What's the noun for parasitically? Here's the word you're looking for.
(pejorative) A person who lives on other people's efforts or expense and gives little or nothing back. [from 16th c.]
(biology) An organism that lives on or in another organism, deriving benefit from living on or in that other organism, while not contributing towards that other organism sufficiently to cover the cost to that other organism.
(literary) A climbing plant which is supported by a wall, trellis etc. [from 19th c.]