Introduction to Earthworm Science

Earthworm Science is one of the Worm Watch programs for students, teachers, and parents. The four hands-on investigations and supporting information are designed to help participants learn about the role earthworms play in the ecosystem, as well as the care and handling of these organisms. Earthworm Science is specifically designed to help students develop the skills required for scientific inquiry, including problem solving, communicating scientific ideas and results, and making informed decisions. Students participating in this program will also develop specific skills within four areas of scientific inquiry:

1. Initiating and Planning: develops questions and hypothesis, identifying problems, and developing preliminary ideas and work plans.
2. Performing and Recording: gathering evidence by observation and manipulating materials and equipment, and improve organizational skills.
3. Analyzing and Interpreting: information and evidence, presenting and interpreting data, evaluating results, evaluating potential applications of the results on local, regional, and global scales.
4. Communication and Teamwork: In science, as in other areas, communication skills are essential at every stage where ideas are being developed, tested, interpreted, debated, and agreed upon. Teamwork skills also are important to collaborative processes in both society and the classroom.

The four hands-on investigations in Earthworm Science are:

1. Investigation #1: Establishing an Earthworm Colony: In this investigation, students construct a terrarium to maintain a healthy population of earthworms required for the other Earthworm Science activities.
2. Investigation #2: Earthworms in Action: Students are required to design their own experiment as they explore how earthworms affect layers of soil.
3. Investigation #3: What Do Your Earthworms Like to Eat? Each species of earthworm has its favorite foods. Students design their own experiment to determine what their earthworms like to eat.
4. Investigation #4: How Much Do Your Earthworms Eat? Many species of earthworms are excellent garbage eaters. They eat and expel their own body weight each day. Students design their own experiment to determine the mass of food consumed by earthworms.

Earthworm Science Background Information

Soil is an important natural resource that many of us take for granted. Living soil supports the growth of all terrestrial plants. Do you think about healthy soil when you eat your cereal in the morning or when you eat the apple in your lunch? When you are writing notes on paper in science class do you think about the elements in soil? Do you worry about soil when you put on a pair of denim jeans or a cotton T-shirt?

The vegetables, fruits, and grains that you eat come from plants. Livestock, such as cattle and pigs, feed on grasses and grains. Paper is made mostly from the fibres from plants and trees. The fabric used to make blue jeans and t-shirts is made from fibres from the cotton plant. Plants, grasses, and trees all grow in soil. Without soil, food cannot be grown, livestock cannot be fed, and trees will not grow. Our lives and the atmosphere of this planet would be very different without plants.

Good soil grows healthy nutritious plants. Soil is a mixture of rock fragments, organic matter (material from living things), minerals, water, and air. Organic matter is what organisms (living things such as plants, birds or animals) use as food. This allows them to grow and reproduce. Nutrient is the term generally used to describe the chemical elements that living things need in order to survive. Plants, for example, require the elements nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur. Without a continual supply of these nutrients, plants will not grow.

Nutrients flow through food chains from producers to consumers and then to decomposers. Producers get their nutrients from the soil, water, and air. Plants are an example of a producer. Herbivores (plant eaters) are examples of consumers and they get their nutrients when they eat the producers. Carnivores (meat eaters) are also consumers who obtain their nutrients when they eat other animals. The decomposers then break down animal wastes and dead organisms. The action of the decomposers releases the nutrients back into the soil, water, and air so producers can use them again. In this way, nutrients are continually cycled through the ecosystem.

Healthy soil is home to small rodents, insects, earthworms, algae, fungi, and bacteria. As soil develops, organic material (matter from living things) decays until the original form of the matter has been changed. The decaying matter eventually turns into a dark coloured material called humus. Humus provides nutrients such as nitrogen, phosphorous, potassium, and sulfur for plants. Humus also promotes good soil structure and helps soil hold water and air. As earthworms, insects and small mammals burrow through the soil, they mix the humus with the other material creating an even better habitat for plants and other soil organisms.

THE LIVING SOIL: EARTHWORMS

Of all the members of the soil food web, earthworms are probably the most familiar. Most of you become familiar with these soft, slimy, invertebrates at a young age. Earthworms are major decomposers of dead and decomposing organic matter. They obtain their nutrition from the bacteria and fungi that grow upon these materials. Earthworms also break up the organic matter and play a major role in recycling the nutrients contained in organic matter.

WHAT DO EARTHWORMS DO?

Earthworms dramatically affect soil structure, water movement, nutrient cycling, and plant growth. They are not essential to have in the soil, but their presence can be an indicator of good soil quality. Earthworms perform several beneficial functions:

Decomposition and nutrient release. Many organisms are responsible for assisting in the decaying of organic matter that eventually reaches the soil. Soil microorganisms are the primary agents of decomposition, breaking down plant and animal residues into useable nutrients for plants and other soil organisms. Not all plant material is subjected to immediate decomposition by soil microorganisms. Some plant materials are broken up and made into smaller pieces by other soil animals. Earthworms contribute break up larger plant organic matter by their feeding activities.

Mixing and castings. Earthworms feed on plant litter as well as a wide range of decaying organic substances. Earthworms remove plant litter, dung or manure, and other organic materials from the surface of the soil and within the soil. Charles Darwin calculated that earthworms could move large amounts of soil from the lower layers of the earth to the surface and also carry organic matter down into the deeper soil layers. A large proportion of soil passes through the guts of earthworms, and they can turn over the top six inches (15 cm) of soil in ten to twenty years. As they consume organic matter and mineral particles, earthworms excrete wastes in the form of casts. Earthworm casts are excreted masses of mineral soil often mixed with smaller bits of digested plant residues. Earthworms that live mostly in horizontal burrows, selecting food from in the soil, deposit casts within their burrows or in other spaces within the soil. Earthworms that make mostly vertical burrows that open to the soil surface often feed on organic materials that are on or just under the soil surface. These earthworms mostly deposit castings on the soil surface. No doubt you have seen piles of castings on your lawn of in your garden in the morning especially if there has been a rain. The earthworm activities of eating, burrowing, mixing, and casting all act to form soil aggregates, aerate the soil, and improve soil water infiltration and holding capacity that improve soil habitat structure.

Aggregates. Soil aggregates are mineral granules that are joined together in such a way that they stay together in what looks like a crumb after wetting, erosion or compaction and remain loose in the soil when the soil is either wet or dry. A soil that is rich in aggregates is well aerated and drained. Scientists have agreed that earthworm casts contain more stable aggregates than other soil. However, earthworms are not essential to the process of forming soil aggregates because the activity of other soil organisms including bacteria and fungi can also stabilise soil aggregates.

Increased air and water infiltration. Earthworms improve the amount of air that is contained in the soil (aeration) by their burrowing activity and at the same time they improve soil porosity by improving the overall structure of the soil as a habitat for themselves and other soil organisms. This means that soils with earthworms not only contain more air but also fill and drain water faster. Earthworms enhance porosity in the soil by creating tiny holes as they move through it. This allows water to soak into the soil more easily. Some species make permanent burrows deep into the soil. These burrows can persist long after the earthworm has died, and can be major channels for soil drainage, particularly under heavy rainfall. At the same time, the burrows limit the loss of soil on the surface of the land that might otherwise be eroded by water collecting there..

Provide channels for root growth. The channels made by deep-burrowing earthworms are lined with readily available nutrients. This makes it easier for roots to penetrate deep into the soil and for food to be available for plants to grow.