As urbanization drastically alters the natural landscape and generates novel habitats within cities, the potential for changes to gene flow for urban-dwelling species increases. The Western black widow spider (Latrodectus hesperus) is a medically-relevant urban adapter pest species, for which we have previously identified population genetic signatures consistent with urbanization facilitating gene flow, likely due to human-mediated transport. Here, in an analysis of 1.9 million genomewide SNPs, we contrast broad-scale geographic analyses of 10 urban...