Júlio came up with the correct answer to the questions in the last post.
Species 5 is Acromyrmex versicolor, and this worker was carrying a very large piece of caterpillar frass. As I noted in the comment, the frass is most likely from a Manduca rustica caterpillar, as there was a host tree nearby.
(I apologize for the quality of the photograph. I was lying flat on my stomach on the sidewalk in a very public place while this ant was moving rapidly along.)
Júlio also wondered about an Acromyrmex versicolor worker carrying frass, which is something other leafcutters like Mycocepurus or Cyphomyrmex or even Trachymyrmex are more like to do.
I did locate the nest entrance. The workers were variable in size, showing different castes.
They appeared to have three pairs of spines on the mesosoma.
The workers were definitely collecting plant material. So, I think it is safe to say these ants were Acromyrmex versicolor.
And there's a Dorymyrmex making an appearance.
As for the ant-finding challenge, I thought I did pretty well to find honeypot ants and leafcutters within two hours, but then again it is pretty easy to find cool ants in Tucson.
I found a total of eight different ant species, less than the expert at the Tucson airport, but still a lot of fun.
Forelius, probably mccooki
plus one species I, gulp, could not identify and the photographs are not a help.
I know I could have found more if I could have flipped rocks or tore into trees, but this was a public place with prohibitions on that sort of thing. Surprisingly, there were no harvester ants in the list. I'm not sure why not, because I find them quite often in other places.
So, what do you think about Acromyrmex carrying caterpillar frass? Is that common behavior or not?