parasite [ˈpærəˌsaɪt]
noun
An animal or plant that lives in or on another (the host) from which it obtains nourishment. The host does not benefit from the association and is often harmed by it. In the case of some parasites they can take over the host body, controlling or morphing it to suite their inherent needs. Parasites are transmitted through many means: contact with an infected host, the sharing of liquids, and, in some cases, parasites may even hunt their intended prey.

Edited by:
Burraku_Pansa
and Millennial Dan

Cover art by:
finaglerific

As Featured on Equestria Daily:
http://www.equestriadaily.com/2012/05/story-of-parasites.html