Social cooperative spiders from diverse taxonomic families share life-history and demographic traits, including highly inbred colony structure. The combination of traits suggests constrained pathways for social evolution in spiders. The genus Stegodyphus has three independently evolved social species, which can be used as replicate samples to analyse population constraints in evolutionary time. We tested colony structure and population history of the social S. mimosarum from South and East Africa using mitochondrial DNA variation, and we compared the results to published data for the independently evolved social congener S. dumicola. S. mimosarum had many and diverse haplotypes (5–7% sequence divergence for ND1) but colonies were monomorphic and genealogically similar haplotypes occurred in abutting regions. These findings are nearly identical to results for S. dumicola and imply similar colony-level processes over evolutionary time in independently evolved social species. These population dynamics are discussed with respect to the apparent lack of cladogenesis in social spiders.