I've spent the past few hours writing, and I've settled a few things:
—The fungus will come about as a bioweapon, which will be a significant plot point.
—I will probably go with the eyes as the point of emergence (the idea actually came to me just before I came to check replies to this thread; it seems so obvious in retrospect.)
—The fungus will probably be pathogenic to other mammals, most significantly horses and other beasts of burden. This will explain why a human with immunity has to dispose of the bodies (and the immunity isn't the [rant]unexplained pure chance variety that so many stories use as a convenient plot device[/rant]; rather the protagonist is immune because he is descended from the people who engineered the fungus and altered their own DNA so they wouldn't fall victim to their own weapon.)
—I was thinking about the possibility of having the fungus influence the host, but I'm not sure it would work. It seems the fungus does it to ants by altering their ability to detect pheromones, which are pretty much the #1 factor in anything an ant does. AFAIK, the most pheromones can do to humans is slightly alter their mood or push them towards a different decision. It's still a possibility, but it's not really related to the plot, so I'm not going to worry about it too much.
I really appreciate the help so far! One thing I want to point out, however, is that this is meant to be soft science fiction, in the sense that it's main concern is with the characters rather than the science. Basically, while things like Charlie's comment about immunity are helpful (and appreciated
), they probably won't end up in the story since the narrator isn't particularly well-versed in science. The main reason I'm pointing this out is because I know how ridiculously helpful many xkcd forumites are, and I'd feel bad if someone actually went and did a bunch of research that I ended up not needing. (But feel free to post anything you happen to know as it may come in handy.)