Heterotrophs, mainly bacteria and fungi, also includes some protozoa and saprophytes. There are two kinds of decomposers in the pond, one is bacteria and fungi, the other is crabs, some kinds of mollusks and worms. The decomposers on land include bacteria and fungi living in litter and soil, as well as invertebrates such as earthworms and mites.

Earthworms and dung beetles are heterotrophic microorganisms, such as bacteria, fungi, soil protozoa and some small invertebrates. They make a living by decomposing animal and plant residues and are called decomposers. Microorganisms play a role in recycling nutrients in the ecosystem. Small invertebrates in soil, such as nematodes, earthworms, etc., crush plant residues and accelerate the decomposition and transformation of organic matter under the action of microorganisms. In addition, these soil animals can also be decomposed in the body, transforming organic matter into inorganic salts for plants to absorb and utilize again.