“A host-parasite pair in which the parasite mushroom has taken over the host bug. Prefers damp places.” – Pokemon Red/Blue
“When nothing's left to extract from the bug, the mushrooms on its back leave spores on the bug's egg.” – Pokemon Crystal
Parasect, the evolved form of Paras, has a dead look in its eyes. That’s because it’s actually dead. In almost all of Parasect’s Pokedex entries the game mentions it scattering spores around the forest. This is normal since it has a huge mushroom on its back, but in Pokemon Red and Blue, and later in Crystal, the entries allude to the mushroom being a parasite that has completely taken over the host bug.