The composting machinery

A compost bin is like an efficient factory in which organic waste is transformed, obtaining one of the best foods for our crops; the compost. This is what we see from the outside, but the real magic happens inside.

As in any factory, there are many “machines” in the composter carrying out different tasks in a chain, all working with a common goal. The difference is that in the compost bin the “machines” are actually living beings… And there are not a few!

In a normal garden compost bin, billions of living beings can exist feeding and transforming the organic waste that we add. Hard to believe, right? Well, nothing better than seeing to believe.


  • 6-12 years.


  • 1 session.


  • Gloves.
  • Bag of compost from our orchard or that of a family member (about 5 litres).
  • Trays (although they are not as suitable, we could also use several sheets of newspaper to distribute the compost).
  • loupes.
  • Dchotomous identification guide of the inhabitants of the compost bin (click here).


  • Know the decomposing organisms.
  • Observe living beings with appropriate instruments.
  • Classify invertebrates.
  • Learn to use a dichotomous identification guide.
  • Promote respect for life based on the premise that every living being has a role in the theater of life.


On this occasion we are going to meet the animals that make the compost and we will try to name them using a simple dichotomous guide, a resource widely used by scientists when they have to identify species.

Session 1

We will begin by reading the following text:

“Many groups of animals and billions of microscopic beings can coexist in a composter. All these living beings find in the compost the ideal conditions to live comfortably; It is a warm place, protected from the rain and where food is never lacking. They feed on organic waste, gradually transforming it into compost.

When we add their food, the animals that we can see with the naked eye (worms, ball bugs, slugs) begin to eat first. The crumbs and poop of these small animals serve as food for other smaller animals (we need a magnifying glass to describe them; mites and springtails). The leftovers and remains of these serve as food for microscopic beings (bacteria, fungi), after the action of which we would already have well-made compost. Microscopic beings can be considered the most important group of beings among those who carry out composting; this is because they are the most abundant and diverse group of all those who live in the composter.”

Next, we will divide the class into groups of 4 members.

With the compost bag on the floor in a corner of the class, we will distribute the compost in as many trays as groups have been created. A glass of compost (250 ml) will be distributed approximately per tray, taking care not to harm the little animals that live in it.

Next we will observe the samples and describe the beings that we are observing as well as their abundance (less than 5; from 5 to 10, more than 10). When we have observed those on the surface, we will carefully remove the compost with tweezers or sticks. We will use the magnifying glass to observe the animals that we cannot describe with the naked eye.

Once we have described all the animals in our compost sample, we will use the dichotomous guide (click here) to try to identify them and be able to call them by name.

To conclude this activity we will share the different groups of animals observed and their abundance, and we will reflect on their relative importance in the composting process.

— Dani Trigueros

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