Selfish genetic elements have been found in the genomes of many species, yet our understanding of their evolutionary dynamics is only partially understood. A number of distinct selfish Medea elements are naturally present in many populations of the red flour beetle (Tribolium castaneum). Although these Medea elements are predicted by models to increase in frequency within populations because any offspring of a Medea-bearing mother that do not inherit at least one Medea allele will die, experiments demonstrating an increase in a naturally occuring Medea element are lacking. Our survey of the specific Medea element, M¹, in the United States showed that it had a patchy geographic distribution. From the survey it could not be determined if this distribution was caused by a slow process of M¹ colonization of discrete populations or if some populations lacked M¹ because they had genetic factors conferring resistance to the Medea mechanism. We show that populations with naturally low to intermediate M¹ frequencies likely represent transient states during the process of Medea spread. Furthermore, we find no evidence that genetic factors are excluding M¹ from US populations where the element is not presently found. We also show how a known suppressor of Medea can impair the increase of M¹ in populations and discuss the implications of our findings for pest-management applications of Medea elements.