Tochukaso spores are attached to Paras Eggs, causing hatchlings to be doused in them upon birth. As the Paras grows, so does the tochukaso. The tochukaso orders its host to suck nutrients from tree roots and trunks, then absorbs most of the nutrition itself. When the Paras evolves into Parasect, the tochukaso takes complete control of the host and does all the thinking.
Tochukaso prefer damp, dark places, so Parasect are typically found in those locations. The fungus scatters its toxic spores from the mushroom cap, and uses the host to help distribute these spores.
In anime episode Clefairy and the Moon Stone, the lighting Team Rocket hung up in Mt. Moon confused the Paras, causing them to remove their tochukaso and plant them in the ground, as the fungus dislikes bright light.
Tochukaso spores can be used to make a herbal medicine which can be used to extend life. This medicine is commonly made in China.
In anime episode The Problem with Paras, Cassandra tried to evolve her Paras into Parasect in order to harvest its spores to produce a miracle potion, which improves a Pokémon's attack power, defenses, concentration, determination, and intellect. Her Paras eventually evolved, so she and her grandmother set up a business to produce and sell miracle potions.
Tochukaso is the Japanese name of caterpillar fungus (Ophiocordyceps sinensis), a real-world endoparasitoid fungus that replaces the host tissue and can affect the behavior of its insect host. The fungus is often used in traditional Chinese medicine, specifically as an aphrodisiac and for treatment for ailments such as fatigue and cancer.
In Parasect, the tochukaso has caused neoteny.
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