Grades 1 – 3: Decomposer Detectives

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earthwormRecommended grade level: 1 – 3
Presentation time: 50 minutes


“Cycle” is the root of “recycle” and decomposers rule the recycling world! When human beings recycle, we are copying a model that works everywhere in the natural world. In the natural world, everything is used efficiently and there is very little waste.
Life on earth is a part of a never ending cycling of matter. In this lesson, we will explore only a part of that larger cycle. We will look at the flow of nutrients in the cycle of decomposition. After achieving an understanding of the relationships in this cycle, students will investigate mature compost to discover some of the decomposers present.


By the end of this activity, students will understand:

  • All living things depend on the cycling of nutrients
  • Plants depend on decomposers returning nutrients to the soil in a form they can use
  • Composting food scraps and yard waste returns nutrients to the decomposition cycle
  • There are many different decomposers


By the end of this activity, students will be able to:

  • Identify the parts of the decomposition cycle and sequence the flow of nutrients
  • State at least two choices people have for food and yard waste disposal and relate what happens to the  nutrients in each choice
  • Generate a short list of what can and cannot be composted at home
  • Describe three different decomposers


  • Compost – noun; a mixture of decaying matter that is used for fertilizing, verb; a process for converting organic waste into humus
  • Consumer – organism that eats other organisms
  • Cycle – a recurring sequence of events
  • Decomposer – any of the organisms that eat and digest dead plants and
  • animals, their waste product is humus
  • Food Chain – how organisms use one another for food
  • Humus – a brown or black material that is the result of the digestion of dead plants and animals by decomposers, rich in plant available nutrients
  • Nutrient – anything that provides nourishment
  • Producer – level of organisms in the food chain that manufacture their own food from carbon dioxide, water, sunlight and minerals.


  • Tally board and cards
  • Well decayed compost, with decomposers present
  • Foil pie pans and plastic utensils for exploring compost samples
  • Hand lenses (one per student, or enough for small groups to share)
  • Three numbered samples of decomposing organic matter in stages of decay
  • “Compost Critters” worksheet (one per student)
  • Crayons, pencils or markers (from classroom supplies)

magnifying glassProcedure

Presenter chooses six students to play the parts and narrates the activity.

  • Eat and Be Eaten – Skit Outline

First child portrays the sun, source of all energy needed by living organisms on earth. Presenter prompts children, suggesting “let’s see you beam energy to all living things on earth,” or with more directivity, “hold your arms over your head like the mighty sun!”

Next two children portray green plants. They can crouch down low and grow up tall, or otherwise dramatize vegetation. Ask these children to feel the sun’s energy, and how they receive it (in the forms of heat –– thermal energy, and light — radiant energy). Point out to the class that green plants can make food from the sun’s energy, and we call them producers.

Now select one child to portray a plant-eating animal of their choice, and direct that child to enact the animal they choose to be. Have the animal “snack” on or “consume” one of the plants, and point out that animals must eat food produced by plants from sunshine energy, or they eat other animals that eat plants, so we call all living things that eat other things, consumers.

Narrate how plants and animals live, grow and reproduce (keep it simple, this is a fast activity). Ask the class, “What happens at the end of life for all living things?” Then the plants and animal actors get to die (big dramatic high point of the skit).

Finally, cast the stars of this little show, the decomposers. They can be mushrooms, bacteria, earthworms, millipedes, sowbugs, pillbugs – ask the class what kinds of living creatures break down the dead bodies of animals and plants, and ask your young actors to show how that’s done. Explain how the decomposers eat and digest the bodies of the dead animals and plants, their waste products have turned them back into nutrients that mix in the soil –these nutrients are stuff that plants need in order to grow.

You can say that the green plants left some seeds in the ground before they died. What happens to seeds in good soil full of nutrients when the sun shines on them? Refer to the “sun,” have him/her beam a little. With the sun’s energy, new plants grow using those nutrients made available by decomposers. Those new plants become more food for animals. The adult animals have young born before they die and the cycle continues.

What would happen to this cycle if there were no decomposers? The earth would be covered with dead plant and animal bodies, and all the useful nutrients in those bodies would be wasted.

Would the plants be able to grow? No they would not. Plants depend on the decomposers to recycle nutrients back into the soil. Animals depend on plants. Decomposers depend on the dead remains of plants and animals.

Have all the players take a bow and return to their seats.

Now we will investigate compost and meet some real decomposers.

Compost Observation

These compost samples contain many types of decomposers. Every group will keep track of the decomposers you find with the decomposer cards. Everytime you find a new decomposer, look for a matching card. The picture on the card will not be the same size as the decomposers you will find. To see the bacteria, the smallest decomposers in your sample, you would need to use a microscope. Everyone has bacteria in their compost sample so that will be your first card. Use the hand lenses to look at others that are very tiny (instruct students on how to use the hand lens if they are unfamiliar with them.) Make a pile of cards of all decomposers you find. If you find something unusual let me know and we can share it with the rest of the class using our petri dishes.

  • Presenter distributes foil pans containing compost samples and plastic utensils, making the point that decomposers are living creatures, with small delicate bodies, and should be observed with care and respect. Working  in groups of 2-4 students, use hand lenses to explore samples of well-decayed compost.
  • As students find decomposers that are unusual or interesting , put them in a covered petri dish so that other groups can see them.
  • Have a student from each group post their cards on the display board.
    • Did the groups find the same things or did they find different things?
    • What did they find the most of?
  • Presenter shows students three samples of decomposing organic matter – ranging from fresh yard and/or kitchen waste to partially decomposed matter to a sample of the finished compost they have just been exploring. Ask a student to rank these samples in an order of least decomposed (#1) to most decomposed (#3), discussing reasons for ranking (e.g., pieces are larger in first sample, colors and shapes of materials change as decomposition proceeds, etc.)
    • If you were a green plant, with roots needing to be securely surrounded by rich soil, which of your three samples they would choose to grow in? Why?
  • Review important concepts by using discussion questions. Collect all materials. Some compost can be left with the class to use in seed-growing experiments, if they would like some.

Discussion Questions

  • What would the earth be like if there were no decomposers at work?
  • What kinds of materials do households and schools regularly throw away?
  • Which of these materials could go into compost?
  • Why is composting important?