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Billions of Microorganisms in the Worm Bin

In addition to the visible macro-organisms that inhabit your worm bin, there are billions of microorganisms who help the composting process along.

Inside Your Worms

Worm castings are full of beneficial micro-organisms.

Worm castings are full of beneficial microorganisms.

Within a composting worm, there are multitudes of microscopic organisms working hard to aid digestion and produce nutrient-rich compost. These microbes are either swallowed with an earthworm’s food, or are already present in a worm’s gut. They include: bacteria, fungi, nematodes, and protozoa. Earthworms actually lack the enzymes to break down much of what they eat, so they rely on these microbes to do it for them. It is the nutrients produced by the bacteria that are absorbed into the worm’s bloodstream as nourishment. Then the broken-down organic matter is excreted as a worm cast (and is teeming with microbes), and we can use it in our gardens.

In her wonderful book “Worms Eat My Garbage”, Mary Appelhof states: “The composting process continues after a worm casting has been deposited. In fact, the bacterial population of a cast is much greater than the bacterial population of either ingested soil, or the earthworm’s gut” (68).

A deposited worm cast joins a soil ecosystem already chock full of bacteria, protozoa, amoeba, fungi, and nematodes. A teaspoon of good garden soil, according to microbial geneticists, contains a billion bacteria, several yards of fungal hyphae, several thousand protozoa, and a few dozen nematodes. In a teaspoon! It is this incredible community of life that supports all gardening, all agriculture, and all forestry in our world. By adding worm casts to this equation, you boost it and help it flourish. In this way, worm casts are the ultimate organic fertilizer – the opposite­ of chemical pesticides that poison and kill everything in the soil in the name of abundant yields.

Inside Your Worm Bin


Bacteria are the single most important organisms in your worm bin.

A vermicomposting bin is small, but it contains billions of organisms. These include the microorganisms mentioned above: bacteria, protozoa, and nematodes, fungi (including molds).

Bacteria are the most numerous organisms in the vermicompost system, and the primary decomposers of organic matter on earth. They work on organic material by secreting enzymes which break the bonds holding molecules together, thus simplifying and reducing the molecules to their component elements for absorption. As bacteria simplify the organic matter they make it available to earthworms and other organisms in the system as well.

Actinomycetes are basically a higher form of bacteria, which have several very notable characteristics. Just for starters, close your eyes for a moment, and imagine the beautiful smell so commonly associated with fresh soil. That’s actinomycetes you’re smelling. Now think of all the wonderful benefits you have heard of being derived from humus. The actinomycetes are crucial to the formation of humus. Often working very deep in the soil, these ambitious bacteria convert dead organics into a type of peat, and also release various nutrients such as nitrogen and carbon, making it available for mixture into the topsoil. Since actinomycetes possess the ability to produce antibiotics, many other bacterial populations decrease as the number of actinomycetes increases.

Mold grows on food that has been sitting for a while in your worm bin.

Mold grows on food that has been sitting for a while in your worm bin.

Molds and fungi are common organisms in a healthy worm system. Fungi are simple living organisms. Fungi are not classified as plant or animal, but are organized into their own group. The Kingdom of Fungi includes yeasts, molds, and mushrooms. They survive on energy which they obtain from the organic matter in dead plants and animals. They feed on decaying organic matter with tiny, hair-like hyphae, secreting enzymes which break down and simplify the organic material. They are also an additional food source to other organisms in the system, including earthworms. Mold is a good indicator of whether or not the feeding rate is adequate. Because they grow most prolifically in still, quiet environments, large amounts of mold and fungi indicate there is more food than the system can quickly manage and the feeding rate should be decreased.

Mold and fungi pose no threat to the garden or the animals living in the worm bin, but can cause irritation to humans with mold allergies. If you are allergic to molds, your bin should be kept outdoors or in a garage or basement that is well ventilated to reduce or eliminate irritation.

Nematodes are very small, translucent, unsegmented roundworms that mineralize nutrients contained in bacteria and fungi. There are about 20,000 species of nematodes on the planet, and there will be several of them in your worm bin. They are mostly beneficial in your bin, eating bacteria and fungi and helping to break down the nutrients contained in those organisms to make them plant-available.

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