People who go to u-pick vegetable farms usually come home with lettuce or corn or tomatoes. When I went to a u-pick vegetable farm near Phoenix, Arizona, I came home with photographs of ants, instead.
It wasn't surprising to see numerous circular mounds with a single entrance hole in the center.
The nests are made by a common ant in the low desert, Dorymyrmex bicolor. As I've written previously, D. bicolor seems to prefer to nest along dirt paths or roads. The garden had plenty of those.
After seeing about three dozen or so circular nests like those above, I found this one.
Same rough shape, but notice anything different?
Where are all the ants?
Finally, I can see some ants, but those aren't Dorymyrmex bicolor workers.
The workers exiting from this nest are uniform in color. They have a petiole and a postpetiole. Notice anything else about them?
The Dorymyrmex worker ants from the same perspective have large eyes. See any noticeable eyes from this view?
Having no noticeable eyes is a characteristic of Neivamyrmex army ants (Note: They do have a single eye facet, but it isn't obvious.)
The exact species is much more difficult to figure out.
Wayne P. Armstrong found some similar Neivamyrmex near the Superstition Mountains in Arizona, which are close to the farm where I found these ants. Gordon Snelling identified Armstrong's ants as Neivamyrmex leonardi. The ones I found could be N. leonardi or one of several similar species.
In any case, Neivamyrmex army ants resemble their larger namesakes because they are always on the move. They don't make permanent or long term nests like the Dorymyrmex, but instead raid nests of other ants stealing the brood for food. Seems like in this case a Dorymyrmex bicolor colony was a target of their raid. Armstrong reports Neivamyrmex workers raid Pheidole nests, as well.
So, I didn't bring home lettuce, but maybe something even better from the u-pick farm.
Have you ever seen Neivamyrmex army ants?