Key Points
This section will give you the main information you should know to teach the activity.

• Decomposers are organisms that break down non-living organic material by feeding on it. By doing this, decomposers help return nutrients to the ecosystem, which can then be used by plants and other living things.
• Earthworms are decomposers that feed on organic material in the soil. They cannot feed on inorganic material. Plants in the community depend on earthworms because their feces contains the nutrients they need to survive.

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Detailed Information
This section gives more in-depth background to increase your own knowledge, in case you want to expand upon the activity or you are asked detailed questions by students.

South Carolina is home to many different species of worms. Some are carnivores, like the aquatic chaetognaths, with protrusible jaws that are used to capture prey. Many worms that live on land, like earthworms, and many that live in the water, like ice cream cone worms, are decomposers and recycle nutrients by ingesting soil or mud and pieces of non-living organic matter (like pieces of leaves, grass clippings, salt marsh grass), and returning those nutrients to their communities through the process of defecation. Worms enrich the soil or mud in the community in which they live by recycling nutrients from organic material that would otherwise be unavailable, and returning them to the soil. By creating vast networks of tunnels that help air and water to reach other soil-dwelling decomposers (millipedes, centipedes, bacteria, beetles), worms help to speed up the rate of decomposition. Believe it or not, more than 5 billion organisms may be contained in a single cup of soil!

All of the organisms that inhabit a particular area comprise a community. Within a community, decomposers, like earthworms, depend on plants. Non-living pieces of plants (leaves, fallen tree trunks) provide food for decomposers. Likewise, plants depend on decomposers. Plants are producers and can harvest energy from the sun to make their food. This is done through the process of photosynthesis. However, terrestrial plants also need to uptake minerals from the soil using roots in order to survive. Decomposers provide these essential minerals to plants in a form that the plants can use. Because plants depend on decomposers, decomposers play a key role in food chains (and food-webs) in both terrestrial and aquatic systems. Producers depend on decomposers and consumers (herbivores, omnivores and carnivores) depend directly or indirectly on plants.

A population of organisms consists of all individuals of a species that occur together at a given place and time. Each worm recycling center will contain its own population of worms. All of the different populations that are living in the same place and the physical factors with which they interact compose an ecosystem. Each worm recycling center will be an ecosystem created by soil, water, and non-living organic and inorganic material (the physical factors), a population of worms and possibly an array of other living organisms. A niche is the role an organism plays in its community or ecosystem; in the worm recycling centers the worms play the role of decomposer. Students can observe how worms speed the process of decomposition and enrich soil by placing worms in containers that house a variety of organic and inorganic material. The worms, in addition to bacteria and fungi, will begin to decompose the organic and some of the inorganic materials. The rate of decomposition of each material will depend on its molecular make-up. Those materials, like vegetable scraps, coffee grounds, and grass clippings, with a carbon to nitrogen ratio close to 30:1 will be decomposed the fastest. Students should observe how the worms cause change in the environment in which the worms are living. Inorganic materials, like plastic and Styrofoam, take hundreds of years to decompose. Thus, students will observe no change over time in the appearance of inorganics and should be encouraged to think about or discuss the ways in which humans cause change in the environment where they live.

There are more than 3,000 species of earthworms and earthworms live almost everywhere that there is moist soil. One acre of cultivated land may be home to as many as 500,000 earthworms, each making the soil a better place for plants.

The four-inch long, pale red garden worm is often called nature’s plow. The earthworm pushes through soft earth with the point of its head. If the soil is hard, the worm eats its way through, forming interconnected burrows, some several feet deep. Earthworms, like chickens, have a digestive system equipped with a gizzard. A gizzard is a sac with muscular walls. The muscles of the gizzard, combined with mineral particles and very small stones ingested by the earthworm, help to grind food thoroughly. Burrows loosen the soil, admitting air and water and helping roots grow.

As an earthworm feeds, organic matter passes through its body and is excreted as granular dark castings (fecal matter). You may see these small casting piles in your garden. An earthworm produces its weight in castings daily. Wormcasts are rich in nutrients otherwise unavailable to plants. When you add nitrogen-rich compost to your soil, you help worms. An earthworm’s body is 72% protein, so it requires lots of nitrogen (the building blocks of protein) to maintain itself. However, adding synthetic nitrogen fertilizers may repel earthworms. Worms are sensitive to physical and chemical changes and will flee the salty conditions that result from an application of chemical fertilizer. Earthworms will not burrow into soil with a pH below a certain level, which varies from species to species. Acid-sensitive nerve fibers are present all over the body. Thus, earthworms can be used as bioindicators ( ₁₎.

The effects of earthworms on the soil are many. Both the castings, which become mixed with the soil, and the open channels created by burrowing ease the downgrowth of roots and enhance the fertility of the soil by increasing aeration and increasing drainage. The thorough grinding of soil in the gizzard is an effective kind of soil cultivation. When earthworms are present in the soil, agricultural productivity is generally higher, and in some cases greater crop yields have been achieved by introducing earthworms into soils ₍₂₎.

Earthworms are segmented and their bodies look like a series of attached rings. Each segment of an earthworm contains four pairs of bristles. These bristles aid the worm in locomotion and also can make it very difficult for a bird or a curious human to pull it out of its burrow.

Earthworms, like seastars, are also capable of regenerating lost body parts. Both the head and the tail of an earthworm can be regenerated, within limits. The extent of regeneration depends on the species, as well as on the position of the "wound" and the size of the worm fragment that remains (₂).

Life cycle:
In cold weather, a soil search will turn up mature and young earthworms as well as eggs. By late spring, most worms are mature. As temperatures rise, activity slows; many lay eggs and then die. By midsummer, most worms are very young or protected by egg capsules. As the weather cools, young worms emerge. With wet weather, they grow active, making new burrows and eating extra food, resulting in more worm casts. Egg laying again occurs. Activity continues as long as soil stays damp.

After a heavy rain, earthworms often appear above ground. They haven’t drowned. Fresh water doesn’t disturb earthworms--they need ongoing skin moisture to breathe--but stagnant or contaminated water forces them from their burrow ₍₁₎.

Earthworms are hermaphroditic which means that each worm has a complete set of male and female body parts!

Earthworms are eaten by some snakes, centipedes, large beetles and birds (primarily the robin and the woodcock). The niche an earthworm fills in an ecosystem is as a decomposer.

Horticulturalists at the South Carolina Aquarium have added a species of earthworm, Lumbricus terrestus, to the soil in the mountain forest aviary. They know that the earthworms will help to keep the plants in the exhibit healthy.

1. (Year). Bradley, Fern M., and B. Ellis. Rodale’s All-New Encyclopedia of Organic Gardening: the Indispensable Resource for Every Gardner. Saint Martin’s Press.
2. (1987). Pearse, Vicki and J. Pearse et al. Living Invertebrates. Blackwell Scientific Publications and the Boxwood Press.