Burning of tallgrass prairie is hypothesized to have positive effects on the resource base for belowground-feeding earthworms, but negative effects on the suitability of the soil climate for earthworms. To a certain extent these are inseparable due to the physiology of the grasses that dominate the ecosystem. A four- by-two factorial design using spring burning, autumn burning, addition of natural mulch, and control, with irrigation and without, was used to partially separate the different effects of burning on earthworm populations and to analyze the mechanisms of the responses. The biomass of native prairie earthworms Diplocardia smithii and D. verrucosa increased 135 and 67%, respectively, with burning; the former species was unaffected by irrigation, and the latter was positively affected. Biomass of an introduced European species Aporrectodea turgida declined from 1.3 g/m2 on unburned plots to 0.85 g/m2 on burned plots and increased with irrigation. These responses reflect increases in the resource base on burned plots, as indicated by an 11% increase in soil organic matter, and different physiological requirements of the three species. Key words: Aporrectodea, Diplocardia, earthworms, fire, irrigation, soil climate, soil organic matter, tallgrass prairie