Feeding Earthworms: Do Different Diets Affect Them and the Soil They Enrich?
AbstractInterested in helping the environment, and don't mind getting dirty? In this project you get to mix it up with earthworms, soil, and various types of organic kitchen scraps. The basic idea is to set up small earthworm colonies to compost different types of food waste. You test the soils in each type to see how diet affects both the earthworm population and the nutrients they put back into the soil. This project takes a little time, but it's worth it. You'll help the environment and learn about the remarkable recycling skills of the under-appreciated earthworm.
Darlene E. Jenkins, PhD
Edited by Sabine De Brabandere, PhD, Science Buddies
The idea for this project came from this DragonflyTV podcast:
- TPT. (2006). Worm Farm by Kevin Twin Cities Public Television. Retrieved October 7, 2015.
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.
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 will discover in this project, earthworms are critical players in the environmental food web 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.
The DragonflyTV video (see Bibliography) 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 oligochaetologist (OH-lee-o-KEY-tal-o-gist). You can see from Kevin's enthusiasm that he appreciates the importance of earthworms for composting 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, Eisenia fetida, recommended for this project from various local or Internet sources. You will 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.
Figure 1. Red wigglers are a good option to start worm composting (also called vermicomposting).
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 introduce air into 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 will 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 will 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.
Now get started on your reading, order those worms, and start thinking about what type of garbage to collect for your new pets. Who knows, maybe you too will become a champion for earthworm recycling and help change their public image in the process. Planet Earth, and the earthworms, would certainly be grateful.
Good luck, have fun, and here's to a better world through earthworm waste management!
Terms and Concepts
To do this project, you should do research that enables you to understand the following terms and concepts:
- Soil food web
- Soil nutrients
- Earthworm biology
- How do earthworms benefit the soil?
- What is the role of a decomposer in a food web?
- What types of earthworms exist, and how does each live in and affect the soil?
- How do earthworms reproduce?
- What do earthworms, in particular red wigglers need to thrive?
BibliographyHere is a short, helpful overview of earthworm facts, benefits, and biology:
- Shivers, L. (2002). Earthworms: Six Inch Soil Savers. Kansas State University. Retrieved September 20, 2007.
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. Retrieved September 20, 2007.
Short description of the anatomy, biology, and value of earthworms:
- Day, L., (1996). The City Naturalist: Earthworm. The 79th Street Boat Basin Flora and Fauna Society, New York. Retrieved October 14, 2013.
- Office of Sustainability, County of San Mateo (n.d.). Composting. Retrieved July 5, 2018.
The basic idea for this project came from this DragonflyTV podcast:
- Twin Cities Public Television. (2006). Worm Farm by Kevin. DragonflyTV. PBS Kids. Retrieved September 20, 2007.
Materials and Equipment
To do this experiment you will need the following materials and equipment:
- Red wigglers or redworms, scientifically known as Eisenia fetida (160 to 200 worms). These can be purchased from an online supplier, such as Carolina Biological Supply Company, item #141650.
- Soil test kit that tests pH, nitrogen, phosphorus, and potassium. This can be purchased from an online supplier, such as Carolina Biological Supply Company, item #665404. Note: Potassium is also called potash.
- Four, 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 this scale available from Carolina Biological Supply Company, item #702358
- Black plastic bags to cover the pots. Note: Worms prefer a dark environment.
- Catch tray(s) to place under the pots for drippings and escaping worms
- Scoop for soil transfer
- Spray bottle. One can be purchased locally or from an online supplier, such as Carolina Biological Supply Company, item #665565.
- Large paper cups (8)
- Gardening gloves, if you prefer, for handling soil and/or worms
- Different diets to feed the redworms. See the Procedure for details.
- Lab notebook
- Pen or pencil
- Marking pen
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Setting up Your Earthworm Colonies
- Place potting soil in each pot to about three-fourths of the way up. Sprinkle the soil with some water so that it is 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-fourths.
- 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 it if necessary. Allow the pot to drain for at least 30 minutes before adding the worms.
- Label the pots.
- Weigh one empty large paper cup, in grams, on the scale. Write the mass of the cup on the cup. Repeat for the three other paper cups.
- Add the number of earthworms you plan to put into one pot in each cup. Try to select worms of similar size and length for each cup, if possible. Up to 40–50 worms or more per pot should be fine, depending on the depth of your pots. Any extra worms you have leftover from your shipment can be deposited into your yard or garden.
- Weigh each cup again with the worms. Write the mass of the cup filled with worms on the cup. Subtract the mass of the cup alone from this total to determine the starting group mass of the worms. Record the group mass in a table like Table 1.
|Food Type||Initial Count of Worms||Initial Group Mass of Worms||Final Count of Worms||Final Group Mass of Worms||Final Appearance of Worms|
- Optional: It might be helpful to take a picture of your worms at this point so you can compare the appearance of the worms at the end of your experiment.
- Gently put the worms from one cup onto the soil of one pot. Add more moist potting soil on top of the worms so that the soil level reaches about 5 cm (2 inches) from the top edge of the pot. Repeat for the other three pots.
Six images show the steps to adding worms into a composting pot from top-left to bottom-right. The first image shows a bucket filled with soil. Next a paper cup is filled with worms. The paper cup of worms is weighed on a scale. Then the cup of worms is added to the soil. A small spade is used to add more moist soil on top of the newly added worms. Finally, wet newspaper is placed over the composting pot and pressed against the surface of the soil.
Figure 2. This figure shows the main steps to set up one earthworm colony. You will prepare four colonies for your experiment.
- Cover all the pots with moist newspaper.
- Wrap each pot in a dark plastic bag. Be sure to poke some small air holes into the top of the bags.
Figure 3. Cover the pot to conserve moisture and provide darkness. Do not forget to add air holes in the plastic.
- Store your pots on drainage trays in a cool spot. Ensure all pots experience similar conditions like temperature, humidity, etcetera.
- Important notes about working with earthworms:
- Earthworms cannot hurt you; they have no teeth. But you can hurt them if you do not handle them gently.
- 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.
- 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.
- Redworms do not tolerate extreme temperatures. The ideal temperature range is 10–16°C (50–60°F). Prolonged exposure to temperatures below freezing or above 35°C (95°F) will kill them.
- Earthworms prefer the dark. Keep your pots covered unless you are adding water or food.
Preparing the Worm Diets
- Complete your background research on how to care for composting worms if you did not do so yet. A solid foundation of knowledge before you start can prevent delays and challenges during your experiment.
- Select four different types of diets to feed your worms. Some suggestions include:
- Finely crushed egg shells
- Fruit pieces with peels
- Vegetable pieces and skins
- Grass clippings and dry leaves
- Coffee grounds
- Moist shredded newspaper (avoid colored pages)
- Cereal (non-sugared) and grains
- 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, or freeze them for later use.
- Do NOT feed your worms dairy, meat, or fish; and stay away from junk food like chips or candy.
Starting Your Experiment
- Prepare a data table for each pot to record what you do and observe. Include: Start date, initial number of worms, group mass of worms, date and time of food additions, mass of food added, date and amount of water added, along with any other special notes about the leftover food's appearance, worm activity, or pot drainage.
- Weigh and record, in grams, the mass of each type of food before you put it in a pot.
- Place a layer of one type of food under the newspaper into each of the four pots. Cover the food with the moist newspaper.
- Label each pot with the type of food it received. Add the choice to your table like Table 1.
- Sprinkle some water on top, if needed, to keep the food, soil, and newspaper moist.
- Cover the pots with black plastic bags; be sure the air holes are still at the top of the pot.
Figure 4. To feed your worm population: weigh the food, place it under the moist newspaper, and cover the pots back up.
- 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 potting soil bag.
- Check the pots every 2–3 days, and add food or water as needed. Note that worms need a moist environment and do not like to be overfed. Check if most of the food disappeared before adding a new batch of food.
- 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 (a mass of mud thrown up by a worm after it has passed through the worm's body) on the surface. Note any types of fluids leaking out the bottom of the pots.
- Track the health of your worms. As you feed the worms a very specific diet, the chosen diet might not be sufficient for your worms to thrive or even survive. If you see decreased activity (you should see worms crawling back into the dirt as soon as you lift up the newspaper or decaying food) or a decrease in population, end the experiment early for this pot. Take notes on what you observed, perform the final worm count and soil analysis for this pot, and prepare a new home for these worms or release them in the garden.
Final Worm Count and Soil Analysis
- After two months (longer might even be better), count and record the number of worms and their group mass 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.
- Weigh an empty paper cup on the scale and record the cup's mass, in grams. Add the worms to the cup as you count them.
- Record the number of worms you find in each pot in your table like Table 1.
- Calculate the group mass of the worms and record that in your table.
- Note and record any general changes in appearance or size of the worms in each pot compared to the first day of your experiment.
- Optional: Take pictures of your worms to go on your display board.
Figure 5. A picture of a few worms can communicate the appearance of the worms. If there is a large variety of sizes in the worm population, include a few of the thinner and a few of the thicker worms in your picture. Remember to add a legend explaining what is depicted.
- Follow the instructions that came with the 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.
- Record the soil analysis results for each pot in your lab notebook.
Analyzing Your Data
- Calculate the group mass change, in grams, for each pot of worms from day one to your final day of the experiment.
- Prepare a bar graph showing the final total number of worms you counted in each pot at the end of your experiment alongside the group mass change for each pot. Did some pots show a greater increase in number of worms or group mass than others?
- Calculate the total mass, in grams, of the food added to each pot during the entire experiment. Prepare a bar graph showing the total mass of food added to each pot.
- Prepare a data table showing the soil analysis results for each pot.
- 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?
- For help with data analysis and setting up tables, see Data Analysis & Graphs.
- For a guide on how to summarize your results and write conclusions based on your data, see Conclusions.
Ask an Expert
- Soil enrichment. This science project focuses on how diet affects the worm population. To make the change in soil composition the center of your project, add an extra pot with soil but no worms as a control. The control allows you to measure how the soil composition changes when no compost but only water is added. As measurements tend to fluctuate, you will need several measurements to support your conclusions. In this case, have at least two pots for each diet so you have at least two soil composition measurements for each diet.
- 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:
- For other Science Buddies projects related to earthworms, see:
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