The occurrence of worker reproduction in queenright and orphaned conditions was studied in the monogynous south-east Asian ponerine ant Odontomachus simillimus. Age (physiological factor), body size and number of ovarioles (morphological factors) and antagonistic interactions among workers and egg cannibalism (social factors) were measured as possible correlates of reproductive activity. In presence of the queen, the majority of the dissected workers had weakly or undeveloped ovaries. Worker egg laying was only rarely observed and these eggs were offered to and eaten by the queen. After a two week orphanage period though, half of the workers had acquired moderately developed ovaries. Three weeks later, there was a drop in ovarian development of the majority of workers, but a small portion of the workers (+/- 20%) acquired strongly developed ovaries. Observations have shown that these were also the main egg layers, so male production in the absence of the queen was performed by only a limited portion of the workers. Ovarian development of workers was not correlated with body size or number of ovarioles, but there was a clear relationship with age, the young workers being the reproductive individuals. Vigorous antennations among the egg layers and attempts to steal each other's eggs were observed and their significance as social factors regulating reproduction is discussed. Egg cannibalism occurred mostly during the first two weeks after orphanage, but its role concerning the regulation of worker reproduction is not clear.