The worms

First of all it is important to remember that earthworms are annelids, belong to oligochaeta class and Lumbricidae family, and there are the only group with terrestrial life, so there are organisms that have been evolved from an aquatic medium to a terrestrial one, with the adaptations that this needs to be able to solution some kind of problems such:

- To maintain the body form in a low density medium.
- To ensure an embryo development round by vital fluids.
- To adapt the respiratory systems to obtain oxygen from air instead than from water.
- To adapt itself to a terrestrial nutrition and to maintain the interior homeostasis.

Due to all of these characteristics, they need control their interior medium, eliminating the metabolic residues, products without an excessive lost of ions and water. They have also adapted their respiration and excretory systems from an aquatic model of their ancestors. This needs to segregate mucus that could maintain humid the body surface and allows a cutaneous respiration by passive diffusion, and that their excretory system could produce abundant hypotonic urine to eliminate urea and ammonia.
Those animal characteristics are which will decide the parameters that must be controlled in the waste to treat and in the worms culture media, to guarantee their survive and degradative efficiency.

The species

The presence of worms in the soil is associated to soil fertility and health. Their mobility guarantees the soil aeration, increasing its capacity of hydric capture and retention. Some species, like those from genre Eisenia, could ingest in one day the equivalent of their body mass, returning to the soil a colonised organic matter with micro organisms that accelerate the mineralization and humification processes.
But not all the land worms are adequate to be used in composting processes. Like it is logic, it is needed those which tolerance ranges to the substrate adverse conditions can be the most amplest, and that they can be effective at the transformation time, and inside of these, those which growing and reproducing rates can be the optimum ones.
Form an ecological point of view, the land worms can be classified in three big categories: :

a) Epigeous: like their name indicates, they are those that live on soil surface, associated to organic matter residues that are being decomposed, which constitute the high part of their nutrition. Their reproduction is accelerated and numerous due to their exposition to high number of predators for occupying a superficial layer.
b) Endogens: they are in the interior of the soil in a permanent way, feeding with more or less land mixtures with organic matter. They can represent between a 20 and a 50% of the European fertile soil biomass.
c) Anecics: they are those that excavate profound vertical galleries. They drag organic rests to their interior that they use as nutrient once that they are mixtured with the soil.

It is clear that between all these types, the most adequate ones for vermicomposting are the epigeous ones, but there are also necessaries those that, apart to be able to colonize organic wastes in a natural way and degrades them in daily quantities similar to their own body mass, their reproductive strategy would be of the "r" (fast and prolific), because of that the next generations will continually substituting themselves, degrading the residue quickly each time. They must to be also tolerant to high temperature and moisture ranges, to be resistant to their manipulation and to maintain themselves on the culture beds.

Although all around the world there are being realized tests with different species of worms, in the moment to degrade organic wastes, there will be some species more effective than others depending on the geographic area . So in tropical areas, the most effective species are the African Eudrilus eugeniae (Kinberg, 1867) and the Asiatic Perionyx excavatus (Perrier, 1872). Whilst the most used in template areas are Lumbricus rubellus (Hoffmeister, 1843), Dendrobaena veneta (Rosa, 1886), Eisenia fetida (Savigny, 1826) and Eisenia andrei (Bouché, 1972).
The most adequate specie election must be based on, apart latitude and the characteristics of the area where the process is realized, what we want to obtain: vermicompost production, animal protein production or organic waste treatment. So Lumbricus rubellus is the most indicated for animal protein or bait of fishing production, whatever Eisenia fetida is the most adequate for organic wastes treatment.

Eisenia fetida

Eisenia fetida is a detritus feeding epigeous worm, its mean body longitude is between 60 and 120 mm, a diameter between 3 and 6 mm and it has a variation in the number of segments between 80 and 120. The clitelo presents way of chair of mounting, and occupies between 6 and 8 segments, spreading the puberty’s tubers along the ventral rim of the clitelo in three segments. Their cocoons have a mean longitude between 2.4 and 5.2 mm, and a diameter between 2..3 and 44 mm. Its fast growing, its early sexual maturation and its high reproductive potential convert it in the most used in vermiculture. The parameters that characterize the Eisenia fetida biological cycle in optimum conditions are:

Adult mean weight (g) (g) 0,55

Maturation mean time (days) 60

Cocoons production rate (cocoons·adult-1·day-1) 0,32

Viable cocoons (%) 88

Mean number of individuals by cocoon 3

Incubation mean time (days) 25

Net productive rate (individuals·week-1·adult-1) 4,8

Pasted Graphic

In relation with the optimal conditions for its culture in organic solid wastes:

Temperature 15 - 20ºC (limits 8 - 30ºC)

Moisture 80 - 90% (limits 60 - 90%)

Oxygen requirement Aerobic

Biowaste ammonium quantity Low: < 0,5 mg·g-1

Biowaste salts quantity Low: < 0,5%

pH > 5 y < 9