The bug is mostly dead, with the mushroom on its back having become the main body. If the mushroom comes off, the bug stops moving.
Its poisonous spores are also used in traditional medicine. Apparently, spores produced in Alola are not of very good quality.
Mushroom-lacking specimens of this Pokémon lie unmoving in the forest, lending credence to the hypothesis that the large mushroom is in control of Parasect’s actions.