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In a project designed to identify and quantify acarine communities in semiarid eastern Australia, microarthropod populations in surface soil and litter were sampled during different seasons across a range of microhabitats in both heavy- and medium-textured soils. Major differences in mite assemblages were recorded between these soils, as well as between contrasting microhabitats within each soil type. In the medium-textured soil, richness and abundance of Acari taxa were related to soil organic carbon in the surface soil (0-1 cm), particularly for the Prostigmata. This relationship was not apparent in the heavy-textured soil where organic carbon content was considerably higher (4-9.5% cf. 0.4-1.75%). The highest densities on the medium-textured soil (c. 2600 m(-2) dominated by Speleorchestes, Eupodes and Pseudocheylus spp.) were recorded in mulga groves where there was abundant surface litter. However these densities were greatly exceeded under annual grassland on the heavy-textured soil (c. 14,000 m(-2), dominated by Afrotydeus spp.). These are amongst the highest mite densities recorded on semi-arid soils in Australia, possibly due to these grasslands being the least saline of the sites sampled in the chenopod shrublands. Broad similarities in microarthropod composition at family and generic levels in similar ecosystems in Australia and North America suggest either convergent evolution under similar selection pressures or long distance dispersal in the past. Inter-hemisphere dispersal of these microscopic animals may have been facilitated by stronger winds which prevailed during glacial periods, despite the inter-tropical convergence zone over the Pacific Ocean. (C) 1996 Academic Press Limited