The ecology of 14 millipede-species of the Rhein-Main-region was analysed by descriptive, experimental and comparative methods. 2. Quantitative field-investigations showed that 6 species are stenoecic in woodlands, 3 species stenoecic in open country, and 4 species euryoecic; one further species, Cylindroiulus truncorum, has been introduced from North-Africa and is synanthropic, near Wiesbaden it has spread out from a cemetery into the surrounding beech-wood. 3. In 4 typical habitats (leaf-wood, pine-wood, potatoefield on loam, grassland on sand) the microclimate at the surface and in the soil was registred over 24 hours as well as over the year. 4. Sexual activity and behaviour in the habitat were observed. Some species show a marked activity at the surface including herbs and trees. 6 species have a diurnal rhythmic behaviour: they are migrating vertically in soil and litter. 5. A number of factors with possible influence on distribution were analysed by experiments. Locomotion-speed and scototactic orientation are of no influence, food-preference plays a part in 3 species. As shown by preference-experiments, fir litter is not accepted as food; this helps to understand the rareness of millipedes in fir-monocultures. Distribution is mainly determined by abiotic factors. Resistance against desiccation and preference towards a humidity-gradient - both closely correlated by transpiration - agree with distribution in 10 species. Low temperature-resistance is a limiting factor in 4 cases; 1 species living but under barks, Nemasoma varicorne, can be euryoecic only by its high resistance against frost and heat. Preference reactions towards temperature agree with distribution in 11 species, being the only distributional factor to be found in 4 cases. 6. Distribution is determined by specific factorial patterns, which even in related species are rarely the same. 7. In cases of diverging microclimatic claims, unfavourable humidity conditions are tolerated if by this better temperature conditions are available. Some species are not fully agreeing with environments, whereas other millipedes like the stenoecic Orthochordeuma germanicum are completely adapted to their habitat. 8. In Chromatoiulus (2 species analysed) and Cylindroiulus (5 species analysed) intrageneric isolation has taken place, caused by different temperature preferences.
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