Haantjens (1965) has reported patterns of micro-relief on lowland soils bordering the Sepik river floodplain in New Guinea, and has attributed their formation primarily to excavation and heaping of casts by Pheretima tumulifaciens Lee, a large earthworm associated with the micro-relief features. Evidence is presented to show that the micro-relief is probably not due to earthworm activity. It is proposed that the micro-relief results from a combination of wind and water erosion, acting on a landscape partially bared by man-made fires. The association of earthworms with the micro-relief features is probably a necessary ecological adaptation for the survival of a previously forest-dwelling species to the change to grassland induced by fire. The physical and chemical composition of the casts and soil are discussed and evidence is presented to show that the ridges and mounds observed are composed of material from the upper and not from the underlying soil horizons.