Flower crops are valuable in promoting the provision of resources for flower visitors and pollinators in anthropized landscapes. In Mexico, the traditional "Flower of the Dead" (Tagetes erecta, marigold or "Cempas & uacute;chil" in Spanish) is a plant of great biocultural value. However, despite its importance, we know very little about the role of urban temporary crop fields of "Cempas & uacute;chil" as reservoirs of biodiversity. Here, we systematically sampled adult butterflies in 6 urban "Cempas & uacute;chil" crop fields. Our observations revealed that 39 species of diurnal butterflies are flower visitors to "Cempas & uacute;chil" crop fields. Remarkably, 6 of the species recorded undertake autumn migrations, highlighting the importance that "Cempas & uacute;chil" crop fields may represent an important nectar resource for migratory species in urban areas. We also recorded species reported to be in serious population decline actively feeding on "Cempas & uacute;chil" flowers. Although the expansion of agricultural and urban areas has been considered an important driver of butterfly species decline and local extinction, our results emphasize the importance of "Cempas & uacute;chil" crop fields in agricultural and urban landscapes for the maintenance of butterfly biodiversity in an arid city. Thus, we suggest that urban conservation efforts could focus on the creation of "Cempas & uacute;chil" plots that promote biodiversity connectivity and ecosystem service provision in human-dominated-landscapes.