Designating a proposed form of mimicry in which the model is a distasteful or moderately noxious animal and its mimic is a lethal or highly noxious one.
The highly noxious animal could not itself be the model because a predator could not learn to avoid it (being killed by any encounter).
1960s; earliest use found in Robert D. Martin (b. 1942). From the name of Robert Mertens, German zoologist, who described such a pattern of mimicry in 1966 + -ian.