The metaphorical categorization of social and political adversaries as “parasites” has an infamous history in public discourse. For two centuries it has been routinely used for the purpose of racial and socio-political stigmatization: In those cognitive accounts, the parasite-metaphor has usually been treated as an example of semantic transfer from the biological to the social domain. Historically, however, the scientific uses cannot be deemed original or primary, as their emergence in the 17th and 18th centuries was preceded by a much older tradition of religious and social meanings. The paper charts the main traditions of diachronic variation in the discourse history of the parasite-metaphor and discusses the implications of its findings regarding the assumption of “uni-directionality” of metaphorization processes, which has been a central tenet of cognitive analyses. In conclusion, it is asked whether metaphors in political discourse might fruitfully be viewed as a “parasitic” form of communication.