Earthworms are nature's clean-up crew, aiding in the production of lush, humus-rich topsoil from spent plant and animal materials. These elegantly efficient organisms have been on earth for hundreds of thousands of years longer than humankind, largely untouched by evolution due to their nearly perfect adaptation to their role in nature.Humankind has studied and learned to appreciate the talents of the earthworm, developing systems that capitalize on the natural role it plays in recycling organic matter back into humus. We now use earthworms for the remediation of organic “waste” materials, reducing the pressure on landfills and aiding in the regeneration of our valuable top soils.When beginning a foray into the operation of worm driven organics systems it is important to be clear on the intended goal of the project. Worm systems are typically managed for one of three reasons; waste management, production of worm biomass, and production of castings. While worms are being grown, organic materials are being processed, and castings are being generated in all worm beds, management methods will vary to some degree depending on the focus of the system.Vermicomposting is defined as the practice of using concentrations of earthworms to convert organic materials into usable vermicompost or worm castings. These systems focus on the waste material and managing it so that it can be successfully and efficiently processed in a worm system.Castings production systems are worm-processing beds that use feedstocks specially blended so that castings have a specific nutrient value, chemical characteristic or cross section of microorganisms. The focus of these systems is on end product value.Vermiculture systems focus on producing the maximum level of worm biomass possible in a given space.

The Amazing Earthworm

Researchers have identified and named more than 4400 distinct species of earthworm, each with unique physical and behavioral characteristics that distinguish them one from the other. These species have been grouped into three categories, endogeic, anecic and epigeic, descriptive of the area of the natural soil environment in which they are found and defined to some degree by environmental requirements and behaviors.Anecic species, represented by the common nightcrawler (Lumbricus terrestris), build permanent vertical burrows that extend through the upper mineral soil layer, which can be as deep as 4-6 feet. These species coat their burrows with mucous that hardens to prevent collapse of the burrow, providing them a home to which they will always return and are able to reliably identify, even when surrounded by other worm burrows. When deprived of this burrow environment anecic worms will neither breed nor grow.Anecic worms feed in decaying organic matter and are responsible for cycling huge volumes of organic surface debris into humus.Endogeic species build extensive, largely horizontal burrow systems through all layers of the upper mineral soil. These worms rarely come to the surface, spending their lives deep in the soil where they feed on decayed organic matter and mineral soil particles. While most people believe all worms eat soil, it is only the epigeic species that actually feed on significant volumes of soil itself.These worm species help to incorporate mineral matter into the topsoil layer as well as aerating and mixing the soil through their movement and feeding habits.Epigeic earthworm species, represented by the common red worm (Eisenia fetida), are found in the natural environment in the upper topsoil layer where they feed in decaying organic matter. Epigeic worms build no permanent burrows, preferring the loose topsoil layer rich in organic matter to the deeper mineral soil environment. Even in nature these worms are found in highest concentrations in the forest duff layer or in naturally occurring drifts of leaves and organic debris rather than in soil. We can duplicate the preferred environment of these worm species in bin culture, and it is largely for this reason that it is epigeic worms only that are used in vermicomposting and vermiculture systems.

Oxygen Requirements

Earthworms are oxygen-breathing animals that absorb oxygen directly through their skin. Oxygen is dissolved into mucous coating the worm's skin and the dissolved oxygen passes through the skin and the walls of capillaries lacing the skin where it is picked up by hemoglobin in the worm blood and carried throughout the body.

Moisture Requirements

Moisture is critical to the survival of all earthworm species because it is moisture within the worm's body that gives it shape, enables it to move, and aids in the worm's ability to absorb oxygen. To facilitate the absorption of oxygen the skin is very thin and permeable, meaning that the moisture within the body cavity is easily evaporated off, particularly in dry environments. The moisture range for most worm species is from 60-85%, which ensure the worm can absorb as much moisture as may be lost.

Temperature Requirements

Specific temperature requirements and tolerances vary from species to species, though the ideal range for most epigeic worm species is between roughly 60-80° F. The worm's ability to tolerate temperatures outside of ideal is highly dependant on the level of moisture in the system, with hot, dry conditions being the most lethal combination.

Nutritional Requirements

Earthworms lack teeth and sufficient digestive enzymes of their own, relying instead on microorganisms to begin to rot and soften organic matter so it can be ingested, then relying on naturally occurring bacteria and fungi in their gut to digest their food. In the process of taking in this biologically active predigested organic matter the earthworm also ingests small particles of sand and soil, which lodge in their gizzard. As the organic matter and microbial life coating it move past this gizzard they are ground against the gritty particles lodged there and fragmented into smaller pieces, making them easier for the gut organisms to digest.Researchers have recently learned that it is not from the organic matter itself, but from the bodies of the microbial life rotting the organic matter that epigeic earthworms derive the bulk of their most vital nutrients. Once thought to be detritus (debris) feeders, we now understand that the earthworm is actually a predator of microbial life, relying on microscopic bacteria, fungi, protozoa and algae as their major sources of nutrition. Thus, anything that will support microbial activity, that is, anything that rots, is potentially suitable food for earthworms. Materials that support the greatest level of earthworm activity are those that support the greatest and most diverse populations of microbial life.

PH Requirements

As microorganisms break down organic matter it goes through a series of naturally occurring changes in pH. Because earthworms thrive in environments rich in decaying organic matter they are adapted to tolerate these pH fluctuations with little or no change in their activity levels. In nature worms are found in environments with a pH range from 4-9, with processing and reproductive rates being no different at an acidic 4 than they are at an alkaline 9. In fact, all things being otherwise equal, earthworms actually prefer an environment with a pH of 5 to 5.5, contrary to the popular belief that they prefer a neutral pH.With a pH tolerance this wide it is highly unusual for pH to be a limiting factor in any worm system. Further, the radical and artificial adjustment of the pH through the addition of buffering agents like lime can actually have a detrimental effect on the system. The organisms present in a given environment of organic debris are there because they are suited to that environment and whatever fluctuation may naturally occur through the process of decay. When the nature of the system is suddenly and radically altered it forces many of these organisms into dormancy and sometimes kills them outright, thus reducing the availability of nutrition to the worms and potentially slowing the processing rate of the organic matter.The addition of lime to any worm system is generally discouraged except in those extremely rare circumstances where the pH has dropped well below the worms' level of tolerance.

Ultra-Violet Light Response

All earthworms are photophobic to some degree, meaning they react negatively to bright light. The severity of the reaction depends on the species of worm, how bright the light and the level of light to which the worm is accustomed. For example, earthworms accustomed to some light exposure will react less negatively to sudden bright light than will worms accustomed to complete darkness. Some species of worm react negatively to bright light but are actually attracted by dim light.Earthworms sense light through photoreceptive organs along their back and on the prostomium (sensitive lobe of tissue overhanging the mouth that the worm uses to probe and sense its environment).

Reproduction

Earthworms are hermaphrodites, meaning each worm possesses both male and female reproductive organs. Some earthworm species can be self fertile, meaning they can fertilize their own ova to produce young, and some species are parthenogenic, meaning fertilization of the ova by sperm is not necessary to produce young. Most earthworm species, however, require that two worms exchange sperm in order to produce young.When worms mate they lay side by side with their heads pointed in opposite directions, making close contact along the upper segments of their bodies. They excrete a mucous that coats both worms and binds them together, preventing them from being easily pulled apart and ensuring environmental conditions like rain or dew do not interfere with the exchange of sperm.The worms exchange sperm, storing the received seed in a pore on the skin surface just above the clitellum (the differently colored or thickened band that encircles the worm body). Once they exchange sperm, a process that may take hours, the worms move apart and eject their own ova into a pore on their skin surface near the sperm pore. They secrete a thick mucous around the clitellum, which hardens on the outside but remains sticky underneath, forming a band out of which the worm backs, drawing the band over its head. As the band passes over the pores holding sperm and ova they are picked up and held on the sticky underside. Once the worm has backed completely out of the hardened mucous band the ends close forming a cocoon with sperm and ova inside where fertilization takes place. Each worm will continue to produce cocoons until they have used all of the sperm received from their mate.The length of time it takes for the baby worms inside the cocoon to mature and “hatch” out, and the number of young in each cocoon depend on the worm species and environmental conditions.Contrary to popular belief, worms are a closed species, meaning they can produce viable young only with sperm from members of their own species. They cannot be hybridized . In those rare circumstances when two worms from differing species have attempted to mate, the result was either no young being produced or, in rare circumstances, babies that were always sterile.The worm cocoon is an incredibly tough structure, designed to protect the young inside from environmental extremes and even ingestion by other animals. Cocoons can be frozen, submerged in water for extended periods of time, dried and exposed to temperatures far in excess of what can be tolerated by adult worms without damage to the young worms inside. The cocoon can even be eaten by other animals, provided it can make it past the teeth, surviving the digestive process and passing out of the animals body in the manure! In areas of climatic extremes it's likely that the adult members of epigeic worm species do not survive, but the cocoons do, repopulating the environment when environmental conditions return to a range that can support worm activity.