parasite

noun

1.
an animal or plant that lives in or on a host (another animal or plant); it obtains nourishment from the host without benefiting or killing the host
sidefeeder sitos
Antonym:
host
Derived from:
parasitic parasitical
2.
a follower who hangs around a host (without benefit to the host) in hope of gain or advantage
tree worm leech sponge sponger
Derived from:
parasitic parasitical