Getting the ant to clamp onto the underside of a branch or leaf and then stay there until it dies is a bit harder to explain. However I am also inclined to believe there is a localized mechanism at play, such as locating the jaw actuation through connective tissue RNA. Even so, there must be some basic signaling and state detection at play. It's probably the biological equivalent of a music box that just plays the notes it's been fixed to play, but still interesting.

That seems more likely to me too. Imagine a fungus that could provide dopamine directly to the brain when a human host meets a certain condition (e.g. a certain amount of direct sunlight, humidity, wind).

Not exactly this scenario, but the psilocybe genus produces chemicals very similar to serotonin.

Agree, it's more like they're responding to stimuli, could we derive somehow that their genes have evolved some degree of ... intelligence?

Eh, I'd say that's a point for debate, but I would argue stochastic survival probability under some prior conditions that haven't changed enough to force further competition.

I mean, apparently toxoplasmosis or something like it can result in personality changes even in humans.

Like toxoplasmosis?