Cordyceps fungus infiltrate their insect host, where their hyphae then grow into the insect's body and absorb nutrients from non-essential organs while controlling the insect's brain. When the fungus is ready to reproduce, it directs its host to march to a cool, moist location in the forest where spores erupt through the insect’s head to spread in the wind.

Commensalism Mutualism Parasitism Predation
Which one

The relationship described between the cordyceps fungus and its insect host is a form of parasitism.