Parasitism
From DictionGloss
A relationship in which one benefits, while the other is harmed. Example: a flea is a parasite on a dog. The flea benefits by drinking the dog's blood, but the dog, by losing blood and acquiring discomfort and potential disease, is harmed.
Similar to predation in that one species benefits from the relationship and the other is harmed; differs from predation in that parasitism generally not fatal to adversely affected organism.