الفهرس 
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Abstract
The soil is our greatest natural resource and it forms the basis of largest and most important industrial and agricultural projects. A great number of invertebrates spend all or a part of their life in the soil. Soil fauna is extremely diverse and includes pests; predators of pests and beneficial invertebrates that aid in promoting the soil structure and fertility. Clearly, any particular species of invertebrates can belong to more than one of the above groups cited by Edwards in 1977.
Gough (1977) reported that the most important group of inver- tebrates that affect the soil is the Annelida, represented by the earthworms, which create soil channels for drainage and promote the passage of gases. He also added that the earthworms enhance the plant roots growth, but their major effect appears in the process of mixing the soil vertically. In the moist temperate regions, earthworms are said to participate in the biomass of all soil animals up to approximately 80% (van Rhee, 1977). So, they must play a very important role in the distribution of the terrestrial ecosystems due to their particular beneficial effect on the breakdown of organic matter and through their effects on the continuous change of the physical and chemical characteris- tice of the soil (Hopp & Slater, 1949; Satchell, 1967; Edwards & Lofty, 1977; Edwards, 1983 and Syers & Springett, 1983).