1. When field colonies of Solenopsis invicta Buren were orphaned by removing the functioning queen, re-collection 8–10 weeks later showed that 61% had replacement queens that were physogastric and attractive to workers. The weight of the original colony queens increases with the colony mound volume. The weight of replacement queens is inversely related to the number of such queens in the colony (1 to 99, but over half had only 1). 2. Laboratory rearing and later spermathecal dissections of these replacement queens established that 21% of the colonies had an inseminated queen and produced worker pupae. Of the remaining uninseminated replacement queens, about 20% nevertheless produced 1–25 worker pupae, probably by thelytokous parthenogenesis. Checking the brood present in orphaned field colonies showed that about 35% produced worker pupae, indicating an inseminated replacement queen was present. The remainder of the orphaned colonies produced all-male sexual broods only, a conditions not found in unorphaned colonies. 3. Combining the lab and field evidence, 27% of the orphaned colonies produced fertile replacements, and these were concentrated among the smaller, younger colonies. The hypothesis is developed that the inseminated replacements are surviving foundresses from pleometrotic colony founding, and that S. invicta is often polygynous but functionally monogynous.