What a worm is a decomposer

Soil life


The smallest living things in the Edaphon, i.e. fungi and bacteria, make up around three quarters of the mass. In general it can be said: the smaller the life form, the greater its number.

Bacteria are single-celled organisms on the order of a few micrometers. What they lack in size, however, they make up for in number. Several million bacteria can be found in a fingertip full of healthy soil.

Soil bacteria live mainly in the area of ​​the soil that is rooted by plants, the so-called rhizosphere. They are divided into four groups: decomposers, mutualists, pathogens, and lithotrophic or chemoautotrophic bacteria.

The decomposers include the so-called actinomycetes, a large group of soil bacteria that are responsible for the characteristic "earthy" smell of the soil. They can only decompose parts of the litter that are very difficult to degrade, and they are particularly active in basic soils.

They also consume simple carbon compounds that plants excrete through their roots. Some decomposers are also able to break down pesticides and pollutants. Above all, however, their cells are a living "nutrient store", for example for nitrogen, which is thus retained in the root space.

Mutualistic bacteria have developed partnerships with plants over the course of their long development. A well-known example of this is the symbiosis between nodule bacteria and plants from the legume family.

Lured by root excretions, the bacteria penetrate the roots and live here in special thickenings, the so-called nodules. The bacteria are able to convert the nitrogen contained in the air into a form that is available to plants. Legumes are therefore often used as green manure in agriculture.

Pathogenic bacteria can be dangerous for plants and cause diseases that are often visible through the formation of plant galls.

The pathogens are always in competition with the "good" bacteria such as decomposers or mutualists. The plants try to influence this balance in favor of the "good ones" by excreting their roots.

The litotropic or chemoautotrophic bacteria gain their energy independently of carbon compounds. They use nitrogen, sulfur, hydrogen or iron compounds to generate energy. Some of them are important for the nitrogen cycle and the breakdown of pollutants.

Overall, bacteria stand for better soil quality, as they are food for more highly developed organisms in the soil, decompose organic waste, keep nutrients in the soil and filter pollutants from the soil.


Fungi consist of tiny cells that develop into long, narrow fibers or strands (hyphae) with a diameter of just a few micrometers and lengths of up to several meters. The hyphae penetrate the soil as a microscopic network, the so-called mycelium, which is reminiscent of plant roots in thickened areas.

Fungi are the dominant microorganisms in forests or in dry natural areas, while bacteria are more common in open areas used for agriculture. Analogous to bacteria, fungi in the soil are divided into three groups: decomposers, mutualistic fungi and pathogenic or parasitic fungi.

The decomposers break down the resulting organic matter, whereby they are also able to decompose substances that are difficult to break down, such as wood. Their activities create a large part of the permanent humus, which is so important for the soil.

But they also crack some extremely resistant pollutants. Like the bacteria, the fungi are also of great importance as "living" stores for nutrients, which are thus retained by the plants.

Mycorrhiza, a symbiosis between plants and fungi, is one of the mutualistic fungi. Their importance can only be assessed from the fact that around 90 percent of all land plants are in symbiosis with a mycorrhizal fungus. Some researchers suspect that the plants could only conquer the land as a habitat with the help of the mycorrhiza.

Pathogenic or parasitic fungi can severely weaken plants or, if they attack the roots, even lead to the death of the plants. Some representatives of these mushrooms cause heavy losses in agriculture year after year.

But there are also mushrooms that are now used as biological pesticides. Some of them lurk in the ground with their small snares of roundworms, catch them and decompose them.

Since roundworms also act as plant pests in some cases, inoculating the soil with the right fungi can provide effective protection.

Unicellular organisms

The protozoa include amoebas, flagellates and ciliates. They are usually much larger than bacteria (5 to 500 micrometers) and live in thin films of water that are present in the soil. The flagella and eyelashes are their means of locomotion. This allows them to move fluently through the water.

Amoebas can move through the formation of processes called "pseudopods". The protozoa feed on bacteria, related protozoa, organic material or fungi. In healthy soils, around a million single-cell organisms can live in one teaspoon of soil.

Protozoa play an important role in the mineralization of nutrients. The bacteria have a significantly higher nitrogen content in relation to the unicellular organisms.

The excess nitrogen is excreted in the form of plant-available ammonium. As a result, the unicellular organisms release some of the nutrients stored by the bacteria and thus ensure that the plants are constantly supplied.

Another important role played by unicellular organisms is the regulation of bacterial populations. By feeding on bacteria, they are stimulated in their growth. But overgrazing can also occur, which can lead to a decimation of the bacterial population or change the composition of the species.


Roundworms (nematodes) are ground-dwelling roundworms with an elongated body around 50 micrometers in diameter and 1 to 50 millimeters in length.

In forest soils, several hundred of the animals can live in one teaspoon of soil. Their habitat is the water film on soil particles, the lower moist litter layer or the upper horizon of humus-rich soils.

Roundworms use a wide variety of food sources in the soil. Some feed on parts of plants and algae, others feed on bacteria or fungi, and still others hunt unicellular organisms and other roundworms.

Roundworms play an important role in the nutrient cycle by releasing plant-available nitrogen, which is mainly excreted by bacteria- and fungus-eating roundworms.


Springtails (Colembola) are wingless insects with a size of 0.1 to 9 millimeters. They live in the soil and the litter, but can also be found on plants and tree trunks. Up to 100,000 animals live on one square meter of ground.

Some springtails have an elongated body, while others have a stocky, spherical body. Springtails that live in the upper soil or in the litter layer are pigmented and have eyes.

With the name-giving jumping fork on the abdomen, you can catapult yourself out of the danger area if necessary. Springtails that live in the deeper soil layers are white and their eyes and spring forks are stunted.

Springtails are important decomposers in and on the ground. They gnaw on fallen leaves and other plant material and thereby ensure that the organic matter is first crushed.


Woodlice are land-dwelling crustaceans and, like their relatives in the sea, breathe through gills. As a result, they are bound to constant moisture in their habitat. They live mainly on the surface of the soil.

Here they play a major role in the crushing of plant residues, which are converted into humus in their intestines. Several hundred woodlice can live on one square meter of soil.


In general, the arthropods, which include insects, millipedes, crabs, spiders, scorpions and mites, are of great importance for the soil.

They decompose the organic material and thereby increase the surface area that can be colonized by the microorganisms. They play an important role in converting the organic matter into fertile humus.

With their excretions, they also ensure that nutrients are distributed in the soil and transport bacteria and fungi to new food sources on their shell and in their digestive system.

In addition, plant material and microorganisms are optimally mixed in the intestine, which significantly accelerates the decomposition of the organic substance. They also play a major role in the mineralization of plant nutrients, alongside protozoa and roundworms.


Charles Darwin described the earthworm as "the farmers' most important helper". The earthworms that live on one hectare of soil can together weigh up to 2500 kilograms.

They excrete around 600 tons of worm solids annually and the tunnels they dug can reach a total length of around 9,000 kilometers. So it's no wonder that earthworms are counted among the most important soil animals and that their number is an indicator of the health of the soil.

In fact, they are the main decomposers in most habitats. Earthworms belong to the group of little bristles (oligochaetes). The so-called "anectic" earthworms dig vertical tunnels several meters deep. They usually come to the surface at night or when it is damp to forage.

Rotten vegetable and animal remains surround them tightly with their head rests and pull them into their corridors to be protected and eaten here in peace. In doing so, they primarily digest the bacteria and fungi that have already settled on the decaying material.

Through their relentless digging and eating, they bring the organic matter that normally lies on the ground directly into the ground. Their vertical corridors are a kind of "mini canalization": rainwater can quickly penetrate the ground and is not lost as surface runoff.

The so-called "endogean" earthworms dig horizontal tunnels in the top soil layer and plow it slowly and steadily. They are very pale in color because they rarely come to the surface of the earth.

Soil particles, organic matter and microorganisms are literally mixed up in the earthworm's intestines. The decomposition of the organic substance is accelerated accordingly. This also happens after the mixture has been released as a worm solution.

Earthworms also improve the quality of a soil by significantly improving its stability, porosity and ability to store water. For plant roots, the corridors lined with worm solution are a set table with plenty of water and nutrients.