Emergence from hibernation and synchronized nest foundation by foundresses of B. petiolata in the southern Transvaal, appeared to be stimulated largely by a rise in temperature during early and mid August of each season. Initial foundresses on newly built nests were joined by other foundresses during the first few weeks of the nesting season to form foundress associations. Although females were strongly philopatric and able to discriminate between nestmates (from their natal nests) and non-nestmates, former nestmates did not reassociate to a significant degree on new nests. Thus, associated foundresses were, on average, not closely related. Rather than facilitating the reassociation of former nestmates, the advantage of philopatric behaviour appears to lie in ensuring that foundresses return to an area of relatively high nesting density, where their chances of being involved in multiple-foundress groups (irrespective of intra-colonial relatedness) are high. Non-philopatric females which nest away from localities of high nesting density have a low probability of being involved in associations, and may therefore have to attempt colony foundation alone, with little or no chance of reproducing successfully.