Yesterday I finally saw a Pheidole ant in Phoenix.
Okay, so it was only one fast-moving soldier.
You just can't mistake the huge head of Pheidole soldiers. That's why the common name is "big-headed ant."
I tried to follow it, but never did find the nest. It was neat to spot it because I have seen them regularly at higher elevations, but not often here in the low desert.
Although it is easy to identify big-headed ants to genus if you find a soldier, figuring out the species is much more difficult. Antweb lists some 50 species of Pheidole in Arizona, some of which are not named.
With time and an unlimited budget, I might pick up E.O. Wilson's Pheidole in the New World: A Dominant, Hyperdiverse Ant Genus to learn more.
Have you seen a copy of the book? What do you think of it?