The bacterium which is present in the alimentary canal of the earthworm converts organic water to natural fertilizers. The chemical alterations that the organic wastes are put to consist of deorderising and neutralizing. This implies that the pH of the castings is 7 which is neutral. (the tasteful garden) Vermiculture:

The Latin meaning of vermes is worm from which the term vermiculture has been derived. Vermiculture is a process wherein the process of composting, containing the addition of some species of earthworms used to improve the process of conversion of waste and produce an improve product. Vemicomposting varies from composting in a number of ways. Mainly, vermicomposting consists of a mesophillic process in which the microorganisms are utilized and earthworms which are active within a temperature gap of 50-90 degrees Fahrenheit. The process is regarded as faster compared to ordinary composting and since, the material passes through the earthworm gut, a considerable amount of transformation happens, in which the final earthworm castings have plenty of microbial activity as also plant growth regulators, and fortified with pest repellent attributes also. Hence earthworms by a process of biological transformation are capable of transforming garbage into useful bio-fertilizers. Due to this, Charles Darwin has stated that are hardly any other animal whose contribution to the world is so great. Convincing proof have referred to an ideal application of 10-20% earthworm castings in a mixture of container media that generates calculable enhancement in root and shot development, leaf size becoming larger, formation of better quality flowers, increase of crop yield and the total health of plants in preventing diseases. (Vermicomposting Technology for Waste Management & agriculture)

Vermicomposting stems from the fact that the earthworms in their process of eating up break down the soil substrate thus increasing its surface area for additional microbial colonization. At this time, the vital plant nutrients like nitrogen, potassium, phosphorus and calcium available in the feed material are transformed by means of microbial action into forms which are more soluble and available to the plants compared to those available in the parent substrate. As the earthworms are organisms who feed on a large degree of organic waste and while...

(Sharma; Pradhan; Satya; Vasudevan, 8)
As the intestine of the earthworms have a broad spectrum of microorganisms, enzymes, hormones and the like, these partly digested soil substrate decomposes very fast and are converted into a type of vermicompost in a very short period of time. The system happens in the mesophilic temperature range i.e. 35-40 degree centigrade. The earthworm prepares the organic manures and by means of their typical instinct of disintegrating organic matter and combines it with soil particles. The thing that emerges is well humidified, organic fertilizer, with better effects for the soil and it also acts as a stimulant for plant growth and most ideal for agricultural applications and is environmentally viable. The action of earthworm in this procedure is physical as well as mechanical besides being biochemical also. (Sharma; Pradhan; Satya; Vasudevan, 8)

Vermicompost which is a product of a non-thermophilic biodegradation of organic material by means of interaction between the earthworms and microorganisms appears similar to a peat like material having a high porosity, aeration, drainage, water retention capability and microbial action. The plant growth regulators and other plant growth impacting materials such as auxins, cytokinins, humic materials etc. generated by the micro organisms have been demonstrated to have come from vermicompost. The material containing humus drawn from vermicompost has been stated to generate cell growth like auxin and nitrate metabolism of carrots. Besides, vermicompost have been shown to possess a higher Base Exchange capacity and are found to be overabundant in total organic matter, phosphorus, potassium and calcium with a lower electrical conductivity, huge rise in oxidation potential and considerable reductions in water-soluble chemicals. (Sharma; Pradhan; Satya; Vasudevan, 10)

References

Delahaut, Karen; Koval, C.F. Earthworms: beneficial or pests?

http://grounds-mag.com/mag/grounds_maintenance_earthworms_beneficials_pests/index.html

N.A. Advantages of Vermicompost. http://www.organicneem.com/neemvermicompost_advnt.htm

N.A. Beautiful gardens begin with great compost. http://www.happydranch.com/articles/reference.html

N.A. The tasteful garden. http://www.tastefulgarden.com/wormcastings.htm

N.A. Vermicomposting Technology for Waste Management & agriculture. http://www.vermico.com/summary.htm

Sharma, Satyawati; Pradhan, Kaviraj; Satya, Santosh; Vasudevan, Padma. Potentiality of earthworms for Waste management and in other uses, the Journal of American Science, vol. 1, no. 1, pp: 4-16.