Earthworm populations show a considerable amount of variability in time and space, with mean population densities and biomass ranging from fewer than 10 individuals and 1 g m^–2, respectively, to more than 1000 individuals and 200 g m^–2, respectively, under favorable conditions. However, within particular climatic zones, earthworm assemblages, with fairly characteristic species richness, composition, abundance, and biomass, can often be recognized in broadly different habitat types, such as coniferous forests, deciduous woodland, grassland, and arable land. There is a considerable volume of literature describing the earthworm communities of such habitats, and much of this was summarized by Lee (1985) and updated by Edwards and Bohlen (1996). There is also a considerable amount of information describing the influence of various environmental and management factors on earthworm populations, but in comparison with insects, for which the population ecology of 92many species has been subjected to quantitative analysis, earthworm population ecology is still largely at a descriptive stage. Population modeling has been used for particular purposes such as risk assessment (Baveco and De Roos 1996), but development of realistic models of field populations has been hindered by a lack of information on key life history parameters and the factors that influence them.