With the exception of the Polar Regions and deserts, earthworms can be found in most soils. While more than 3.000 species are known worldwide, only 400 species are found in Europe and 40 species in Central Europe. In cropland only 4 to 11 species are com- monly found. Earthworms prefer medium-heavy loam to loamy sand soils. Heavy clay and dry sandy soils are not favourable to their development. In acidic peat soils only specialised species are found that have adapted to such "hostile-to-life" conditions. Earthworms are hermaphrodites and develop slow- ly, with the exception of the leaf litter dwellers. Only one generation with a maximum of 8 to 12 cocoons (eggs) is produced per year. Earthworms live 2 to 8 years, depending on the species. Sexually mature worms can be identified by the "genital belt" (clitel- lum) encircling the body. Peak burrowing activity and reproduction take place in March and April and also in September and October (temperate zone). When it is very dry and hot, many earthworms estivate and retreat to deeper