Primary Consumers are organisms that eat organic residues.

Psychrophiles are aerobic bacteria that thrive in low temperatures of approximately 55 degrees Fahrenheit and will slowly decompose compost even at 0 degrees Fahrenheit.

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Mesophiles are most active at the 70-90 degrees Fahrenheit temperatures. These aerobic bacteria do most of the work.

Thermophiles quickly raise the temperature in the pile to levels that kill most weed seeds.

Actinomycetes resembles fungi but actually are filamentous bacteria. Like other bacteria, they lack nuclei, but they grow multicellular filaments like fungi. In composting they play an important role in degrading complex organics such as cellulose, lignin, chitin, and proteins. Their enzymes enable them to chemically breakdown tough woody materials. Actinomycetes form long, thread-like branched filaments that look like gray spider webs stretching throughout compost, and give the pile a pleasing earthy smell.

Fungi includes molds and yeasts, which lack chlorophyll, the green pigment that allows most plants to convert sunlight into carbohydrate. Most fungi are classified as saprophytes because they obtain nutrients from dead plant matter. In compost, fungi are important because they break down tough debris, enabling bacteria to continue the decomposition process once most of the cellulose has been exhausted. Fungi species are numerous during both mesophilic and thermophilic phases of composting.

Sowbugs are fat bodied crustaceans with delicate plate-like gills along the lower surface of their abdomens, which must be kept moist. They feed on woody materials and durable leaf tissues.

Earthworms play an important role in breaking down organic materials and stabilizing finished compost. They are constantly tunneling and feeding on dead plants and decaying insects during the daylight hours. Their tunneling aerates the compost and enables water, nutrients and oxygen to filter down. They coat organic materials with a mucus-like film that binds small particles together and protect nutrients from leaching.

Millipedes are slower and more cylindrical than centipedes and have two pairs of appendages on each body segment. They feed mainly on decaying plant tissue but will eat insect carcasses and excrement.

Nematodes, or roundworms, are the most abundant invertebrates in the soil. Though there are pest forms of nematodes, most are beneficial. They prey on bacteria, protozoa, fungal spores and each other.

Mites are the second most common invertebrates found in compost. Some can be seen with the naked eye and others are microscopic. They have eight leg-like jointed appendages. Some feed on yeasts in fermenting materials, while others feed on nematodes, eggs, insect larvae and other mites.

Protozoa are one-celled microscopic animals. They are found in water droplets in compost but play a relatively minor role in decomposition. Protozoa obtain their food from organic matter in the same way as bacteria do but also act as secondary consumers ingesting bacteria and fungi.

Springtails are extremely numerous in compost. They are very small wingless insects and can be distinguished by their ability to jump when disturbed. They feed principally on fungi, although they also eat nematodes and small bits of organic detritus.

Tertiary Consumers are organisms that eat secondary consumers.

Centipedes are fast moving predators found mostly in the top few inches of the compost heap. They have formidable claws behind their head, which possess poison glands that paralyze small red worms, insect larvae, newly hatched earthworms, and spiders.

Definitions taken from Cornell University's composting website and Florida's On-line Composting Center.

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