When a prey animal displays to a predator, the prey benefits because it is less likely to be attacked, and the predator benefits because it can break off an attack that is unlikely to succeed because the prey has been alerted. We argue that an ‘I see you’ signal has coevolved between the Asian hive bee, Apis cerana, and its hornet predator, Vespa velutina. When a hornet approaches a bee colony, guards perform a shaking movement that repels the hornet. To test whether this is an ‘I see you’ display, we exposed colonies to free-flying and tethered hornets and tethered butterflies. The intensity of the shaking was correlated with the hornet’s proximity, whereas guard bees barely responded to a nonthreatening butterfly. The signal is likely to be honest, because the bees can kill the hornet by collective mobbing if it lands on the entrance. The Western honeybee, Apis mellifera, which has not evolved in the presence of Asian hornets, does not produce the signal and is ineffective at killing hornets by collective mobbing. We also found that hornets were more successful at catching A. mellifera than A. cerana bees at the hive entrance.