We studied the movement of colonies of the black imported fire ant,Solenopsis riehteriForel, in its native land, Buenos Aires province, Argentina. We established 6 field plots and monthly monitored the number of abandoned and new mounds for 2 yr. We compared the movement of all colonies with the movement of colonies infected with the microsporidiumThelohania solenopsaeKnell, Allen&Hazard. We estimated the distance of colony movement and recorded the duration of the colonies remaining in the same place.S. richtericolonies moved their mounds very often. The mean percentage of abandoned and new mounds per monitoring date was 36 and 30% of all active mounds, respectively. The pathogenT. solenopsaedid not have any effect on colony movement. The mean estimated distance of displacement was 3.7 m and the mean duration of the colonies in the same place was 3.1 mo. Rainfall stimulated colony movement in Argentina.