Loss of intraspecific aggression from reduced genetic diversity has been proposed as a mechanism underlying invasive Argentine ant, Linepithema humile , supercolony formation. However, we determined previously that fusion of unrelated colonies may also explain this phenomenon. Colony pairs displaying low and moderate levels of intraspecific aggression readily merged, while highly aggressive pairs merged only in a few cases. We recently examined possible genetic and biochemical factors involved in colony merging, and found a positive association between fusion of aggressive colony pairs and the similarity of queen and worker cuticular hydrocarbon profiles as well as a positive association between colony fusion and the percentage of alleles shared between colony pairs at seven microsatellite loci. Our results suggest that fusion of Argentine ant colonies varies in relation to the levels of aggression between colony pairs, and that cuticular hydrocarbon and genetic components modulate this process. Although colony fusion may be influenced by these intrinsic factors, their interaction with extrinsic factors in the field remains to be explored.