parasite – Wiktionary

(derogatory) A person who lives on other people’s efforts or expense and gives little or nothing back. [from 16th c.]· (derogatory) A sycophant or hanger-on.· (biology) An organism that lives on or in another organism of a different species, deriving benefit from living on or in that other organism, while not contributing towards that other organism …

https://en.wiktionary.org/wiki/parasite