Explore the Cutting Edge of the Sonoran Desert!
Dr. Alex Mintzer lead a SASI field trip to Organ Pipe Cactus National Monument to visit the unique population of Atta mexicana leafcutting ants living there. There are only 40 colonies of this ant in the United States, all at Organ Pipe. We will observe their diurnal wintertime foraging activity and the relationship of these ants with the desert plants around their nests.

The cost of the trip was only $35.00 per person for SASI Members and $40.00 for non-members to cover handout materials, campground fees and administrative costs. Participants were be responsible for their own transportation, meals and camping equipment. The group campground space limits us to 20 participants and does not allow trailers.

Dr. Alex Mintzer received a Ph.D. in Biological Science at The University of Michigan, with a specialty in ant social behavior and ecology. He is a member of the full-time faculty at Cypress College in Orange County, California. He has been a member of SASI since 1988, and has been studying Mexican Leafcutting Ants at Organ Pipe for considerably longer than that.

In 1985, he led an extensive ground search that identified dozens of colonies of this fascinating ant in the park for the first time. In the late 1980s, he conducted detailed studies on foraging behavior of these ants and led several SASI-sponsored field trips in the park. In 1995, he conducted a 10-year recensus of the population of Atta mexicana at Organ Pipe. He also has served as a consultant and supplier for leafcutting ant exhibits for over a dozen exhibit institutions in the USA, Canada, Great Britain, and Germany.
Photos by Charles Hedgcock
Organ Pipe Cactus National Monument was named after this columnar cactus, which is common in Mexico but limited to this immediate area in the USA. The nest center of Atta mexicana consists of many hundreds of pounds of excavated soil from deep underground, plus the distinctive dark brown discarded fungal waste (at left).
The ants cut, collect, and scavenge about 200 kg (dry weight) of plant materials each year. Each colony has a foraging range as large as the flight deck of an aircraft carrier.
The fungus gardens of Atta mexicana require a saturated, controlled temperature environment and are built in breadbox-sized cavities at least 2 meters underground. Here, workers add cut-up bits of collected plant matter to build these ridges of fungus. Dead ants are carried out of the nest to the designated 'cemetary pile' areas.
Additional Reading:

Leaf-Cutting Ants on Parade (there are numerous references to more reading material at the end of this article at the bottom of the page)

Natural History and Captive Management of Leaf-Cutting Ants in the Genus Atta (Hymenoptera: Formicidae) (there are numerous references to more reading material at the end of this article at the bottom of the page)