Oplostomus haroldi Witte belongs to a unique genus of afro-tropical scarabs that have associations with honey bee colonies, from which they derive vital nutrients. Although the attributes of the honey bee nest impose barriers to communication among nest invaders, this beetle still is able to detect conspecific mates for reproduction. Here, we show, through behavioral studies, that cuticular lipids serve as mate discrimination cues in this beetle. We observed five steps during mating: arrestment, alignment, mounting, and copulation, and a post-copulatory stage, lasting ~40–70 % of the total mating duration, that suggested mate guarding. Chemical analysis identified the same nine straight-chain alkanes (C23–C31), six methyl-branched alkanes (6), and five mono-unsaturated alkenes in the cuticular lipids of both sexes. Methyl alkanes constituted the major component (46 %) of male cuticular lipids, while mono-unsaturated alkenes were most abundant (53 %) in females. (Z)-9-Pentacosene was twice as abundant in females than in males, and ~20 fold more concentrated in beetles than in worker bees. In mating assays, (Z)-9-pentacosene elicited arrestment, alignment, and mounting, but not copulation, by male beetles. These results represent the first evidence of a contact sex pheromone in a scarab beetle. Such contact pheromones may be an essential, cryptic mechanism for arthropods associated with eusocial insects.