The objectives of this research were to test the "migration" and "cryptobiosis" hypotheses and to examine the effect of increased soil moisture and reduced soil temperature on activity patterns of microarthropods in surface litter.... We concluded that the active resident population of soil microarthropods in surface litter accumulations in a desert is a function of time of day, which affects diurnal migrant species, and litter temperature, which affects activity of species that are capable of cryptobiosis. Physiological studies of species that appear capable of cryptobiosis are needed before we can assess the flexibility that this adaptation allows its possessor with respect to utilization of the rich energy and nutrient sources characteristic of leaf litter accumulations. This is especially important in deserts where soil organic matter is often less than 1% by mass.