In recent decades, many of us have been prompted to rethink our views of parasitism. Long perceived in negative terms, parasitism is now taken by many in the biological sciences to have certain value: parasites and other symbionts, it is argued, are integral parts of ecosystems, human immunity, and genetic development. Not only that, but they can help us better understand the entanglements of human and nonhuman life, leading, perhaps, to more ethical and sustainable approaches to existence in the anthropocene. When applied to human life, however, the term is widely reserved for negative use; as an insult, "parasite" remains a staple of American politics, particularly its right wing. What would it mean, however, to apply the nonhuman parasite's increasing association with complexity and even ethical life to human meanings of the term? This talk will consider nineteenth-century writers for whom such application was an important strategy. Tracing the history of the term "parasite," it shows that for a short time in the nineteenth century - before human and nonhuman meanings of the term diverged - the parasite helped writers and intellectuals imagine the ambiguity of matter and the complexity of relations between its forms.