parasite

An organism that lives and feeds on or in an organism of a different species and causes harm to its host.

One who habitually takes advantage of the generosity of others without making any useful return.

One who lives off and flatters the rich; a sycophant.

A professional dinner guest, especially in ancient Greece.

Originally, one who frequents the tables of the rich and earns his welcome by flattery; hence a hanger-on; a fawning fiatterer; a sycophant.