Compost-ology Worm Internal Anatomy Worm Internal Anatomy
Worm Anatomy & Physiology

Even though they don't have a skeleton and can't walk upright, worms do many of the same things people do to survive. They move around, eat, breathe, reproduce and defend themselves. They are sensitive to temperature, moisture, light and vibrations.

Worms are annelids, from the Latin word anulus meaning "ring." Worms are made up of joined, ringed segments. An adult redworm has between 200 to 400 circular rings. Try thinking of the giant sequoia trees and their rings. The tree rings grow around each other while the worm rings are stacked end on end.

The cuticle is the worm's outermost body wall. Beneath the cuticle are:

  1. the epidermis, which is like our skin,
  2. a layer of nerve tissue which performs like our sense of touch,
  3. circular and longitudinal muscles for locomotion.

The epidermis contains many sensory cells that transmit information to the nerve tissue. Within the layer of nerve tissue are cells that forward sensory information to the worm's nerve cord and on to the cerebral ganglion, the worm's version of a brain.

Circular muscles create the worm's body rings. These muscles contract and expand, shortening and lengthening the worm's body. The longitudinal muscles run the length of the worm. Acting in concert these sets of muscles enable the worm to propel forward, backward and sideways. Moisture in their environment lubricates this locomotion.

Additionally, stiff hair-like protusions called setae stick out of almost every ring along each side of the worm. These protusions grip the soil, bedding or any material it is moving through so the worm doesn't just slip and slide randomly. The setae are made of chitin, the same substance that makes up our fingernails and the exoskeleton of many insects. The setae are very strong, assisting the worm as it moves through its environment. The setae help the worm to defend itself by gripping the soil when attacked by a hungry bird or other predator.

Brain and Nervous System
The cerebral ganglion, located at the front of the worm, serves as the brain. This nerve bundle is responsible for receiving external information such as light, heat, moisture and vibrations. The worm relies on the ganglion and a ventral nerve cord for sensory input from the world around them.

While we don't fully understand all the functions of the nervous system, it is believed that body functions such as reproduction and life cycles are regulated within the nerve ganglion.

The circulatory system is powered by five pseudo-hearts. These hearts are merely valved chambers that regulate blood flow and produce a pulse. Branching off these hearts are both a dorsal (forward flow) and a ventral (backward flow) blood vessel. The dorsal and ventral vessels transport the blood, rich with oxygen and nutrients through the body. The circulatory system also transports urinary waste, which is diffused through the cutical, the outer covering, in each ringed segment. In other words, worms breathe and excrete urine through their skin.

Digestion/Gastrointestinal System
Running through the worm's body is the alimentary canal or gut. It starts at the mouth, called the buccal cavity, and moves to the back with the pharynx, esophagus, crop, gizzard, intestine and anus, respectively.

The buccal cavity contains specialized sensory cells which allow worms to locate food and minerals. The cells detect and recognize sucrose, glucose, quinine and saline chemicals from the environment. This allows them to identify and select the foods they eat.

The pharnyx works like a suction pump, drawing particles farther in from the mouth. The esophagus, which opens from the pharnyx as a narrow tube, leads to the crop. Worms and birds both use their crop as a food storage chamber.

Next is the gizzard, the food grinding chamber. It contains sandy grit from the soil to pulverize food into small particles, including leaf litter, mulch and soil organics.

The intestine is a tube going straight back to the anus, taking up almost two-thirds of the length of the worm. The intestine performs the final digestion and absorption of the life sustaining nutrients from the worm's food.

Enzyme Benefits
Many tiny organisms, bactria, fungi, actinomycetes, enzymes and protozoa live in the worm's gastrointestinal systems aiding digestion. They are microscopic and thrive by the hundreds of thousands within a single worm. These organisms assist in preparing the nutrients to be absorbed and utilized by the worm.

The worm produces numerous enzymes which aid in its own survival, including an insecticide and an antibiotic.

These enzymes emulsify with mucus produced in the worm's gut and sheath the castings when expelled through the anus. Plants are able to absorb the insecticidal and antibiotic enzymes through their roots to further utlize them in the plants' ongoing battle to ward off insects and disease. The antibiotic enzymes also protect humans from harmful bacteria while working in the worm bin.

Worms have no specialized respiratory organs. They breathe through their moist skin. Oxygen and carbon dioxide are diffused through the skin to and from the circulating blood stream. Lack of moisture in the worm's environment restricts the breathing process. Prolonged dryness will cause death by suffocation. Exposure to direct sunlight can lead to death in less than three minutes.