Heterostylum robustum is a species of bee fly belonging to the Bombyliidae family. It is found in southwestern Canada, most of the western United States, and Mexico. It is a bomber fly, parasitizing bees and wasps by launching its eggs into their nests. It is the principal parasite of the alkali bee Nomia melanderi, an important alfalfa pollinator across Washington, Oregon, Idaho, and Wyoming. Other hosts of the fly include solitary bees such as Nomia nevadensis bakeri, Dieunomia triangulifera, Calliopsis anthidia, Nomia scutellaris, and Halictus rubicundus.

...