Parasite

noun

1. an organism that lives on or in an organism of another species, known as the host, from the body of which it obtains nutriment.
2. a person who receives support, advantage, or the like, from another or others without giving any useful or proper return, as one who lives on the hospitality of others.
3. (in ancient Greece) a person who received free meals in return for amusing or impudent conversation, flattering remarks, etc.