We report results of a 2-yr study aimed at describing the natural history and mating behavior of Euxesta bilimeki (Hendel) (Diptera: Ulidiidae) a picture-winged fly species associated with Agave atrovirens Karw. ex Salm-Dyck (Agavaceae) in the Mexican altiplano. The study consisted of direct field observations and a year-long population survey in the field complemented with laboratory experiments and observations. E. bilimeki was found to be multivoltine, able to resist temperatures below freezing during winter, and it developed on rotting agave leaves in large larvalpupal aggregations. Adults fed on carbohydrate and protein sources found on the plant, where they could be sighted all year long. Courtship was based on a sequence of visual and tactile displays that could result in female rejection of courting males. Males constantly harassed females, who mated multiple times, but frequently expelled and consumed ejaculates after mating. We discuss hypotheses on the evolution of this rare behavior and highlight the value of performing descriptive studies on the natural history of poorly known taxonomic groups to foster understanding of the evolution of behavior.