Largest fungal "zombie animals"

The largest documented animal that a fungus can infiltrate and turn into a "zombie" (i.e., taking over its cognitive and physical capabilities to meet the fungus' own ends) are green bean stick insects (Diapherodes gigantea), one infected specimen of which, found in the Amazon rainforest in Ecuador in 2004, measured 20 cm (7.8 in) long. These insects are known to be specific hosts for Cordyceps diapheromeriphila, a type of parasitic fungus. The findings were published in the journal Mycologia in January 2014.

Cordyceps and Ophiocordyceps species exhibit an extraordinary level of host specificity, with different insects falling victim to distinct species of these mind-altering fungi. C. diapheromeriphila targets insects belonging to the Diapheromeridae family, commonly known as stick insects, but others specialize in zombifying ants and caterpillars, among others.

Given that the majority of fungal species remain undiscovered, it's entirely possible that even larger insect hosts exist, awaiting their discovery.

Cordyceps fungi have recently found mainstream fame thanks to the videogame (and now TV series) The Last of Us, which centres around the story of a strain of the fungus being able to infect humans and control them in the same way it does insects. Thankfully, for now, this remains in the realm of fiction rather than reality.