Abstract

Objective

The goal of this project is to discover how the diet of earthworms affects their growth, reproduction, and the quality of the soil they process.

Introduction

Click here to watch a video of this investigation, produced by DragonflyTV and presented by pbskidsgo.org

Face it. Worms just don't get the respect they deserve. They till the soil night and day, and still we usually think of them as merely a slimy nuisance to avoid on rain-soaked sidewalks—if we think of them at all. But without earthworms our farms and gardens would be nearly barren. Litter from leaves and dead plants would pile up in smelly heaps on top of the soil. Without the network of tunnels earthworms create, the land would absorb considerably less water during rainstorms, leading to increased surface run-off and floods and decreased ground water supplies for dry spells.

As you'll discover in this project, earthworms are critical players in the environmental foodweb found within soil. Along with bacteria, fungi, other kinds of worms, and insects, the earthworms form a intricate web of decomposers that interact to maintain the soil and to help each other survive. Their busy, complicated underground world contributes to the ecosystem that plants and animals above ground depend upon.

This project video introduces you to Kevin, a kid on a mission about worms. The value of earthworms did not escape the attention of this budding worm scientist, or oliochaetologist (OH-lee-o-KEY-tal-o-gist). You can see from Kevin's enthusiasm that he appreciates the importance of earthworms for recycling not only in farm and natural environments, but also in our homes. Check out the video to see how he set up an easy but impressive scientific study to document how fast his earthworms could consume the daily plant waste produced from his family's kitchen.

Next, read on to find out how you can do a similar project using the soil recycling dynamo, the earthworm. There are many species of earthworms, but you can easily purchase the red wigglers, Isenia fetida, recommended for this project from various local or Internet sources. You'll then set up worm colonies in plastic or clay pots filled with potting soil. After that, your worms won't require much more than a sprinkling of water and addition of food now and then, so caring for them means only minutes of your time every few days. You will have to be patient, however, to give your worms at least the eight weeks of time they need to reproduce and to transform your table scraps into recycled nutrients within the soil.

Earthworms enhance the soil by their burrowing and feeding habits. Earthworms basically eat their way through the soil, and they have a tremendous ability to process the dirt they live in. Some studies suggest that in one acre of top soil, earthworms consume and mix more than 20 to 40 tons of soil per year. That's a lot of dirt. But the worms are also busy eating up the plant debris on the surface of the ground as well. The partially digested plant matter is blended back into the soil within the earthworm's gut and increases the soil levels of nitrogen, phosphorus, potassium, calcium, and other micronutrients. Another excellent source of plant nutrients comes from the excrement (poop) that earthworms produce. These deposits are called castings and are usually found on the surface of the soil. Both these reasons make the lowly earthworm a natural "fertilizer factory" for the soil, and without them in the ground few plants would be able to thrive.

As earthworms muscle their way through the ground, even the tunnels they leave behind benefit the soil. The worms' passageways aerate the soil by allowing oxygen and water to percolate down to growing plant roots and letting carbon dioxide produced from the plants flow back out into the atmosphere. And if all this fertilizing and aerating weren't enough, the earthworms also pitch in to rid the soil of some of the harmful microorganisms that can attack plants and fellow soil dwellers.

This project examines how feeding earthworms different types of food influences their reproduction and the quality of soil they produce. You'll provide each worm colony with a different type of diet. The food sources can come from a variety of leftover food or garden items including bits of fruit, chopped vegetables, egg shells, coffee grounds, or plant clippings from your yard. Earthworms are strict vegetarians, so please don't include any meat scraps in your choices. After about two months, you'll recount the number of worms in each colony to see how well they reproduced and evaluate the different soils for nutrient levels and acidity.

Before you begin your project, do a little background research on earthworms, their diet, biology, and how to properly care for them in worm bins. You'll find a list of search terms, questions, and a bibliography in the next sections to get your started. Once you have gained a basic understanding of earthworms and soil ecology, you will be better able to set up your experiments and interpret your data.

Good luck, have fun, and here's to a better world through earthworm waste management!

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Earthworm biology and anatomy
• Earthworm recycling
• Ecosystem
• Soil foodweb
• Decomposers
• Composting
• Soil nutrients

Questions

• How do earthworms benefit the soil?
• What is the role of a decomposer in a foodweb?
• What types of earthworms exist, and how does each live in and affect the soil?
• How do earthworms reproduce?
• How do scientists measure the acidity and level of nutrients in the soil?

Bibliography

Here are some websites you might want to check out as you start your research:

• Short, helpful overview of earthworm facts, benefits, and biology:
  Shivers, L., 2002. "Earthworms: Six Inch Soil Savers," Kansas State University [accessed September 20, 2007] http://www.oznet.ksu.edu/news/sty/2002/earthworms040302.htm.
• Everything you would want to know about earthworms and what they do:
  Duiker, S., and Stehouwer, R., 2003. "Earthworms," Pennsylvania State University, College of Agricultural Sciences [accessed September 20, 2007] http://pubs.cas.psu.edu/freepubs/pdfs/UC182.pdf.
• Short description of the anatomy, biology, and value of earthworms:
  Day, L., 1996. "The City Naturalist—Earthworms," The 79th Street Boat Basin Flora and Fauna Society, New York, NY [accessed September 20, 2007] http://www.nysite.com/nature/fauna/earthworm.htm.
• Tips on how to build, maintain, and harvest a worm bin:
  Discovery Communications, 2000. "Worms as Recyclers," Discovery Kids website [accessed September 23, 2007] http://yucky.discovery.com/noflash/worm/pg000224.html.
• The basic idea for this project came from this DragonflyTV podcast:
  TPT, 2006. "Worm Farm by Kevin," Twin Cities Public Television [accessed September 20, 2007] http://pbskids.org/dragonflytv/show/wormfarm.html.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• 1 lb. worms—red wigglers or redworms, Eisenia fetida (These can be purchased online and delivered by mail.)
• Soil test kit (available online from several manufacturers; order one that tests pH, N, P, and K)
• Five, ten–inch diameter clay or plastic pots (these must have drainage holes at the bottom)
• Potting soil, without added fertilizers or amendments (available in bags at home garden departments)
• Metric scale, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com
• Black plastic bags to cover the pots (worms prefer a dark environment)
• Catch tray(s) to place under the pots for drippings and escaping worms
• Scoop for soil transfer
• Spray bottle
• Large paper cups
• Newspaper
• Gardening gloves, if you prefer, for handling soil and/or worms
• Notebook or paper
• Pen or pencil
• Marking pen

Experimental Procedure

Set Up Your Earthworm Colonies

1. Place potting soil in each pot to about three quarters the way up. Sprinkle the soil with some water so that it's damp, but not soaking wet, and pat the soil down into the pot a bit. Add more moist soil, if necessary, to bring the level back up to three quarters.
2. Note:If the soil is very dry (does not form a ball when squeezed in your hand), pour tap water slowly over the soil until the water drains from the pot. Tap the soil down again and refill if necessary. Allow the pot to drain for at least 30 minutes before adding the worms.
3. Weigh one empty large paper cup or container, in grams, on the scale. Add in the number of earthworms you plan to put into one pot. Try to select worms of similar size and length, if possible. Up to 40 to 50 worms or more per pot should be fine depending on the depth of your pots. Any extra worms you have left over from your shipment can be deposited into your yard or garden.
4. Weigh the cup again with the worms. Subtract the weight of the cup alone from this total to determine the starting group weight of the worms. Record the group weight of the worms in your notebook.
5. Option: It might be helpful to take a picture of your worms at this point so you can compare sizes of the worms at the end of your experiment.
6. Gently put the worms onto the soil of one pot. Add more moist potting soil on the top of the worms so that the soil level reaches about 5 cm (2 inches) from the top edge of the pot.
7. Wrap the pot in a plastic bag. Be sure to poke some small air holes into the top of the bag.
8. Count and weight the earthworms for the remaining four pots.
9. Store your pots on drainage trays in a cool spot.
10. Special hints on working with earthworms:
    1. Earthworms can't hurt you; they have no teeth. But you can hurt them if you don't handle them gently.
    2. Earthworms, like plants, do best with moderate levels of soil moisture. Too much or too little moisture is bad for them. They may migrate out of the soil if the correct moisture or temperature level is not maintained in the soil.
    3. Earthworms breathe through their skin, and the skin has to be moist to allow air exchange. If they dry out, they will suffocate. When your worms are out of the soil for any length of time, place them on damp paper and mist them with water to keep them moist.
    4. Earthworms don't tolerate extreme temperatures. The ideal temperature range is between 10–16 °C (50–60 °F). Prolonged exposure to temperatures below freezing or above 35 °C (95 °F) will kill them.
    5. Earthworms prefer the dark. Keep your pots covered unless you are adding water or food.

Prepare the Worm Diets

1. Select four different types of diets to feed your worms. Some suggestions include:
   • Crushed egg shells
   • Fruit pieces with peels
   • Vegetable pieces and skins
   • Grass clippings and dry leaves
   • Coffee grounds
   • A mixture of any of the above
   • You can collect these items beforehand and store them separately for a few days at a time in covered containers in your refrigerator.

Start Your Experiment

1. Prepare a data table for each pot to record what you do and observe. Include: start date, initial number of worms, group weight of worms, date and time of food additions, weight of food added, date and amount of water added, along with any other special notes about the food's appearance, worm activity, or pot drainage.
2. Weigh and record, in grams, the weight of each type of food before you put it a pot.
3. Place a layer of one type of food into each of the four pots. As a control, a fifth pot should receive water only, no additional food source.
5. Follow the instructions that came with a soil analysis kit to measure the acidity (pH), and relative levels of potassium (K), nitrogen (N), and phosphorus (P) of the soil from the control pot or from the potting soil bag.
6. Sprinkle some water on top, if needed, to keep the food and soil moist.
7. Cover the pots with black plastic bags; be sure the air holes are still at the top of the pot.
8. Label each pot with the type of food it received.
9. Check the pots every 2–3 days, and add food or water as needed.
10. Record the food and water additions each time you make them. Also make notes of what you observe in each pot. What does the food look like while it is decomposing? Are there any changes in the surface or appearance of the soil? Look for deposits of worm casts on the surface. Note any types of fluids leaking out the bottom of the pots.

Final Worm Count and Soil Analysis

1. After two months (longer might even be better), count and record the number of worms and their group weight in each pot. Do this by dumping out the soil from one pot at a time onto a large tray or pan lined with newspaper. Gently push away the soil to find the worms.
2. Weigh an empty container on the scale and record the container's weight in grams. Add the worms to the container as you count them.
3. Record the number of worms you find in each pot in your notebook.
4. Calculate the group weight of the worms and record that in your notebook.
5. Note and record any general changes in appearance or size of the worms in each pot compared to the first day of your experiment.
6. Follow the instructions that came with a soil analysis kit to measure the acidity (pH), and relative levels of potassium (K), nitrogen (N), and phosphorus (P) of the soil from each pot.
7. Record the soil analysis results for each pot in your notebook.

Analyzing Your Data

1. Calculate the group weight change, in grams, for each pot of worms from day one to your final day of the experiment.
2. Prepare a bar graph showing the final total number of worms you counted in each pot at the end of your experiment along side the group weight change for each pot. Did some pots show a greater increase in number of worms or group weight than others?
3. Calculate the total weight, in grams, of the food added to each pot during the entire experiment. Calculate the average weight per feeding by dividing the total weight by the number of feedings. Prepare a bar graph showing the total and average weight of food added to each pot.
4. Prepare a data table showing the soil analysis results for each pot.
5. Summarize your results for worm population and soil changes in a table. Did one type of food affect the worm population or the soil quality more than another? What diet had the least effect on the worms and soil?
6. For help with data analysis and setting up tables, see Data Analysis & Graphs.
7. For a guide on how to summarize your results and write conclusions based on your data, see Conclusions.

Variations

• Different worms. Try a similar experiment using the larger earthworm known as the night crawler. These worms live in deeper tunnels and come up at night time to feed on the surface. Compare your results with night crawlers to the results you get with the red wigglers. Do the different types of earthworms produce different types of soil nutrients?
• Use and test the soil. Save the soil from each pot and add equal amounts to amend potting soil to new pots for growing one or two types of plants. Does one soil seem to produce plants that are healthier or larger than another soil? For instructions on how to set up this type of plant experiment, see the Science Buddies projects and instruction sheet:
  • Growing, Growing, Gone: An Experiment on Nitrogen Fertilizers
  • Humic Acid and the Optimum Soil for Plants
  • Measuring Plant Growth
• For other Science Buddies projects related to earthworms, see:
  • Earthworms: Nature's Tiller?
  • How Much Worm is a Worm?

• For more science project ideas in this area of science, see Environmental Science Project Ideas.

Credits

Darlene E. Jenkins, Ph.D.

Sources

The idea for this project came from this DragonflyTV podcast:

• TPT, 2006. "Worm Farm by Kevin," Twin Cities Public Television http://pbskids.org/dragonflytv/show/wormfarm.html.

Last edit date: 2011-11-18 11:00:00