      You can add crushed eggs shells, or the shell whole! The worms will be able to consume it either way. The same will apply to the coffee ground.

      Uncle Jim’s Worm Farm

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