Vermicomposting is the process in which organic materials are converted into humus using earthworms that break down the organic materials. Earthworms are voracious feeders on organic wastes and while utilising only a small portion for their body synthesis they secrete a large part of these consumed waste materials in a half digested form. Since the intestines of earthworms harbour wide ranges of microorganisms, enzymes, hormones etc., these half digested vermicasts decompose rapidly and are transformed into a form of vermicompost that is homogenous, rich in plant nutrients with superior plant growth characteristics and increases water holding capacity of the soil (Appelhof, 1997; Edwards, 1995). Moreover, pathogens cannot survive the vermicomposting process (Edwards, 1995).

The earthworms species: Eisenia fetida and Eisenia andrei are most commonly used for the vermicomposting. Other suitable species include Lumbricus rubellus, Eudrillus eugenie and Perionyx excavatus. The latter two species are from Africa and Asia and cannot withstand low temperatures.

In the composting process, the organic materials have to be turned regularly or aerated in some way in order to maintain aerobic conditions. In vermicomposting, the earthworms, which survive only under aerobic conditions, take over both theroles ofturning and maintaining the organic materials in an aerobic condition, thereby lessening the need for expensive engineering. The major constraint to vermicomposting is that, in contrast to composting, vermicomposting systems must be maintained at temperatures under 35 °C. Exposure of the earthworms to temperatures above this, even for short periods, will kill them. To avoid such overheating careful management is required. The processing of organic materials occurs most rapidly at temperatures between 15 °C and 25 °C, at moisture content of 70 to 90 % and pH of 6.5 - 7.5 (Edwards, 1995). Outside these limits, earthworm activity and productivity, and thus the rate of waste processing, falls dramatically.