Decomposers are living things that break down dead plants and other leftovers, and people call them nature's clean-up crew. They recycle nutrients from dead plants back into the soil, which helps plants grow. Decomposition starts right after any living thing dies, when microbes break proteins down and some of the gases released become chemical cues that signal opportunity to some animals. Forest Service researchers who compared forests using the same kind of leaf found that invertebrate detritivores in tropical forests had a stronger influence on leaf decomposition than they did in cold temperate forests. In a Puerto Rico rainforest, early inventories at El Verde found that about half of the soil animals' weight was in the thin top layer of soil and the litter layer, which is where fallen leaves are broken down.

You may have heard that leafcutter ants eat leaves; in fact, they carry bits of leaves to their nest, do not eat them, and use them to grow a fungus that they eat. The ants chew the leaf pieces into tiny bits before they add them to the fungus garden. Leaves have little nitrogen, which the ants' fungus needs. Leafcutter gardens host bacteria that pull nitrogen out of the air, while the leaves get richer in nitrogen as they pass through the garden. Only some ants farm, and all the fungus-farming ants live in the New World, mostly in the tropics of Central and South America. When a young leafcutter queen starts a new nest, she carries a piece of the fungus garden in her mouth to start the new garden.

A leafcutter ant colony can hold millions of ants; a Texas leafcutter colony can top 2 million, and the largest leafcutter colonies have over 8 million. In South America, a big colony eats about as much fresh plant material each day as a cow, and the ants in it would weigh about as much as a cow. Fungus-farming ants must guard their garden from other molds and bacteria. A Smithsonian scientist says an ant visits every square centimeter of the garden every few seconds. If the ants find a bad mold or bacteria they try to pluck it out, and if they cannot, they apply antibiotics to it, which come from glands on the ants or from bacteria growing on them.

Most termites cannot digest wood alone, and tiny one-celled living things called protists in a termite's gut help turn wood into food for the colony. Decay fungi in rotting wood break down cellulose into smaller pieces before the termites bite, so termites eat decayed wood faster than sound wood. They eat the soft part of the wood grain first and leave the harder part. Termites pass gut contents between nest mates, which is called trophallaxis. This shares food and also passes the cellulose-digesting protozoans along, so young termites get the microbes they need. Scientists call termites eusocial, using three traits: adults care for the young together, some individuals are sterile and work for the colony, and two or more generations overlap in the colony.

Black soldier flies came from warm regions and cannot survive cold well. In Utah they usually cannot overwinter outdoors, so year-round farms keep them in enclosed, netted buildings. Their larvae give off heat as they eat and speed up decay. They can finish waste much faster than ordinary composting while also eating dairy, meat and citrus that backyard compost piles usually leave out. Black soldier fly frass contains chitin, a part of the larval skin. Chitin can help suppress pests when frass goes onto farm soil, so the leftovers do more than feed plants. Food waste accounts for the greatest percentage of landfill methane emissions. Methane is a more potent global warming gas than carbon dioxide (as of January 2025).

A working compost pile gets warm, and the heat comes from the tiny living things that are eating inside it. In a compost pile, bacteria work first and their numbers jump. When the pile cools, centipedes, millipedes, sowbugs and earthworms carry on the work. Decomposition happens much faster in a compost pile because the pile can be made ideal for the microbes. A pile that is too small does not get hot enough. In moist soil that is rich in rotting plant matter, springtails can number in the thousands per square foot. Healthy soil teems with life: a single teaspoon can hold more living things than there are people on Earth. A USDA scientist says all the soil life in one acre equals about two African elephants in weight.

Burying beetles chirp by rubbing the edges of hardened wing cases against ridges on the abdomen, and University of Bayreuth biologists note that even Darwin suggested this sound likely plays a role in caring for young. Purdue and University of Florida scientists studied what termites do when their diet changes. Termites and their gut protists fed woody, lignin-rich diets changed the activity of about 500 genes, which the lead scientist believes may be important for breaking down lignin. Earthworms live in soil and eat dead leaves and bits of soil. Their droppings are called casts, and they hold soil, bits of plants and tiny microbes, and they feed the soil. Earthworm casts have about 50 percent more calcium, nitrogen, phosphate, potassium and bacteria than the surrounding soil. They also contain calcium carbonate, which lowers soil acidity.

Words to know

• decomposers: clean-up crew
• detritivores: leftover eaters
• chitin: hard skin stuff
• trophallaxis: food sharing
• antibiotics: germ-killing chemicals