What is the Difference Between Compost Worms and Earthworms?

Angelo (admin)

1 year ago

Almost every gardener that has ever done composting has found earthworms in their finished compost. Some gardeners mistakenly think that earthworms that appear in the compost are the same as compost worms because of where they are located.

The confusion arises from the misunderstanding of the term “compost worm”, which does not refer to worms in the compost, but to specific species of worms such as tiger worms (Eisenia foetida) used in vermicomposting (literally ‘worm composting’) systems such as worm farms, that are quite different from common earthworms (such as the purple worm Aporrectodea trapezoids and common earthworm or nightcrawler Lumbricus terrestris). They differ significantly in habitat preferences, diet, and roles in soil ecology.

Here’s a detailed comparison across these areas of difference between earthworms and compost worms:

1. Habitat Preferences

Earthworms: Earthworms are soil-dwelling worms and live deep in the soil, often burrowing several feet below the surface. They create permanent, vertical burrows in soil, which they use to move between surface layers and subsoil. These burrows help aerate the soil and improve water infiltration. Earthworms are not suited to living in compost piles because they prefer the stable, cool, and moist conditions found in undisturbed soil.
Compost Worms: Compost worms, such as red wigglers (Eisenia fetida), are adapted to live in environments rich in decaying organic matter and are commonly found in the upper layers of compost, manure, and leaf litter. They thrive in environments with high microbial activity, where temperatures are warmer, and food is plentiful. They do not burrow deeply and are therefore unable to avoid high soil surface temperatures in summer, and as a consequence are unable to survive for the long-term in the soil.

2. Diet and Feeding Behavior

Earthworms: Earthworms feed primarily on soil and organic matter mixed within it, digesting decomposing leaf litter and plant roots, as well as other soil-based organic particles. They ingest soil particles along with organic material, which enhances nutrient cycling and soil structure. Their diet makes them beneficial for soil improvement but not particularly efficient at processing large quantities of organic waste quickly.
Compost Worms: Compost worms are efficient decomposers of organic matter, feeding on a variety of decomposing plant materials, vegetable scraps, and other organic waste commonly found in compost heaps. They consume twice as much organic matter as earthworms do. Their fast feeding and reproduction rates make them ideal for converting organic waste into nutrient-rich vermicompost. Compost worms prefer a consistent, ample supply of food in an environment with temperatures between 15-25°C (59-77°F), making them ideal for worm farms which provide a regular food supply and controlled environmental conditions.

3. Role in Soil and Composting

Earthworms: Earthworms play a vital role in soil aeration, nutrient cycling, and improving soil structure. Their burrowing activity creates channels in the soil, allowing roots to access oxygen and water more easily, and their castings (worm droppings) add essential nutrients to the soil. They are beneficial to the overall health of garden or agricultural soils and are particularly effective in no-till or minimally disturbed environments.
Compost Worms: Compost worms are more specialized for composting systems and less for soil improvement. Their rapid breakdown of organic material produces vermicompost, a nutrient-rich compost that improves soil health when added to gardens or farms. The natural habitat of compost worms is surface layers of decomposing organic matter., such as leaf litter, manure piles and other rotting vegetation in grasslands or along the edges of forests that accumulate on the soil surface. Unlike earthworms, they do not contribute to deep soil aeration but rather are beneficial within compost bins or piles, where they transform organic waste into a stable, soil-like substance quickly.

4. Reproductive and Life Cycle Differences

Earthworms: Earthworms tend to reproduce at a slower rate and have a longer life cycle than compost worms. They are also less likely to tolerate high-density living conditions found in composting systems. Earthworms require soil for burrowing and depositing cocoons, which limits their suitability for confined compost bins.
Compost Worms: Compost worms have a higher reproductive rate and thrive in the high-density, nutrient-rich conditions found in compost piles. They lay cocoons in organic-rich environments, and under ideal conditions, they can double their population in as little as 90 days. This rapid reproduction and tolerance for crowded conditions make them ideal for vermiculture and composting.

The Three Different Types of Earthworms

To make an even finer distinction, there are over 1,000 species of earthworms, which can be categorized into three main groups:

Litter Dwellers (Epigeic Species)
These earthworms live in organic material, such as crop or forest litter, and are not commonly found in agricultural soils. They do not ingest large quantities of soil, but consume large amounts of organic matter. An example is the tiger, manure or red worm (Eisenia foetida) used in worm farms as a compost worm.
Topsoil Dwellers (Endogeic Species)
These earthworms inhabit the upper 5–7.5 cm (2–3 inches) of soil and feed on partially decomposed organic matter already mixed into the soil. As they move through the soil, they create horizontal burrows filled with their excrement. Endogeic species consume and mix large amounts of soil with digested plant material in their digestive system.
Subsoil Dwellers (Anecic Species)
These earthworms live in deep, permanent vertical burrows that can extend 1.5–2 meters (5–6 feet) below the surface. They rely on decomposing plant matter on the soil surface for sustenance and cap their burrows with these materials, which they pull to the entrance. Anecic species consume significant quantities of soil, mixing it with digested plant residues, and deposit most of their excrement on the soil surface. The nightcrawler (Lumbricus terrestris) is a well-known example of this group.

How Do Earthworms End Up in Compost Bins and Plant Pots?

Other than their proper home in the soil, gardeners can find earthworms in compost bins and under pots in the garden. These soil-dwelling worms emerge before rain to avoid drowning in their burrows and often get washed away to end up in compost bins or pots situated on hard surfaces such as concrete. They lay eggs in soil, so adding garden soil to a compost pile can introduce them into there. They’ll survive in a compost pile or compost bin if it doesn’t become too hot. and multiply there, feeding on organic matter.

As a handy tip, if you have a compost bin sitting on the soil, and it looks finished, the presence of earthworms is a good indicator that the compost has cooled down, and is ready to use! When the composting process is in progress and is too hot, the earthworm will burrow into the soil away from the compost and return after it has finished breaking down.

In summary, earthworms and compost worms fulfill different roles in natural and managed ecosystems. Earthworms are vital for soil health and structure, while compost worms excel at breaking down organic waste in compost systems. Each has evolved to thrive in different habitats and serve distinct ecological functions.