Black widows in an urbanized desert: spatial variation and condition dependence of the red hourglass

Abstract Urbanization is an incredibly prevalent form of human-induced rapid environmental change. Certain taxa dominate urban habitats and condition-dependent phenotypic changes may be the mechanism by which these species flourish in disturbed habitats. The western black widow spider (Latrodectus hesperus) forms infestations in urban habitats. Here, we show that urban spiders are significantly larger than desert spiders. Other measures of morphology and color showed spatial variation across collection sites, despite not being different between urban and desert habitats. Further, we show that the size of the black widow’s red hourglass is condition-dependent. As the hourglass is assumed to play an aposematic role, our results show that spatial heterogeneity in body condition predicts variation in hourglass area and potentially aposematic signaling, enemy risk and survival.