Decomposer Definition

A decomposer is an organism that decomposes, or breaks down, organic material such as the remains of dead organisms. Decomposers include bacteria and fungi. These organisms carry out the process of decomposition, which all living organisms undergo after death. Decomposition is an important process because it allows organic material to be recycled in an ecosystem.

Function of Decomposers

Decomposers play an important role in every ecosystem. Without decomposers, dead organisms would not be broken down and recycled into other living matter. The reason decomposers decompose, however, is simply because they need to survive. Decomposers are heterotrophic, which means they get their energy from ingesting organic material. 

A dead organism provides nutrients for decomposers like bacteria and fungi to use in order to grow and reproduce, propagating their own species. The side effect of this basic need to survive is that organic material and nutrients are cycled throughout the ecosystem as other organisms consume the bacteria and fungi.

Decomposers and Detritivores

Some organisms perform a similar function as decomposers, and are sometimes called decomposers, but are technically detritivores. The difference lies in the way decomposers and detritivores break down organic material. Detritivores must digest organic material within their bodies in order to break it down and gain nutrients from it. 

Decomposers do not need to digest organic material internally in order to break it down; instead, they can break down matter through biochemical reactions. Organisms that are detritivores include invertebrates such as earthworms, woodlice, sea stars, slugs, and fiddler crabs.

Decomposers and Scavengers

Scavengers are the first to arrive at a dead organism’s remains, and they directly eat the dead plant and animal material. Once scavengers are done with the remains, decomposers and detritivores take over and consume the parts that the scavengers have left behind. 

Many predators will scavenge on occasion; examples of these sometime scavengers include lions, jackals, wolves, raccoons, and opossums. Vultures are obligate scavengers, meaning that scavenging is how they obtain all of their food. They are the only members of the animal kingdom that have to scavenge in order to eat.

Stages of Decomposition

When an organism dies and decomposers do the work of decomposition, the organism’s remains go through five stages of decomposition: fresh, bloat, active decay, advanced decay, and dry/remains. There are two main processes that occur in a decomposing organism: autolysis and putrefaction. 

Autolysis is when cellular enzymes in the dead organism’s own body break down cells and tissues, while putrefaction is when microbes grow and reproduce throughout the body after death. Here is a brief summary of the five stages.


This stage begins as soon as an organism’s heart stops beating. With no more oxygen coming into the body and a buildup of carbon dioxide, autolysis begins to occur. Putrefaction also begins to occur.


Due to putrefaction, a buildup of gases occurs and the organism’s remains appear bloated in what is known as the bloat stage. Some gases and fluids are purged from the body.

Active Decay

The remains lose mass, and liquefaction and disintegration of tissues begins to occur. Bacteria produce chemicals such as ammonia, hydrogen sulfide, and methane, which cause strong odors.

Advanced Decay

The organism has lost a lot of mass, so there is not much left to be decomposed. If the organism is on or in soil, the surrounding soil will show an increase in nitrogen, an important nutrient for plants.


In this stage, only dry skin, cartilage, and bones are left. Plant growth may occur around the remains because of the increased nutrient levels in the soil. Eventually, only the bones of the organism will remain.

Examples of Decomposers


Bacteria are microscopic, unicellular organisms found nearly everywhere on Earth, including inside the human body. When an organism dies, it provides many nutrients for bacteria to grow and reproduce, and they become numerous in the process of putrefaction during decomposition. 

Bacteria are themselves a cause of sickness and even death when they infect organisms. Serious and often fatal diseases such as typhus, tuberculosis, and cholera are caused by bacterial infections. Bacteria that kill their hosts end up inadvertently providing nutrients for other bacteria during decomposition.


Fungi are the main decomposers in many environments. Some examples of fungi are yeasts, molds, and mushrooms. Fungi have hyphae, which are branching filaments, and these hyphae are able to enter organic matter, making fungi effective decomposers. 

Wood-decay fungi have specific enzymes that digest compounds in wood, and are the main decomposers in forests. In fact, wood-decay fungi are the only producers of these enzymes, so they play a very important role in decomposition.

Related Biology Terms

  • Detritivore – An organism that eats detritus, which is decomposing plant and animal matter as well as feces; it has a similar function in an ecosystem as a decomposer.
  • Ecosystem – A community of living organisms along with all the non-living parts of their environment.
  • Putrefaction – A process that occurs during decomposition when microbes proliferate throughout the remains of a dead organism.
  • Hyphae – Long, branching filaments on fungi that make them better able to decompose organic material and are also used in reproduction.

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