Fourth Grade NGSS
Biogeology and Heat Generation

Decomposer Identification


  •  Identifying microorganisms in compost. 
  • ·    Exploring the ecosystem of rot.  

  • thermophilic
  •  actinomyetes
  • fungi
  • Bacteria 
  • mesophilic


    ·         Microscope 

    ·         Petri dishes or paper plates

    ·         White spoons

    ·         Compost from local composter

    ·        Decomposer worksheets



    Bacteria and fungi digest organic matter and convert it into different chemical forms that are used by other microbes, invertebrates and plants.  During thermophilic composting the populations of various types of microorganisms will change as conditions change. The world of microbes in compost is diverse and mysterious.  The energy that they release during their struggle to stay alive, creates another ecosystem that helps to further digest and change organic material.  

    There is always a challenge in compost in that your mixture produces an end product that has carbon and nitrogen in balance.  Making compost at the beginning can produce “smells” but once it gets an “earthy smell” then the compost is ready.  

    In this lesson we will have the student explore the different microbes that they can find.  It is not important what their names are, but that students look for organisms that help this complex chemical process.  Below are some of the organisms the students may see.  Drawing pictures can help them look at the organism careful. 

    Nematodes, or roundworms, are an abundant invertebrates in the soil. Typically less than one millimeter in length, they prey on bacteria, protozoa, fungal spores, and each other. Though there are pest forms of nematodes, most of those found in soil and compost are beneficial.

    Fermentation Mites

    Fermentation mites, also called mold mites, are transparent-bodied creatures that feed primarily on yeast in fermenting masses or organic debris. Literally thousands of these individuals can develop into a seething mass over a fermenting surface. As a result, they often become pest species in fermenting industries, such as wineries and cheese factories. They are not pests in the compost pile.

    Springtails, or collembola, along with nematodes and mites, dominate in numbers among the soil invertebrates. They are a major factor in controlling fungi populations. They feed principally on fungi, but also on nematodes and small bits of organic detritus

    Redworms and Earthworms
    Redworms and earthworms play an important part in the break-down of organic materials and in forming finished compost. Red worms are usually 2-3 inches long and are important in warm composting debris.  The more common earthworms are important in natural soil.  As worms process organic materials, they coat the material with a mucus film that binds small particles together into stable
    aggregates and helps to protect nutrients from being leached out by rain. These stable aggregates give soil a loose and well-draining structure.

    Ground Beetles
    Ground beetles have many representatives lurking through litter and soil spaces. Most of them feed on other organisms, but some feed on seeds and other vegetable matter.

    Wolf Spiders
    Wolf spiders are truly "wolves" of the soil and compost communities. They don't build webs, but run freely, hunting their prey. Depending on the size of the spider, their prey can include all sizes of arthropods- invertebrate animals with jointed legs and segmented bodies.

    Centipedes are frequently found in soil and in compost communities. They prey on almost any type of soil invertebrate near their size or slightly larger


    1.    Provide students with copies of the organisms used in composting. 

    2.    Get compost from the Jora compost and put in petri dishes.  However, if you do not have enough time

    One method of collecting invertebrates is to take grab samples of compost from various locations in the heap. Some organisms such as centipedes and sowbugs will be more likely to be found near the surface. Others will be found deeper in the heap. Spread each compost sample in a large tray or pan, preferably light in color for maximum contrast. Students should use wooden tongue depressors, plastic spoons, or other instruments that will not hurt the organisms, to sort through the compost. Flashlights and magnifying lenses can be used to enhance the observation. The larger organisms, such as worms, centipedes, millipedes, sowbugs, earwigs, spiders, ants, beetles, snails, slugs, some mites, etc., can be observed with the naked eye. To get a closer look, place samples of the compost in petri dishes or watch glasses and observe them under a dissecting microscope.

    3.    Have them look at the material and identify different organisms that they find.  You can have them use the work sheet and circle what they see, or you can give them a blank piece of paper and have them draw what they see and have them try to identify it with the hand out on microbes (preferred). 


    4.     Have the students write down (on the board) what they are finding.  If they find something that is not on the chart have them draw it, and see if anyone can identify.


    5.     Discuss what they have seen.  Refer back to last lab and see if they can figure out what part they play in the decomposition.


    Return to NGSS Model