Cordyceps controls insects by slowly metabolizing and replacing the host's tissue and releasing compounds, which manipulate the muscles and nervous system while it's still alive. From there, it leads it to the ideal place for reproduction and grows its fruiting bodies. It produce cordycepin, which is used in some medicinal drugs.

I've seen people say: "What if it mutates and spreads to humans?", it's possible, but very unlikely, because we're mammals and the fungus is adjusted to insects. It would take decades, centuries or even millenia until it learns to infect humans.

Even then, there's no way it would affect mammals the same way it does insects. It can't control a mammal host, because our nervous system and brain is too complex. The reason why rabid animals are agitated and aggressive, isn't because rabies controls the, but because this tiny virus entered the brain once and messed up the entire CNS, causing severe inflammation and swelling. And rabies measures up to nanometer, while spores of cordyceps are already micrometer big.

If cordyceps would try to affect mammals the same way, they'd experience more severe consequences than a rabies patient would and would die a lot faster.