A great variety of arthropods inhabit the semiarid soils of the grama-buffalo grass prairies (shortgrass steppe). One approach to dealing with this variety has been to divide soil arthropods into faunal size classes. The mesofauna are those arthropods greater than 1 mm in length. The larger members of the mesofauna are sometimes called macroarthropods. However, most soil arthropods are very small, generally less than 1 mm in length, and collectively are referred to as microarthropods. The majority of these animals are members of the decomposer subsystem, consumers of the microbial decomposers of decaying plant and animal material, or predators of those consumers. The microarthropods of semiarid grasslands, unlike those of forest soils, are tolerant of dry conditions. They occur in great numbers throughout the soil profile, at least to the depth of the hardpan. Root-feeding arthropods, including some important arthropod pests of grasses, spend all or part of their life cycle belowground. A simplified food web emphasizing the position of belowground arthropods in the shortgrass steppe is presented in Figure 19.1. The substrate pool consists of the products of primary production (roots, exudates, algae, litter), and returns to the substrate pool (microbial and animal bodies, feces, microbial products, etc.). Returns to the substrate pool via death, defecation, etc., are not shown. A more detailed food web may be found in Hunt et al. (1987).