I took a lovely picture this summer of a giant robber fly eating a cicada. The picture was taken in Washington county, Oklahoma. I observed the take-down myself while working in the garage. The robber fly ambushed the cicada while it was sitting on an overhanging branch of the nearby hackberry tree.
In the above picture, the cicada is still alive. The panicked trills and beating of the wings allowed for me to easily find where the pair landed. The giant robber fly eating a cicada in this picture is of the genus Promachus. The species is difficult to know for certain without detailed observation of the specimen, but it appears to bear similar traits to Promachus hinei based on information available from BugGuide. Promachus hinei’s range extends through Oklahoma, making this a reasonable candidate. The yellow and black pattern, detailed in this picture, appears to be a distinctive trait.