Earthworms have been referred as “ecosystem engineers”, because they can influence organic matter decomposition, carbon and nitrogen content of soils, soil aggregate structure, porosity and water infiltration. They also affect abundance and biodiversity of soil fauna and flora. Geographical location, seasonal and climatic differences and land use have a significant impact on the abundance, distribution and activity of earthworms. For example, the Mediterranean climate strongly affects the abundance of earthworms, with a local population far below 50 ind./m2, in comparison with moderate continental climate, where number of earthworms can be up to 500 ind./m2. A big influence has also parent material and soil pH. Most types of earthworms grow at pH 6 to 7. Agricultural production systems have a profound effect on earthworm populations, because mechanical disturbance changes the environment in which they live. These effects include changes in soil temperature, moisture content, soil organic matter content and the availability of food. Earthworms are also sensitive to a variety of environmental pollutants such as pesticides and heavy metals. That is why earthworms are suggested as potential indicators of the sustainability of agricultural practices and also for pollution assessment. For complete interpretation and assessment of soil quality, it is also important to monitor physico-chemical indicators is well.