There is a story on the Internet of a myrmecologist (unfortunately unnamed) finding 10 species of ants, including army ants, while waiting for a flight at the Tucson, Arizona airport. I had two hours in Tucson on Saturday morning, so I wondered if I could do as well. For the next few days we'll see if I was up for the challenge.
The first ant I found was a worker of the genus Crematogaster, named for its lovely heart-shaped rear section or gaster. This cutie is Crematogaster opuntiae, a specialist often found feeding on the extrafloral nectaries of cacti. This particular cactus is a cholla, Cylindropuntia.
Although Crematogaster opuntiae workers are known for chasing herbivores away from cacti in defense of the extrafloral nectaries, they are also predators of other insects, such as termites.
For more information, try:
Charles H. Pickett and W. Dennis Clark. (1979).The Function of Extrafloral Nectaries in Opuntia acanthocarpa (Cactaceae) American Journal of Botany. 66(6):618-625.
Discover Life has a photograph of Crematogaster opuntiae raiding termites
Alex Wild also has some fabulous photographs
Finally, if your French is good, Fourmis et Cactus à Nectars Extra-Floraux