The question, “Do worms eat compost?” is inaccurate. Worms do not consume finished compost; they are active participants in creating it. This process, known as vermicomposting, translates organic materials like kitchen scraps and bedding into a beneficial soil amendment called vermicast, or worm castings. Vermicomposting relies on specific worm species and microorganisms to achieve this transformation.
Differentiating Composting Worms
Not every type of earthworm is suitable for vermicomposting. Earthworms are categorized into three main ecological groups based on their habitat. Deep-burrowing types, called anecic worms, drag surface matter down into vertical tunnels.
The worms used for converting kitchen waste are epigeic species, which live and feed on decaying organic matter at the soil’s surface. They thrive in environments rich with decomposing material, such as a worm bin. The two most popular species are Eisenia fetida (Red Wiggler) and Eisenia hortensis (European Nightcrawler). Red Wigglers are favored for their surface-dwelling preference and rapid consumption rates.
What Worms Truly Consume
The misunderstanding about worm diets is the assumption that they directly consume large pieces of food waste. Composting worms lack the digestive enzymes necessary to break down complex organic molecules on their own. Their true diet consists primarily of the vast populations of microorganisms, such as bacteria and fungi, that have already colonized and begun decomposing the organic waste.
These microbes secrete enzymes onto the food scraps and bedding, breaking the material down into a softer, pre-digested slurry. When the worm ingests this matter, it is grazing on the bacteria and fungi present on the surface. The worm’s digestive system processes this nutrient-rich microbial biomass, which provides the majority of its sustenance. Therefore, organic material must first start to rot before it becomes a viable food source.
Worms also consume the bedding material, such as shredded paper or coconut coir, because these materials host the microbial community. Pre-decomposition explains why smaller food scraps are processed faster, as they offer a greater surface area for microbial colonization. The ingested mixture passes through the worm’s muscular gizzard, where fine particles are ground down into smaller components, often aided by grit or eggshells.
The Process of Creating Worm Castings
The consumed material travels through the worm’s digestive tract, undergoing a significant physical and biological transformation. Within the gut, the material is exposed to the worm’s digestive enzymes and an internal population of beneficial microbes. This internal process alters the chemical composition of the food waste, reducing potentially harmful pathogens and stabilizing the organic matter.
The final excreted product, known as worm castings or vermicast, is a highly refined organic amendment richer in plant-available nutrients than the initial feedstock. Castings are coated in a mucus layer packed with beneficial bacteria, which helps bind the material into small, pellet-like aggregates. This material contains elevated levels of macronutrients like nitrogen, phosphorus, and potassium, with NPK ratios ranging from 1-0-0 to 5-5-3, depending on the worm’s diet.
The nutrients in the castings are often water-soluble, making them easily available for immediate plant uptake. The microbial activity within the castings helps improve the soil’s structure, increasing its water-holding capacity and promoting nutrient cycling. This final product provides the true value of vermicomposting as a slow-release, biologically active fertilizer.