When you have an empty bottle, do you recycle it so the plastic or glass can be used again? Nature has its own recycling system: a group of organisms called decomposers.

Decomposers feed on dead things: dead plant materials such as leaf litter and wood, animal carcasses, and feces. They perform a valuable service as Earth’s cleanup crew. Without decomposers, dead leaves, dead insects, and dead animals would pile up everywhere. Imagine what the world would look like!

More importantly, decomposers make vital nutrients available to an ecosystem’s primary producers—usually plants and algae. Decomposers break apart complex organic materials into more elementary substances: water and carbon dioxide, plus simple compounds containing nitrogen, phosphorus, and calcium. All of these components are substances that plants need to grow.

Some decomposers are specialized and break down only a certain kind of dead organism. Others are generalists that feed on lots of different materials. Thanks to decomposers, nutrients get added back to the soil or water, so the producers can use them to grow and reproduce.

Most decomposers are microscopic organisms, including protozoa and bacteria. Other decomposers are big enough to see without a microscope. They include fungi along with invertebrate organisms sometimes called detritivores, which include earthworms, termites, and millipedes.

Fungi are important decomposers, especially in forests. Some kinds of fungi, such as mushrooms, look like plants. But fungi do not contain chlorophyll, the pigment that green plants use to make their own food with the energy of sunlight. Instead, fungi get all their nutrients from dead materials that they break down with special enzymes.

The next time you see a forest floor carpeted with dead leaves or a dead bird lying under a bush, take a moment to appreciate decomposers for the way they keep nutrients flowing through an ecosystem.