This book compiles recent knowledge on soil macroinvertebrates, emphasizing the earthworms of the acid-soil savannas of Colombian Eastern Plains. An inventory of biological resources, including abundance and diversity of soil macrofauna, and their specific ecologies, were produced for natural and agricultural systems at "Centro Nacional de Investigacion Carimagua", together with an evaluation of the impact of those resources on soil and plants. In addition, the volume details the effects of the ecosystem engineers' functional group of earthworms on the soil's physical, chemical, and biological properties. Options for conserving and using the biological resources found in soils under different land management practices are presented.