||The herbivorous jumping spider, Bagheera kiplingi, uniquely exploits the Mesoamerican ant-acacia mutualism by consuming the nutritional Beltian bodies that Vachellia shrubs produce as rewards for Pseudomyrmex ant mutualists. Despite aggressive defense by these ants, B. kiplingi nests on these plants. I use a combination of experimental and observational approaches to investigate the nesting ecology of B. kiplingi relative to the benefits and costs of ant-acacia exploitation. Artificial nest tube colonization patterns suggest that occupancy is primarily driven by ant density. Nest content analyses demonstrate that while females guard eggs and spiderlings, males only defend mates from ants, contrasting previous speculation regarding derived behaviors. Video analyses indicate that maternal nest guarding, an ancestral salticid behavior, reduces nesting costs associated with ants. The exploitation of low ant density nest sites, coupled with preadaptations, may have facilitated occupancy of ant-acacias by B. kiplingi as a precursor to its subsequent dietary shift to herbivory.