The number and biomass of earthworms in grassland may vary widely in space as well as temporally. In old grassland in the Netherlands, numbers normally range from 300 to 900 m-2 with an average population density of 500 m-2 and biomass of 250 0 kg ha -1. Allolobophora caliginosa is the most common species in grassland soil and other common species are A. rosea, A. chlorotica, A. cupulifera, A.longa, Lumbricus terrestris, L. rubellus, L. castaneus and Octolasium cyaneum (van Rhee, 1970). Nevertheless in some grassland soils earthworms may be scarce or absent because of unfavourable climatic or edaphic conditions, application of certain pesticides or fertilizers, or flooding; in grassland seeded on arable land the number is low initially.